High-hardness optical windows with anti-reflection coatings that have low reflectance and transmittance in the visible range for infrared detection systems

Abstract

Described herein is a window (24) comprising a first multilayer (36) and a second multilayer (38). The first multilayer (36) has a maximum hardness of at least 8 GPa, as measured by Berkovich hardness testing, which enhances the durability and scratch resistance of the window (24). The quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer (36) and second multilayer (38) are configured to provide the window (24) with a dark, opaque appearance when viewed through the first multilayer (36) and to provide the window (24) with a relatively high transmittance (e.g., greater than 90%) and low reflectance (e.g., less than 5%) in a 50 nm wavelength range of interest centered between 850 nm and 950 nm.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 414,128, filed October 7, 2022, and U.S. Provisional Patent Application No. 63 / 525,029, filed July 5, 2023, the entire disclosures of which are incorporated herein by reference. [Technical Field]

[0002] The present disclosure relates to a protective cover for a sensor system, and more particularly to a protective cover including a multilayer film configured to have an opaque dark appearance and exhibit anti-reflection properties in a 50 nm wide target wavelength range from 850 nm to 950 nm. [Background technology]

[0003] A light detection and ranging (LIDAR) system includes an electromagnetic emitter and a detector. The electromagnetic emitter emits an electromagnetic emitter beam. The emitted beam may be reflected by an object, and the reflected beam is detected by a detector. The electromagnetic emitter beam may be continuous, pulsed, or frequency-modulated to spread radially and detect objects within its field of view. Information about the object can then be deciphered from the characteristics of the detected reflected beam. The distance from the electromagnetic emitter to the object can be determined from the time of flight of the beam between the emission of the electromagnetic emitter beam and the detection of the reflected beam. If the object is moving, the path and velocity of the object can be determined by measuring the radial shift of the reflected beam as a function of time, and in some cases, by measuring the Doppler frequency.

[0004] Infrared detection systems installed in exposed environments, such as LIDAR systems in automobiles (e.g., infrared detection systems in aerospace and home security applications), require protection from the environment and various damaging factors, for example, by cover lenses or cover glass windows. Other applications include equipping vehicles with LIDAR systems to enable assisted, semi-autonomous, or fully autonomous driving through the spatial mapping capabilities they provide. In such applications, the electromagnetic radiation detector is mounted on the roof or low in the front of the vehicle. For vehicular LIDAR applications, electromagnetic emitters emitting electromagnetic waves with wavelengths outside the visible light range, such as 905 nm and 1550 nm, are being considered. To protect the electromagnetic radiation detector from impacts from objects such as stones, a window is typically installed between the electromagnetic radiation detector and the outside world, in the line of sight of the detector. Similarly, in other LIDAR system applications, such as aerospace and home security applications, a window is typically installed between the electromagnetic emitter / detector and the outside world. Summary of the Invention [Problem to be solved by the invention]

[0005] However, when an object such as a stone hits a window, the window is scratched or otherwise damaged, causing the emitted electromagnetic wave emitter beam and the reflected electromagnetic wave emitter beam to scatter, thereby reducing the effectiveness of the LIDAR system. [Means for solving the problem]

[0006] The present disclosure addresses these problems with a window including a first multilayer film and a second multilayer film. When the window is installed in a LIDAR system, the first multilayer film can face away from the electromagnetic wave emitter / detector. The first multilayer film can incorporate a scratch-resistant layer to provide damage resistance. Therefore, even if an object such as a stone strikes the window, the window is less likely to develop defects that would scatter the emitted or reflected electromagnetic wave emitter beam, improving performance. Furthermore, the first and second multilayer films include alternating layers of materials with different refractive indices (including materials that provide hardness and scratch resistance). The number and thickness of the alternating layers can be configured to provide high transmittance and low reflectance for a desired wavelength range (e.g., a 50-nm wavelength range centered between 850 nm and 950 nm). Furthermore, the alternating material layers can be selected to provide relatively low transmission and reflection of waves in the visible spectrum. This reduces signal noise due to visible light impinging on the LIDAR system's detector, while also providing an aesthetically pleasing dark appearance to the window.

[0007] Aspect (1) of the present disclosure relates to a window for a detection system. The window includes a substrate, a first multilayer film, and a second multilayer film. The substrate has a first surface and a second surface, which are the main surfaces of the substrate. The first multilayer film is disposed on the first surface of the substrate. The first multilayer film includes alternating layers of one or more high-refractive-index materials and one or more low-refractive-index materials, where the refractive index of the one or more high-refractive-index materials in the first multilayer film is higher than the refractive index of the one or more low-refractive-index materials in the first multilayer film. The second multilayer film is disposed on the second surface of the substrate. The second multilayer film includes alternating layers of one or more high-refractive-index materials and one or more low-refractive-index materials, where the refractive index of the one or more high-refractive-index materials in the second multilayer film is higher than the refractive index of the one or more low-refractive-index materials in the second multilayer film. The maximum hardness of the window measured by Berkovich indentation hardness testing of the first multilayer film is at least 8 GPa. The quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the average transmittance of the window calculated in a 50 nm wide target wavelength range with a center wavelength in the range of 850 nm to 950 nm for light incident on the first and second surfaces at an angle of incidence of 15° or less is greater than 90%, the average reflectance of the window calculated in a 50 nm wide target wavelength range with a center wavelength in the range of 850 nm to 950 nm for light incident on the first and second surfaces at an angle of incidence of 15° or less is less than 4%, and the average transmittance of the window calculated in the range of 400 nm to 700 nm for light incident on the first and second surfaces at an angle of incidence of 15° or less is less than 5%.

[0008] Aspect (2) of the present disclosure relates to a window according to aspect (1), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the average P-polarized light transmittance and average S-polarized light transmittance of the window exceed 85% when calculated in a target wavelength range of 50 nm for light incident on the first and second surfaces at an angle of incidence of 60° or less.

[0009] Aspect (3) of the present disclosure relates to the window according to aspect (2), wherein the window has an average P-polarized light transmittance and an average S-polarized light transmittance of greater than 89% when calculated over a 50 nm wide target wavelength range for light incident on the first and second surfaces at an angle of incidence of 60° or less.

[0010] Aspect (4) of the present disclosure relates to a window according to any one of aspects (1) to (3), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the CIELAB L* value of the reflection of the window for an incident angle of 60° or less relative to the first multilayer film is 37 or less.

[0011] Aspect (5) of the present disclosure relates to the window according to aspect (4), wherein the CIELAB L* value of reflection at an incident angle of 50° or less relative to the first multilayer film is 25 or less.

[0012] Aspect (6) of the present disclosure relates to a window according to any one of aspects (1) to (5), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the CIELAB a* and b* values ​​of the reflection of the window when viewed from the first multilayer film side are between −6.0 and 6.0.

[0013] Aspect (7) of the present disclosure relates to a window according to any one of aspects (1) to (6), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the average transmittance of the window, calculated in a target wavelength range of 50 nm width, for light incident perpendicularly to the first and second surfaces exceeds 95%.

[0014] An embodiment (8) of the present disclosure relates to a window according to any one of embodiments (1) to (7), wherein the refractive index of the substrate with respect to electromagnetic waves having a wavelength of 905 nm is about 1.45 to about 1.55, the substrate is a glass substrate or a glass ceramic substrate, the refractive index of the one or more high refractive index materials is about 1.7 to about 4.0, the refractive index of the one or more low refractive index materials is about 1.3 to about 1.6, and the difference in refractive index between any one of the one or more high refractive index materials and any one of the one or more low refractive index materials is about 0.5 or more.

[0015] Aspect (9) of the present disclosure relates to a window according to any one of aspects (1) to (8), wherein one of the alternating layers in the first multilayer film that is furthest from the substrate constitutes the material of the window edge, the material of the window edge comprising a low refractive index material, and the first multilayer film comprises a scratch-resistant layer, the scratch-resistant layer being formed from one of one or more high refractive index materials and having a thickness of 1500 nm or more and 5000 nm or less.

[0016] Aspect (10) of the present disclosure relates to the window of aspect (9), wherein the scratch-resistant layer is spaced from the end face by multiple layers of the alternating layers of one or more low refractive index materials and one or more high refractive index materials in the first multilayer film.

[0017] An embodiment (11) of the present disclosure relates to the window according to embodiment (10), wherein the scratch-resistant layer is spaced at least 1000 nm from the edge.

[0018] Aspect (12) of the present disclosure relates to a window according to any one of aspects (1) to (11), wherein one or more high refractive index materials of the second multilayer film contain silicon having an extinction coefficient of 0.01 or less in a 50 nm wide wavelength range of interest.

[0019] A thirteenth aspect of the present disclosure relates to the window according to the twelfth aspect, wherein the extinction coefficient of silicon in a 50 nm wide wavelength range of interest is 0.005 or less.

[0020] A fourteenth aspect of the present disclosure relates to the window according to the thirteenth aspect, wherein the second multilayer film comprises two or more silicon layers.

[0021] Aspect (15) of the present disclosure relates to the window according to aspect (14), wherein the thickness of the silicon layer of the second multilayer film closest to the substrate is the smallest among the two or more silicon layers.

[0022] A sixteenth aspect of the present disclosure relates to the window according to the fifteenth aspect, wherein the silicon layers included in the second multilayer film have a total thickness of 500 nm or more.

[0023] A seventeenth aspect of the present disclosure relates to the window according to any one of the twelfth to sixteenth aspects, wherein the one or more layers of high refractive index material in the second multilayer film include a layer other than silicon.

[0024] An aspect (18) of the present disclosure relates to a window according to any one of aspects (1) to (17), wherein the maximum hardness of the window, measured by performing a Berkovich indentation hardness test on the first multilayer film, is at least 15 GPa.

[0025] Aspect (19) of the present disclosure relates to a window according to any one of aspects (1) to (18), wherein the hardness of the first multilayer film measured by performing a Berkovich indentation hardness test is at least 14 GPa over a depth range of 400 nm to 1000 nm.

[0026] Aspect (20) of the present disclosure relates to a window for a detection system. The window includes a substrate, a first multilayer film, and a second multilayer film. The substrate has a first surface and a second surface, the first surface and the second surface being the main surfaces of the substrate. The first multilayer film is disposed on the first surface of the substrate. The first multilayer film includes alternating layers of one or more high refractive index materials and one or more low refractive index materials, where the refractive index of the one or more high refractive index materials in the first multilayer film is higher than the refractive index of the one or more low refractive index materials in the first multilayer film. The second multilayer film is disposed on the second surface of the substrate. The second multilayer film includes alternating layers of one or more high refractive index materials and one or more low refractive index materials, where the refractive index of the one or more high refractive index materials in the second multilayer film is higher than the refractive index of the one or more low refractive index materials in the second multilayer film. The maximum hardness of the window measured by Berkovich indentation hardness testing of the first multilayer film is at least 8 GPa. The quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the average reflectance of the window calculated in a target wavelength range of 50 nm with a center wavelength in the range of 850 nm to 950 nm for light incident on the first and second surfaces at an angle of 15° or less is less than 4%, the CIELAB L* value of the window reflection for an incident angle of 60° or less to the first multilayer film is 37 or less, and the CIELAB a* value and b* value of the window reflection when viewed from the first multilayer film side are between -6.0 and 6.0.

[0027] Aspect (21) of the present disclosure relates to the window according to aspect (20), wherein the CIELAB L* value of reflection at an incident angle of 50° or less relative to the first multilayer film is 25 or less.

[0028] Aspect (22) of the present disclosure relates to a window according to aspect (20) or (21), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the average transmittance of the window, calculated over a 50 nm wide wavelength range of interest, exceeds 95% for light incident on the first and second surfaces at an angle of incidence of 15° or less.

[0029] Aspect (23) of the present disclosure relates to a window according to any one of aspects (20) to (22), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the average transmittance of the window calculated in the range of 400 nm to 700 nm for light incident on the first and second surfaces at an angle of incidence of 15° or less is less than 5%.

[0030] Aspect (24) of the present disclosure relates to a window according to any one of aspects (20) to (23), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the average P-polarized light transmittance and average S-polarized light transmittance of the window, calculated in a target wavelength range with a width of 50 nm, exceeds 85% for light incident on the first and second surfaces at an angle of incidence of 60° or less.

[0031] Aspect (25) of the present disclosure relates to a window according to aspect (24), wherein the window has an average P-polarized light transmittance and an average S-polarized light transmittance greater than 89% when calculated over a 50 nm wide wavelength range of interest for light incident on the first and second surfaces at an angle of incidence of 60° or less.

[0032] Aspect (26) of the present disclosure relates to a window according to any one of aspects (20) to (25), wherein the maximum hardness of the window measured by performing a Berkovich indentation hardness test on the first multilayer film is at least 15 GPa.

[0033] Aspect (27) of the present disclosure relates to a window according to any one of aspects (20) to (26), wherein one of the alternating layers in the first multilayer film that is furthest from the substrate constitutes the material of the edge of the window, the material of the edge of the window includes a low refractive index material, and the first multilayer film includes a scratch-resistant layer, the scratch-resistant layer being formed from one of one or more high refractive index materials and having a thickness of 1500 nm or more and 5000 nm or less.

[0034] Aspect (28) of the present disclosure relates to the window according to aspect (27), wherein the scratch-resistant layer is spaced from the edge by multiple layers of the alternating layers of one or more low refractive index materials and one or more high refractive index materials in the first multilayer film, and the scratch-resistant layer is spaced from the edge by at least 1000 nm.

[0035] Aspect (29) of the present disclosure relates to a window according to any one of aspects (20) to (28), wherein one or more high refractive index materials of the second multilayer film contain silicon having an extinction coefficient of 0.004 or less in a 50 nm wide wavelength range of interest.

[0036] An embodiment (30) of the present disclosure relates to the window according to embodiment (29), wherein the second multilayer film comprises two or more silicon layers.

[0037] An embodiment (31) of the present disclosure relates to the window according to embodiment (30), wherein the thickness of the silicon layer of the second multilayer film closest to the substrate is the smallest among the two or more silicon layers.

[0038] An embodiment (32) of the present disclosure relates to the window according to embodiment (31), wherein the total thickness of the silicon layers included in the second multilayer film is 500 nm or more.

[0039] An embodiment (33) of the present disclosure relates to the window according to any one of embodiments (29) to (32), wherein the one or more layers of high refractive index material in the second multilayer film include a layer other than silicon.

[0040] Aspect (34) of the present disclosure relates to a window for a detection system. The window includes a substrate, a first multilayer film, and a second multilayer film. The substrate has a first surface and a second surface, the first surface and the second surface being the main surfaces of the substrate. The first multilayer film is disposed on the first surface of the substrate. The first multilayer film includes alternating layers of one or more high refractive index materials and one or more low refractive index materials, where the refractive index of the one or more high refractive index materials in the first multilayer film is higher than the refractive index of the one or more low refractive index materials in the first multilayer film. The second multilayer film is disposed on the second surface of the substrate. The second multilayer film includes alternating layers of one or more high refractive index materials and one or more low refractive index materials, where the refractive index of the one or more high refractive index materials in the second multilayer film is higher than the refractive index of the one or more low refractive index materials in the second multilayer film, where the one or more high refractive index materials in the second multilayer film include silicon. The maximum hardness of the window, as measured by performing a Berkovich hardness test on the first multilayer film, is at least 15 GPa. The quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the average reflectance of the window, calculated over a 50-nm target wavelength range with a center wavelength of 850 nm to 950 nm, for light incident on the first and second surfaces at an angle of 15° or less is less than 4%, and the average transmittance of the window, calculated over a 50-nm target wavelength range for light incident on the first and second surfaces at an angle of 15° or less, is greater than 95%.

[0041] Aspect (35) of the present disclosure relates to the window according to aspect (34), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the average transmittance of the window calculated in the range of 400 nm to 700 nm for light incident on the first and second surfaces at an angle of incidence of 15° or less is less than 5%.

[0042] Aspect (36) of the present disclosure relates to a window according to aspect (34) or (35), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the average P-polarized light transmittance and average S-polarized light transmittance of the window are greater than 85% for light incident on the first and second surfaces at an angle of incidence of 60° or less, calculated in a 50 nm wide target wavelength range with a center wavelength of 850 nm to 950 nm.

[0043] Aspect (37) of the present disclosure relates to a window according to aspect (36), wherein the average P-polarized light transmittance and the average S-polarized light transmittance of the window are greater than 89% when calculated in a 50-nm wide target wavelength range with a center wavelength ranging from 850 nm to 950 nm for light incident on the first and second surfaces at an angle of incidence of 60° or less.

[0044] Aspect (38) of the present disclosure relates to a window according to any one of aspects (34) to (37), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the CIELAB L* value of the reflection of the window for an incident angle of 60° or less relative to the first multilayer film is 37 or less.

[0045] An embodiment (39) of the present disclosure relates to the window according to embodiment (38), wherein the CIELAB L* value of reflection at an incident angle of 50° or less relative to the first multilayer film is 25 or less.

[0046] Aspect (40) of the present disclosure relates to a window according to any one of aspects (34) to (39), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the CIELAB a* and b* values ​​of the reflection of the window when viewed from the first multilayer film side are between −6 and 6.

[0047] Aspect (41) of the present disclosure relates to a window according to any one of aspects (34) to (40), wherein one of the alternating layers in the first multilayer film that is furthest from the substrate constitutes the material of the edge of the window, the material of the edge of the window comprising a low refractive index material, and the first multilayer film comprising a scratch-resistant layer, the scratch-resistant layer being formed from one of one or more high refractive index materials and having a thickness of 1500 nm or more and 5000 nm or less.

[0048] Aspect (42) of the present disclosure relates to the window of aspect (41), wherein the scratch-resistant layer is spaced from the edge by multiple layers of the alternating layers of one or more low refractive index materials and one or more high refractive index materials in the first multilayer film, and the scratch-resistant layer is spaced from the edge by at least 1000 nm.

[0049] Aspect (43) of the present disclosure relates to a window according to any one of aspects (34) to (42), wherein the second multilayer film includes two or more silicon layers having an extinction coefficient of 0.01 or less in a 50 nm wide wavelength range of interest.

[0050] An embodiment (44) of the present disclosure relates to the window according to embodiment (43), wherein the thickness of the silicon layer of the second multilayer film closest to the substrate is the smallest among the two or more silicon layers.

