Design method and preparation method of germanium-based 2-5.9 [mu] m waveband cut-off 6.3-14 [mu] m high-transmittance optical filter film

Abstract

The invention provides a design method and a preparation method of a germanium substrate 2-5.9 [mu] m waveband cut-off 6.3-14 [mu] m high-transmittance optical filter film. The design method comprises the steps that 550 nm serves as a reference wavelength of 1 / 4 wavelength thickness of an optical thin film, 2.1 (L2HL) 10, 2.8 (L2HL) 10, 3.6 (L2HL) 9 and 4.5 (L2HL) 9 of a Sub / S1 face and 42 (L2HLKL) 3 and 59 (K2LK) 1AIR of a S2 face are used, Sub is a germanium substrate, AIR represents air, H represents Ge, L represents ZnSe, and K represents YbF3; 75 layers of an S1 surface and 12 layers of an S2 surface are generated, the S1 surface is bottomed ZnSe, the outermost ZnSe is adopted, middle Ge and ZnSe are alternated, and the S2 surface is Ge / ZnSe / Ge / ZnSe / Ge / ZnSe / YbF3 / ZnSe / Ge / ZnSe / YbF3 / ZnSe; optimizing to obtain the optimal film layer thickness; and inputting into a coating machine.

Description

Technical Field

[0001] The present disclosure relates to the field of infrared optical film technology, and more specifically to a design method and a preparation method of a germanium-based 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film. Background Art

[0002] As an infrared lens material, germanium not only has excellent imaging performance in high and low temperature environments, but also has been widely used in germanium detectors with the development of the times. With the rapid development of various processing technologies, the market demand is also increasing. Due to the complex stress performance of germanium sheets, the film layer has poor firmness, forcing the need to continuously update and improve the process. Compared with the traditional germanium substrate film system design, the same germanium substrate 2-14.5μm band generally fails to reach the optimal state of light transmission interference ability of the film layer prepared on the lens due to the differences in film layer design methods, and the durability of the film layer is also insufficient. Summary of the invention

[0003] In view of the problems existing in the background technology, an object of the present invention is to provide a design method and a preparation method for a germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film, which can enable the designed and prepared germanium substrate together with the film system on both sides to achieve the target transmittance in the 2-5.9μm band and the 6.3-14μm band and pass the bubble test and the adhesion test.

[0004] Thus, a method for designing a germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film includes the following steps: Sa, the film system design uses 550nm as the reference wavelength for the design of an optical film with a thickness of 1 / 4 wavelength, and uses a film stack expression: Sub / S1 surface film stack 2.1(L2HL)^10, 2.8(L2HL)^10, 3.6(L2HL)^9, 4.5(L2HL)^9 / S2 surface film stack .42(L2HLKL)^3, .59(K2LK)^1AIR, wherein Sub is a germanium substrate, AIR represents air, and in the film stack expression: H represents a high refractive index material Ge (germanium) with a thickness of 1 / 4 wavelength; L represents a low refractive index material ZnSe ( Zinc selenide); K represents YbF3 (ytterbium fluoride), a low-refractive-index material with a thickness of 1 / 4 wavelength; Sb, through the input film stack formula, generates a film structure of 75 layers on the S1 side and 12 layers on the S2 side. The S1 side is ZnSe as the base, ZnSe as the outermost protective layer, and Ge and ZnSe alternate in the middle. The S2 side is Ge / ZnSe / Ge / ZnSe / Ge / ZnSe / YbF3 / ZnSe / Ge / ZnSe / YbF3 / ZnSe; Sc, the film thickness is optimized through thin film design software to obtain the optimal film thickness. The optimized film structure has a cutoff of 6.3-14μm in the 2-5.9μm band and achieves the target transmittance; Sd, the optimized optimal film thickness is input into the control computer of the coating machine.

