Wide-angle-incidence color-insensitive intermediate infrared window film

Abstract

The invention provides a wide-angle-incidence color-insensitive intermediate infrared window film which structurally comprises a substrate material G, a transition layer M1, a transition layer M2, a dielectric film system C and an air layer A from bottom to top. The invention aims to realize high transmittance of an infrared window in a medium-wave infrared spectrum range under incidence at a wide angle of 0-60 degrees, and the infrared window has the characteristic of insensitivity to the color of visible light at the same time. The transition layer is composed of two oxides and is used for improving the firmness of the film layer. The dielectric film system structure is formed by alternately depositing high-refractive-index materials and low-refractive-index materials, and the dielectric film system can ensure that an infrared window has high permeability in a medium wave band range under wide-angle incidence and has insensitivity to visible light color display. The wide-angle-incidence color-insensitive intermediate infrared window film can be widely applied to the optical system fields of optical detection, imaging and the like.

Description

Technical Field

[0001] The present invention relates to the design and preparation method of a wide-angle incident color-insensitive mid-infrared window film, in particular to a film that is insensitive to visible light color under a wide angle of incidence of 0 to 60 degrees and has high-efficiency mid-infrared transmittance, belonging to the field of thin film optical technology. Background Art

[0002] Mid-infrared windows play a vital role in infrared detection, sensor technology, optoelectronic display systems, and other fields. Commonly used mid-infrared window substrates generally have a high refractive index and severe surface reflectivity, necessitating the application of an antireflection coating to improve the window's overall transmittance in the mid-infrared band.

[0003] Existing mid-infrared window film technology often focuses solely on the high transmittance requirements of the mid-infrared band, overlooking the impact of visible light reflection on optical systems. At wide angles of incidence, the window surface can produce color non-uniformity due to varying visible light reflections. In severe cases, this can affect the practical application of precision optical components in optical systems. With the advancement of optical technology, optical systems are placing higher demands on the spectral performance of multi-band optical film components, encompassing shortwave, near-infrared, and infrared. Furthermore, as a critical component connecting the system's internal and external environments, windows are often exposed to harsh operating environments, placing even higher demands on the durability and robustness of window films. Therefore, on the one hand, we aim to achieve high transmittance in the mid-infrared band while maintaining insensitivity to visible light color. On the other hand, we also aim to achieve excellent robustness in our mid-infrared window films. Summary of the Invention

[0004] The purpose of the present invention is to provide a wide-angle incident color-insensitive mid-infrared window film, which achieves high transmittance in the target infrared band through a specific film layer structure design and has the characteristic of being insensitive to visible light color display.

[0005] The technical solutions provided by the present invention are as follows:

[0006] A wide-angle incident color-insensitive mid-infrared window film has a structure of G / M1M2 / C / A, wherein G represents a substrate material, M1 represents a transition layer 1, M2 represents a transition layer 2, C represents a dielectric film system, and A represents an incident medium air layer. The dielectric film system is formed by alternately depositing a low-refractive-index dielectric material and a high-refractive-index dielectric material.

[0007] The initial structure expression of the film is G / M1M2(xHyL)^n / A, where G is the substrate material, M1 represents transition layer 1, M2 represents transition layer 2, H is a high refractive index material with an optical thickness of λ / 4, L is a low refractive index material with an optical thickness of λ / 4, n is the number of dielectric film periods, x and y are the thickness coefficients of the high refractive index and low refractive index film layers, respectively, and A is the air layer.

[0008] The number of dielectric film layer periods n is selected in the range of 1 to 10, the thickness coefficients x and y of the low refractive index and high refractive index film layers are between 0.1 and 5, and the ratio of the total thickness coefficients ∑y(L) / ∑x(H) of the low refractive index film layer and the high refractive index film layer of the optimized film system is also between 0.1 and 5.

[0009] The substrate material is sapphire, zirconium oxide, yttrium oxide, calcium fluoride, zinc sulfide or zinc selenide.