[0051] An embodiment (45) of the present disclosure relates to the window according to embodiment (44), wherein the total thickness of the silicon layers included in the second multilayer film is 500 nm or more.

[0052] An embodiment (46) of the present disclosure relates to the window according to any one of embodiments (43) to (45), wherein the one or more layers of high refractive index material in the second multilayer film include a layer other than silicon.

[0053] Aspect (47) of the present disclosure relates to the window according to aspect (46), wherein the layer other than silicon among the one or more layers of high refractive index material in the second multilayer film is the layer among the one or more layers of high refractive index material closest to the substrate.

[0054] Aspect (48) of the present disclosure relates to the window according to any one of aspects (34) to (47), further comprising a perfluoropolyether layer disposed on the first multilayer film.

[0055] An embodiment (49) of the present disclosure relates to the window according to embodiment (14) or (30), wherein the second multilayer film comprises a TCO material layer, and two or more silicon layers are disposed between the TCO material layer and the substrate.

[0056] An embodiment (50) of the present disclosure relates to a window according to embodiment (49), wherein the sheet resistance of the TCO material layer is 140 Ω / □ or more and 210 Ω / □ or less, and the thickness of the TCO material layer is 20 nm or more and 30 nm or less.

[0057] Aspect (51) of the present disclosure relates to the window according to aspect (50), wherein the TCO material layer is indium tin oxide and has an extinction coefficient of 0.05 or less across the entire wavelength range of interest, which is 50 nm wide.

[0058] An embodiment (52) of the present disclosure relates to a window according to any one of embodiments (1) to (51), wherein the two or more silicon layers are spaced from the inner edge of the second multilayer film by an inner AR stack including at least two layers other than silicon as the one or more layers of high refractive index material.

[0059] Aspect (53) of the present disclosure relates to a window according to aspect (52), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the average reflectance of the window calculated in a target wavelength range with a width of 50 nm for light incident on the inner end face at an angle of incidence of 15° or less is less than 0.5%.

[0060] Aspect (54) of the present disclosure relates to a window according to any one of aspects (51) to (53), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the average transmittance of the window calculated in the range of 400 nm to 700 nm for light incident perpendicularly to the first and second surfaces is less than 1%.

[0061] An embodiment (55) of the present disclosure relates to the window of any of embodiments (51) to (54), wherein the second multilayer film includes at least 10 silicon layers, and the inner AR stack includes fewer than two layers of non-silicon as the one or more layers of high refractive index material.

[0062] Aspect (56) of the present disclosure relates to a window according to aspect (55), wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the fluctuation range (difference between the maximum and minimum values) of the polarized average reflectance of the window calculated in the wavelength range of 850 nm to 950 nm for light incident on the first multilayer film at an incident angle of 15° is less than 0.5%.

[0063] Additional features and advantages are set forth in the detailed description that follows, and will become apparent to those skilled in the art in part from the description, or may be learned by practice of the embodiments described herein, including the following detailed description, claims, and accompanying drawings.

[0064] It is to be understood that both the foregoing general description and the following detailed description are exemplary only and are intended to provide an overview or framework for understanding the nature and features of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate one or more embodiments and, together with the following detailed description, serve to explain the principles and operation of various embodiments. [Brief explanation of the drawings]

[0065] [Figure 1] FIG. 1 is a side view of a vehicle in an external environment, showing a LIDAR system on the roof of the vehicle and another LIDAR system on the front of the vehicle, in accordance with one or more embodiments of the present disclosure. [Figure 2]2 is a schematic diagram of one of the LIDAR systems of FIG. 1 , illustrating an electromagnetic wave emitter within the housing emitting electromagnetic waves that exit the housing through a window and return as reflected waves through the window, in accordance with one or more embodiments of the present disclosure. [Figure 3] FIG. 3 is a cross-sectional view of the window shown in FIG. 2 at region III of FIG. 2, illustrating the window comprising a substrate, a multilayer film on a first side of the substrate, and a second multilayer film on a second side of the substrate, in accordance with one or more embodiments of the present disclosure. [Figure 4] 4 is a cross-sectional view of the window shown in FIG. 3 in region IV of FIG. 3 , illustrating a multilayer film including alternating layers of one or more high refractive index materials and one or more low refractive index materials, wherein the edge of the multilayer film closest to the external environment is provided by one of the one or more layers of low refractive index materials, in accordance with one or more embodiments of the present disclosure. [Figure 5] FIG. 4 is a cross-sectional view of the window shown in FIG. 3 at region V of FIG. 3 , illustrating a second multilayer film including alternating layers of one or more high refractive index materials and one or more low refractive index materials, wherein an end face of the second multilayer film closest to the electromagnetic radiation detector is provided by one of the one or more layers of low refractive index material, in accordance with one or more embodiments of the present disclosure. [Figure 6A] 1 is a graph showing the refractive index and extinction coefficient of silicon materials that can be used in multilayer films in the wavelength range of 350 nm to 1000 nm, in accordance with one or more embodiments of the present disclosure. [Figure 6B] 6B is a graph showing the extinction coefficient of the silicon material shown in FIG. 6A in the wavelength range of 800 nm to 1000 nm, in accordance with one or more embodiments of the present disclosure. [Figure 7] 1 is a graph showing modeled two-sided transmittance for light incident at a 15° angle of incidence on the first multilayer coating of the window of Example 1 in the infrared wavelength range of interest, 850 nm to 950 nm, according to one or more embodiments of the present disclosure. [Figure 8]1 is a graph showing the S-polarized light transmittance and P-polarized light transmittance of two surfaces in the infrared wavelength range of interest, 850 nm to 950 nm, for light incident at an angle of incidence of 60° on the first multilayer coating of the window of Example 1, as obtained by modeling, in accordance with one or more embodiments of the present disclosure. [Figure 9] 1 is a graph showing modeled two-sided reflectance for light incident on the first and second multilayer coatings of the window of Example 1 at a 15° angle of incidence in the infrared wavelength range of interest, 850 nm to 950 nm, according to one or more embodiments of the present disclosure. [Figure 10] 1 is a graph showing modeled two-sided transmittance for light in the visible spectrum incident at a 15° angle of incidence through the first multilayer coating of the window of Example 1, in accordance with one or more embodiments of the present disclosure. [Figure 11A] 1 is a graph showing CIELAB color space a* and b* values ​​of the reflection obtained by modeling for light incident on the first multilayer coating of the window of Example 1 at multiple angles of incidence, in accordance with one or more embodiments of the present disclosure. [Figure 11B] 1 is a graph showing CIELAB lightness L* values ​​of reflection obtained by modeling for light incident at multiple angles of incidence on the first multilayer coating of the window of Example 1, in accordance with one or more embodiments of the present disclosure. [Figure 12] 1 is a graph showing nanoindentation hardness as a function of depth into the first multilayer film of one sample constructed according to the window of Example 1, in accordance with one or more embodiments of the present disclosure. [Figure 13] 1 is a graph showing the two-sided transmittance for light in the spectral range of 350 nm to 1500 nm incident on the first multilayer coating of the window of Example 2, obtained by modeling, in accordance with one or more embodiments of the present disclosure. [Figure 14] 1 is a graph showing modeled two-sided reflectance for light in the spectral range of 350 nm to 1500 nm incident on the first and second multilayer coatings of the window of Example 2, in accordance with one or more embodiments of the present disclosure. [Figure 15]1 is a graph showing CIELAB color space a* and b* values ​​of the reflection obtained by modeling for light incident at multiple angles of incidence on the first multilayer coating of the window of Example 2, in accordance with one or more embodiments of the present disclosure. [Figure 16] 10 is a graph showing the two-sided transmittance for light in the spectral range of 350 nm to 1500 nm incident on the first multilayer coating of the window of Example 3, as obtained by modeling, in accordance with one or more embodiments of the present disclosure. [Figure 17A] 1 is a graph showing modeled two-sided reflectance for light in the spectral range of 350 nm to 1500 nm incident on the first and second multilayer coatings of the window of Example 3, according to one or more embodiments of the present disclosure. [Figure 17B] 1 is a graph showing modeled two-sided reflectance for light in the 850 nm to 950 nm spectral range incident on the first and second multilayer coatings of the window of Example 3, according to one or more embodiments of the present disclosure. [Figure 18] 1 is a graph showing CIELAB color space a* and b* values ​​of the reflection obtained by modeling for light incident at multiple angles of incidence on the first multilayer coating of the window of Example 3, in accordance with one or more embodiments of the present disclosure. [Figure 19] 10 is a graph showing the two-sided transmittance for light in the spectral range of 350 nm to 1600 nm incident on the first multilayer coating of the window of Example 4, obtained by modeling, in accordance with one or more embodiments of the present disclosure. [Figure 20A] 10 is a graph showing the reflectance of light in the spectral range of 350 nm to 1700 nm incident on the first multilayer coating of the window of Example 4, as obtained by modeling, in accordance with one or more embodiments of the present disclosure. [Figure 20B] 10 is a graph showing the reflectance of light in the spectral range of 350 nm to 1700 nm incident on the second multilayer coating of the window of Example 4, as obtained by modeling, in accordance with one or more embodiments of the present disclosure. [Figure 20C]10 is a graph showing the reflectance of light in the spectral range of 800 nm to 1050 nm incident at a 15° angle of incidence on the first multilayer coating of the windows of Example 3 and Example 4, as obtained by modeling, in accordance with one or more embodiments of the present disclosure. [Figure 20D] 10 is a graph showing the reflectance of light in the spectral range of 800 nm to 1050 nm incident at a 60° angle of incidence on the first multilayer coating of the windows of Example 3 and Example 4, as obtained by modeling, in accordance with one or more embodiments of the present disclosure. [Figure 20E] 10 is a graph showing the reflectance of the second multilayer coating of the windows of Example 3 and Example 4 for light in the spectral range of 800 nm to 1050 nm incident at an angle of incidence of 15°, obtained by modeling, in accordance with one or more embodiments of the present disclosure. [Figure 21] 1 is a graph showing CIELAB color space a* and b* values ​​of the reflection obtained by modeling for light incident at multiple angles of incidence on the first multilayer coating of the window of Example 4, in accordance with one or more embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0066] Embodiments of windows for use in LIDAR detectors are now described in detail. The same reference numerals are used throughout the drawings to indicate identical or similar parts whenever possible. The windows described herein can include first and second multilayer films composed of alternating layers of high and low refractive index materials. The first and second multilayer films are configured to provide relatively high transmittance and low reflectance in a desired infrared wavelength range of interest. When mounted in a LIDAR system, the first multilayer film can face away from the detector / radiation emitter, i.e., the side exposed to the outside world, while the second multilayer film faces the detector / radiation emitter. In other words, the first multilayer film can be mounted so that it is visible to an outside observer of the LIDAR system. Light emitted from the radiation emitter can first enter the second multilayer film and then propagate through the substrate. According to the present disclosure, the first multilayer film of the window described herein can include one or more relatively thick (e.g., 500 nm or greater) scratch-resistant layers of a high refractive index material. The scratch-resistant layers can be embedded in the first multilayer film so that the maximum nanoindentation hardness of the window, measured by Berkovich indentation hardness testing of the first multilayer film, is 8 GPa or greater (e.g., 10 GPa or greater, 12 GPa or greater, 14 GPa or greater). The nanoindentation hardness of the first multilayer film at a depth of 1 μm can be as described above. Providing such nanoindentation hardness has the advantage of providing scratch resistance and improving the performance of the LIDAR system.

[0067] Additionally, in aspects, the alternating layers in the first and second multilayers of the windows described herein are configured to provide desirable optical performance attributes for LIDAR system operation in the infrared spectrum. In embodiments, the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayers are configured to provide an average transmittance of the window greater than 90% (e.g., 95% or greater) for light incident on the first and second surfaces at an angle of incidence of 15° or less, as calculated over at least a 50-nm, 60-nm, 70-nm, 80-nm, or 90-nm wavelength band of interest generally centered between 850 nm and 950 nm. In embodiments, the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayers are configured to provide an average transmittance of the window greater than 90% (e.g., 95% or greater) for light incident at normal incidence across the entire spectral range of 850 nm to 950 nm. In addition, the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured so that the average P-polarized light transmittance and average S-polarized light transmittance of the window calculated in a target wavelength range of 50 nm width (or 60 nm width, or 70 nm width, or 80 nm width, or 90 nm width) for light incident on the first surface and the second surface at an incident angle of 60 degrees or less are greater than 85% (e.g., 89% or more, 90% or more, 93% or more). In some embodiments, the thicknesses, number of layers, and materials of the alternating layers in the first and second multilayer films are configured to provide an average window reflectance of 5.0% or less (e.g., 4.0% or less, 3.0% or less, 2.0% or less, 1.0% or less) calculated over a 50 nm wide (or 60 nm wide, or 70 nm wide, or 80 nm wide, or 90 nm wide) wavelength range of interest for light incident on the first and second surfaces at an angle of incidence of 15° or less. In some aspects, the quantitative composition, thicknesses, number of layers, and materials of the alternating layers in the first and second multilayer films are configured to provide an average window reflectance (average reflectance for S-polarized light and P-polarized light) of less than 4.0% (e.g., 3.0% or less, 2.0% or less, 1.0% or less) at angles of incidence less than 15°.In some embodiments, the thicknesses, number of layers, and materials of the alternating layers in the first and second multilayers are configured to provide an average reflectance (average reflectance for S-polarized light and P-polarized light) of the window below 5.5% (e.g., 5.0% or less, 4.0% or less, 3.5% or less, 3.0% or less, 2.0% or less, 1.0% or less) at angles of incidence less than 45°. In some embodiments, the thicknesses, number of layers, and materials of the alternating layers in the first and second multilayers are configured to provide an average reflectance (average reflectance for S-polarized light and P-polarized light) of the window below 8.0% (e.g., 7.5% or less, 7.0% or less, 6.5% or less, 6.0% or less, 5.0% or less, 5.0% or less, 4.0% or less, 3.5% or less, 3.0% or less, 2.0% or less, 1.0% or less) at angles of incidence less than 60°.

[0068] In yet further aspects, the first and second multilayer films of the windows described herein can be constructed to have relatively low reflectance and transmittance of visible light. This can provide an aesthetically pleasing dark appearance for the window while eliminating signal noise. In some embodiments, for example, the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured to provide an average transmittance of the window of less than 5% (e.g., 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, 2.5% or less, 2.0% or less) for light incident on the first multilayer film at an angle of incidence of 15° or less, calculated over a wavelength range of 400 nm to 700 nm. In some embodiments, for example, the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured to provide an average transmittance of the window of less than 1% (e.g., 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, 2.5% or less, 2.0% or less) for light incident perpendicularly to the first multilayer film, calculated over a wavelength range of 450 nm to 650 nm. Such low visible light transmittance can be achieved by incorporating the absorbing layer in the second multilayer film in amounts described herein.

[0069] The window can also be configured to reduce reflection in the visible wavelength range. In various embodiments, for example, the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the average reflectance of the window calculated over a wavelength range of 450 nm to 650 nm for light incident on the first multilayer film at an angle of incidence of 15° or less is less than 10% (e.g., 9.0% or less, 8.0% or less, 7.0% or less, 6.0% or less, 5.0% or less, 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, 2.5% or less, or 2.0% or less). In several embodiments, the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the average reflectance of the window calculated in the range of 450 nm to 650 nm for light incident on the first multilayer film at an angle of incidence of 45° or less is less than 12% (e.g., 11% or less, 10% or less, 9.0% or less, 8.0% or less, 7.0% or less, 6.0% or less, 5.0% or less, 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, 2.5% or less, 2.0% or less). In several embodiments, the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured so that the average reflectance of the window calculated in the range of 450 nm to 650 nm for light incident on the first multilayer film at an angle of incidence of 60° or less is less than 16% (e.g., 15% or less, 14% or less, 13% or less, 12% or less, 11% or less, 10% or less, 9.0% or less, 8.0% or less, 7.0% or less, 6.0% or less, 5.0% or less, 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, 2.5% or less, 2.0% or less).

[0070] This allows the windows described herein to exhibit a CIELAB lightness L* value of 40 or less (e.g., 37 or less, 35 or less, 30 or less) when viewed from the first multilayer film (i.e., from outside the LIDAR detector) at an angle of 60 degrees or less. Furthermore, when illuminated at a plurality of different light source incident angles ranging from 0° to 60°, the windows described herein can exhibit a CIELAB color space a* and b* value of 2.5 or greater to 6 or less (e.g., -5 or greater to 5 or less, -4 or greater to 4 or less, -3 or greater to 3 or less, -2.5 or greater to 2.5 or less). To minimize the window's visibility to an outside viewer, the window's color when viewed from the first multilayer film side can be black or a relatively dark color. In some embodiments, the window exhibits a CIELAB color space a* and b* value of 2.5 or greater to 2.5 when illuminated at a plurality of different light source incident angles ranging from 0° to 90°.

[0071] In a further aspect, the windows described herein can be characterized by a combination of a relatively high transmittance (e.g., 90% or greater) in a 50-nm-wide (or 60-nm-wide, or 70-nm-wide, or 80-nm-wide, or 90-nm-wide) wavelength range of interest centered between 850 nm and 950 nm, and a relatively low average transmittance (e.g., 5% or less) in the visible spectrum (400 nm to 700 nm). The difference in transmittance between such relatively close spectral ranges can be achieved by incorporating an absorbing layer with a relatively low extinction coefficient in the 50-nm-wide (or 60-nm-wide, or 70-nm-wide, or 80-nm-wide, or 90-nm-wide) wavelength range of interest. In some embodiments, the extinction coefficient of the absorbing layer in a 50 nm wide (or 60 nm wide, or 70 nm wide, or 80 nm wide, or 90 nm wide) wavelength range of interest from 850 nm to 950 nm should be 0.01 or less (e.g., 0.009 or less, 0.008 or less, 0.007 or less, 0.005 or less, 0.004 or less, 0.0035 or less, 0.0030 or less, 0.0025 or less, 0.0020 or less, 0.0015 or less, or 0.0010 or less). In some embodiments, the extinction coefficient of the absorbing layer in the visible spectrum can be relatively high (e.g., 0.05 or more, 0.06 or more, 0.07 or more, or 0.08 or more) to adequately absorb visible light and facilitate achieving the opaque dark appearance described herein. Exemplary materials for the absorbing layers described herein include silicon materials, which have a low extinction coefficient in the 50 nm wide (or 60 nm wide, or 70 nm wide, or 80 nm wide, or 90 nm wide) wavelength range of interest. Incorporation of such layers into the first and second multilayer films in the amounts described herein can provide sufficient absorption of visible light to achieve a suitable dark appearance, while also achieving relatively high transmittance in the 50 nm wide (or 60 nm wide, or 70 nm wide, or 80 nm wide, or 90 nm wide) near-infrared wavelength range of interest.

