A mid- and far-infrared wide-band high-transmission infrared window and its preparation method

Abstract

A mid- and far-infrared wide-band high-transmission infrared window and its preparation method, relating to an infrared window and its preparation method. The present invention aims to solve the technical problem that the average transmittance of existing multi-spectral ZnS infrared windows is only about 60%, which cannot meet the application requirements. By using the principle of matching high and low refractive indices, high refractive index ZnS and low refractive index YF3-based film materials are selected. Considering that the infrared window needs to have high mechanical properties to resist extreme environments, a high-hard film Y2O3 is used as a protective layer on the outermost layer of the film system. The mid- and far-infrared wide-band high-transmission infrared window of the present invention takes into account high transmission in the mid- and far-infrared bands, with a transmittance higher than 85% in the range of 3μm to 12μm, and has good mid- and far-infrared optical properties. The realization of this infrared window can provide technical support for the wide-band operation of aircraft, and greatly improve the service performance of aircraft.

Description

Technical Field

[0001] The invention relates to an infrared window and a preparation method thereof. Background Art

[0002] For aircraft, infrared sensing, imaging and guidance systems can help them navigate and find targets, especially in air attack, air defense, night intelligence reconnaissance and other aspects. These systems are usually composed of two parts: photoelectric detection and infrared windows. The photoelectric detection is the main functional component for searching signals, imaging and guiding the work of the aircraft, while the infrared window is mainly installed on the surface of the aircraft, located at the front end of the photoelectric system, and plays the role of transmitting target signals and protecting the main structural components of the internal photoelectric system. The flight speed of aircraft in the new era is extremely fast, and the flight environment faces a variety of deserts, oceans and inland areas. The photoelectric response band has also developed from a single band to a wide-band multi-spectrum direction. Therefore, the following urgent requirements are put forward for infrared optical windows: First, it can resist extreme environments such as aerodynamic heat, sand erosion and rain erosion under high-speed flight, that is, the infrared window is required to have strong and high mechanical strength; second, in response to the needs of wide-band operation of the photoelectric system, the infrared window needs to have wide-band multi-spectrum high transmittance. Commonly used infrared window materials are sapphire, magnesium fluoride, yttrium oxide (Y 2 O 3 ), spinel, germanium (Ge), aluminum oxynitride (AlON), zinc sulfide (ZnS), zinc selenide (ZnSe), etc. These infrared window materials have their own advantages in the use of bands, and most materials cannot achieve high transmittance performance in multiple bands at the same time. In addition, for example, materials such as MgF, ZnS and ZnSe are relatively soft in texture and cannot resist aerodynamic heat, sand erosion and rain erosion under high-speed flight conditions, and they are damaged, scratched, worn, etc., forming structural and functional damage. At present, the industry's research on infrared windows includes the design of infrared window surface coating to improve the mechanical properties of the window so that it has the performance of resisting extreme environments; there are also studies on the design and coating of infrared window single-band transmittance improvement, but there are relatively few studies on the design and preparation of infrared window wide-band high transmittance. In order to meet the requirements of resistance to extreme environments and take into account the performance of wide-band high transmittance, it is necessary to develop an infrared optical window that can resist extreme environments and has the ability to transmit wide-band high transmittance in the mid- and far-infrared, which is crucial to improving the performance of aircraft. Although the traditional multi-spectral ZnS infrared window has the characteristic of transmittance in a wide band of mid-infrared and far-infrared (3μm~5μm and 8μm~12μm), its average transmittance is only about 60%, which cannot meet the needs of application. At present, most of the research on ZnS infrared windows is to prepare an anti-reflection protective film layer on its surface to achieve high transmittance in the long infrared, while there are relatively few studies that take into account the mid-infrared or mid-to-far infrared. Summary of the invention

[0003] The present invention aims to solve the technical problem that the existing multi-spectral ZnS infrared window has an average transmittance of only about 60%, which cannot meet the application requirements, and provides a mid- and far-infrared wide-band high-transmittance infrared window and a preparation method thereof.

