Design and manufacturing method of medium-long wave infrared anti-reflection microstructure window

Abstract

The invention provides a design and manufacturing method of a medium-long wave infrared anti-reflection microstructure window, and relates to the technical field of infrared window processing and application. The method specifically comprises the following steps: performing simulation design on a medium-long wave infrared anti-reflection microstructure according to material characteristics and application requirements of a window substrate, and determining key dimension parameters to be processed; an outer surface anti-reflection microstructure and an inner surface anti-reflection microstructure are machined on the surfaces of the two sides of the window substrate respectively through multi-pulse femtosecond laser Bessel beams. The method has wide adaptability and flexibility, and efficient design and high-quality manufacturing of the anti-reflection microstructure on the surface of any window material can be achieved. The problem that an existing window material is low in medium-wave and long-wave infrared transmittance is solved, meanwhile, the window material has good structural durability and environmental adaptability, and the strict performance requirement of a common-caliber infrared dual-waveband imaging technology for an infrared window is met.

Description

Technical Field

[0001] The invention relates to the field of infrared window processing and application technology, and in particular to a design and manufacturing method for a medium- and long-wave infrared anti-reflection microstructure window. Background Art

[0002] Co-aperture infrared dual-band imaging technology is a high-end optoelectronic reconnaissance technology of the future. It integrates information from medium-wave infrared (3-5μm) and long-wave infrared (8-12μm) to enhance the performance of target detection, identification and tracking. To achieve this technology, the required infrared window material should exhibit high transmittance throughout the 3-12μm band. However, the substrate transmittance of existing wide-band infrared window materials is generally low, for example, zinc sulfide is about 74%, zinc selenide is about 70%, and germanium is about 50%. These low transmittances will lead to significant infrared signal loss, affecting the receiving efficiency of the detector.

[0003] The traditional method of multilayer antireflection film has been proven to effectively improve the transmittance of the window. However, for the 3-12μm wide-band antireflection film, the design complexity, multilayer film material limitations, manufacturing process difficulty and cost considerations have all increased significantly. At present, only a few materials have been studied for dual-band antireflection films. Patent CN 108330440 A discloses a technology for preparing a multilayer antireflection film (Ge-YF3-DLC-ZnS) on a zinc sulfide substrate using an ion sputtering method, which successfully increases the transmittance to more than 90%, but the antireflection film still has problems with thermal expansion failure, poor environmental resistance and insufficient long-term stability, which limits its application in infrared imaging technology in extremely complex environments.

[0004] Ultrafast laser direct writing technology processes anti-reflection microstructures on the surface of window substrate materials, providing an innovative solution to overcome the defects of traditional anti-reflection films. Patent CN 118727157A uses femtosecond laser direct writing assisted wet etching to manufacture micro-conical anti-reflection microstructures on the surface of zinc sulfide windows, achieving a maximum increase of 73% to 85.6% in the substrate transmittance in the 8-12μm band, but its transmittance drops sharply in the 3-5μm band, and the transmittance at a wavelength of 3μm is only about 20%. This increase in transmittance does not cover the required full band, especially in the mid-wave infrared, where the transmittance performance drops significantly, and cannot meet the performance requirements of the common-aperture infrared dual-band imaging technology.

[0005] Therefore, in order to meet the requirements of mid- and long-wave infrared dual-band imaging technology and achieve the optimized design and high-precision manufacturing of mid- and long-wave infrared anti-reflection microstructure windows, the following key issues need to be resolved: the infrared window will not fail in complex application environments such as high temperature and high pressure, while ensuring that the anti-reflection microstructure window has improved transmittance in the full band of 3-12μm. This requires design optimization of the key size parameters of the anti-reflection microstructure and high-quality and precise manufacturing to achieve high anti-reflection effects in a wide band and meet the stringent performance requirements of the common-aperture infrared dual-band imaging system for the infrared window. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a design and manufacturing method for a medium- and long-wave infrared anti-reflection microstructure window. Through the design method provided by the present invention, the optimized design of the surface infrared anti-reflection microstructure of various window substrate materials can be achieved, which can meet the transmittance requirements of various application scenarios. The anti-reflection microstructure is manufactured on the surface of the window substrate material using a multi-pulse femtosecond laser Bessel beam, and the high-quality and efficient manufacturing of the medium- and long-wave infrared anti-reflection microstructure window can be achieved by adjusting the femtosecond laser processing parameters.