[0005] A method for preparing a high-transmittance filter film with a germanium substrate 2-5.9μm band cutoff of 6.3-14μm comprises the following steps: step 1, cleaning the germanium substrate product and the accompanying coating sheet as a lens before coating, and preparing three kinds of film materials: ZnSe, Ge, and YbF3; step 2, configuring the coating process conditions and process files, wherein the coating process conditions and process files include coating temperature, background vacuum before coating, film thickness, evaporation mode of film material, deposition rate of film material, use and parameters of ion source assisted deposition, wherein the film thickness is based on the aforementioned germanium substrate 2-5.9μm band cutoff of 6.3-14μm The design method of high-transmittance filter film described in the optimal film thickness stored in the control computer of the coating machine; step three, put the cleaned lens into the fixture, hang the fixture with the lens in place into the cavity of the coating machine, close the door and vacuum and heat; step four, pre-melting the film material; step five, ion source cleaning; step six, film coating and monitoring, according to the coating process conditions of step two and the configuration of the process file, the film is coated on the S2 surface of the lens; step seven, keep a constant temperature after coating; step eight, cool down and take out the piece; step nine, repeat steps one to eight, and coat the film on the S2 surface of the lens.

[0006] The beneficial effects of the present disclosure are as follows.

[0007] In the design method of a germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film according to the present disclosure, through steps Sa to Sd, not only the film layer structure achieves the target transmittance in the 2-5.9μm band cutoff and the 6.3-14μm band, but also the test process of the two-sided film system also takes into account the bubble test and the adhesion test.

[0008] In the method for preparing a high-transmittance filter film with a germanium substrate having a 2-5.9μm band and a cutoff of 6.3-14μm according to the present invention, based on steps one to nine and based on the optimal film thickness stored in the control computer of the coating machine in the design method of the aforementioned high-transmittance filter film with a germanium substrate having a 2-5.9μm band and a cutoff of 6.3-14μm, as verified by the test, the prepared germanium substrate together with the film system on both sides can achieve the target transmittance in the 2-5.9μm band and the 6.3-14μm band, and can pass the bubble test and the adhesion test. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 This is a transmittance curve diagram designed by the design method of the germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film of Example 1.

[0010] Figure 2 It is a transmittance curve diagram of the accompanying plate and the film system on both sides after the coating is completed in the method for preparing the high-transmittance filter film with a 2-5.9 μm band cutoff of 6.3-14 μm on the germanium substrate of Example 1.

[0011] Figure 3 The following are photos of the method for preparing a high-transmittance filter film with a 2-5.9 μm band cutoff and a 6.3-14 μm cutoff on a germanium substrate in Example 1, after coating is completed, of the accompanying plated film before and after the adhesion test and before and after the blister test. DETAILED DESCRIPTION

[0012] It is understood that the disclosed embodiments are merely examples of the present disclosure, which may be implemented in various forms, and therefore, the specific details disclosed herein should not be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to variously implement the present disclosure.

[0013] [Design method for high-transmittance filter film with 2-5.9μm cutoff and 6.3-14μm cutoff on germanium substrate]

[0014] The design method of the germanium substrate 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film according to the present disclosure comprises the following steps:

[0015] Sa, the film system design uses 550nm as the reference wavelength for the 1 / 4 wavelength thickness of the optical film design, and uses the film stack expression: Sub / S1 film stack 2.1(L2HL)^10, 2.8(L2HL)^10, 3.6(L2HL)^9, 4.5(L2HL)^9 / S2 film stack .42(L2HLKL)^3, .59(K2LK)^1AIR, where Sub is the germanium substrate, and AIR represents air. In the film stack expression:

[0016] H represents the high refractive index material Ge (germanium) with a thickness of 1 / 4 wavelength;

[0017] L represents the low refractive index material ZnSe (zinc selenide) with a thickness of 1 / 4 wavelength;

[0018] K represents the low refractive index material YbF3 (ytterbium fluoride) with a thickness of 1 / 4 wavelength;

[0019] Sb, through the input film stack formula, generates a film structure of 75 layers on the S1 surface and 12 layers on the S2 surface. The S1 surface is ZnSe as the base, ZnSe as the outermost protective layer, and Ge and ZnSe alternate in the middle. The S2 surface is Ge / ZnSe / Ge / ZnSe / Ge / ZnSe / YbF3 / ZnSe / Ge / ZnSe / YbF3 / ZnSe;

[0020] Sc, the film thickness is optimized by thin film design software to obtain the best film thickness. The optimized film structure has a cutoff of 6.3-14μm in the 2-5.9μm band and the transmittance in the 2-5.9μm band reaches the target;

[0021] Sd, input the optimized best film thickness into the control computer of the coating machine.