[0004] The structure of the mid- and far-infrared wide-band high-transmittance infrared window of the present invention is as follows:

[0005] The ZnS substrate is located in the middle, and multiple layers of thin films are arranged on both sides of the ZnS substrate; the inner film system structure of the mid- and far-infrared wide-band high-transmittance infrared window is an alternating film stack of YF 3 thin films and ZnS thin films. The number of YF 3 thin films and ZnS thin films is equal. The side close to the ZnS substrate is YF 3 thin film. The total number of YF 3 thin films and ZnS thin films is N layers, and N is an even number greater than or equal to 8;

[0006] The outer side of the mid- and far-infrared wide-band high-transmittance infrared window is an alternating film stack of YF 3 thin films and ZnS thin films. The number of YF 3 thin films and ZnS thin films is equal. The side close to the ZnS substrate is YF 3 thin film. The total number of YF 3 thin films and ZnS thin films is M layers, and N minus M is equal to 2. One layer of YF 3 thin film and one layer of Y 2 O 3 thin film are further arranged on the outermost ZnS thin film, and Y 2 O 3 thin film is on the outermost side.

[0007] The preparation method of the mid- and far-infrared wide-band high-transmittance infrared window of the present invention is as follows:

[0008] I. Cleaning the substrate: Ultrasonically clean the ZnS substrate in acetone, alcohol, and deionized water in sequence, then take out the sample and dry the surface moisture with nitrogen to obtain a clean substrate ZnS.

[0009] II. Fix the cleaned ZnS substrate on the sample stage of a thermal evaporation coating machine. Put ZnS, YF 3 and Y 2 O 3 in three tungsten boats respectively. Close the coating machine cabin door, evacuate to a vacuum state, and perform coating according to the above-mentioned film layer structure. Control the thickness of each layer of film by controlling the deposition time. After depositing one side of the ZnS substrate, turn the ZnS substrate over and continue to deposit the other side. After deposition is completed, shut down the machine and take out the sample to obtain a mid- and far-infrared wide-band high-transmittance infrared window.

[0010] The present invention utilizes the principle of matching high and low refractive indices, and selects high refractive index ZnS and low refractive index YF 3 as the film materials for the film system. Considering that the infrared window needs to have high mechanical properties to resist extreme environments, a hard film Y 2 O 3 is used as the protective layer (Y 2 O 3 is on the side facing outward from the optical window).

[0011] The mid-infrared and far-infrared wide-band high-transmission infrared window of the present invention takes into account high transmission in the mid-infrared and far-infrared bands, and the transmittance in the range of 3 μm to 12 μm is higher than 85%, having good mid-infrared and far-infrared optical properties. The realization of this infrared window can provide technical support for the wide-band operation of aircraft, and greatly improve the service performance of aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic structural diagram of the mid-infrared and far-infrared wide-band high-transmission infrared window in the first specific embodiment;

[0013] Figure 2 is a transmittance test chart of the mid-infrared and far-infrared wide-band high-transmission infrared window in Test 1;

[0014] Figure 3 is a schematic structural diagram of the mid-infrared and far-infrared wide-band high-transmission infrared window in Test 1. SPECIFIC EMBODIMENTS

[0015] Specific Embodiment 1: This embodiment is a mid-infrared and far-infrared wide-band high-transmission infrared window, as Figure 1 shown, its structure is:

[0016] The ZnS substrate is located in the middle, and multiple layers of thin films are arranged on both sides of the ZnS substrate; the inner film system structure of the mid-infrared and far-infrared wide-band high-transmission infrared window is an alternating film stack of YF 3 thin films and ZnS thin films. The number of YF 3 thin films and ZnS thin films is equal. The side close to the ZnS substrate is a YF 3 thin film. The total number of YF 3 thin films and ZnS thin films is N layers, and N is an even number greater than or equal to 8;

[0017] The outside of the mid-infrared and far-infrared wide-band high-transmission infrared window is an alternating film stack of YF 3 thin films and ZnS thin films. The number of YF 3 thin films and ZnS thin films is equal. The side close to the ZnS substrate is a YF 3 thin film. The total number of YF 3 thin films and ZnS thin films is M layers, and N minus M equals 2; a layer of YF is further arranged on the ZnS thin film on the outside3 A thin film and a layer of Y 2 O 3 The thin film, Y 2 O 3 The thin film is on the outermost side.

[0018] Embodiment 2: The difference between this embodiment and Embodiment 1 is that: N is 20. Others are the same as Embodiment 1.

[0019] Embodiment 3: The difference between this embodiment and Embodiment 1 or 2 is that: the thickness of the ZnS substrate is 20 mm. Others are the same as Embodiment 1 or 2.

