A mid-far infrared optical film based on potassium bromide film and a preparation method thereof

Abstract

The application discloses a mid-far infrared optical film based on potassium bromide film and a preparation method thereof, and relates to far infrared waveband optical film technology. The mid-far infrared optical film comprises a substrate, a front anti-reflection film system and a back anti-reflection film system. The front anti-reflection film system is located on one side of the substrate, and the back anti-reflection film system is located on the other side of the substrate. The mid-far infrared optical film window is prepared by alternately depositing zinc selenide as a high-refractive-index film material and potassium bromide as a low-refractive-index film material. The mid-far infrared optical film based on potassium bromide film provided by the application can realize wide-spectrum anti-reflection in the far infrared waveband of 5-28 microns, the average transmittance is 87.64%, and the highest transmittance is 91.44%.

Description

Technical Field

[0001] This invention relates to the field of far-infrared optical thin film technology, and in particular to a mid-far-infrared optical thin film based on potassium bromide thin film and its preparation method. Background Technology

[0002] The rapid development of infrared detection and imaging technologies in fields such as astronomical observation, deep space exploration, atmospheric and environmental monitoring, and high-power infrared laser protection has led to higher demands on the comprehensive performance of mid- and far-infrared (5–28 μm) optical windows, requiring high transmittance, broad spectrum, stability, and environmental adaptability. Especially in onboard or extreme environments, window materials must not only possess low absorption and a wide transparency range, but also high thermal conductivity, thermal shock resistance, and a high laser damage threshold. CVD diamond, with its extremely wide transmission band from 220 nm to >50 μm, along with ultra-high thermal conductivity and excellent corrosion resistance, has become one of the preferred substrates for far-infrared windows.

[0003] However, the high refractive index (n approximately 2.4) of the diamond substrate leads to significant Fresnel reflection, limiting its intrinsic transmittance. Several publicly disclosed approaches exist for antireflection and functionalization of diamond far-infrared windows: First, antireflection films are prepared on diamond using fluoride or oxide materials to reduce surface reflection near 5–12 μm; however, oxides / fluorides often exhibit intrinsic multiphonon absorption in the longer wavelength, far-infrared region, resulting in limited broadband transmittance. Second, composite spectroscopic or protective film structures using a "binder layer + metal layer + protective layer" can achieve a wider operating bandwidth and better mechanical stability on infrared substrates such as KBr; however, these structures are more suited for spectroscopic / protective applications and not specifically for broadband antireflection of diamond windows. Third, narrowband-optimized double-sided antireflection films or micro / nano structures can significantly improve the window's transmittance in the target wavelength band, but broadband consistency across 5–28 μm remains a challenge.

[0004] In summary, existing technologies are mostly limited to monochromatic / narrowband optimization (e.g., for 10.6μm laser windows) or focus on beam splitting and filtering functions (e.g., PbTe / CsI, PbTe / CdTe systems). Due to the intrinsic absorption of materials in the long wavelength range (>20μm), existing solutions struggle to meet the ultra-wideband anti-reflection requirements of 5–28μm. For example, while research using lead telluride (PbTe) and cadmium telluride (CdTe) as coating materials has extended the transmittance range to 5–50μm, its average transmittance is only 58.90%, and optical performance still needs improvement. Therefore, for CVD diamond far-infrared optical windows targeting the 5–28μm working range, there is an urgent need to explore a new mid- and far-infrared optical thin film. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a mid- and far-infrared optical film based on potassium bromide film. This optical film achieves broad-spectrum anti-reflection in the mid- and far-infrared bands of 5-28 micrometers by depositing multiple layers on a substrate.

[0006] A further technical problem to be solved by the present invention is to provide a method for preparing the above-mentioned mid- and far-infrared optical thin film based on potassium bromide thin film.

[0007] The present invention also provides an optical element comprising the above-mentioned mid- and far-infrared optical thin film based on potassium bromide film.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A mid- to far-infrared optical film based on potassium bromide film includes a substrate, a front antireflection film system, and a back antireflection film system; wherein the front antireflection film system is located on one side of the substrate, and the back antireflection film system is located on the other side of the substrate.