[0007] In order to achieve the above-mentioned purpose, the present invention provides a method for designing a mid- and long-wave infrared anti-reflection microstructure window, comprising the following steps:

[0008] Step S11, calculating the period p1≤3 / n1 of the anti-reflection microstructure according to the refractive index n1 of the window substrate at a wavelength of 3 μm;

[0009] Step S12, fixing the anti-reflection microstructure period p1 and height h0, and comparing the average transmittances of different widths d in the mid- and long-wave infrared bands through simulation to obtain the optimal width d1;

[0010] Step S13, fixing the anti-reflection microstructure period as p1 and width as d1, solving the average transmittance of different heights h in the mid- and long-wave infrared bands through simulation, and solving the corresponding relationship between the height h and the transmittance;

[0011] Step S14: according to the transmittance requirement of the application scenario, determine the key size parameters of the anti-reflection microstructure: period p1, width d1, height h1, to guide the processing.

[0012] Further, in step S11, the window substrate material includes any one of zinc sulfide, zinc selenide, gallium arsenide, germanium, and barium fluoride.

[0013] Furthermore, in steps S11 to S14, the anti-reflection microstructure is any one of a hole-type, cone-type, and grating-type structure, and the anti-reflection microstructure is located on both side surfaces of the window substrate material and is distributed periodically.

[0014] 4. The method for designing a mid- and long-wave infrared anti-reflection microstructure window according to claim 1, characterized in that in steps S12 to S13, the simulation adopts FDTD, COMOSOL or Rsoft simulation software.

[0015] The present invention also provides a method for manufacturing the above-mentioned mid- and long-wave infrared anti-reflection microstructure window, comprising the following steps:

[0016] Step S21, using a multi-pulse femtosecond laser Bessel beam to perform processing tests on the surface of the window substrate, exploring femtosecond laser processing parameters, and determining optimal manufacturing parameters that match key size parameters of the anti-reflection microstructure;

[0017] Step S22, processing the outer surface anti-reflection microstructure and the inner surface anti-reflection microstructure on both side surfaces of the window substrate respectively with the optimal manufacturing parameters;

[0018] Step S23, ultrasonically cleaning the manufactured sample to finally obtain a mid- and long-wave infrared anti-reflection microstructure window.

[0019] Further, in step S21, the multi-pulse Bessel beam is generated by a laser burst mode and a 175° axicon.

[0020] Furthermore, in step S21, the femtosecond laser processing parameters include: laser focus position, laser energy, pulse number and processing path and its scanning speed and interval, etc.

[0021] In general, the above technical solution conceived by the present invention has the following advantages compared with the prior art:

[0022] (1) Efficient improvement of infrared transmittance across bands: Through the design method of mid- and long-wave infrared anti-reflection microstructure windows, the transmittance in the entire 3-12μm band is efficiently improved, meeting the high performance requirements of the window for co-aperture infrared dual-band composite imaging technology.

[0023] (2) Good structural durability and environmental adaptability: Directly processing the anti-reflection microstructure on the window substrate maintains the mechanical stability of the window and its adaptability to different environmental conditions, solving the failure problem caused by the mismatch of thermal expansion coefficients faced by traditional multi-layer anti-reflection films.

[0024] (3) High-precision manufacturing and flexibility in material selection: By adjusting the manufacturing process parameters of multi-pulse femtosecond laser Bessel beams, high-quality and efficient manufacturing of anti-reflection microstructures on the surface of any infrared window material can be achieved, which has wide adaptability and flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a three-dimensional structural model of the mid- and long-wave infrared anti-reflection microstructure window of an embodiment of the present invention.

[0026] Figure 2 It is a schematic diagram of a multi-pulse femtosecond laser Bessel beam processing system according to an embodiment of the present invention.