[0020] Embodiment 4: The difference between this embodiment and any one of Embodiments 1 to 3 is that: the thickness of the Y 2 O 3 thin film is 50 nm. Others are the same as any one of Embodiments 1 to 3.

[0021] Embodiment 5: The difference between this embodiment and Embodiment 4 is that: the average transmittance of the mid-infrared wide-band high-transmittance infrared window in the range of 3 μm to 12 μm is higher than 85%. Others are the same as Embodiment 4.

[0022] Embodiment 6: This embodiment is the preparation method of the mid-infrared wide-band high-transmittance infrared window in Embodiment 1, specifically:

[0023] I. Cleaning the substrate: Ultrasonically clean the ZnS substrate in acetone, alcohol, and deionized water in sequence, then take out the sample and dry the surface moisture with nitrogen to obtain a clean substrate ZnS;

[0024] II. Fix the cleaned ZnS substrate on the sample stage of the thermal evaporation coating machine, put ZnS, YF 3 and Y 2 O 3 in three tungsten boats respectively, close the coating machine cabin door, evacuate to a vacuum state, deposit the film according to the film layer structure described above, control the thickness of each layer of film by controlling the deposition time, turn the ZnS substrate over after depositing one side of the ZnS substrate and continue to deposit the other side, turn off the machine and take out the sample after deposition to obtain a mid-infrared wide-band high-transmittance infrared window.

[0025] Embodiment 7: The difference between this embodiment and Embodiment 6 is that: in step I, the ZnS substrate is ultrasonically cleaned in acetone, alcohol, and deionized water for 15 min to 30 min respectively, then take out the sample and dry the surface moisture with nitrogen to obtain a clean substrate ZnS. Others are the same as Embodiment 6.

[0026] Embodiment 8: The difference between this embodiment and Embodiment 7 is that: the thickness of the ZnS substrate described in Step 1 is 20 mm. Others are the same as Embodiment 7.

[0027] Embodiment 9: The difference between this embodiment and Embodiment 6 is that: in Step 2, the vacuum is pumped to below 5×10 -4 Pa. Others are the same as Embodiment 6.

[0028] Embodiment 10: The difference between this embodiment and Embodiment 6 is that: in Step 2, the thickness of the deposited Y 2 O 3 film is 50 nm. Others are the same as Embodiment 6.

[0029] The present invention is verified by the following tests:

[0030] Test 1: This test is a mid-infrared wide-band high-transmission infrared window, as Figure 3 shown, and its structure is:

[0031] The ZnS substrate is located in the middle, and multiple layers of films are arranged on both sides of the ZnS substrate; the inner film system structure of the mid-infrared wide-band high-transmission infrared window is an alternating film stack of YF 3 films and ZnS films. The number of layers of YF 3 films and ZnS films is equal. The side close to the ZnS substrate is a YF 3 film. The total number of layers of YF 3 films and ZnS films is N layers, and N is an even number greater than or equal to 8;

[0032] The outer side of the mid-infrared wide-band high-transmission infrared window is an alternating film stack of YF 3 films and ZnS films. The number of layers of YF 3 films and ZnS films is equal. The side close to the ZnS substrate is a YF 3 film. The total number of layers of YF 3 films and ZnS films is M layers, and N minus M is equal to 2; on the outer ZnS film, one layer of YF 3 film and one layer of Y 2 O 3 film are further arranged. The Y 2 O 3 film is on the outermost side. The thickness of each layer of film is shown in Table 1.

[0033] The preparation method of the above mid-infrared wide-band high-transmission infrared window is as follows:

[0034] I. Cleaning the substrate: Ultrasonically clean the ZnS substrate in acetone, alcohol, and deionized water for 15 minutes each in sequence. Then take out the sample and dry the surface moisture with nitrogen to obtain a clean-surface ZnS substrate; the thickness of the ZnS substrate is 20 mm.

[0035] II. Fix the cleaned ZnS substrate on the sample stage of the thermal evaporation coating machine. Place ZnS, YF 3 and Y 2 O 3 in three tungsten boats respectively. Close the coating machine chamber door and evacuate to below 5×10 -4 Pa. Coat the film according to the film layer structure described above, and control the thickness of each layer of film by controlling the deposition time. After depositing one side of the ZnS substrate, turn the ZnS substrate over and continue to deposit the other side. After the deposition is completed, turn off the machine and take out the sample to obtain a mid-infrared wide-band high-transmission infrared window.