[0010] The mid-to-far-infrared optical thin film is prepared by alternating deposition of zinc selenide as a high-refractive-index thin film material and potassium bromide as a low-refractive-index thin film material.

[0011] Preferably, the substrate in this invention is diamond.

[0012] The front antireflective coating is composed of alternating deposits of zinc selenide film and potassium bromide film, wherein the first zinc selenide film is deposited on the substrate.

[0013] Preferably, the membrane structure of the front antireflective film system is as follows:

[0014] Substrate / 0.39H 0.31L 1.11H 0.81L 0.54H 1.97L 0.19H / Air;

[0015] Where H represents a zinc selenide film with an optical thickness of λ0 / 4, L represents a potassium bromide film with an optical thickness of λ0 / 4, λ0 is the center wavelength, λ0 is 5 micrometers, and the numbers before H and L are the λ0 / 4 optical thickness ratio coefficients.

[0016] The reverse antireflective film is composed of alternating deposits of zinc selenide film layers and potassium bromide film layers, wherein the first zinc selenide film layer is deposited on the substrate.

[0017] Preferably, the membrane structure of the reverse antireflective membrane system is as follows:

[0018] Substrate / 0.39H 0.31L 1.11H 0.81L 0.54H 1.97L 0.19H / Air;

[0019] Where H represents a zinc selenide film with an optical thickness of λ0 / 4, L represents a potassium bromide film with an optical thickness of λ0 / 4, λ0 is the center wavelength, λ0 is 5 micrometers, and the numbers before H and L are the λ0 / 4 optical thickness ratio coefficients.

[0020] An optical element comprising the aforementioned mid- to far-infrared optical thin film based on potassium bromide film.

[0021] The above-mentioned method for preparing mid- and far-infrared optical thin films based on potassium bromide thin films includes the following steps:

[0022] The substrate to be plated is cleaned.

[0023] An alternating deposition process is used to sequentially deposit zinc selenide and potassium bromide films of predetermined thicknesses on the front side of a cleaned substrate to obtain a front antireflection membrane system.

[0024] An alternating deposition process is used to sequentially deposit zinc selenide and potassium bromide films of predetermined thicknesses on the reverse side of a cleaned substrate to obtain a reverse antireflection membrane system.

[0025] The deposition rate of the zinc selenide film is 3.0 nm / s, and the deposition rate of the potassium bromide film is 4.0 nm / s.

[0026] In the alternating deposition process, the thin film deposition vacuum is 1~2×10⁻⁶. -3 Pa, the deposition temperature of the substrate is controlled at 200±2℃.

[0027] The cleaning process employs ion source-assisted bombardment cleaning, with the ion source having an anode voltage of 180 volts, a cathode current of 4 amperes, and bombardment lasting 8-10 minutes.

[0028] The beneficial effects of this invention are as follows:

[0029] (1) The mid- and far-infrared optical film based on potassium bromide film provided by the present invention can achieve wide-spectrum transmission enhancement in the far-infrared band of 5-28μm, with an average transmittance of 87.64% and a maximum transmittance of 91.44%.

[0030] (2) The far-infrared band optical thin film window of the present invention can be applied to infrared astronomical observation, earth radiation detection, far-infrared target identification and deep space exploration. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the structure of the mid- and far-infrared optical thin film based on potassium bromide film of the present invention.

[0032] Figure 2 The image shows the spectral transmittance curve of the mid-to-far-infrared optical thin film based on potassium bromide film of the present invention.

[0033] In the attached figures, the labels are: 1-front antireflection membrane system; 2-substrate; 3-reverse antireflection membrane system. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] The inventors discovered that potassium bromide, with its wide transmittance and low refractive index in the deep ultraviolet to long-wave infrared range, is widely used as a low refractive index material component in infrared optical substrates and optical formulations for low refractive index materials used in windows.