[0072] Thus, the windows described herein provide durable anti-reflective performance for the desired wavelength range of 850 nm to 950 nm, while also providing a black or dark appearance that is aesthetically pleasing and provides performance benefits. The windows described herein can improve the performance of LIDAR detectors over existing detectors by preventing visible light from entering the detector, improving the signal-to-noise ratio. Additionally, the windows described herein can reduce unpleasant glare to the eyes of outside viewers.

[0073] Unless otherwise noted, the total reflectance, specular reflectance, and average reflectance values ​​given herein are two-sided reflectance values ​​that represent the total reflectance of the entire window, including the reflectance associated with each material interface of the window (e.g., air-to-multilayer interface, multilayer-to-substrate interface, etc.) Also, unless otherwise noted, reflectance values ​​in the infrared are measured from the side of the second multilayer described herein (e.g., the side facing the detector / emitter of a LIDAR system), and reflectance values ​​in the visible are measured from the side of the first multilayer described herein (e.g., the side facing the outside world of a LIDAR system).

[0074] Unless otherwise specified in this specification, the average transmittance and average reflectance values ​​are determined using the reflectance values ​​(%) and transmittance values ​​(%) at various wavelengths within a specified wavelength range. The average transmittance and average reflectance values ​​can be determined by averaging the values ​​of integer wavelengths within a specified wavelength range.

[0075] Unless otherwise specified in this specification, the CIELAB color space a* value, b* value and lightness L* value are values ​​measured / simulated under the conditions of a standard observer with a 10-degree field of view using a D65 light source.

[0076] As used herein, the terms "dark appearance" or "black appearance" refer to the reflective appearance of a window when viewed from the exterior surface. Windows having a dark or black appearance according to the present disclosure have an average transmittance of 5% or less in the range of 400-700 nm when viewed at an angle of 60° or less, and a CIELAB lightness L* value of less than 45 when viewed at an angle of 60° or less.

[0077] Unless expressly stated otherwise, no method described herein is intended to be construed as requiring the steps (operations) to be performed in a particular order. Accordingly, no order of steps is intended to be inferred in any way, unless a method claim actually recites the order of the steps, or unless the claims or detailed description expressly state that the steps are limited to a particular order. This applies to all implicit matters that may be a basis for interpretation, such as matters of reasoning regarding the sequence or sequence of steps, common meanings derived from grammatical construction or punctuation, and the number or type of embodiments described herein.

[0078] As used herein, the term "and / or," when used in conjunction with a list of two or more items, means that any one of the listed items may be used alone, or any two or more of the listed items may be used in any combination. For example, if a composition is described as containing components A, B, and / or C, the composition can contain A alone, B alone, C alone, a combination of A and B, a combination of A and C, a combination of B and C, or a combination of A, B, and C.

[0079] Modifications of the present disclosure will occur to those skilled in the art and to those who make or use the present disclosure. Accordingly, it should be understood that the above-described embodiments illustrated in the drawings are for illustrative purposes only and are not intended to limit the scope of the present disclosure. The scope of the present disclosure is defined by the following claims, which are to be construed in accordance with patent law principles, including the doctrine of equivalents.

[0080] As used herein, relational terms such as first and second, top and bottom, etc., are used solely to distinguish one entity or operation from another and do not necessarily require or imply any actual relationship or order between those entities or operations. The terms "comprise," "including," "having," and other variations thereof have a non-exclusive inclusion meaning. Thus, when a process, method, article, or apparatus "comprises" ("includes" or "has") enumerated elements, it does not include only the enumerated elements but may also include other elements not expressly enumerated and elements inherent to such process, method, article, or apparatus. When an element preceded by the article "a" is described as "comprising" ("including" or "having"), it does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the enumerated elements, unless a further limiting condition is provided.

[0081] As used herein, the term "about" means that a quantitative element or characteristic, such as an amount, size, composition, or parameter, need not be exact or necessarily be the exact value. Rather, the quantitative element or characteristic can be approximate and / or vary, incorporating tolerances, conversion factors, rounding, measurement error, and other factors known to those skilled in the art, as necessary. Thus, when the term "about" is used to describe a value or one endpoint of a range, it is understood that the specific value or endpoint is included in the present disclosure. It should be noted that, regardless of whether a numerical value or one endpoint of a range is described herein with "about," the endpoint of the numerical value or range is intended to encompass both embodiments, those modified by "about" and those not modified by "about." It should also be understood that the endpoints of each range are both relative to and independent of each other.

[0082] Additionally, the term "formed from" can mean one or more of "comprise," "consist essentially of," or "consist of." For example, if a component is "formed from" a particular material, the component may comprise, consist essentially of, or consist of the particular material.

[0083] Also, as used herein, the terms "article," "glass-article," "ceramic-article," "glass-ceramic," "glass element," and "glass-ceramic article(s)" are used interchangeably in their broadest sense and include any object made in whole or in part from glass and / or glass-ceramic materials.

[0084] As used herein, the term "disposed" is used to refer to a layer or sublayer that is provided on a surface by methods such as coating, vapor deposition, forming, etc. The term "disposed" can include providing a layer / sublayer directly on an adjacent layer / sublayer, or providing a layer / sublayer separated by an intervening material that may or may not form a layer.

[0085] Unless otherwise specified herein, the refractive index of the materials described herein is measured at 905 nm.

[0086] As used herein, the term "extinction coefficient" or "k" refers to a dimensionless physical property based on the product of the absorption coefficient of a material and the wavelength of light divided by 4π.

[0087] 1, a vehicle 10 is equipped with one or more LIDAR systems 12. The one or more LIDAR systems 12 may be located anywhere on or within the vehicle 10. For example, the one or more LIDAR systems 12 may be located on a roof 14 of the vehicle 10, a front portion 16 of the vehicle 10, or both.

[0088] 2 , each of the one or more LIDAR systems 12 includes an electromagnetic radiation detector 18 as known in the art. The electromagnetic radiation detector 18 may be housed within a housing 20. The electromagnetic radiation detector 18 emits an electromagnetic wave 22 having a wavelength or range of wavelengths. The emitted electromagnetic wave 22 exits the housing 20 through a window 24 that is on the emission path of the electromagnetic wave. If an object (not shown) in the external world 26 is on the emission path of the electromagnetic wave 22, the emitted electromagnetic wave 22 will reflect off the object and return to the electromagnetic radiation detector 18 as a reflected wave 28. The reflected wave 28 also passes through the window 24 to reach the electromagnetic radiation detector 18. In various embodiments, the emitted wave 22 and the reflected wave 28 may include light within an appropriate wavelength range of interest. For example, in some embodiments, emitted wave 22 and reflected wave 28 can be between 850 nm and 950 nm (e.g., between 875 nm and 925 nm, between 890 nm and 910 nm, or about 905 nm). It is contemplated that electromagnetic waves other than reflected wave 28 (e.g., electromagnetic waves having wavelengths in the visible spectrum, some ultraviolet range, etc.) may also interact with window 24. As described herein, window 24 can include a multilayer film having a layer structure designed to absorb light in the visible spectrum and reflect a relatively small amount of light in the visible spectrum, thereby giving the window a dark or black appearance when viewed from outside enclosure 20.

[0089] The "visible spectrum" refers to the portion of the electromagnetic spectrum visible to the human eye and generally refers to electromagnetic waves with wavelengths between 400 nm and approximately 700 nm. The "ultraviolet range" is the portion of the electromagnetic spectrum with wavelengths between approximately 10 nm and approximately 400 nm. The "infrared range" of the electromagnetic spectrum is the region with long wavelengths above approximately 700 nm. The sun generates solar electromagnetic waves, commonly called "sunlight," whose wavelengths fall within these three ranges.

[0090] Referring now to FIG. 3 , each window 24 of the one or more LIDAR systems 12 includes a substrate 30. The substrate 30 has a first surface 32 and a second surface 34. The first surface 32 and the second surface 34 are major surfaces of the substrate 30. The first surface 32 is the surface closest to the external environment 26. The second surface 34 is the surface closest to the electromagnetic radiation detector 18. The emitted wave 22 encounters the second surface 34 before encountering the first surface 32. Meanwhile, the reflected wave 28 encounters the first surface 32 before encountering the second surface 34. The substrate 30 also includes a first multilayer film 36 disposed on the first surface 32 of the substrate 30 and a second multilayer film 38 disposed on the second surface 34 of the substrate 30. It should be understood that the window 24 described herein is not limited to vehicle applications, but may be used in any application where the window 24 would be beneficial in providing the improved crashworthiness and optical performance described in detail herein.

[0091] Substrate 30 can be constructed from a variety of different materials consistent with the teachings of this disclosure. In embodiments, substrate 30 can be constructed from any type of glass, glass-ceramic, ceramic, or suitable polymer-based material. Various examples of the structure and composition of substrate 30 are now described in detail.

[0092] In embodiments, substrate 30 comprises a glass composition or is a glass article. Substrate 30 can comprise, for example, borosilicate glass, aluminosilicate glass, soda-lime glass, chemically strengthened borosilicate glass, chemically strengthened aluminosilicate glass, or chemically strengthened soda-lime glass. In embodiments, the glass composition of substrate 30 is a composition that can be chemically strengthened by an ion exchange process. In embodiments, this composition can be a lithium-ion-free composition.

[0093] Alkali aluminosilicate glass compositions suitable for substrate 30 include alumina, at least one alkali metal, and SiO. In some embodiments, the glass composition includes more than 50 mol% SiO, in other embodiments at least 58 mol% SiO, and in still other embodiments at least 60 mol% SiO, and has a ratio (AlO+BO) / Σ 修飾物質 (i.e., the sum of the modifiers) is greater than 1, the component ratios are expressed in mole percent, and the modifiers in the formula are alkali metal oxides. In a particular embodiment, the composition comprises 58-72 mole percent SiO, 9-17 mole percent AlO, 2-12 mole percent BO, 8-16 mole percent NaO, and 0-4 mole percent KO, and the ratio (AlO+BO) / Σ 修飾物質 is greater than 1.

[0094] Another alkali aluminosilicate glass composition suitable for substrate 30 includes 64-68 mol% SiO, 12-16 mol% NaO, 8-12 mol% AlO, 0-3 mol% BO, 2-5 mol% KO, 4-6 mol% MgO, and 0-5 mol% CaO, where 66 mol%≦SiO+BO+CaO≦69 mol%, NaO+KO+BO+MgO+CaO+SrO>10 mol%, 5 mol%≦MgO+CaO+SrO≦8 mol%, (NaO+BO)-AlO≦2 mol%, 2 mol%≦NaO-AlO≦6 mol%, and 4 mol%≦(NaO+KO)-AlO≦10 mol%.

[0095] Other alkali aluminosilicate glass compositions suitable for substrate 30 include 2 mol % or more of Al2O3 and / or ZrO2, or 4 mol % or more of Al2O3 and / or ZrO2.

[0096] An example glass composition includes SiO, BO, and NaO, where (SiO + BO) > 66 mol% and NaO > 9 mol%. In one embodiment, the composition includes at least 6 wt% aluminum oxide. In a further embodiment, the composition of one or more alkaline earth oxides, e.g., the alkaline earth oxide content, is at least 5 wt%. In some embodiments, a suitable composition further includes at least one of KO, MgO, and CaO. In a specific embodiment, the composition of substrate 30 includes 61-75 mol% SiO, 7-15 mol% AlO, 0-12 mol% BO, 9-21 mol% NaO, 0-4 mol% KO, 0-7 mol% MgO, and 0-3 mol% CaO.

[0097] Yet another exemplary composition suitable for substrate 30 includes 60-70 mol% SiO, 6-14 mol% AlO, 0-15 mol% BO, 0-15 mol% LiO, 0-20 mol% NaO, 0-10 mol% KO, 0-8 mol% MgO, 0-10 mol% CaO, 0-5 mol% ZrO, 0-1 mol% SnO, 0-1 mol% CeO, less than 50 ppm AsO, and less than 50 ppm SbO, where 12 mol%≦(LiO+NaO+KO)≦20 mol%, and 0 mol%≦(MgO+CaO)≦10 mol%.

[0098] Yet another exemplary glass composition suitable for substrate 30 includes 63.5-66.5 mol% SiO, 8-12 mol% AlO, 0-3 mol% BO, 0-5 mol% LiO, 8-18 mol% NaO, 0-5 mol% KO, 1-7 mol% MgO, 0-2.5 mol% CaO, 0-3 mol% ZrO, 0.05-0.25 mol% SnO, 0.05-0.5 mol% CeO, less than 50 ppm AsO, and less than 50 ppm SbO, where 14 mol%≦(LiO+NaO+KO)≦18 mol%, and 2 mol%≦(MgO+CaO)≦7 mol%.

[0099] The substrate 30 can be a substantially flat or sheet-like substrate, although other embodiments may utilize substrates that are formed or shaped into other shapes, such as curved shapes. The length and width of the substrate 30 can vary depending on the desired dimensions of the window 24. The substrate 30 can be formed using a variety of methods, including float glass processes and downdraw processes (e.g., fusion draw, slot draw). The substrate 30 can be used in an untempered state. A commercially available example of an untempered substrate 30 suitable for the window 24 is Corning® Glass Code 2320, a sodium aluminosilicate glass substrate.

[0100] The glass forming the substrate 30 can be modified so that the region continuous with the first surface 32 and / or the region continuous with the second surface 34 is under compressive stress ("CS"). In such a case, the region under compressive stress extends from the first surface 32 and / or the second surface 34 to the compression depth. This compressive stress also creates a region under tensile stress in the center. The tensile stress reaches a maximum value at the center of this central region, which is referred to as the central tension (CT). The central region extends between the compression depths and is under tensile stress. The tensile stress in the central region balances (acts to counteract) the compressive stress in the region under compressive stress. As used herein, "depth of compression" and "DOC" refer to the depth within the substrate 30 at which stress changes from compressive to tensile. The compression depth is the depth at which the stress changes from positive (compressive) to negative (tensile), and thus the stress value is zero. The compression depth protects the substrate 30 from cracks caused by sharp impacts to the first surface 32 and / or the second surface 34 of the substrate 30 from propagating beyond the compression depth, and the compressive stress minimizes the likelihood of a propagated crack breaking through the compression depth. In embodiments, each compression depth is at least 20 μm. In embodiments, the absolute value of the maximum compressive stress C in the region subjected to compressive stress is at least 200 MPa, at least about 400 MPa, at least 600 MPa, or up to about 1000 MPa.

[0101] Two methods for extracting a detailed and accurate stress profile (stress as a function of depth) of a substrate 30 having regions under compressive stress are disclosed in U.S. Patent No. 9,140,543, entitled "Systems and Methods for Measuring Stress Profile of Ion-Exchanged Glass," filed May 3, 2012, by Douglas Clippinger Alan et al., which claims the benefit of priority to U.S. Provisional Patent Application No. 61 / 489,800, filed May 25, 2011, the entire disclosure of which is incorporated herein by reference.

[0102] In some embodiments, creating a compressively stressed region in substrate 30 involves subjecting substrate 30 to an ion-exchange chemical tempering process (chemical tempering is often referred to as "chemical strengthening"). In an ion-exchange chemical tempering process, ions at or near first and second sides 32 and 34 of substrate 30 are replaced with larger ions, typically of the same valence or oxidation state. In embodiments in which substrate 30 comprises (or consists essentially of) an alkali aluminosilicate glass, an alkali borosilicate glass, an alkali aluminoborosilicate glass, or an alkali silicate glass, the ions in the surface layer of the glass and the larger ions are typically selected from the group consisting of Na, ... + (Li + is present in the glass), K + , Rb + , Cs + Alternatively, the monovalent cations in or near the first surface 32 and the second surface 34 may be replaced with monovalent cations other than alkali metal cations, such as Ag + etc.) can also be substituted.

[0103] In some embodiments, the ion-exchange process is performed by immersing the substrate 30 in a molten salt bath containing larger ions to replace the smaller ions in the substrate 30. Parameters of the ion-exchange process include, but are not limited to, bath composition and temperature, immersion time, number of times the glass is immersed in one or more salt baths, use of multiple salt baths, and additional steps such as annealing and washing. Those skilled in the art will appreciate that the parameters of such ion-exchange processes are typically determined by the composition of the substrate 30 and the desired compressive depth and compressive stress of the substrate 30 as a result of the strengthening process. By way of example, ion-exchange of an alkali-metal-containing glass substrate can be performed by immersing it in at least one molten bath containing salts of larger alkali metal ions (e.g., but not limited to, nitrates, sulfates, chlorides, etc.). In some embodiments, the molten salt bath includes potassium nitrate (0-100% by weight), sodium nitrate (0-100% by weight), and lithium nitrate (0-12% by weight), with the combined weight percentage of potassium nitrate and sodium nitrate ranging from 88% to 100% by weight. In embodiments, the temperature of the molten salt bath typically ranges from about 350°C to about 500°C, and the immersion time ranges from about 15 minutes to about 40 hours, e.g., from about 20 minutes to about 10 hours. However, other temperatures and immersion times can also be used. The substrate 30 can be subjected to a process such as acid polishing to remove or reduce the effects of surface defects.