[0036] This experiment realized the preparation of a mid-infrared wide-band high-transmission infrared window based on multi-spectral ZnS by thermal evaporation. The outer film of this experiment is an 18-layer YF 3 and ZnS overlapping structure combined with a single layer of YF 3 and Y 2 O 3 ; This window takes into account the high transmission in the mid-infrared band, and the average transmittance in the range of 3 μm to 12 μm is higher than 85%, and has good mid-infrared optical properties (such as Figure 2 , the dotted line corresponds to the ordinate 85%). The realization of this infrared window can provide technical support for the wide-band operation of the aircraft and greatly improve the service performance of the aircraft.

[0037] Table 1 Thickness values of each layer of thin film in Experiment 1

[0038]

Claims

1. A mid-infrared wide-band high-transmission infrared window, characterized in that The structure of the mid-infrared wide-band high-transmission infrared window is as follows: the ZnS substrate is located in the middle, and multiple layers of thin films are arranged on both sides of the ZnS substrate; the inner film system structure of the mid-infrared wide-band high-transmission infrared window is a stack of alternating YF 3 thin films and ZnS thin films, and the number of YF 3 thin films and ZnS thin films is equal. The side close to the ZnS substrate is YF 3 thin film, and the total number of YF 3 thin films and ZnS thin films is N layers, where N is an even number greater than or equal to 8; The outer side of the far-infrared wide-band high-transmission infrared window is YF 3 thin film and ZnS thin film alternating film stack, YF 3 The number of layers of the YF thin film and the ZnS thin film is equal. The side close to the ZnS substrate is YF 3 thin film, YF 3 The total number of layers of the YF thin film and the ZnS thin film is M layers, and N minus M equals 2; On the outer ZnS thin film, another layer of YF 3 thin film and a layer of Y 2 O 3 thin film are provided. The Y 2 O 3 thin film is on the outermost side.

2. The mid-infrared wide-band high-transmission infrared window according to claim 1, characterized in that N is 20.

3. The mid-infrared wide-band high-transmission infrared window according to claim 1, characterized in that the thickness of the ZnS substrate is 20 mm.

4. The mid-infrared wide-band high-transmission infrared window according to claim 1, characterized in that The described Y 2 O 3 The thickness of the thin film is 50 nm.

5. The mid-infrared wide-band high-transmission infrared window according to claim 1, characterized in that the average transmittance of the mid-infrared wide-band high-transmission infrared window in the range of 3 μm to 12 μm is higher than 85%.

6. A preparation method of the mid-infrared wide-band high-transmission infrared window according to claim 1, characterized in that the preparation method of the mid-infrared wide-band high-transmission infrared window is as follows: I. Cleaning the substrate: Ultrasonically cleaning the ZnS substrate in acetone, alcohol and deionized water in sequence, then taking out the sample and drying the surface moisture with nitrogen to obtain a clean ZnS substrate. II. Fix the cleaned ZnS substrate on the sample stage of the thermal evaporation coating machine. Put ZnS, YF 3 and Y 2 O 3 in three tungsten boats respectively. Close the coating machine chamber door, evacuate to a vacuum state, and deposit films according to the above film layer structure. Control the thickness of each layer of film by controlling the deposition time. After depositing one side of the ZnS substrate, turn the ZnS substrate over and continue to deposit the other side. After deposition is completed, shut down the machine and take out the sample to obtain a mid- and far-infrared broadband high-transmission infrared window.

7. The preparation method of the mid-infrared wide-band high-transmission infrared window according to claim 1, characterized in that in step I, ultrasonically cleaning the ZnS substrate in acetone, alcohol and deionized water for 15 min to 30 min respectively, then taking out the sample and drying the surface moisture with nitrogen to obtain a clean ZnS substrate.

8. The preparation method of the mid-infrared wide-band high-transmission infrared window according to claim 1, characterized in that the thickness of the ZnS substrate in step I is 20 mm.

9. The preparation method of the mid-infrared wide-band high-transmission infrared window according to claim 1, characterized in that In step two, evacuate to below 5×10 -4 Pa.

10. The preparation method of the mid-infrared wide-band high-transmission infrared window according to claim 1, characterized in that Depositing Y in Step 2 2 O 3 The thickness of the thin film is 50 nm.

Images