[0036] Zinc selenide (ZnSe) is a mature high-refractive-index thin-film material with mature applications in the 10.6 μm range. The typical refractive index of the thin film and the bulk material is approximately n≈2.4, making it commonly used in infrared multilayer films to form high / low refractive index pairs with low-n materials. Engineering products also show that the effective operating band of ZnSe-based devices often extends to the mid-to-long wavelength region. The resulting ZnSe / KBr combination can theoretically support phase and impedance matching across a wide spectral range, providing a material science basis for achieving low reflectivity in the 5–28 μm region.

[0037] The inventors designed the mid-to-far-infrared optical thin film based on potassium bromide film according to the technical approach of "reasonable pairing of high / low refractive index materials" and "double-sided synergistic anti-reflection design". This technical approach aims to significantly reduce surface reflection on both sides of the substrate while taking into account the stability of the preparation process and environmental adaptability, thereby achieving high-efficiency transmission in the target wavelength band.

[0038] This invention provides a mid-to-far-infrared optical film based on potassium bromide film, with an anti-reflection spectral range of 5-28 μm. Zinc selenide (ZnSe) is selected as the high refractive index film material, and potassium bromide (KBr) is selected as the low refractive index film material.

[0039] The far-infrared optical thin film of this invention employs a multilayer irregular film structure for both the front antireflection film system 1 and the back antireflection film system 3. The film deposition process utilizes a complementary monitoring method combining quartz crystal monitoring and direct optical monitoring to control deposition errors in the film thickness, achieving results close to the design specifications.

[0040] For details, see Figure 1A mid-to-far-infrared optical thin film based on potassium bromide thin film is disclosed, comprising a substrate 2, a front antireflection film system 1, and a back antireflection film system 3; wherein the front antireflection film system 1 is located on one side of the substrate 2, and the back antireflection film system 3 is located on the other side of the substrate 2. In this embodiment, the mid-to-far-infrared optical thin film is prepared by alternating deposition of zinc selenide (ZnSe) as a high-refractive-index thin film material and potassium bromide (KBr) as a low-refractive-index thin film material.

[0041] Specifically, the front antireflective film system 1 is composed of alternating deposits of zinc selenide film layer and potassium bromide film layer, wherein the first layer of zinc selenide film layer is deposited on the substrate 2, and the outermost zinc selenide film layer is in contact with air to avoid the potassium bromide film from deliquescing due to direct contact with air.

[0042] More preferably, the membrane structure of the front antireflection membrane system 1 is as follows:

[0043] Substrate / 0.39H 0.31L 1.11H 0.81L 0.54H 1.97L 0.19H / Air;

[0044] Where H represents a zinc selenide film with an optical thickness of λ0 / 4, L represents a potassium bromide film with an optical thickness of λ0 / 4, λ0 is the center wavelength, λ0 is 5 micrometers, and the numbers before H and L are the λ0 / 4 optical thickness ratio coefficients.

[0045] Similarly, the reverse antireflective film system 3 is composed of alternating deposits of zinc selenide film layer and potassium bromide film layer, wherein the first layer of zinc selenide film layer is deposited on the substrate 2, and the outermost zinc selenide film layer is in contact with air to avoid the potassium bromide film from deliquescing due to direct contact with air.

[0046] More preferably, the membrane structure of the reverse antireflection membrane system 3 is as follows:

[0047] Substrate / 0.39H 0.31L 1.11H 0.81L 0.54H 1.97L 0.19H / Air;

[0048] Where H represents a zinc selenide film with an optical thickness of λ0 / 4, L represents a potassium bromide film with an optical thickness of λ0 / 4, λ0 is the center wavelength, λ0 is 5 micrometers, and the numbers before H and L are the λ0 / 4 optical thickness ratio coefficients.

[0049] The above-mentioned method for preparing mid- and far-infrared optical thin films based on potassium bromide thin films includes the following steps:

[0050] The substrate to be plated is cleaned; in this embodiment, the substrate is a diamond substrate.

[0051] An alternating deposition process was used to sequentially deposit zinc selenide film and potassium bromide film of a predetermined thickness on the front side of the cleaned substrate 2 to obtain the front antireflection membrane system 1.

[0052] An alternating deposition process was used to sequentially deposit zinc selenide and potassium bromide films of predetermined thicknesses on the reverse side of the cleaned substrate 2 to obtain the reverse antireflection membrane system 3.