[0104] In some embodiments, the substrate 30 includes a glass-ceramic material having both a glass phase and a ceramic phase. Exemplary glass-ceramics include those in which the glass phase is formed by silicate, borosilicate, aluminosilicate, or aluminoborosilicate, and the ceramic phase is formed by β-spodumene, β-quartz, nepheline, kalsilite, or carnegieite. The term "glass-ceramic" includes materials fabricated using controlled glass crystallization. Examples of suitable glass-ceramics include LiO-AlO-SiO (i.e., LAS-based) glass ceramics, MgO-AlO-SiO (i.e., MAS-based) glass ceramics, ZnO×AlO×nSiO (i.e., ZAS-based) glass ceramics, and / or glass ceramics containing β-quartz solid solution, β-spodumene, cordierite, lithium disilicate, or the like as the primary crystalline phase. Glass-ceramic substrates can be strengthened using chemical strengthening processes.

[0105] In embodiments, substrate 30 comprises a ceramic material, such as an inorganic crystal, such as an oxide, nitride, carbide, oxynitride, and / or carbonitride. Exemplary ceramics include materials having an alumina phase, an aluminum titanate phase, a mullite phase, a cordierite phase, a zircon phase, a spinel phase, a perovskite phase, a zirconia phase, a ceria phase, a silicon carbide phase, a silicon nitride phase, a silicon aluminum oxynitride phase, or a zeolite phase.

[0106] In some embodiments, the substrate 30 comprises an organic or suitable polymeric material. Examples of suitable polymers include, but are not limited to, thermoplastic resins such as polystyrene (PS) (including styrene copolymers and blends), polycarbonate (PC) (including copolymers and blends), polyester (including copolymers and blends such as polyethylene terephthalate copolymers and polyethylene terephthalate copolymers), polyolefins (PO) and cyclic polyolefins (cyclic PO), polyvinyl chloride (PVC), acrylic polymers (including copolymers and blends) including polymethyl methacrylate (PMMA), thermoplastic urethanes (TPU), polyetherimides (PEI), and blends of these polymers. Other exemplary polymers include epoxy resins, styrene resins, phenolic resins, melamine resins, and silicone resins.

[0107] In some embodiments, the substrate 30 includes multiple layers or sublayers. The layers or sublayers of the substrate 30 may be the same or different from one another. In some embodiments, for example, the substrate 30 includes a glass laminate structure. In some embodiments, the glass laminate structure includes a first glass sheet and a second glass sheet, which are bonded to one another via a suitable interlayer (e.g., a polymer interlayer) disposed between the first glass sheet and the second glass sheet. In some embodiments, the glass laminate structure includes a glass-on-glass laminate structure (e.g., a laminate structure formed by a fusion draw process). Glass-polymer laminates are also within the scope of the present disclosure. Any material capable of meeting the optical requirements described herein may be used for the substrate 30.

[0108] In embodiments, substrate 30 exhibits a modulus of elasticity (Young's modulus) in the range of about 30 GPa to about 120 GPa. In some examples, the modulus of elasticity of the substrate can be in the range of about 30 GPa to about 110 GPa, about 30 GPa to about 100 GPa, about 30 GPa to about 90 GPa, about 30 GPa to about 80 GPa, about 30 GPa to about 70 GPa, about 40 GPa to about 120 GPa, about 50 GPa to about 120 GPa, about 60 GPa to about 120 GPa, about 70 GPa to about 120 GPa, and all ranges and sub-ranges therebetween.

[0109] In embodiments, substrate 30 exhibits an average transmittance in the visible wavelength region of about 85% or greater, about 86% or greater, about 87% or greater, about 88% or greater, about 89% or greater, about 90% or greater, about 91% or greater, or about 92% or greater. In embodiments, substrate 30 includes a coloring component (e.g., a coloring layer or colorant) and can optionally exhibit a color such as white, black, red, blue, green, yellow, orange, etc.

[0110] As shown in FIG. 3 , substrate 30 has a thickness 35, defined as the shortest linear distance between first surface 32 and second surface 34. In some embodiments, thickness 35 of substrate 30 is between about 100 μm and about 5 mm. In some embodiments, physical thickness 35 of substrate 30 can be between about 100 μm and about 500 μm (e.g., 100 μm, 200 μm, 300 μm, 400 μm, or 500 μm). In other embodiments, thickness 35 is between about 500 μm and about 1000 μm (e.g., 500 μm, 600 μm, 700 μm, 800 μm, 900 μm, or 1000 μm). Thickness 35 can also be greater than about 1 mm (e.g., about 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, or 7 mm). In one or more specific embodiments, thickness 35 is 2 mm or less or 1 mm or less.

[0111] In embodiments, thickness 35 is sufficiently uniform that substrate 30 has a planar shape (e.g., thickness 35 varies by less than 1% across the substrate). In embodiments, thickness 35 is non-uniform, having a value that varies as a function of position on substrate 30. For aesthetic and / or functional reasons, thickness 35 can vary along one or more of its dimensions. For example, the edges of substrate 30 can be thicker than the center of substrate 30. The length, width, and physical thickness dimensions of substrate 30 can also vary depending on the intended use of article 30.

[0112] In some embodiments, substrate 30 includes a layer of a material that absorbs visible light and transmits infrared light. Examples of such materials include acrylic sheets that transmit infrared light and absorb visible light, such as those commercially available from ePlastics under the tradenames Plexiglas® IR acrylic 3143 and CYRO under the tradenames ACRYLITE® IR acrylic 1146. "Plexiglas" IR acrylic 3143 has approximately 0% (at least less than 10%, or even less than 1%) transmittance for electromagnetic waves with wavelengths of approximately 700 nm or less, but approximately 90% (greater than 85%) transmittance for wavelengths between 800 nm and approximately 1100 nm (including 905 nm).

[0113] In embodiments, substrate 30 exhibits a refractive index in the range of about 1.45 to about 1.55. In embodiments, the substrate exhibits an average transmittance of 95% or greater (e.g., 96% or greater, 97% or greater, 98% or greater, 99% or greater, 99.5% or greater) across the spectral range of 1400 nm to 1600 nm.

[0114] 4 and 5, both the first multilayer film 36 and the second multilayer film 38 are constructed by stacking a certain number of alternating layers of one or more high refractive index materials 40 and one or more low refractive index materials 42. Although the same reference numerals are used to identify the layers of the one or more high refractive index materials 40 and the one or more low refractive index materials 42, it should be understood that the use of the same reference numerals does not imply that the layers are made of the same materials or have the same structure. In both the first multilayer film 36 and the second multilayer film 38, different layers of the high refractive index materials 40 and the low refractive index materials 42 can have different compositional or structural characteristics.

[0115] As used herein, the terms "higher refractive index" and "lower refractive index" refer to refractive index values ​​relative to one another, meaning that the refractive index of one or more high refractive index materials 40 is higher than the refractive index of one or more low refractive index materials 42. In embodiments, the refractive index of one or more high refractive index materials 40 is from about 1.7 to about 4.5. In embodiments, the refractive index of one or more low refractive index materials 42 is from about 1.3 to about 1.6. In embodiments, the refractive index of one or more low refractive index materials 42 is from about 1.3 to about 1.7, and the refractive index of one or more high refractive index materials 40 is from about 1.9 to about 3.8. The difference in refractive index between any one of the one or more high refractive index materials 40 and any one of the one or more low refractive index materials 42 can be about 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, 0.8 or more, 0.9 or more, 1.0 or more, 1.5 or more, 2.0 or more, 2.1 or more, 2.2 or more, or even 2.3 or more. Because of the difference in refractive index between the one or more high refractive index materials 40 and the one or more low refractive index materials 42, by manipulating the quantitative composition (number of layers) and thicknesses of the alternating layers, electromagnetic waves within a certain wavelength range can be selectively transmitted through the window 24 and, independently, electromagnetic waves within a certain wavelength range can be selectively reflected by the first multilayer film 36. Thus, the first multilayer film 36 (and the second multilayer film 38, if utilized) is a thin-film optical filter having predetermined optical properties configured as a function of the quantitative composition, thickness, number of layers, and materials selected as the one or more high refractive index materials 40 and the one or more low refractive index materials 42.

[0116] Some examples of materials suitable for use as the one or more low refractive index materials 42 include SiO2, Al2O3, GeO2, SiO, and AlO x N y , SiO x N y , Si u Al v O x N y, MgO, MgAl2O4, MgF2, BaF2, CaF2, DyF3, YbF3, YF3, CeF3, etc. The one or more low refractive index materials 42 may include, for example, AlO x N y , SiO x N y , Si u Al v O x N y The nitrogen content (in materials such as SiO2) can be minimized.

[0117] Some examples of materials suitable for use as the one or more high refractive index materials 40 include Si, amorphous silicon (a-Si), SiN x , SiN x :H y , AlN x , Si u Al v O x N y , Ta2O5, Nb2O5, AlN, Si3N4, AlO x N y , SiO x N y , HfO2, TiO2, ZrO2, Y2O3, Al2O3, MoO3, diamond-like carbon, etc. The materials used as the high refractive index material 40 (especially SiN x material or AlN x The oxygen content in the material can be minimized. x N y The material is oxygen-doped AlN x In other words, AlN x The one or more high refractive index materials 40 may have a crystal structure of AlON (e.g., a wurtzite structure), but need not have a crystal structure of AlON. x N y The material may contain between about 0 atomic % and about 20 atomic % oxygen, or between about 5 atomic % and about 15 atomic % oxygen and between 30 atomic % and about 50 atomic % nitrogen. u Alv O x N y can contain about 10 atomic % to about 30 atomic %, or about 15 atomic % to about 25 atomic % silicon, about 20 atomic % to about 40 atomic %, or about 25 atomic % to about 35 atomic % aluminum, about 0 atomic % to about 20 atomic %, or about 1 atomic % to about 20 atomic % oxygen, and about 30 atomic % to about 50 atomic % nitrogen. Furthermore, hydrogen can be added to the above materials up to about 30 mass %. Note that the refractive indices of the one or more high-refractive-index materials 40 and the one or more low-refractive-index materials 42 are relative to each other, so the same material (e.g., Al2O3) may be considered suitable for one or more high-refractive-index materials 40 based on the refractive index of the material selected for one or more low-refractive-index materials 42, or may be considered suitable for one or more low-refractive-index materials 42 based on the refractive index of the material selected for one or more high-refractive-index materials 40.

[0118] In some embodiments, the one or more low refractive index materials 42 of the first multilayer 36 are comprised of SiO layers, and the one or more high refractive index materials 40 of the first multilayer 36 are comprised of SiO layers. x N y layer or SiN x In some embodiments, the one or more low refractive index materials 42 of the first multilayer 36 are comprised of SiO2 layers, and the one or more high refractive index materials 40 of the first multilayer 36 are comprised of SiN x layer or SiO x N y In some embodiments, the one or more low refractive index materials 42 of the second multilayer 38 are SiO layers, and the one or more high refractive index materials 40 of the second multilayer 38 include silicon layers (e.g., a-Si layers). In some embodiments, the one or more low refractive index materials 42 of the first multilayer 36 are SiO layers, and the one or more high refractive index materials 40 of the first multilayer 36 include SiN layers. x layer or SiO x N y The one or more low refractive index materials 42 of the second multilayer film 38 are made of SiO2 layers, and the one or more high refractive index materials 40 of the second multilayer film 38 are made of amorphous silicon layers (a-Si layers) and SiN xlayer or SiO x N y and a layer.

[0119] The quantitative composition of the alternating layers of high-refractive-index materials 40 and low-refractive-index materials 42 stacked alternately in either the first multilayer film 36 or the second multilayer film 38 is not particularly limited. In some embodiments, the number of alternating layers in the first multilayer film 36 is 7 or more, 9 or more, 11 or more, 13 or more, 15 or more, 17 or more, 19 or more, 21 or more, 23 or more, 25 or more, 51 or more, or 81 or more. In some embodiments, the number of alternating layers in the second multilayer film 38 is 7 or more, 9 or more, 11 or more, 13 or more, 15 or more, 17 or more, 19 or more, 21 or more, 23 or more, 25 or more, 51 or more, or 81 or more. In various embodiments, the number of alternating layers in the first and second multilayer films 36, 38 comprising the window 24 (excluding the substrate 30) is 14 or more, 20 or more, 26 or more, 32 or more, 38 or more, 44 or more, 50 or more, 72 or more, or 100 or more. In general, the greater the number of layers in the first and second multilayer films 36, 38, the more narrowly the range of transmittance and reflectance characteristics of the window 24 is tailored to one or more particular wavelengths or wavelength ranges.

[0120] The alternating layers of the first multilayer 36 and the alternating layers of the second multilayer 38 have a thickness. The thickness selected for each alternating layer determines the optical path length of light propagating through the window 24 and determines the amplification or attenuation due to interference between various light rays reflected at each material interface of the window 24. Thus, the thickness of each alternating layer, in combination with the refractive indices of the one or more high refractive index materials 40 and one or more low refractive index materials 42, determines the reflectance and transmittance spectra of the window 24.

[0121] 3, 4, and 5, when the reflected wave 28 interacts with the window 24, it first encounters an end face 44 of the first multilayer film 36. The end face 44 may be open to the external world 26. In one embodiment, the end face 44 is formed from one of one or more layers of low-index material 42, which more closely matches the refractive index of the end face 44 to that of air in the external world 26, thereby reducing reflection of the electromagnetic wave (whether the wave is the reflected wave 28 or not) incident on the end face 44. The layer of the one or more layers of low-index material 42 that constitutes the end face 44 is the layer in the first multilayer film 36 that is furthest from the substrate 30. Similarly, in some embodiments, when the one or more low-index materials 42 are SiO, the one or more SiO layers are disposed directly on the first surface 32 of the substrate 30 (which typically has a large mole percentage of SiO). Without wishing to be bound by theory, it is believed that the substrate 30 and the one or more adjacent layers of low refractive index material 42 both containing SiO2 may enhance bond strength.

[0122] On the other hand, when the output wave 22 interacts with the window 24, it first encounters the end face 48 of the second multilayer film 38. In one embodiment, the end face 48 is constructed from one of the one or more layers of low-index material 42, which more closely matches the refractive index of the end face 48 to the refractive index of the air within the enclosure 20, thereby reducing reflection of the output wave 22 incident on the end face 48. The layer of the one or more layers of low-index material 42 that constitutes the end face 48 is the layer of the second multilayer film 38 that is furthest from the substrate 30. Similarly, in some embodiments, when the one or more low-index materials 42 are SiO, the SiO layer of the one or more layers of low-index material 42 is disposed directly on the second surface 34 of the substrate 30.

[0123] A material with a relatively high refractive index may also have a relatively high hardness, providing scratch resistance and impact resistance. An example of a high hardness material that may be one of the one or more high refractive index materials 40 is SiO 2 . x N y Another example of a high hardness material that can be one of the one or more high refractive index materials 40 is SiN.x , SiN x :H y , Si3N4. Relatively thick (for example, 500 nm or thicker) SiO x N y It has been determined that employing a layer (or other suitable high refractive index material layer) can enhance the scratch resistance, damage resistance, or both, of window 24. Such enhanced scratch and damage resistance may be particularly beneficial in first multilayer 36, which is more likely to encounter debris impact from external environment 26. Accordingly, in some embodiments, one of the layers of one or more high refractive index materials 40 in first multilayer 36 has a thickness of 500 nm or greater (e.g., 1000 nm or greater, 1500 nm or greater, 2000 nm or greater). Such a high refractive index layer having a thickness of 500 nm or greater is referred to herein as a "scratch resistant layer."

[0124] In embodiments, optimizing the thickness and location of the scratch-resistant layer within the first multilayer film 36 can provide a desired level of hardness and scratch resistance to the first multilayer film 36, and therefore the entire window 24. The desired thickness of the scratch-resistant layer of high refractive index material 40, which functions as the layer that provides hardness and scratch resistance to the window 24, can vary depending on the application of the window 24. For example, the thickness of the scratch-resistant layer of high refractive index material 40 required for a window 24 protecting a LIDAR system 12 on a vehicle 10 may be different from the thickness required for a window 24 protecting a LIDAR system 12 in an office building. In embodiments, the thickness of the scratch-resistant layer of high refractive index material 40, which functions as the layer that provides hardness and scratch resistance to the window 24, can be between 500 nm and 50,000 nm, such as between 500 nm and 10,000 nm, for example, between 2,000 nm and 5,000 nm. In some embodiments, the thickness of the scratch-resistant layer of high refractive index material 40 is 30% or more, 40% or more, 50% or more, 65% or more, or 85% or more, or 86% or more of the thickness of the first multilayer 36. Note that the scratch-resistant layer of high refractive index material 40, which functions as the layer that provides hardness and scratch resistance to window 24, is typically, but not necessarily, part of the first multilayer 36 that faces the outside world 26, rather than the second multilayer 38 that is protected by the housing 20.

[0125] As described in further detail below, the quantitative composition, thickness, number, and materials of the remaining layers of first multilayer 36 and second multilayer 38 can be tailored to provide the desired optical properties (transmittance and reflectance at desired wavelengths) for window 24. This can be achieved largely independent of the thickness of the scratch-resistant layer of high refractive index material 40, which provides hardness and scratch resistance to window 24. The overall optical properties of window 24 are less sensitive to the thickness of the scratch-resistant layer of high refractive index material 40, which provides hardness and scratch resistance to window 24, when the scratch-resistant layer material has relatively low or negligible optical absorption for the targeted wavelength or wavelength range (e.g., 850 nm to 950 nm, 905 nm). For example, Si3N4 has negligible absorption for wavelengths between 700 nm and 2000 nm.

[0126] In this way, because the overall optical characteristics are less affected by the thickness of the scratch-resistant layer made of high refractive index material 40 in the first multilayer film 36, it is possible to preset the thickness of the scratch-resistant layer to meet predetermined hardness or scratch-resistance requirements. For example, the hardness and scratch-resistance requirements of the first multilayer film 36 for the window 24 used in the roof 14 of the vehicle 10 are likely to be different from those of the first multilayer film 36 for the window 24 used in the front portion 16 of the vehicle 10, and therefore the thickness required for the scratch-resistant layer made of high refractive index material 40 is likely to be different. The thickness of the scratch-resistant layer can be set in accordance with such requirements without significantly changing the transmittance and reflectance characteristics of the first multilayer film 36 as a whole.