[0022] In the design method of a germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film according to the present disclosure, through steps Sa to Sd, not only the film layer structure achieves the target transmittance in the 2-5.9μm band cutoff and the 6.3-14μm band, but also the two-sided film system also passes the bubble test and the adhesion test in the later-described testing process.

[0023] In one example, in step Sc, the optimal film thickness of the S1 surface and the S2 surface is as follows:

[0024]

[0025]

[0026] In one example, in step Sc, the average transmittance of the optimized film structure in the 2-5.9 μm band is less than 1%, and the average transmittance in the 6.3-14 μm band is greater than 88%.

[0027] In one example, in step Sa to step Sd, the design software is TFCalc or Essential Macleod.

[0028] [Preparation method of germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film]

[0029] The method for preparing a germanium substrate 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film according to the present disclosure comprises the following steps:

[0030] Step 1: Clean the germanium substrate and accompanying plating sheet before plating, and prepare the three film materials of ZnSe, Ge and YbF3;

[0031] Step 2, configuration of coating process conditions and process files, including coating temperature, background vacuum before coating, film thickness, film material evaporation mode, film material deposition rate, use and parameters of ion source assisted deposition, wherein the film thickness is based on the optimal film thickness stored in the control computer of the coating machine in the aforementioned design method of the germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film;

[0032] Step 3: Put the cleaned lens into the fixture, hang the fixture with the lens into the cavity of the coating machine, close the door, and vacuum and heat;

[0033] Step 4: pre-melting the film material;

[0034] Step 5, ion source cleaning;

[0035] Step 6: coating and monitoring the film layer, coating the film layer on the S2 surface of the lens according to the coating process conditions and configuration of the process file in step 2;

[0036] Step 7: After coating, keep the temperature constant;

[0037] Step 8, cooling down and picking up the items;

[0038] Step nine, repeat steps one to eight to perform film coating on the S2 surface of the lens.

[0039] In the method for preparing a high-transmittance filter film with a germanium substrate having a 2-5.9μm band and a cutoff of 6.3-14μm according to the present invention, based on steps one to nine and based on the optimal film thickness stored in the control computer of the coating machine in the aforementioned design method for a high-transmittance filter film with a germanium substrate having a 2-5.9μm band and a cutoff of 6.3-14μm, as verified by subsequent tests, the prepared germanium substrate together with the film system on both sides can achieve the target transmittance in the 2-5.9μm band and the 6.3-14μm band, and can pass the bubble test and the adhesion test.

[0040] In one example, in step one, the product of step one is a (50±0.1) mm×(10±0.1) mm wafer, and the accompanying plating wafer is a (25±0.1) mm×(2±0.1) mm wafer.

[0041] The cleaning in step 1 makes the surface of the lens clean, which is conducive to the adhesion and bonding of the film layer. In one example, the lens is polished with aluminum oxide polishing liquid and then cleaned with ultrasonic pure water. For example, the aluminum oxide polishing liquid uses a 0.1 μm polycrystalline diamond liquid produced by Nanjing Henry Precision Optics Co., Ltd.