[0027] Figure 3 This is the relationship between the width and height of the structure of Example 1 of the present invention and the average transmittance in the mid- and long-wave infrared bands.

[0028] Figure 4 This is the transmittance curve after the optimized design of the anti-reflection microstructure window in Example 1 of the present invention.

[0029] Figure 5 This is the relationship between the width and height of the structure of Example 2 of the present invention and the average transmittance in the mid- and long-wave infrared bands.

[0030] Figure 6 This is the transmittance curve after the optimized design of the anti-reflection microstructure window in Example 2 of the present invention. DETAILED DESCRIPTION

[0031] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings; it should be understood that the preferred embodiments are only for illustrating the present invention rather than for limiting the protection scope of the present invention.

[0032] Embodiment 1:

[0033] In this embodiment, zinc sulfide is used as the window substrate material, and the hole-shaped structure is used as the anti-reflection microstructure. Application requirements: The transmittance of the zinc sulfide window in the mid- and long-wave infrared is increased by about 20% on average.

[0034] Figure 1 The three-dimensional structural model of the mid- and long-wave infrared anti-reflection microstructure window is shown, which includes three key dimensional parameters: structural period p, width d and height h. Figure 2 A multi-pulse femtosecond laser Bessel beam processing system was demonstrated. Compared with traditional laser light sources (Gaussian beams), this system has higher processing accuracy and efficiency. By adjusting the number of pulses per unit area, precise manufacturing of high aspect ratio anti-reflection microstructures can be achieved.

[0035] First, the key size parameters of the antireflection microstructure are designed:

[0036] (1) The refractive index n1 of the zinc sulfide window at a wavelength of 3 μm is about 2.25. It is calculated by the formula p1≤3 / n1, and the period p1 is taken as 1.3 μm;

[0037] (2) The anti-reflection microstructure period is fixed at 1.3 μm and the height is 1.0 μm. The relationship between the width d and the average transmittance in the mid- and long-wave infrared bands is simulated as follows: Figure 3As shown in the figure, when the width is 1.3μm, the anti-reflection effect of the microstructure is the best. Therefore, the width d1 is set to 1.3μm;

[0038] (3) The period and width are fixed to 1.3 μm, and the average transmittance at different heights h in the mid- and long-wave infrared bands is solved by simulation. The corresponding relationship between height h and transmittance is obtained as follows: Figure 3 shown.

[0039] (4) According to the application requirements (mid- and long-wave infrared is improved by about 20%), the processing is carried out with a period of 1.3 μm, a width of 1.3 μm, and a height of 1.2 μm.

[0040] Then, the femtosecond laser processing parameters were explored: the ultrafast laser output light source wavelength was set to 515nm, the pulse width was 900fs, the repetition frequency was 20kHz, the laser focus position was 12μm, the processing path was arc scanning, the scanning speed was 26mm / s and the interval was 1.3μm, and the laser energy and pulse number were adjusted to obtain the corresponding key size parameters. The periodic hole-type anti-reflection microstructure was processed on both sides of the zinc sulfide window substrate with the manufacturing parameters.

[0041] Using the above method, from Figure 4 It can be seen that the transmittance of the medium- and long-wave infrared anti-reflection microstructure zinc sulfide window with a period of 1.3μm, a width of 1.3μm, and a height of 1.2μm has an average increase of about 20% in the 3-12μm band, and can reach up to more than 94%.

[0042] Embodiment 2:

[0043] In this embodiment, barium fluoride is used as the window substrate material, and the hole-shaped structure is used as the anti-reflection microstructure. Application requirements: Make the transmittance of the barium fluoride window in the mid- and long-wave infrared reach about 98%.

[0044] First, similar to Example 1, the key size parameters of the anti-reflection microstructure are designed:

[0045] (1) The refractive index n1 of the barium fluoride window at a wavelength of 3 μm is approximately 1.46, which is calculated using the formula p1≤3 / n1, with the period p1 being 2.0 μm;

[0046] (2) The anti-reflection microstructure period is fixed at 2.0 μm and the height is 1.0 μm. The relationship between the width d and the average transmittance in the mid- and long-wave infrared bands is simulated as follows: Figure 5 As shown in the figure, when the width is 2.0μm, the anti-reflection effect of the microstructure is the best. Therefore, the width d1 is set to 2.0μm;

[0047] (3) The period is fixed at 2.0 μm and the width is 2.0 μm. The average transmittance at different heights h in the mid- and long-wave infrared bands is solved by simulation. The corresponding relationship between height h and transmittance is obtained as follows: Figure 5 shown.