[0127] The hardness of the first multilayer 36 having a scratch-resistant layer of high refractive index material 40, and therefore the window 24, can be quantified. In some embodiments, the maximum hardness of the window 24 measured by performing a Berkovich indenter hardness test on the first multilayer 36 having a scratch-resistant layer of high refractive index material 40 at one or more indentation depths ranging from 50 nm to 2000 nm (measured from the end face 44), or even 2000 nm to 5000 nm, can be about 8 GPa or greater, about 10 GPa or greater, about 12 GPa or greater, about 14 GPa or greater, about 15 GPa or greater, about 16 GPa or greater, or about 18 GPa or greater. As used herein, the term "Berkovich indenter hardness test" includes measuring the hardness of a material at its surface by indenting a diamond Berkovich indenter into the surface. The Berkovich indentation hardness test includes the steps of indenting the end surface 44 of the first multilayer film 36 with a diamond Berkovich indenter to a depth ranging from about 50 nm to about 2000 nm (or the entire thickness of the first multilayer film 36) and measuring the maximum hardness from the indentations across the entire indentation depth range or within a portion of this indentation depth range (e.g., a range from about 100 nm to about 600 nm). This method is typically described in Oliver, W.C., Pharr, G.M., "An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments," J. Mater. Res., Vol. 7, No. 6, 1992, pp. 1564-1583, and Oliver, W.C., Pharr, G.M., "Measurement of Hardness and Elastic Modulus by Instrument Indentation: Advances in Understanding and Refinements to Methodology," J. Mater. Res., Vol. 19, No. 1, 2004, pp. 3-20.The above levels of hardness improve the window 24's resistance to damage when struck by objects such as sand, pebbles, and debris that may be encountered while using the LIDAR system 12 for its intended purpose (e.g., installation in the vehicle 10 (see FIG. 1)). Therefore, the above levels of hardness reduce or prevent damage from impacts that could otherwise cause the LIDAR system 12 to scatter light and degrade performance.

[0128] In some embodiments, at least a portion of the first multilayer film 36 is disposed between the scratch-resistant layer of high refractive index material 40 and the end face 44. In some embodiments, the first multilayer film 36 includes alternating layers of one or more low refractive index materials 42 and one or more high refractive index materials 40 between the end face 44 and the scratch-resistant layer. Such alternating layer stacks disposed between the scratch-resistant layer and the end face 44 are referred to herein as "optical control layers." In some embodiments, the optical control layers disposed between the scratch-resistant layer and the end face 44 have a total thickness of 500 nm or greater (e.g., 600 nm or greater, 700 nm or greater, 800 nm or greater, 900 nm or greater, 1000 nm or greater, 1100 nm or greater, 1200 nm or greater, 1300 nm or greater). The quantity, composition, and thickness of the optical control layers can be selected to provide the desired anti-reflective performance attributes described herein at the operating wavelength of the LIDAR system 12, which is in the range of 850 nm to 950 nm, thereby enabling the first multilayer film 36 to be designed to provide the desired optical performance characteristics, as described herein, in the visible and / or UV spectrum.

[0129] In some embodiments, at least 25% (e.g., at least 26%, at least 27%, at least 28%, at least 29%, or at least 30%) of the thickness 46 of the first multilayer film 36 is disposed between the scratch-resistant layer and the end face 44. Positioning the scratch-resistant layer in the first multilayer film 36 at such a depth is believed to facilitate achieving a relatively high nanoindentation hardness (measured by Berkovich indentation hardness testing) of the first multilayer film 36 over a relatively long depth range within the first multilayer film 36. In some embodiments, the nanoindentation hardness of the first multilayer film 36 in a depth range of 50 nm to 2000 nm is 8 GPa or greater. In some embodiments, the nanoindentation hardness of the first multilayer film 36 in a depth range of 100 nm to 1000 nm is 10 GPa or greater. In several embodiments, the nanoindentation hardness of the first multilayer film 36 is 14 GPa or more in a depth range of 400 nm to 1000 nm of the first multilayer film 36. By achieving such a hardness value, it becomes easier to obtain scratch resistance and damage resistance against cracks of a relatively wide range of depths.

[0130] Referring now to FIGS. 4 and 5 , the first multilayer film 36 has a thickness 46, and the second multilayer film 38 has a thickness 50. The thickness 46 of the first multilayer film 36, which is expected to include one or more scratch-resistant layers of high refractive index material 40, can be approximately 1 μm or greater to achieve the transmittance and reflectance characteristics described herein. In some embodiments, the thickness 46 is in the range of 1 μm to slightly more than 50 μm, e.g., in the range of about 1 μm to about 10 μm, or about 2800 nm to about 5900 nm. The lower limit of approximately 1 μm is approximately the minimum thickness 46 that provides stiffness and scratch resistance to the window 24. Meanwhile, the upper limit of the thickness 46 is limited by the cost and time required to deposit the layers of the first multilayer film 36 on the substrate 30. Additionally, the upper limit of the thickness 46 is also limited by the need to prevent the first multilayer film 36 from causing warpage of the substrate 30. This limit depends on the thickness of the substrate 30. The thickness 50 of the second multilayer film 38 can be any thickness deemed necessary to impart the desired transmittance and reflectance characteristics to the window 24. In some embodiments, the thickness 50 of the second multilayer film 38 is in the range of about 800 nm to about 7000 nm.

[0131] The quantitative composition, thickness, number of layers, and materials of the layers in the first multilayer film 36 and the second multilayer film are determined to solve the problem described in the "Problem to be Solved by the Invention" section above by maximizing the thickness of the high refractive index material 40 to impart hardness, impact resistance, and scratch resistance to the window 24, while also configuring the window 24 to have a relatively high infrared transmittance in the range of 850 nm to 950 nm. In several embodiments, the thicknesses, number of layers, and materials of the alternating layers in the first multilayer film 36 and the second multilayer film 38 are configured so that the average transmittance of the window 24 calculated in a 50 nm wide target wavelength range with a center wavelength in the range of 850 nm to 950 nm (e.g., a 20 nm wide target wavelength range centered at a wavelength of 905 nm) for light incident on the first surface 32 and the second surface 34 at an angle of 15° or less relative to the normal to the first surface 32 and the second surface 34 is 90% or more (e.g., 91% or more, 92% or more, 93% or more, 94% or more, 95% or more).

[0132] In several embodiments, the thicknesses, number of layers, and materials of the alternating layers in the first multilayer film 36 and the second multilayer film 38 are configured so that the average reflectance of the window 24 calculated in a 50 nm wide target wavelength range with a center wavelength in the range of 850 nm to 950 nm (e.g., a 20 nm wide target wavelength range centered at a wavelength of 905 nm) for light incident on the first surface 32 and the second surface 34 at an angle of 15° or less relative to the normal to the first surface 32 and the second surface 34 is 4.0% or less (e.g., 3.5% or less, 3.0% or less, 2.5% or less, 2.0% or less, 1.5% or less, 1.0% or less). In several embodiments, the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film 36 and the second multilayer film 38 are configured so that, for light incident on the first surface 32 and the second surface 34 at an angle of 60° or less relative to the normal to the first surface 32 and the second surface 34 (e.g., an incident angle of 0° to 60°, 0° to 50°, 0° to 40°, 0° to 30°), the average P-polarized light transmittance and average S-polarized light transmittance of the window calculated in a 50 nm wide target wavelength range with a center wavelength in the range of 850 nm to 950 nm (e.g., a 20 nm wide target wavelength range centered at a wavelength of 905 nm) is greater than 85% (e.g., 86% or more, 87% or more, 88% or more, 89% or more, 90% or more, 91% or more, 92% or more). As used herein, the term "reflectance" is defined as the fraction of optical power of incident light of wavelengths within a given wavelength range that is reflected by a material (e.g., window 24, substrate 30, first multilayer film 36, second multilayer film 38, or portions thereof).

[0133] In various embodiments, the thicknesses, number of layers, and materials of the alternating layers in the first multilayer film 36 and the second multilayer film 38 are configured to provide an average transmittance of 95% or greater (e.g., 95.5% or greater, 96% or greater, 96.5% or greater, 97.5% or greater, 98% or greater) through the window 24 for light incident perpendicularly on the first surface 32 and the second surface 34, calculated over a 50 nm wavelength range of interest (e.g., a 20 nm wavelength range of interest centered at 905 nm) with a center wavelength ranging from 850 nm to 950 nm. The terms "transmittance" and "percentage transmission" are used interchangeably herein to refer to the percentage of optical power transmitted through a material (e.g., the window 24, the substrate 30, the first multilayer film 36, the second multilayer film 38, or portions thereof) of incident light having a wavelength within a given wavelength range.

[0134] Additionally, in some embodiments, the thicknesses, number of layers, and materials of the alternating layers of first multilayer film 36 and second multilayer film 38 are further configured (as well as configured to meet the infrared optical performance requirements described herein) to impart a desired dark appearance to window 24. For example, when viewed from outside 26 (see FIG. 1 ), window 24 can exhibit a CIELAB color space a* value of −6.0 to 6.0 inclusive (e.g., −5.0 to 5.0 inclusive, −4.0 to 4.0 inclusive, −3.0 to 3.0 inclusive, −2.5 to 2.5 inclusive, or −2.5 to 0 inclusive) for light incident on first surface 32 at an angle of incidence between 0° and 90°. Additionally, window 24 can exhibit a CIELAB color space b* value of -6.0 or greater and 6.0 or less (e.g., -5.0 or greater and 5.0 or less, -4.0 or greater and 4.0 or less, -3.0 or greater and 3.0 or less, -2.5 or greater and 2.5 or less, or -2.5 or greater and 0 or less) for light incident on first surface 32 at an angle of incidence between 0° and 90°. Such color space values ​​can be achieved even in embodiments in which substrate 30 has a relatively high transmittance (e.g., 90% or greater) and a relatively low reflectance (e.g., 22% or less) across the visible spectrum.

[0135] In embodiments, the thicknesses, number of layers, and materials of the alternating layers in first multilayer film 36 and second multilayer film 38 are configured to provide window 24 with a CIELAB lightness L* value of 45 or less (e.g., 40 or less, 35 or less, 30 or less) when viewed at an angle of incidence of 60° or less. In embodiments, the thicknesses, number of layers, and materials of the alternating layers in first multilayer film 36 and second multilayer film 38 are configured to provide window 24 with a CIELAB lightness L* value of less than 20 when reflecting light that is normally incident on first multilayer film 36. The above sets of CIELAB color space values ​​and lightness values ​​represent a relatively dark appearance of window 24 when viewed at various angles of incidence.

[0136] The window 24 can be given a dark appearance by including a suitable material (referred to herein as an "absorber layer") that absorbs in the visible spectrum, such as silicon (e.g., a-Si), in the second multilayer 38 as one of the one or more high refractive index materials 40. Silicon is suitable for the absorber layer because of its relatively high refractive index (approximately 4.0 at 905 nm) and its relatively high optical absorption in the ultraviolet and visible regions. Thus, the thickness and quantitative composition of the silicon layer, in addition to the other layers in the first multilayer 36 and second multilayer 38, can provide the window 24 with low electromagnetic transmittance in the ultraviolet and visible regions (due in part to the absorbance of silicon in both wavelength regions), while having high transmittance in a desired portion of the infrared region. In some embodiments, the second multilayer 38 includes one or more silicon layers (e.g., a-Si layers) as one of the one or more high refractive index materials 40, while the first multilayer 36 does not include a silicon layer. Such a structure has the advantage that the silicon is located only on the backside of the substrate 30, thereby protecting the silicon from the external environment 26. Thus, the nanoindentation hardness values ​​described herein can be achieved by incorporating a scratch-resistant layer in the first multilayer 36, and the dark appearance can be achieved by including silicon in the second multilayer 38.

[0137] In some embodiments, the silicon material used to form at least one of the one or more layers of high refractive index material 40 can be modified to provide a relatively high optical transmittance over a 50 nm wide wavelength range of interest centered approximately between 850 nm and 950 nm. Specifically, it has been determined that the extinction coefficient of the silicon material (or other suitable material that absorbs more electromagnetic radiation in the visible spectrum than other high refractive index materials 40 described herein) should be 0.01 or less (e.g., 0.009 or less, 0.008 or less, 0.007 or less, 0.005 or less, 0.004 or less, 0.0035 or less, 0.0030 or less, 0.0025 or less, 0.0020 or less, 0.0015 or less, 0.0010 or less) at wavelengths within the wavelength range of interest (the wavelength range of interest being determined by the peak operating wavelength associated with at least one of the emitter and detector of radiation detector 18). The wavelength range may be up to, and in some embodiments, from 890 nm to 910 nm, and in various embodiments, about 890 nm, about 891 nm, about 892 nm, about 893 nm, about 894 nm, about 895 nm, about 896 nm, about 897 nm, about 898 nm, about 899 nm, about 900 nm, about 901 nm, about 902 nm, about 903 nm, about 904 nm, about 905 nm, about 906 nm, about 907 nm, about 908 nm, about 909 nm, and about 910 nm, as well as any and all ranges incorporating any of these values. In some embodiments, the silicon material preferably has an extinction coefficient of less than 0.005 at the above wavelengths, while also having a relatively high extinction coefficient across the visible spectrum (e.g., 0.06 or greater, 0.07 or greater, 0.08 or greater, 0.09 or greater, 0.1 or greater). Thus, by using a silicon material with a low extinction coefficient in the 50 nm wavelength range of interest and a relatively high extinction coefficient across the visible spectrum, it is possible to add enough silicon to reduce the visible transmittance to the ranges described herein without significantly affecting the transmittance within the wavelength range of interest.

[0138] In some embodiments, the alternating layers in second multilayer film 38 that are made of silicon have a combined thickness of 250 nm or more (e.g., 300 nm or more, 325 nm or more, 350 nm or more, 375 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 550 nm or more, 600 nm or more, 650 nm or more, 700 nm or more). In some embodiments, the combined thickness of the silicon layers in second multilayer film 38 accounts for at least 20% (e.g., at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%) of thickness 50 of second multilayer film 38. Applicant has found that such a silicon thickness sufficiently absorbs visible light such that the average transmittance of window 24 calculated over the range of 400 nm to 700 nm for light incident on first surface 32 and second surface 34 at angles within 15° of the normal to first surface 32 and second surface 34 is less than 5% (e.g., 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, 2.5% or less, 2.0% or less, 1.5% or less, 1.0% or less, 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, 0.2% or less, 0.1% or less). This prevents the portion of reflected wave 28 (see FIG. 2 ) containing visible light from reaching radiation detector 18, thereby improving the signal-to-noise ratio of LIDAR system 12.

[0139] In some embodiments, the second multilayer film 38 includes two or more layers formed from silicon. In some embodiments, at least one of the two or more layers formed from silicon has a thickness of 150 nm or more (e.g., 160 nm or more, 170 nm or more, 180 nm or more, 190 nm or more, 200 nm or more). In some embodiments, at least two (but fewer than all) of the two or more layers formed from silicon in the second multilayer film 38 have a thickness of 150 nm or more. In some embodiments, at least seven of the alternating layers in the second multilayer film 38 are disposed between one of the silicon layers having a thickness of 150 nm or more and the second surface 34. In embodiments, each of the less than 150 nm silicon layers in second multilayer film 38 on second surface 34 is 70 nm or less (e.g., 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 30 nm or less, 25 nm or less, 20 nm or less). This spacing of the relatively thick silicon layers from substrate 30 is believed to help reduce reflectance in the visible spectrum.

[0140] In embodiments, the alternating layers in first multilayer 36 and second multilayer 38 are constructed to have a relatively low average reflectance across the visible spectrum. For example, in embodiments, the average reflectance of the window, calculated over the wavelength range of 400 nm to 700 nm, is 10% or less (e.g., 9% or less, 8% or less, 7% or less). This low reflectance has the advantage of preventing the window 24 from appearing tinted when viewed from the outside world 26 (see FIG. 1 ) and facilitating the achievement of the CIE color space a* and b* values ​​and lightness L* values ​​described herein.

[0141] In some embodiments, to reduce the reflectance of the window in the visible spectrum, the silicon layer in the second multilayer 38 closest to the substrate 30 is the thinnest silicon layer in the second multilayer 38. That is, of the layers in the second multilayer 38 in which the one or more high refractive index materials 40 are silicon, the layer closest to the substrate 30 has the smallest thickness. In some embodiments, the silicon layer in the second multilayer 38 closest to the substrate 30 has a thickness of 15 nm or less (e.g., 10 nm or less, 8 nm or less, 7 nm or less, 6 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2 nm or less). Applicants have found that such a structure has the advantage of preventing colored reflectance from being introduced by the silicon-containing layer in the second multilayer 38, while contributing to maintaining the visible transmittance at the relatively low values ​​described herein.

[0142] In some embodiments, the layer of the one or more layers of high refractive index material 40 in the second multilayer 38 closest to the substrate 30 is a layer other than silicon. In some embodiments, for example, the layer of the one or more layers of high refractive index material 40 closest to the substrate 30 is made of the same high refractive index material (e.g., SiN) as the high refractive index material used in the first multilayer. x , SiO x N y , SiN). In some embodiments, the layer of one or more layers of high refractive index material 40 in second multilayer 38 closest to substrate 30 is the only layer of high refractive index layers in second multilayer 38 that is not composed of silicon. Without wishing to be bound by theory, applicants believe that such a structure can contribute to reduced reflectance in the visible spectrum when second multilayer 38 includes silicon, particularly when each silicon layer in second multilayer 38 has a thickness of 8 nm or greater.

[0143] Each layer in the first multilayer film 36 and the second multilayer film 38 (i.e., the layers of high refractive index material 40 and the layers of low refractive index material 42) can be formed by any method known in the art, such as a discontinuous deposition process or a continuous deposition process. In one or more embodiments, the layers can be formed exclusively by a continuous deposition process or an exclusively discontinuous deposition process. [Example]

[0144] All of the following examples are modeling examples that utilize computer-aided modeling to demonstrate how the quantitative composition, thickness, number of layers, and materials of the layers in first multilayer film 36 and second multilayer film 38 can be set to achieve desired average transmittance and average reflectance of window 24 as a function of wavelength and angle of incidence of incident electromagnetic waves.