[0053] Preferably, the deposition rate of the zinc selenide film is 3.0 nm / s, and the deposition rate of the potassium bromide film is 4.0 nm / s.

[0054] Preferably, in the alternating deposition process, the thin film deposition vacuum is 1-2 × 10⁻⁶. -3 Pa, the deposition temperature of the substrate is controlled at 200±2℃.

[0055] Preferably, the cleaning process employs ion source-assisted bombardment cleaning, wherein the anode voltage of the ion source is 180 volts, the cathode current is 4 amperes, and the bombardment lasts for 8-10 minutes.

[0056] Preferably, the cleaning process for the substrate to be plated includes the following steps: ultrasonic cleaning in an alcohol-ether mixture (volume ratio 1:1) for 10 minutes, followed by wiping and cleaning with a lint-free cloth specifically for optical films.

[0057] Figure 2 This is the spectral transmittance curve of the mid-to-far-infrared optical thin film window of the present invention. From... Figure 2 As can be seen, the mid- and far-infrared optical film of the present invention has an average transmittance of 87.64% in the 5-28 micrometer band, with a maximum transmittance of 91.44%.

[0058] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Parts not described in detail in this specification are well-known in the art. The above embodiments are provided merely for the purpose of describing the present invention and are not intended to limit the scope of the present invention. The scope of protection of the present invention is defined by the appended claims. All equivalent substitutions and modifications made without departing from the spirit and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A mid-to-far-infrared optical thin film based on potassium bromide thin film, characterized in that, The mid-to-far infrared optical film includes a substrate, a front antireflection film system, and a back antireflection film system; wherein the front antireflection film system is located on one side of the substrate, and the back antireflection film system is located on the other side of the substrate; The front antireflection film system and the back antireflection film system are prepared by alternating deposition of zinc selenide as a high refractive index thin film material and potassium bromide as a low refractive index thin film material. The substrate is diamond; The membrane structure of the front antireflective film system is as follows: Substrate / 0.39H 0.31L 1.11H 0.81L 0.54H 1.97L 0.19H / Air; The membrane structure of the reverse antireflective membrane system is as follows: Substrate / 0.39H 0.31L 1.11H 0.81L 0.54H 1.97L 0.19H / Air; Where H represents a zinc selenide film with an optical thickness of λ0 / 4, L represents a potassium bromide film with an optical thickness of λ0 / 4, λ0 is the center wavelength, λ0 is 5 micrometers, and the numbers before H and L are the λ0 / 4 optical thickness ratio coefficients.

2. An optical element, characterized in that, Including the mid- and far-infrared optical thin film based on potassium bromide film as described in claim 1.

3. The method for preparing mid-to-far-infrared optical thin films based on potassium bromide thin films according to claim 1, characterized in that, Includes the following steps: The substrate to be plated is cleaned. An alternating deposition process is used to sequentially deposit zinc selenide and potassium bromide films of predetermined thicknesses on the front side of a cleaned substrate to obtain a front antireflection membrane system. An alternating deposition process is used to sequentially deposit zinc selenide and potassium bromide films of predetermined thicknesses on the reverse side of a cleaned substrate to obtain a reverse antireflection membrane system.

4. The method for preparing mid-to-far-infrared optical thin films based on potassium bromide thin films according to claim 3, characterized in that, The deposition rate of the zinc selenide film is 3.0 nm / s, and the deposition rate of the potassium bromide film is 4.0 nm / s.

5. The method for preparing mid-to-far-infrared optical thin films based on potassium bromide thin films according to claim 3, characterized in that, In the alternating deposition process, the thin film deposition vacuum is 1~2×10⁻⁶. -3 Pa, the deposition temperature of the substrate is controlled at 200±2℃.

6. The method for preparing mid-to-far-infrared optical thin films based on potassium bromide thin films according to claim 3, characterized in that, The cleaning process employs ion source-assisted bombardment cleaning, with an anode voltage of 180 volts, a cathode current of 4 amperes, and bombardment for 8 to 10 minutes.

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