[0010] The materials of the transition layer 1 and the transition layer 2 are Al2O3 and Y2O3 respectively, and the thickness of the transition layer 1 and the transition layer 2 are both less than 50nm.

[0011] The high refractive index dielectric material is TiO2, Ta2O5, ZrO2, HfO2 or ZnS.

[0012] The low refractive index dielectric material is SiO2, YF3 or YbF3.

[0013] Compared with the prior art, the present invention has the following technical effects:

[0014] 1. Under the premise of ensuring high transmittance of the infrared window in the mid-infrared band, the system achieves insensitivity to visible light color at a wide angle of incidence of 0 to 60°.

[0015] 2. It has the advantages of thin film thickness and good mechanical stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the structure of a wide-angle incident color-insensitive mid-infrared window film of the present invention.

[0017] Figure 2 This is the final film structure of Example 1.

[0018] Figure 3 This is the single-side transmittance spectrum curve of the window in the range of 0-60° for the film system in Example 1.

[0019] Figure 4 (a) and (b) are the chromaticity diagram and color patch diagram of the film system in Example 1 in the range of 0-60°, respectively.

[0020] Figure 5 This is the final film structure of Comparative Example 1.

[0021] Figure 6 This is the single-side transmittance spectrum curve of the window in the range of 0-60° for Comparative Example 1.

[0022] Figure 7 (a) and (b) are the chromaticity diagram and color patch diagram of the film of Comparative Example 1 in the range of 0-60°, respectively.

[0023] Figure 8 This is the final film structure of Comparative Example 2.

[0024] Figure 9 This is the single-side transmittance spectrum curve of the window in the range of 0-60° for comparative example 2.

[0025] Figure 10 (a) and (b) are the chromaticity diagram and color patch diagram of the film of Comparative Example 2 in the range of 0-60°, respectively.

[0026] Figure 11 This is the final film structure of Example 2.

[0027] Figure 12 This is the single-side transmittance spectrum curve of the window in the range of 0-60° in Example 2.

[0028] Figure 13 (a) and (b) are the chromaticity diagram and color patch diagram of the film of Example 2 in the range of 0-60°, respectively. DETAILED DESCRIPTION

[0029] The specific examples of the present invention are described in detail below with reference to the accompanying drawings.

[0030] Figure 1 The present invention discloses a wide-angle incident color-insensitive mid-infrared window film, whose structure is G / M1M2 / C / A, wherein G represents the substrate material, M1 represents the transition layer 1, M2 represents the transition layer 2, C represents the dielectric film system, and A represents the incident medium air layer. The dielectric film system is formed by alternating deposition of a low-refractive-index dielectric material and a high-refractive-index dielectric material.

[0031] The design indicators of the infrared window film required by Example 1 are: achieving an average transmittance greater than 90% within the range of 3700nm to 4800nm, an incident angle of 0-60°, and insensitivity to visible light color on the zirconia window.

[0032] The design steps are as follows:

[0033] 1. Based on the spectral characteristics of the target wavelength, select broadband, high-transmittance coating materials: high-refractive-index Ta2O5 and low-refractive-index SiO2. The initial film structure is G / M1M2(0.5HL)^4 / A, where H represents Ta2O5 with a quarter-wavelength optical thickness, L represents SiO2 with a quarter-wavelength optical thickness, M1 and M2 represent Al2O3 and Y2O3, respectively. The initial thickness of transition layer 1 and transition layer 2 is set to 30nm. The refractive index parameters of the high-refractive-index Ta2O5 and low-refractive-index SiO2 are determined by the Sellmeier formula, as shown in Table 1.