[0145] Example 1 The window 24 in Example 1 included a first multilayer film 36 and a second multilayer film 38. The second multilayer film 38 included a layer of silicon material, designated as the "low-k" material in FIGS. 6A and 6B. The low-k material was formed using amorphous silicon as a support in a manner similar to that used for existing materials. However, the processing conditions for the film formation process were modified. As shown in the figures, the extinction coefficient of the low-k material is lower than that of certain existing silicon materials throughout the entire wavelength range of 350 nm to 1000 nm. Therefore, throughout the wavelength range of 850 nm to 950 nm, the extinction coefficient of the low-k material is 0.01 or less (e.g., 0.004 or less in this example). Furthermore, throughout the wavelength range of 890 nm to 910 nm, the extinction coefficient of the low-k silicon material is less than 0.002 (approximately 0.0016 at 905 nm). This represents an order of magnitude decrease compared to existing silicon materials, which have an extinction coefficient of 0.044 or greater across the entire wavelength range of 850 nm to 950 nm. Furthermore, as shown in Figure 6A, in the wavelength range of 400 nm to 700 nm, the extinction coefficient of the low-k material is comparable (less than an order of magnitude difference) to that of existing silicon materials. From 400 nm to 700 nm, the extinction coefficients of the low-k materials ranged from 0.078 to 1.92. Thus, because the low-k silicon materials have relatively high extinction coefficients across the visible spectrum, they can be incorporated in sufficient amounts to absorb visible light and provide the opaque dark appearance described herein, while their relatively low extinction coefficients across the 50 nm wavelength range of interest prevent significant adverse effects on transmittance within that wavelength range.

[0146] The window 24 of Example 1 had a first multilayer film 36 on the first surface 32 of a substrate 30 made of aluminosilicate glass (Corning Code 2320). The window 24 of Example 1 also had a second multilayer film 38 on the second surface 34 of the substrate 30. The first multilayer film 36 was configured by alternately stacking 33 layers of SiO2 as the low refractive index material 42 and SiN as the high refractive index material 40. The 24th layer was a 2000 nm thick scratch-resistant layer made of the high refractive index material 40. The 1st to 23rd layers were light control layers that separated the scratch-resistant layer from the end face 44. The total thickness of the 1st to 23rd layers was 1307.01 nm. The 25th to 33rd layers were refractive index matching layers that separated the scratch-resistant layer from the first surface 32. The total thickness of the 25th to 33rd layers was 338.45 nm. In this example, the scratch-resistant layer accounted for 54.86% of the thickness of the first multilayer film 36 .

[0147] The second multilayer film 38 was constructed by alternately stacking 23 layers of low-refractive-index materials 42 and high-refractive-index materials 40. In this example, the low-refractive-index material 42 was SiO2, and the high-refractive-index material 40 was a combination of SiN and Si. As shown in the table, layers 35, 37, 39, and 41 (the four high-refractive-index material 40 layers closest to the substrate 30) were SiN, and the other high-refractive-index material 40 layers were low-k Si. Layer 43 (the Si layer closest to the substrate 30) was the thinnest Si layer, with a thickness of 12.04 nm. The total thickness of the silicon layers was 708.4 nm, accounting for 46.6% of the total thickness of the second multilayer film 38.

[0148] The thickness of each layer in the first multilayer film 36 and the second multilayer film 38 was set as shown in Table 1 below, and this was used to calculate the transmittance, reflectance, CIELAB color space values ​​and lightness values ​​of reflection, and nanoindentation hardness values ​​shown in Figures 7 to 12.

[0149] [Table 1-1]

[0150] [Table 1-2]

[0151] FIG. 7 is a graph showing the modeled transmittance of the window 24 of Example 1 across the entire spectral range from 850 nm to 950 nm for light incident on the window 24 at a 15° angle of incidence. As apparent from FIG. 7 , the quantitative composition, thickness, number of layers, and materials of the first multilayer coating 36 and the second multilayer coating 38 of the window 24 of Example 1 are configured such that the transmittance of the window 24 for light incident on the first surface 32 or the second surface 34 at an angle of incidence less than 15° exceeds 93% across the entire wavelength range from 850 nm to 950 nm. Indeed, throughout the entire wavelength range from 850 nm to 950 nm, the transmittance of the window 24 for light incident at a 15° angle of incidence exceeds 93%. Additionally, throughout the wavelength range from 860 nm to 950 nm, the transmittance exceeds 95%. At 905 nm, the transmittance is approximately 97%. 8, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 1 are configured so that the average P-polarized light transmittance and average S-polarized light transmittance of the window 24 calculated in the target wavelength range of 850 nm to 950 nm exceeds 89% for light incident on the first and second surfaces at angles within 60° of the normal to the first and second surfaces. Furthermore, in the wavelength range of 890 nm to 910 nm, the S-polarized light transmittance and P-polarized light transmittance exceed 91% throughout that range.

[0152] Furthermore, as is clear from FIG. 9 , the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 in Example 1 are configured so that the reflectance at the end face 44 of the first multilayer film 36 and the reflectance at the end face 48 of the second multilayer film 38 of the window 24 for light incident on the substrate 30 at an incident angle of 15° are generally less than 4% within the wavelength range of 850 nm to 950 nm. The reason that the reflectance at the end face 44 is similar to the reflectance at the end face 48 is because the first multilayer film 36 and the second multilayer film 38 are made of materials with relatively low absorbance in the above-mentioned wavelength range. As shown, the reflectance was less than 1.6% throughout the entire wavelength range of 860 nm to 950 nm. Furthermore, within the wavelength range of 850 nm to 950 nm, the reflectance reached a minimum value at a wavelength of 925 nm, which was less than 1.0% (approximately 0.8%).

[0153] As is apparent from FIG. 10 , the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 1 are configured so that the transmittance of the window 24 for light incident on the window 24 at an angle of incidence of 15° or less is less than 12% across the entire visible spectrum. The transmittance in the visible spectrum from 400 nm to 650 nm is also less than 3%. Furthermore, the transmittance in the visible spectrum for wavelengths shorter than 600 nm is also less than 0.2%. These low transmittance values ​​are likely due in part to the absorption of visible light by the silicon layer of the second multilayer film 38. The average transmittance of the window 24 in the wavelength range from 400 nm to 700 nm is 5.0% or less.

[0154] As is apparent from FIGS. 11A and 11B, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 1 are configured to give the window 24 a dark appearance when viewed from the end face 44 of the first multilayer film. FIG. 11 shows CIELAB reflected color data for light reflected from the end face 44 of Example 1, obtained through simulation. The color of reflected light can be characterized using CIELAB color coordinates. The a* axis in the color space represents the green to red color component, with negative a* values ​​corresponding to green and positive a* values ​​corresponding to red. The b* axis in the color space represents the blue to yellow color component, with negative b* values ​​corresponding to blue and positive b* values ​​corresponding to yellow. The closer the a* and b* values ​​are to the origin, the lower the color saturation perceived by a viewer of the reflected light. These CIELAB a* and b* values ​​were generated by performing simulations at multiple different light source incident angles ranging from 0° to 90°. As shown, the a* values ​​range from about 0 to about 4.5, and the b* values ​​range from about −0.8 to about 0.8, indicating that the window 24 according to Example 1 has a low-saturation appearance when viewed from the outside world 26 (see FIG. 1).

[0155] 11B is a graph showing the CIELAB lightness L* values ​​of the reflections obtained by modeling as a function of the angle of incidence on the end face 44. As shown, the lightness L* values ​​for angles of incidence of 60° or less are 35 or less. The lightness L* values ​​for angles of incidence of 50° or less are 25 or less. The lightness L* values ​​for angles of incidence of 35° or less are 20 or less. This indicates that the window 24 according to Example 1 has a dark appearance when viewed from the outside world 26 (see FIG. 1).

[0156] FIG. 12 shows the nanoindentation hardness measured as a function of depth for a sample constructed according to Example 1 herein. The hardness values ​​simulate the results of Berkovich indentation hardness testing, as described herein, performed on the first multilayer film 36 side. Sample measurements were performed at depths ranging from 50 nm to 1000 nm. As shown in FIG. 12, this sample exhibited a maximum hardness of over 15.5 GPa at a depth of approximately 750 nm. While not wishing to be bound by theory, the maximum hardness is located above the scratch-resistant layer because the indenter stress field propagates below the scratch-resistant layer at depths of 1050 nm. As demonstrated in FIG. 12, the window 24 according to Example 1 exhibits a nanoindentation hardness of over 8 GPa throughout the entire depth range from 50 nm to 1000 nm. Furthermore, the window 24 according to Example 1 exhibits a nanoindentation hardness exceeding 10 GPa throughout the entire depth range of 100 nm to 1000 nm. Furthermore, the window 24 according to Example 1 exhibits a nanoindentation hardness exceeding 12 GPa throughout the entire depth range of 200 nm to 1000 nm. Furthermore, the window 24 according to Example 1 exhibits a nanoindentation hardness exceeding 14 GPa throughout the entire depth range of 400 nm to 1000 nm. Furthermore, the window 24 according to Example 1 exhibits a nanoindentation hardness exceeding 15 GPa throughout the entire depth range of 600 nm to 1000 nm. This demonstrates that the present examples provide scratch resistance / damage resistance suitable for a variety of applications.

[0157] Embodiments of the present disclosure can be further understood by considering the following information.

[0158] In some embodiments, one of the first multilayer film 36 and the second multilayer film 38 includes one or more layers formed of a transparent conductive oxide ("TCO") material. One of the layers of high refractive index material 40 can be replaced with a TCO material. The TCO material layer(s) can be communicatively (e.g., conductively) coupled to a power source (not shown) for heating the window 24. Such heating enables one or more LIDAR systems 12 to operate in low-temperature environments. The TCO material can be selected from suitable optically transparent, electrically conductive materials, such as indium tin oxide ("ITO"), aluminum-doped zinc oxide ("AZO"), indium-doped cadmium oxide, etc. In some embodiments, ITO is preferred due to its superior thermal durability compared to other existing TCO materials.

[0159] The TCO material layer(s) are disposed in the second multilayer film 38. In some embodiments, the TCO material layer is disposed closer to the edge 48 than the absorbing layer (e.g., a Si layer) in the second multilayer film 38, such that the absorbing layer is positioned between the TCO material layer and the substrate 30. This structure has the advantage that the opaque, dark appearance of the window 24 described herein is less affected by the addition of the TCO material. In some embodiments, the TCO material layer is disposed between layers of low-index material 42 due to the moderate refractive index of the TCO material. However, embodiments in which the TCO material layer is disposed adjacent to the substrate 30 (e.g., between one of the first and second multilayer films 36 and 38 and the substrate 30) are also contemplated. In some embodiments, the second multilayer film 38 can include a single TCO material layer (e.g., an ITO layer). This single TCO material layer is positioned at the layer of high refractive index material 40 furthest from substrate 30, with multiple absorbing layers (e.g., Si layers) (and / or other layers of high refractive index material 40) positioned between the TCO material layer and substrate 30.

[0160] The thickness of the TCO material layer(s) can be selected based on several factors, including the desired sheet resistance required to heat the window 24 and the calculated optical performance of the window 24. In various embodiments, each TCO material layer has a thickness of 50 nm or less (e.g., 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, or 20 nm to 30 nm) and an extinction coefficient (extinction coefficient) at 905 nm of 0.05 or less (e.g., 0.04 or less). While embodiments in which the TCO material layer(s) is / are greater than 50 nm are contemplated, maintaining an extinction coefficient of less than 0.05 across the entire spectral range from 840 nm to 1020 nm advantageously minimizes absorption across the wavelength range of interest while maintaining the excellent transmission performance of the multilayer films described herein. That is, the TCO material layer provides sufficient sheet resistance to heat the window 24 without significantly affecting the transmission characteristics of the window 24 across the wavelength range of interest. In this respect, ITO has been confirmed to be an appropriate TCO material. By depositing ITO to a thickness of 20 to 30 nm, it is possible to obtain a sheet resistance suitable for heating and to suppress the extinction coefficient (extinction coefficient) in the target wavelength range to less than 0.05.

[0161] Example 2 The window 24 of Example 2 included a first multilayer film 36 and a second multilayer film 38. The second multilayer film 38 included a layer of silicon material, which is described as a "low-k" material in the description of Figures 6A and 6B herein. The window 24 of Example 2 included the first multilayer film 36 on the first surface 32 of the substrate 30. The window 24 of Example 2 also included the second multilayer film 38 on the second surface 34 of the substrate 30. In Example 2, the substrate 30 was the laminate described in U.S. Provisional Patent Application No. 63 / 349,764, entitled "Laminate Windows for Infrared Sensing Systems," filed June 7, 2022, the entire disclosure of which is incorporated herein by reference. Specifically, the substrate 30 had a first glass ply (the outer ply opposite the electromagnetic radiation detector 18) that was a 2.85 mm thick layer of unstrengthened aluminosilicate glass, an optically clear adhesive interlayer, and a second glass ply (the inner ply) that was a 1 mm thick layer of chemically strengthened aluminosilicate glass.

[0162] The first multilayer film 36 was constructed by alternately stacking 31 layers of SiO2 as the low refractive index material 42 and SiN as the high refractive index material 40. The 22nd layer was a scratch-resistant layer of the high refractive index material 40 with a thickness of 2038.98 nm. The 1st to 21st layers were optical control layers that separated the scratch-resistant layer from the end face 44. The total thickness of the 1st to 21st layers was 1352 nm. The 23rd to 31st layers were refractive index matching layers that separated the scratch-resistant layer from the first surface 32. The total thickness of the 23rd to 31st layers was 380.87 nm. In this example, the scratch-resistant layer accounted for 54.06% of the thickness of the first multilayer film 36.

[0163] The second multilayer film 38 was constructed by alternately stacking 23 layers of low-refractive-index materials 42 and high-refractive-index materials 40. In this example, the low-refractive-index material 42 was SiO2, and the high-refractive-index material 40 was a combination of SiN, Si, and ITO. As shown in the table, layers 35, 37, 39, and 41 (the four high-refractive-index material 40 layers closest to the substrate 30) were SiN, and the other high-refractive-index material 40 layers were low-k Si and ITO. Layer 43 (the Si layer closest to the substrate 30) was the thinnest Si layer, with a thickness of 12.22 nm. The total thickness of the silicon layers was 485.01 nm, accounting for 35.9% of the total thickness of the second multilayer film 38. Layer 55 was a TCO material layer. As shown in the table, the refractive index of the TCO layer at 905 nm was 1.72, which was less than half the refractive index of the layer of high-index material 40 closest to the TCO layer at 905 nm. The thickness of the TCO layer was 22 nm to achieve the desired sheet resistance required for heating. The TCO layer was preferably positioned behind the silicon layer (closer to the end face 48). As described herein, this placement of the TCO layer advantageously prevents visible light from being absorbed by the silicon layer and reaching the TCO layer. Thus, adding the TCO layer as described above allows for additional functionality without detracting from the appearance of the window 24 described herein.

[0164] The thickness of each layer in the first multilayer film 36 and the second multilayer film 38 was set as shown in Table 2 below, and this was used to calculate the CIELAB color space values ​​and lightness values ​​of the transmittance, reflectance, and reflection shown in Figures 13 to 15.

[0165] [Table 2-1]

[0166] [Table 2-2]

[0167] Figure 13 is a graph showing the modeled transmittance of window 24 according to Example 2 across the spectral range from 350 nm to 1500 nm for light incident on window 24 at angles of incidence of 15° and 60°. As is apparent from Figure 13, the quantitative composition, thickness, number of layers, and materials of first multilayer coating 36 and second multilayer coating 38 of window 24 of Example 2 are configured such that the transmittance of window 24 for light incident on first surface 32 or second surface 34 at angles of incidence less than 15° exceeds 95% across the entire wavelength range from 850 nm to 950 nm. In fact, throughout the entire wavelength range from 850 nm to 950 nm, the transmittance of window 24 for light incident at an angle of incidence of 15° exceeds 96%. Furthermore, as shown in FIG. 13, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 2 are configured so that the average polarized transmittance of the window 24 calculated in the target wavelength range of 850 nm to 950 nm exceeds 89% for light incident on the first and second surfaces at an angle of 60° or less relative to the normal to the first and second surfaces.

[0168] Furthermore, as is clear from FIG. 13 , the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 2 are configured so that the transmittance of the window 24 for light incident on the window 24 (end face 44) at an angle of incidence of 15° or less is less than 10% across the entire visible spectrum. Furthermore, in the range of 400 nm to 700 nm, the average transmittance of the window 24 of Example 2 for light incident perpendicularly is less than 2%. These low transmittance values ​​are attributable in part to the absorption of visible light by the silicon layer of the second multilayer film 38. Furthermore, as is clear from FIG. 13 , the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 2 are configured so that the transmittance of the window 24 for light incident on the window 24 (end face 44) at an angle of incidence of 60° or less is less than 13% across the entire visible spectrum.

[0169] 14, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and second multilayer film 38 of window 24 in Example 2 are configured so that the average polarized reflectance at end face 44 of first multilayer film 36 of window 24 for light incident on substrate 30 at an incident angle of 15° is less than 1% in the wavelength range of approximately 850 nm to 950 nm. The reason that the reflectance at end face 44 is similar to the reflectance at end face 48 is because first multilayer film 36 and second multilayer film 38 are made of materials with relatively low absorbance in the above-mentioned wavelength range.

[0170] As is apparent from FIG. 15 , the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 2 are configured to give the window 24 a dark appearance when viewed from the edge 44 of the first multilayer film. FIG. 15 shows simulated CIELAB reflected color data for light reflected from the edge 44 of Example 2. The CIELAB a* and b* values ​​were generated by performing simulations at multiple different light source incident angles ranging from 0° to 90°. As shown, the a* values ​​range from approximately −1.2 to approximately 0.8, and the b* values ​​range from approximately −0.3 to approximately 6. This indicates that the window 24 of Example 2 has a low-saturation appearance when viewed from the outside world 26 (see FIG. 1 ).