[0048] (4) According to the application requirements (mid- and long-wave infrared is increased to about 98%), the selected period is 2.0 μm, the width is 2.0 μm, and the height is 2.4 μm for processing.

[0049] Then, the femtosecond laser processing parameters were explored: the ultrafast laser output light source wavelength was set to 515nm, the pulse width was 900fs, the repetition frequency was 20kHz, the laser focus position was 12μm, the processing path was arc scanning, the scanning speed was 40mm / s and the interval was 2.0μm, and the laser energy and pulse number were adjusted to obtain the corresponding key size parameters. The periodic hole-type anti-reflection microstructure was processed on both sides of the barium fluoride window substrate with the manufacturing parameters.

[0050] Using the above method, from Figure 6 It can be seen that the average transmittance of the medium- and long-wave infrared anti-reflection microstructure barium fluoride window with a period of 2.0μm, a width of 2.0μm, and a height of 2.4μm can reach about 98% in the 3-12μm band.

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

Claims

1. A design method for a mid- and long-wave infrared anti-reflection microstructure window, characterized in that: The design method comprises the following steps: Step S11, calculating the period p1≤3 / n1 of the anti-reflection microstructure according to the refractive index n1 of the window substrate at a wavelength of 3 μm; Step S12, fixing the anti-reflection microstructure period p1 and height h0, and comparing the average transmittances of different widths d in the mid- and long-wave infrared bands through simulation to obtain the optimal width d1; Step S13, fixing the anti-reflection microstructure period as p1 and width as d1, solving the average transmittance of different heights h in the mid- and long-wave infrared bands through simulation, and solving the corresponding relationship between the height h and the transmittance; Step S14: according to the transmittance requirement of the application scenario, determine the key size parameters of the anti-reflection microstructure: period p1, width d1, height h1, to guide the processing.

2. The method for designing a mid- and long-wave infrared antireflection microstructure window according to claim 1, characterized in that: In step S11, the window substrate material includes any one of zinc sulfide, zinc selenide, gallium arsenide, germanium, and barium fluoride.

3. The method for designing a mid- and long-wave infrared antireflection microstructure window according to claim 1, characterized in that: The anti-reflection microstructure is any one of a hole-type, a cone-type, and a grating-type structure, and the anti-reflection microstructure is located on both side surfaces of the window substrate material and is distributed periodically.

4. The method for designing a mid- and long-wave infrared antireflection microstructure window according to claim 1, characterized in that: In steps S12 to S13, the simulation uses FDTD, COMOSOL or Rsoft simulation software.

5. A method for manufacturing a mid- and long-wave infrared anti-reflection microstructure window, characterized in that: The manufacturing method comprises the following steps: Step S21, using a multi-pulse femtosecond laser Bessel beam to perform processing tests on the surface of the window substrate, exploring femtosecond laser processing parameters, and determining optimal manufacturing parameters that match key size parameters of the anti-reflection microstructure; Step S22, processing the outer surface anti-reflection microstructure and the inner surface anti-reflection microstructure on both side surfaces of the window substrate respectively with the optimal manufacturing parameters; Step S23, ultrasonically cleaning the manufactured sample to finally obtain a mid- and long-wave infrared anti-reflection microstructure window.

6. The method for manufacturing a mid- and long-wave infrared anti-reflection microstructure window according to claim 5, characterized in that: In step S21, the multi-pulse Bessel beam is generated by a laser burst mode and a 175° axicon.

7. The method for manufacturing a mid- and long-wave infrared anti-reflection microstructure window according to claim 5, characterized in that: In step S21, the femtosecond laser processing parameters include: laser focus position, laser energy, pulse number and processing path and its scanning speed and interval, etc.

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