[0034] Table 1: Refractive index parameters of high and low refractive index materials in Example 1

[0035] <![CDATA[A1]]> <![CDATA[B1]]> <![CDATA[A2]]> <![CDATA[B2 <!-- 2 -->]]> <![CDATA[Ta2O5]]> 3.26145 0.0295957 4.07352 202.585 <![CDATA[SiO2]]> 1.10828 0.0071807 2.08973 200.268

[0036] 2. Set the optimization targets to achieve a transmittance of ≥99.5% in the mid-infrared band (3700-4800nm) and 90% in the visible band (400-780nm). Set the incident angles to 0°, 10°, 20°, 30°, 40°, 50°, and 60°. Optimize the initial film structure using the simplex and simulated annealing optimization algorithms in the film design software.

[0037] 3. The optimal membrane structure obtained by optimization is: G / 0.05M10.12M20.25H0.21L0.16H1.92L0.14H0.91L0.2H0.65L / A, such as Figure 2 As shown, the total thickness is 752 nanometers, the number of film layers is 10, the thickness coefficient ratio of L and H materials is ∑y(L) / ∑x(H)=4.95, and the stress calculation results show that the fracture factor of the film structure is 1.56. In the range of 0-60° incident angle, the single-side transmittance spectrum curve of the infrared window is as follows Figure 3 The chromaticity diagram and color patch diagram of the film in the range of 0-60° incident angle are shown as follows: Figure 4 As shown in (a) and (b).

[0038] Comparative Example 1: The difference between this comparative example and Example 1 is that the design optimization target is only to achieve a transmittance greater than or equal to 99.5% in the mid-infrared band of 3700-4800nm, and no color-sensitive design considerations are taken into account. The optimized film structure is: G / 0.32M10.35M20.42H1.52L2.2H2.89L2.98H2.17L0.42H2.89L / A, as shown in the figure. Figure 5As shown in the figure, the total thickness is 2462 nanometers, the number of film layers is 10, and the stress calculation results show that the fracture factor of the film structure is 14.9, and the film layer has a greater risk of firmness. The single-sided transmittance spectrum curve within the 0-60° incident angle range is shown in the figure. Figure 6 As shown in the figure, the chromaticity diagram and color patch diagram in the incident angle range of 0-60° are respectively as follows Figure 7 As shown in (a) and (b), the results show that the chromaticity diagram and the color scale diagram change significantly with the change of angle, that is, they are sensitive to the visible light color display and cannot meet the requirements.

[0039] Comparative Example 2: The difference between this comparative example and Example 1 is that there is no M1 and M2 buffer layer in the film structure. The optimized film structure is: G / 1.75H0.07L0.18H0.08L0.14H0.28L0.08H3.16L0.08H0.23L0.09H0.07L / A, as shown in the figure. Figure 8 As shown, the total thickness is 950 nanometers, the number of film layers is 12, and the stress calculation results show that the fracture factor of the film structure is 4.35. The single-side transmittance spectrum curve within the incident angle range of 0-60° is as follows Figure 9 As shown in the figure, the chromaticity diagram and color patch diagram in the incident angle range of 0-60° are respectively as follows Figure 10 As shown in (a) and (b), the results show that although the spectral performance in the range of 0-60° can meet the requirements, the fracture factor of the film structure is 4.35, which is 3 times that of the film structure in Example 1, indicating that the film layer has a greater risk of firmness.

[0040] The design indicators of the infrared window film required by Example 2 are: achieving an average transmittance of >90% within the range of 3700nm to 4800nm, an incident angle of 0-60°, and insensitivity to visible light color on the sapphire window.

[0041] The design steps are as follows:

[0042] 1. Based on the spectral characteristics of the target wavelength, select broadband, high-transmittance coating materials: high-refractive-index TiO2 and low-refractive-index SiO2. The initial film structure is G / M1M2(0.5HL)^5 / A, where H represents TiO2 with a quarter-wavelength optical thickness, L represents SiO2 with a quarter-wavelength optical thickness, M1 and M2 represent Al2O3 and Y2O3, respectively. The initial thickness of transition layer 1 and transition layer 2 is set to 30nm. The refractive index parameters of the high-refractive-index TiO2 and low-refractive-index SiO2 are determined by the Sellmeier formula, as shown in Table 2.