[0171] It has been determined that separating the silicon layer from the facet 48 in the second multilayer 38 by one or more other layers of high refractive index material 40 can improve anti-reflection performance over a 50 nm wavelength range of interest, particularly performance against reflection from the facet 48. Accordingly, in some embodiments, the second multilayer 38 can be configured such that the innermost silicon layer farthest from the substrate 30 (closest to the facet 48) is separated from the facet 48 by an “inner AR stack” that includes at least one layer of low refractive index material 42 and at least one layer of a high refractive index material other than silicon 40 (e.g., a suitable high refractive index material such as SiN). If an inner AR stack is included, the inner AR stack can be disposed between the innermost silicon layer and the facet 48. While the design according to Example 2 herein provides good performance, the addition of this inner AR stack has been found to further reduce the reflectivity of window 24 across the 50 nm wavelength range of interest, particularly for light incident on facet 48 at angles of incidence less than 15°. The inner AR stack reduces the maximum reflectivity of second multilayer 38 to 0.5% or less across the entire wavelength range from 890 nm to 950 nm for light incident on second multilayer 38 at angles of incidence less than 15°.

[0172] In some embodiments, the inner AR stack of the second multilayer film 38 can include at least two (e.g., at least three, at least four) layers of high refractive index material 40 other than silicon or TCO layers, or at least four (e.g., at least six, at least eight) alternating layers of high refractive index material 40 and low refractive index material 42. Additionally, a TCO layer, such as that described in Example 2 herein, can be incorporated between the inner AR stack and the end face 48, which allows the window 24 to be heated without damaging its appearance, as described in Example 2 herein.

[0173] Example 3 The window 24 of Example 3 included a first multilayer film 36 and a second multilayer film 38. The second multilayer film 38 included a layer of silicon material, which is described as a "low-k" material in the description of Figures 6A and 6B herein. The window 24 of Example 3 included the first multilayer film 36 on the first surface 32 of the substrate 30. The window 24 of Example 3 also included the second multilayer film 38 on the second surface 34 of the substrate 30. In Example 3, the substrate 30 was the laminate described in U.S. Provisional Patent Application No. 63 / 349,764, entitled "Laminate Windows for Infrared Sensing Systems," filed June 7, 2022, the entire disclosure of which is incorporated herein by reference. Specifically, the substrate 30 had a first glass ply (the outer ply opposite the electromagnetic radiation detector 18) that was a 2.85 mm thick layer of unstrengthened aluminosilicate glass, an optically clear adhesive interlayer, and a second glass ply (the inner ply) that was a 1 mm thick layer of chemically strengthened aluminosilicate glass.

[0174] The first multilayer film 36 was constructed by alternately stacking 31 layers of SiO2 as the low refractive index material 42 and SiN as the high refractive index material 40. The 22nd layer was a scratch-resistant layer made of the high refractive index material 40 with a thickness of 2038.98 nm. The 1st to 21st layers were optical control layers that separated the scratch-resistant layer from the end face 44. The total thickness of the 1st to 21st layers was 1226.23 nm. The 23rd to 31st layers were refractive index matching layers that separated the scratch-resistant layer from the first surface 32. The total thickness of the 23rd to 31st layers was 355.85 nm. In this example, the scratch-resistant layer accounted for 55.83% of the thickness of the first multilayer film 36.

[0175] The second multilayer film 38 was constructed by alternately stacking 33 layers of low-refractive-index materials 42 and high-refractive-index materials 40. In this example, the low-refractive-index material 42 was SiO2, and the high-refractive-index material 40 was a combination of SiN, Si, and ITO. As shown in the table, layers 35, 37, and 39 (the three high-refractive-index material 40 layers closest to the substrate 30) were made of SiN. Layers 41, 43, 45, 47, 49, 51, 53, 55, and 57 were made of silicon layers. Layer 41 (the Si layer closest to the substrate 30) was the thinnest Si layer, with a thickness of 9.55 nm. The total thickness of the silicon layers was 742.34 nm, accounting for 21.8% of the total thickness of the second multilayer film 38. Layer 65 was a TCO material layer. As shown in the table, the refractive index of the TCO layer at 905 nm was 1.54. The TCO layer was preferably positioned behind the silicon layer (closer to the end face 48). As described herein, this positioning of the TCO layer has the advantage that visible light is absorbed by the silicon layer and does not reach the TCO layer. Thus, adding the TCO layer as described above allows for the addition of additional functionality while preventing the TCO layer from detracting from the appearance of the window 24 described herein.

[0176] In Example 3, layers 58 through 64 correspond to the inner AR stack, which separates the silicon layer from the TCO layer. The high-refractive-index material included in the inner AR stack was SiN. As shown in the table, three SiN layers separate the innermost silicon layer from the facet 48. The inner AR stack included seven layers, with a total thickness of 1251.11 nm, which corresponds to 36.82% of the total thickness of the second multilayer film 38. As shown in the table, the inner AR stack also included two relatively thick SiO layers (layers 58 and 62) with thicknesses greater than 350 nm. The provision of such thick layers significantly reduces the reflectivity inside the window 24, helping to prevent signal noise due to back reflection of the output wave.

[0177] The thicknesses of each layer in the first multilayer film 36 and the second multilayer film 38 in Example 3 were set as shown in Table 3 below, and were used to calculate the transmittance, reflectance, CIELAB color space values, and lightness values ​​shown in Figures 16 to 18.

[0178] [Table 3-1]

[0179] [Table 3-2]

[0180] 16 is a graph showing the modeled transmittance (polarization average) of window 24 according to Example 3 across the spectral range from 350 nm to 1500 nm for light incident on window 24 at angles of incidence of 15° and 60°. As apparent from FIG. 16 , the quantitative composition, thickness, number of layers, and materials of first multilayer coating 36 and second multilayer coating 38 of window 24 according to Example 3 are configured such that the transmittance of window 24 for light incident on first surface 32 or second surface 34 at angles of incidence less than 15° exceeds 95% across the entire wavelength range from 850 nm to 950 nm. Indeed, throughout the entire wavelength range from 850 nm to 950 nm, the transmittance of window 24 for light incident at an angle of incidence of 15° exceeds 96%.

[0181] 16, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 3 are configured so that the average polarized light transmittance of the window 24 exceeds 85% in the target wavelength range of 850 nm to 950 nm for light incident on the first and second surfaces at angles of 60° or less relative to the normal to the first and second surfaces. Furthermore, as is clear from FIG. 16, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 3 are configured so that the transmittance of the window 24 for light incident on the window 24 (end surface 44) at an angle of 60° or less is less than 5% across the entire visible spectrum. Furthermore, in the range of 400 nm to 700 nm, the average transmittance of the window 24 according to Example 3 for perpendicularly incident light is less than 0.1%. The visible light transmittance is lower than in Example 2 because the number of silicon layers and the total thickness are increased.

[0182] 17A, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 3 are configured so that the average polarized reflectance at the end face 44 of the first multilayer film 36 of the window 24 for light incident on the substrate 30 at either the end face 44 or the end face 48 at an angle of incidence of 15° is less than 1% in the wavelength range of approximately 850 nm to 950 nm. Furthermore, as is clear from FIG. 17B, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 3 are configured so that the average reflectance (polarized average) at the end face 44 of the first multilayer film 36 and the end face 48 of the second multilayer film 38 for light incident at an angle of incidence of 15° is less than 0.5% in the wavelength range of approximately 890 nm to 950 nm. The reflectivity is also lower than in Example 2 due to the addition of the inner AR stack.

[0183] As is apparent from FIG. 18 , the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 3 are configured to give the window 24 a dark appearance when viewed from the end face 44 of the first multilayer film. FIG. 18 shows simulated CIELAB reflected color data for light reflected from the end face 44 of Example 3. The CIELAB a* and b* values ​​were generated by performing simulations at multiple different light source incident angles ranging from 0° to 90°. As shown, the a* values ​​range from approximately −2.3 to approximately 4.5, and the b* values ​​range from approximately −1.65 to approximately 0. This indicates that the window 24 of Example 3 has a low-saturation appearance when viewed from the outside world 26 (see FIG. 1 ). Furthermore, the windows of Examples 2 and 3 exhibited L* values ​​below 26 for light incident on the end face 44 at incident angles ranging from 0° to 45°. This provides the effect that the window 24 is easily perceived as a dark color at viewing angles in the range of 0° to 45°.

[0184] As an alternative embodiment, the configuration of Example 3 can be modified by increasing the number of silicon layers in the second multilayer film 38 and reducing the relative number of layers in the inner AR stack. By making such modifications, compared to Example 3, it is possible to obtain an advantage of flattening the reflectance spectrum from the facet 44 while maintaining low reflectance characteristics for light incident on the facet 48. Specifically, it has been confirmed that by reducing the size of the inner AR stack, including fewer than three layers (i.e., one or two) of high-refractive-index material 40 between the Si layer and the TCO layer, and providing at least ten (e.g., 10, 11, 12, 13, 14, or even 15) Si layers in the second multilayer film, it is possible to obtain an advantage of flattening the reflectance spectrum around the 50-nm target wavelength range. Such a flattening of the reflectance spectrum provides the advantage of increasing the manufacturing tolerance for achieving high transmission and low reflection performance in the 50-nm target wavelength range described herein, thereby improving production throughput. In this way, by increasing the number of silicon layers and reducing the number of layers in the inner AR stack, it is possible to reduce the fluctuation range (difference between maximum and minimum values) of the window's reflectance for light in the wavelength range of 850 nm to 970 nm incident on facet 44 at an incident angle of 15° to less than 0.05%. In addition, in this embodiment, it is also possible to reduce the fluctuation range (difference between maximum and minimum values) of the window's reflectance for light in the wavelength range of 850 nm to 950 nm incident on facet 44 at an incident angle of 60° to less than 3%.

[0185] Example 4 The window 24 of Example 4 included a first multilayer film 36 and a second multilayer film 38. The second multilayer film 38 included a layer of a silicon material, which is described herein as a "low-k" material. The window 24 of Example 4 had the first multilayer film 36 on a first surface 32 of the substrate 30. The window 24 of Example 4 also had the second multilayer film 38 on a second surface 34 of the substrate 30. The substrate 30 of Example 4 had the same structure as that of Example 3.

[0186] The first multilayer film 36 was constructed by alternately stacking 27 layers of SiO2 as the low refractive index material 42 and SiN as the high refractive index material 40. The 20th layer was a scratch-resistant layer made of the high refractive index material 40 with a thickness of 2055.93 nm. The 1st to 19th layers were optical control layers that separated the scratch-resistant layer from the end face 44. The total thickness of the 1st to 19th layers was 1108.71 nm. The 21st to 27th layers were refractive index matching layers that separated the scratch-resistant layer from the first surface 32. The total thickness of the 21st to 27th layers was 222.41 nm. In this example, the scratch-resistant layer accounted for 60.7% of the thickness of the first multilayer film 36.

[0187] The second multilayer film 38 was constructed by alternately stacking 33 layers of low-refractive-index materials 42 and high-refractive-index materials 40. In this example, the low-refractive-index material 42 was SiO2, and the high-refractive-index material 40 was a combination of SiN, Si, and ITO. As shown in the table, the 29th and 31st layers (the two high-refractive-index material 40 layers closest to the substrate 30) were SiN. The 33rd, 35th, 37th, 39th, 41st, 43rd, 45th, 47th, 49th, 41st, 43rd, and 55th layers were silicon layers. Therefore, the number of silicon layers included in Example 4 was greater than that of Example 3. The 33rd layer (the Si layer closest to the substrate 30) was the thinnest Si layer, with a thickness of 8.05 nm. The total thickness of the silicon layers was 522.03 nm, accounting for 31.7% of the total thickness of the second multilayer film 38. Thus, in Example 4, the number of silicon layers was greater than in Example 3. Furthermore, in Example 4, the total thickness of the silicon layers was thinner than in Example 3, but the proportion of the total thickness of the silicon layers to the total thickness of the second multilayer film was high (more than 30%). The 59th layer was a TCO material layer. As shown in the table, the refractive index of the TCO layer at 905 nm was 1.54. The TCO layer was disposed at a position behind the silicon layer (on the end face 48 side), which is considered to be a preferred position.

[0188] In Example 4, layers 56 to 58 correspond to the inner AR stack, which separates the silicon layer from the TCO layer. The high-refractive index material included in the inner AR stack was SiN. As shown in the table, one SiN layer separates the innermost silicon layer from the end face 48. The inner AR stack included three layers, with a total thickness of 109.28 nm, which corresponds to 6.62% of the total thickness of the second multilayer film 38. Thus, in Example 4, the size of the inner AR stack was significantly reduced compared to Example 3, and its proportion of the total thickness of the second multilayer film 38 was significantly reduced (to less than 10%). Furthermore, in Example 4, the inner AR stack included two relatively thin SiO layers (layers 56 and 58) with thicknesses of 10 nm and 20 nm. Without wishing to be bound by theory, in Example 4, the inner AR stack is thinner, but is compensated for by the addition of a Si layer, which helps achieve good reflectivity performance for light incident on facet 48.

[0189] The thicknesses of each layer in the first multilayer film 36 and the second multilayer film 38 in Example 4 were set as shown in Table 4 below, and were used to calculate the transmittance, reflectance, CIELAB color space values, and lightness values ​​shown in Figures 19 to 21.

[0190] [Table 4-1]

[0191] [Table 4-2]

[0192] 19 is a graph showing the modeled transmittance (polarization average) of window 24 according to Example 4 across the spectral range from 350 nm to 1600 nm for light incident on window 24 at angles of incidence of 15° and 60°. As apparent from FIG. 19 , the quantitative composition, thickness, number of layers, and materials of first multilayer coating 36 and second multilayer coating 38 of window 24 according to Example 4 are configured such that the transmittance of window 24 for light incident on first surface 32 or second surface 34 at angles of incidence less than 15° exceeds 95% across the entire wavelength range from 850 nm to 950 nm. Indeed, throughout the entire wavelength range from 850 nm to 950 nm, the transmittance of window 24 for light incident at an angle of incidence of 15° exceeds 95%.

[0193] 19, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 4 are configured so that the polarized average transmittance of the window 24 calculated in the target wavelength range of 850 nm to 950 nm exceeds 90% for light incident on the first and second surfaces at angles of 60° or less relative to the normal to the first and second surfaces. Furthermore, as is clear from FIG. 19, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 4 are configured so that the transmittance of the window 24 for light incident on the window 24 (end face 44) at an angle of 60° or less is less than 20% across the entire visible spectrum. Furthermore, in the wavelength range of 400 nm to 600 nm, the transmittance of the window 24 according to Example 4 for light incident on the end face 44 at an angle of 60° is less than 0.1% throughout that range. In the entire wavelength range of 400 nm to 700 nm, the average transmittance of the window 24 according to Example 4 is below 1% for both perpendicularly incident light and light incident at an incident angle of 15°.

[0194] 20A, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 4 are configured so that the average polarized reflectance at the end face 44 of the first multilayer film 36 of the window 24 for light incident on the substrate 30 at an incident angle of 15° is less than 1% in the wavelength range of approximately 850 nm to 950 nm. Furthermore, as is clear from FIG. 20B, the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 4 are configured so that the average polarized reflectance at the end face 48 of the second multilayer film 38 of the window 24 for light incident on the substrate 30 at an incident angle of 15° is less than 0.5% in the wavelength range of approximately 850 nm to 950 nm. Furthermore, in the window 24 of Example 4, the average polarized reflectance for light incident on either end face 44 or end face 48 at an incident angle of 60° is below 10% in the wavelength range of approximately 850 nm to 950 nm.

[0195] 20C, 20D, and 20E are graphs comparing the reflectivity of the windows according to Examples 3 and 4 in the wavelength range of 850 nm to 950 nm. FIG. 20C is a graph showing the average polarized reflectivity for light incident on the end face 44 of Examples 3 and 4 at an incident angle of 15°, and FIG. 20D is a graph showing the average polarized reflectivity for light incident on the end face 44 of Examples 3 and 4 at an incident angle of 60°. As is clear from FIG. 20C, in Example 4, by changing the configuration of the second multilayer film 38, it was possible to reduce the reflectivity for light incident at an incident angle of 15° across the entire wavelength range of 860 nm to 950 nm (to less than 0.1%). Furthermore, the fluctuation range of the reflectivity (the difference between the maximum and minimum values) in the wavelength range of 850 nm to 950 nm was approximately 0.2% in Example 3, while it was less than 0.05% in Example 4. 20D, by changing the configuration of the second multilayer film 38 in Example 4, the reflectance for light incident at an incident angle of 60° could be reduced (to less than 7%) across the entire wavelength range of 850 nm to 950 nm. The fluctuation range of the reflectance (the difference between the maximum and minimum values) across the wavelength range of 850 nm to 950 nm was greater than 5% in Example 3, whereas it was less than 3% in Example 4. Also, as is clear from FIG. 20E, by changing the configuration of the second multilayer film 38 in Example 4, the reflectance for light incident on the end face 48 at an incident angle of 15° across the entire wavelength range of 850 nm to 950 nm could be reduced (to less than 0.2%). These results indicate that, compared to Example 3, Example 4 achieves a reduced reflectance and a flattened reflectance spectrum across the entire wavelength range of 850 nm to 950 nm. As described herein, such a configuration allows for easier production of multilayer films.

[0196] As is apparent from FIG. 21 , the quantitative composition, thickness, number of layers, and materials of the first multilayer film 36 and the second multilayer film 38 of the window 24 of Example 4 are configured to give the window 24 a dark appearance when viewed from the end face 44 of the first multilayer film. FIG. 21 shows simulated CIELAB reflected color data for light reflected from the end face 44 of Example 4. The CIELAB a* and b* values ​​were generated by performing simulations at multiple different light source incident angles ranging from 0° to 90°. As shown, the a* values ​​range from approximately −0.58 to approximately 0.9, and the b* values ​​range from approximately −0.2 to approximately 1.4. This indicates that the window 24 of Example 4 has a low-saturation appearance when viewed from the outside world 26 (see FIG. 1 ). Furthermore, the windows of Examples 2 and 3 exhibited L* values ​​below 37 for light incident on the end face 44 at incident angles ranging from 0° to 60°. This provides the effect that the window 24 is easily recognized as a dark color at viewing angles in the range of 0° to 60°.

[0197] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit and scope of the claims.

[0198] Preferred embodiments of the present invention will be described below in detail.

[0199] Embodiment 1 a substrate having a first surface and a second surface, the first surface and the second surface being major surfaces of the substrate; a first multilayer film disposed on the first surface of the substrate, the first multilayer film including alternating layers of one or more high refractive index materials and one or more low refractive index materials, the refractive index of the one or more high refractive index materials being higher than the refractive index of the one or more low refractive index materials of the first multilayer film; a second multilayer film disposed on the second surface of the substrate, the second multilayer film including alternating layers of one or more high refractive index materials and one or more low refractive index materials, the refractive index of the one or more high refractive index materials of the second multilayer film being higher than the refractive index of the one or more low refractive index materials of the second multilayer film; A window for a detection system comprising: the maximum hardness of the window is at least 8 GPa as measured by performing a Berkovich indentation hardness test on the first multilayer film; The quantitative composition, thickness, number of layers, and material of the alternating layers in the first multilayer film and the second multilayer film are: the average transmittance of the window is greater than 90% when calculated in a target wavelength band of 50 nm having a center wavelength in the range of 850 nm to 950 nm for light incident on the first surface and the second surface at an incident angle of 15° or less; the average reflectance of the window calculated in the target wavelength range of 50 nm having a center wavelength in the range of 850 nm to 950 nm for light incident on the first surface and the second surface at an angle of 15° or less is less than 4%, A window configured so that the average transmittance of the window calculated in the range of 400 nm to 700 nm for light incident on the first surface and the second surface at an incident angle of 15° or less is less than 5%.

[0200] Embodiment 2 2. The window of claim 1, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the average P-polarized light transmittance and average S-polarized light transmittance of the window are greater than 85% calculated over a 50 nm wide wavelength range of interest for light incident on the first and second surfaces at an angle of incidence of 60° or less.

[0201] Embodiment 3 3. The window of claim 2, wherein the average P-polarized light transmittance and the average S-polarized light transmittance of the window are greater than 89% calculated over a 50 nm wide wavelength range of interest for light incident on the first and second surfaces at an angle of incidence of 60° or less.

[0202] Embodiment 4 4. The window of any of claims 1 to 3, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured such that the CIELAB L* value of the reflection of the window for an angle of incidence of 60° or less relative to the first multilayer film is 37 or less.

[0203] Embodiment 5 5. The window of embodiment 4, wherein the reflection has a CIELAB L* value of 25 or less for angles of incidence of 50° or less relative to the first multilayer film.

[0204] Embodiment 6 A window as described in any one of embodiments 1 to 5, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured so that the CIELAB a* and b* values ​​of the reflection of the window when viewed from the side of the first multilayer film are between -6.0 and 6.0.

[0205] Embodiment 7 7. The window of any one of embodiments 1 to 6, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured such that the average transmittance of the window, calculated in the target wavelength range of 50 nm width, for light incident perpendicularly to the first surface and the second surface is greater than 95%.

[0206] Embodiment 8 the refractive index of the substrate for electromagnetic waves having a wavelength of 905 nm is about 1.45 to about 1.55; the substrate is a glass substrate or a glass ceramic substrate, the refractive index of said one or more high refractive index materials is about 1.7 to about 4.0, and the refractive index of said one or more low refractive index materials is about 1.3 to about 1.6; 8. The window of any one of embodiments 1 to 7, wherein the difference in refractive index between any one of the one or more high refractive index materials and any one of the one or more low refractive index materials is about 0.5 or more.

[0207] Embodiment 9 one layer of the alternating layers in the first multilayer film that is located farthest from the substrate constitutes a material of an edge surface of the window, and the material of the edge surface of the window includes the low refractive index material; 9. The window of any one of claims 1 to 8, wherein the first multilayer film includes a scratch-resistant layer, the scratch-resistant layer being formed from one of the one or more high refractive index materials and having a thickness of 1500 nm or more and 5000 nm or less.

[0208] Embodiment 10 10. The window of claim 9, wherein the scratch-resistant layer is spaced from the edge by multiple layers of the alternating layers of the one or more low refractive index materials and the one or more high refractive index materials in the first multilayer film.

[0209] Embodiment 11 11. The window of claim 10, wherein the scratch-resistant layer is spaced from the edge by at least 1000 nm.

[0210] Embodiment 12 12. The window of any one of embodiments 1 to 11, wherein the one or more high refractive index materials of the second multilayer film comprise silicon having an extinction coefficient of 0.01 or less in the target wavelength range having a width of 50 nm.

[0211] Embodiment 13 13. The window of embodiment 12, wherein the extinction coefficient of silicon in the wavelength range of interest 50 nm wide is 0.005 or less.

[0212] Embodiment 14 14. The window of embodiment 13, wherein the second multilayer film comprises two or more silicon layers.

[0213] Embodiment 15 15. The window of embodiment 14, wherein the second multilayer film comprises a TCO material layer, and the two or more silicon layers are disposed between the TCO material layer and the substrate.

[0214] Embodiment 16 16. The window of embodiment 15, wherein the TCO material layer has a thickness of at least 20 nm and not more than 30 nm.

[0215] Embodiment 17 17. The window of embodiment 16, wherein the TCO material layer is indium tin oxide and has an extinction coefficient of 0.05 or less across the 50 nm wide wavelength range of interest.

[0216] Embodiment 18 18. The window of any one of embodiments 14 to 17, wherein the silicon layer of the second multilayer closest to the substrate has the smallest thickness of the two or more silicon layers.

[0217] Embodiment 19 19. The window of embodiment 18, wherein the silicon layers in the second multilayer film have a total thickness of 450 nm or greater.

[0218] Embodiment 20 20. The window of any one of embodiments 12 to 19, wherein the one or more layers of high refractive index material in the second multilayer film include a layer other than silicon.

[0219] Embodiment 21 21. The window of claim 20, wherein the two or more silicon layers of the second multilayer film are spaced from the inner edge of the second multilayer film by an inner AR stack including at least one layer other than silicon as the layer of the one or more high refractive index materials.

[0220] Embodiment 22 22. The window of embodiment 21, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured such that the average reflectance of the window calculated in the target wavelength range of 50 nm width is less than 0.5% for light incident on both the first end face of the first multilayer film and the second end face of the second multilayer film at an incident angle of 15° or less.

[0221] Embodiment 23 23. The window of embodiment 21 or 22, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured such that the average transmittance of the window calculated in the range of 400 nm to 700 nm for light incident perpendicularly to the first surface and the second surface is less than 1%.

[0222] Embodiment 24 the second multilayer film comprises at least 10 silicon layers; 24. The window of any one of embodiments 21-23, wherein the inner AR stack comprises fewer than two layers of non-silicon as layers of the one or more high refractive index materials.

[0223] Embodiment 25 The window of embodiment 24, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured so that the fluctuation range (difference between the maximum and minimum values) of the polarized average reflectance of the window calculated in the wavelength range of 850 nm to 950 nm for light incident on the first multilayer film at an incident angle of 15° is less than 0.5%.

[0224] Embodiment 26 26. The window of any one of embodiments 1 to 25, wherein the maximum hardness measured by Berkovich hardness testing of the first multilayer film is at least 15 GPa.

[0225] Embodiment 27 27. The window of any one of embodiments 1 to 26, wherein the first multilayer film has a hardness of at least 14 GPa over a depth range of 400 nm to 1000 nm as measured by Berkovich hardness testing.

[0226] Embodiment 28 a substrate having a first surface and a second surface, the first surface and the second surface being major surfaces of the substrate; a first multilayer film disposed on the first surface of the substrate, the first multilayer film including alternating layers of one or more high refractive index materials and one or more low refractive index materials, the refractive index of the one or more high refractive index materials being higher than the refractive index of the one or more low refractive index materials of the first multilayer film; a second multilayer film disposed on the second surface of the substrate, the second multilayer film including alternating layers of one or more high refractive index materials and one or more low refractive index materials, the refractive index of the one or more high refractive index materials of the second multilayer film being higher than the refractive index of the one or more low refractive index materials of the second multilayer film; A window for a detection system comprising: the maximum hardness of the window is at least 8 GPa as measured by performing a Berkovich indentation hardness test on the first multilayer film; The quantitative composition, thickness, number of layers, and material of the alternating layers in the first multilayer film and the second multilayer film are: the average reflectance of the window is less than 4% when calculated in a target wavelength band of 50 nm having a center wavelength in the range of 850 nm to 950 nm for light incident on the first surface and the second surface at an angle of 15° or less; the CIELAB L* value of the reflection of the window for an angle of incidence of 60° or less relative to the first multilayer film is 37 or less; A window configured so that the CIELAB a* and b* values ​​of the reflection of the window when viewed from the first multilayer film side are between -6.0 and 6.0.

[0227] Embodiment 29 29. The window of embodiment 28, wherein the reflection has a CIELAB L* value of 25 or less for an angle of incidence of 50° or less relative to the first multilayer film.

[0228] Embodiment 30 30. The window of claim 28 or 29, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the average transmittance of the window, calculated over a 50 nm wide wavelength range of interest, is greater than 95% for light incident on the first and second surfaces at an angle of incidence of 15° or less.

[0229] Embodiment 31 A window as described in any of embodiments 28 to 30, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured so that the average transmittance of the window, calculated in the range of 400 nm to 700 nm, for light incident on the first surface and the second surface at an incident angle of 15° or less is less than 5%.

[0230] Embodiment 32 A window as described in any of embodiments 28 to 31, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured so that the average P-polarized light transmittance and average S-polarized light transmittance of the window calculated in the target wavelength range with a width of 50 nm are greater than 85% for light incident on the first surface and the second surface at an incident angle of 60° or less.

[0231] Embodiment 33 33. The window of claim 32, wherein the average P-polarized light transmittance and the average S-polarized light transmittance of the window are greater than 89% calculated over a 50 nm wide wavelength range of interest for light incident on the first and second surfaces at an angle of incidence of 60° or less.

[0232] Embodiment 34 34. The window of any one of embodiments 28 to 33, wherein the maximum hardness measured by Berkovich hardness testing of the first multilayer film is at least 15 GPa.

[0233] Embodiment 35 one layer of the alternating layers in the first multilayer film that is located farthest from the substrate constitutes a material of an edge surface of the window, and the material of the edge surface of the window includes the low refractive index material; 35. The window of any one of claims 28 to 34, wherein the first multilayer film includes a scratch-resistant layer, the scratch-resistant layer being formed from one of the one or more high refractive index materials and having a thickness of 1500 nm or more and 5000 nm or less.

[0234] Embodiment 36 the scratch-resistant layer is spaced from the end face by a plurality of layers among the alternating layers in which the one or more low refractive index materials and the one or more high refractive index materials are alternately stacked in the first multilayer film; 36. The window of embodiment 35, wherein the scratch-resistant layer is spaced at least 1000 nm from the edge.

[0235] Embodiment 37 37. The window of any one of embodiments 28 to 36, wherein the one or more high refractive index materials of the second multilayer film comprise silicon having an extinction coefficient of 0.004 or less in the target wavelength range having a width of 50 nm.

[0236] Embodiment 38 38. The window of embodiment 37, wherein the second multilayer film comprises two or more silicon layers.

[0237] Embodiment 39 39. The window of embodiment 38, wherein the second multilayer film comprises a TCO material layer, and the two or more silicon layers are disposed between the TCO material layer and the substrate.

[0238] Embodiment 40 40. The window of embodiment 39, wherein the TCO material layer has a thickness of at least 20 nm and not more than 30 nm.

[0239] Embodiment 41 41. The window of embodiment 40, wherein the TCO material layer is indium tin oxide and has an extinction coefficient of 0.05 or less across the 50 nm wide wavelength range of interest.

[0240] Embodiment 42 42. The window of any one of embodiments 38 to 41, wherein the silicon layer of the second multilayer closest to the substrate has the smallest thickness of the two or more silicon layers.

[0241] Embodiment 43 43. The window of any one of embodiments 38 to 42, wherein the silicon layers included in the second multilayer film have a total thickness of 450 nm or more.

[0242] Embodiment 44 44. The window of any one of embodiments 38 to 43, wherein the one or more layers of high refractive index material in the second multilayer include a layer other than silicon.

[0243] Embodiment 45 45. The window of embodiment 44, wherein the two or more silicon layers are spaced from the inner edge of the second multilayer film by an inner AR stack including at least two layers other than silicon as the one or more layers of high refractive index material.

[0244] Embodiment 46 46. ​​The window of embodiment 45, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured such that the average reflectance of the window calculated in the target wavelength range of 50 nm width is less than 0.5% for light incident on both the first end face of the first multilayer film and the second end face of the second multilayer film at an incident angle of 15° or less.

[0245] Embodiment 47 the second multilayer film comprises at least 10 silicon layers; 47. The window of embodiment 45 or 46, wherein the inner AR stack comprises fewer than two layers of non-silicon as layers of the one or more high refractive index materials.

[0246] Embodiment 48 The window of embodiment 47, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured so that the fluctuation range (difference between the maximum and minimum values) of the polarized average reflectance of the window calculated in the wavelength range of 850 nm to 950 nm for light incident on the first multilayer film at an incident angle of 15° is less than 0.5%.

[0247] Embodiment 49 49. A window as described in any one of embodiments 45 to 48, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured so that the average transmittance of the window calculated in the range of 400 nm to 700 nm for light incident perpendicularly to the first surface and the second surface is less than 1%. [Explanation of symbols]

[0248] 10 vehicles 12 LIDAR systems 14 Vehicle roof 16 Front of vehicle 18 Electromagnetic radiation detector 20 Case 22 Outgoing electromagnetic wave 24 Windows 26 Outside world 28 Reflected electromagnetic waves 30 Substrates, articles 32 First side of the substrate 34 Second side of the board 35 Board thickness 36 First multilayer film 38 Second multilayer film 40 High refractive index materials 42 Low refractive index materials 44 End face of first multilayer film 46 Thickness of the first multilayer 48 End face of second multilayer film 50 Thickness of the second multilayer

Claims

1. a substrate having a first surface and a second surface, the first surface and the second surface being major surfaces of the substrate; a first multilayer film disposed on the first surface of the substrate, the first multilayer film including alternating layers of one or more high refractive index materials and one or more low refractive index materials, the refractive index of the one or more high refractive index materials being higher than the refractive index of the one or more low refractive index materials of the first multilayer film; a second multilayer film disposed on the second surface of the substrate, the second multilayer film including alternating layers of one or more high refractive index materials and one or more low refractive index materials, the refractive index of the one or more high refractive index materials of the second multilayer film being higher than the refractive index of the one or more low refractive index materials of the second multilayer film; A window for a detection system comprising: the maximum hardness of the window as measured by performing a Berkovich indentation hardness test on the first multilayer film is at least 8 GPa; The quantitative composition, thickness, number of layers, and material of the alternating layers in the first multilayer film and the second multilayer film are: the average transmittance of the window is greater than 90% when calculated in a target wavelength band of 50 nm having a center wavelength in the range of 850 nm to 950 nm for light incident on the first surface and the second surface at an angle of incidence of 15° or less; the average reflectance of the window calculated in the target wavelength range of 50 nm having a center wavelength in the range of 850 nm to 950 nm for light incident on the first surface and the second surface at an angle of 15° or less is less than 4%, A window configured such that the average transmittance of the window is less than 5% calculated over a range of 400 nm to 700 nm for light incident on the first surface and the second surface at an angle of incidence of 15° or less.

2. 10. The window of claim 1, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the average P-polarized light transmittance and average S-polarized light transmittance of the window are greater than 85% calculated over a 50 nm wide wavelength range of interest for light incident on the first and second surfaces at an angle of incidence of 60° or less.

3. 2. The window of claim 1, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer and the second multilayer are configured such that the CIELAB L* value of the reflection of the window for angles of incidence of 60° or less relative to the first multilayer is 37 or less.

4. 2. The window of claim 1, wherein the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first and second multilayer films are configured such that the CIELAB a* and b* values ​​of the reflection of the window when viewed from the first multilayer film side are between -6.0 and 6.

0.

5. the refractive index of the substrate for electromagnetic waves having a wavelength of 905 nm is about 1.45 to about 1.55; the substrate is a glass substrate or a glass ceramic substrate, the refractive index of said one or more high refractive index materials is from about 1.7 to about 4.0, and the refractive index of said one or more low refractive index materials is from about 1.3 to about 1.6; 10. The window of claim 1, wherein the difference in refractive index between any of the one or more high refractive index materials and any of the one or more low refractive index materials is about 0.5 or greater.

6. one layer of the alternating layers in the first multilayer film that is located farthest from the substrate constitutes a material of an edge surface of the window, and the material of the edge surface of the window includes the low refractive index material; the first multilayer film includes a scratch-resistant layer, the scratch-resistant layer being formed from one of the one or more high refractive index materials and having a thickness of 1500 nm or more and 5000 nm or less; 2. The window of claim 1 , wherein the scratch-resistant layer is spaced from the edge by multiple layers of the alternating layers of the one or more low refractive index materials and the one or more high refractive index materials in the first multilayer film.

7. 7. The window of claim 1, wherein the one or more high refractive index materials of the second multilayer film include silicon having an extinction coefficient of 0.01 or less in the wavelength range of interest having a width of 50 nm.

8. 8. The window of claim 7, wherein the second multilayer film comprises a TCO material layer and two or more silicon layers, the two or more silicon layers being disposed between the TCO material layer and the substrate.

9. 8. The window of claim 7, wherein the one or more layers of high refractive index material in the second multilayer include a layer other than silicon.

10. the two or more silicon layers of the second multilayer film are spaced from the inner end surface of the second multilayer film by an inner AR stack including at least one layer other than silicon as the one or more layers of high refractive index material; the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured such that an average reflectance of the window calculated in the target wavelength range having a width of 50 nm is less than 0.5% for light incident on both the first end face of the first multilayer film and the second end face of the second multilayer film at an incident angle of 15° or less; the quantitative composition, thickness, number of layers, and materials of the alternating layers in the first multilayer film and the second multilayer film are configured such that the average transmittance of the window calculated in the range of 400 nm to 700 nm for light perpendicularly incident on the first surface and the second surface is less than 1%; 10. The window of claim 9, wherein the second multilayer comprises at least 10 silicon layers, the inner AR stack comprises fewer than two layers of the one or more high refractive index materials that are not silicon, and the quantitative composition, thicknesses, number of layers, and materials of the alternating layers in the first and second multilayers are configured such that the variation in polarized average reflectance of the window (the difference between the maximum and minimum values) is less than 0.5% for light incident on the first multilayer at an angle of incidence of 15° over a wavelength range of 850 nm to 950 nm.

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