[0043] Table 2: Refractive index parameters of high and low refractive index materials in Example 2

[0044] <![CDATA[A1]]> <![CDATA[B1]]> <![CDATA[A2]]> <![CDATA[B2]]> <![CDATA[TiO2]]> 3.97674 0.0479993 2.31322 96.4369 <![CDATA[SiO2]]> 1.10828 0.0071807 2.08973 200.268

[0045] 2. Set the optimization targets to achieve a transmittance of ≥99.5% in the mid-infrared band (3700-4800nm) and 90% in the visible band (400-780nm). Set the incident angles to 0°, 10°, 20°, 30°, 40°, 50°, and 60°. Optimize the initial film structure using the simplex and simulated annealing optimization algorithms in the film design software.

[0046] 3. The optimal membrane structure obtained by optimization is: G / 0.11M10.12M20.26H0.15L0.32H0.17L0.2H1.67L0.1H2.19L0.15H0.59L / A, such as Figure 11 As shown, the total thickness is 970 nanometers, the number of film layers is 12, the thickness coefficient ratio of L and H materials is ∑y(L) / ∑x(H)=4.71, and the stress calculation results show that the fracture factor of the film structure is 1.71. In the range of 0-60° incident angle, the single-side transmittance spectrum curve of the infrared window is as follows Figure 12 The chromaticity diagram and color patch diagram of the film in the range of 0-60° incident angle are shown as follows: Figure 13 As shown in (a) and (b).

[0047] In addition, considering different window and film material combinations, other typical preferred embodiments are listed below, as shown in Table 3:

[0048] Table 3: Typical preferred embodiments

[0049]

[0050]

[0051] The above description is only a preferred example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A wide-angle incident color-insensitive mid-infrared window film, characterized in that: Its structure is G / M1M2 / C / A, wherein G represents the base material, M1 represents the transition layer 1, M2 represents the transition layer 2, C represents the dielectric film system, and A represents the incident medium air layer, wherein the dielectric film system is formed by alternately depositing a dielectric material with a low refractive index and a dielectric material with a high refractive index; The initial structure expression of the film is G / M1M2(xHyL)^n / A, where G is the substrate material, M1 represents transition layer 1, M2 represents transition layer 2, H is a high refractive index material with an optical thickness of λ / 4, L is a low refractive index material with an optical thickness of λ / 4, n is the number of periods of the dielectric film system, x and y are the thickness coefficients of the high refractive index and low refractive index film layers, respectively, A is the air layer, and λ is the reference wavelength.

2. The wide-angle incident color-insensitive mid-infrared window film according to claim 1, characterized in that: The selection range of the number of periods n of the dielectric film layer is 1 to 10, the thickness coefficients x and y of the low refractive index and high refractive index film layers are between 0.1 and 5, and the total thickness coefficient ratio ∑y(L) / ∑x(H) of the optimized film system low refractive index film layer and high refractive index film layer is between 0.1 and 5.

3. A wide-angle incident color-insensitive mid-infrared window film according to claim 1 or 2, characterized in that: The substrate material is sapphire, zirconium oxide, yttrium oxide, calcium fluoride, zinc sulfide or zinc selenide infrared window.

4. A wide-angle incident color-insensitive mid-infrared window film according to claim 1 or 2, characterized in that: The materials of the transition layer 1 and the transition layer 2 are Al2O3 and Y2O3 respectively, and the thickness of the transition layer 1 and the transition layer 2 are both less than 50nm.

5. The wide-angle incident color-insensitive mid-infrared window film according to claim 1 or 2, characterized in that: The high refractive index dielectric material is TiO2, Ta2O5, ZrO2, HfO2 or ZnS.

6. A wide-angle incident color-insensitive mid-infrared window film according to claim 1 or 2, characterized in that: The low refractive index dielectric material is SiO2, YF3 or YbF3.

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