[0042] In one example, in step 2, the coating temperature is 150±2°C; the background vacuum before coating is (1.5±0.1)×10 -3 Pa; the film thickness in the configuration of the coating process conditions and process files is based on the optimal film thickness stored in the control computer of the coating machine in the design method of the aforementioned germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film; the evaporation mode of the film material is: ZnSe and YbF3 are evaporated by resistance heating, and Ge is evaporated by electron beam heating; the deposition rate of the film material is: the deposition rate of the ZnSe film layer is The deposition rate of the YbF3 film is The deposition rate of the Ge film is The use of ion source assisted deposition is: the ion source is turned on for evaporation of ZnSe film and YbF3 film, and the ion source is not turned on for evaporation of Ge film. Specifically, in step 2, the ion source is a Hall source, and the parameters of the ion source are: neutralization current 1±0.01A, neutralization gas flow 10±0.01sccm, anode voltage 120±2V, anode current 2±0.01A, no oxygen is added during the whole process, and argon accounts for 100% of the neutralization gas.

[0043] In one example, in step 2, for example, the coating machine is Leybold ARES1350.

[0044] In one example, in step 3, the vacuum is first evacuated to 5×10 -2 Pa, then the cavity of the coating machine starts heating to 150°C and then maintains it for 40 minutes.

[0045] In step 4, the film material is pre-melted to release air and remove impurities to ensure the purity of the film material. In step 4, when the vacuum reaches (4.0-5.0)×10 -3 Pa, the three film materials were pre-melted. After the pre-melting of the film materials was completed, the temperature of the chamber of the coating machine reached 150°C and was kept constant for 10 minutes. In step 4, the pre-melting treatment was carried out by electron beam heating and resistance heating. For ZnSe film materials, the current of resistance heating was 720-760mA; for Ge film materials, the current of electron beam heating was 260-290mA; for YbF3 film materials, the current of resistance heating was 860-900mA.

[0046] The ion source cleaning in step 5 uses ion bombardment to clean the surface microstructure of the lens, which can eliminate the surface oxide layer, make the surface cleaner, and facilitate the firm adhesion and growth of the film layer. In one example, in step 5, the vacuum is drawn to make the vacuum degree of the chamber reach 5.0×10 -3 Pa, start ion source cleaning, the ion source is a Hall source, the parameters of the ion source are: neutralization current 1±0.01A, neutralization gas flow rate 10±0.01sccm, anode voltage 120±2V, anode current 2±0.01A, the proportion of argon in the neutralization gas is 100%, and the cleaning time is 5min.

[0047] In one example, in step six, when coating each film layer, no gas is introduced into the cavity of the coating machine from outside the coating machine, and the cavity of the coating machine is kept evacuated, and the coating temperature is kept at 150±2°C; each film layer is coated at a cavity temperature of 150±2°C of the coating machine; the crystal oscillator method is used to monitor the film thickness using the corresponding crystal oscillator of the multiple crystal oscillators of the crystal controller, and after the ion source is cleaned, the crystal controller controls the corresponding operation of a new crystal oscillator among the multiple crystal oscillators, and the crystal oscillator frequency is not less than 5850Hz.

[0048] In one example, in step seven, the chamber is kept at 150° C. for 40 minutes after plating is completed.

[0049] In one example, in step eight, after step S7 is completed, the temperature is first lowered to 120°C at 1°C / min and held for 5 minutes, then lowered to 90°C at 1°C / min and held for 5 minutes, and then lowered to below 60°C at 1°C / min, and the door is opened to take out the items.

[0050] [test]

[0051] Example 1

[0052] Part 1: Design method of high-transmittance filter film with 2-5.9μm cutoff and 6.3-14μm cutoff on germanium substrate

[0053] The design method of the germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film adopts the following steps:

[0054] Sa, the film system design uses 550nm as the reference wavelength for the 1 / 4 wavelength thickness of the optical thin film design. In TFCalc, the film stack expression is used: Sub / S1 film stack 2.1(L2HL)^10, 2.8(L2HL)^10, 3.6(L2HL)^9, 4.5(L2HL)^9 / S2 film stack .42(L2HLKL)^3, .59(K2LK)^1AIR, where Sub is the germanium substrate, and AIR represents air. In the film stack expression:

[0055] H represents the high refractive index material Ge (germanium) with a thickness of 1 / 4 wavelength;

[0056] L represents the low refractive index material ZnSe (zinc selenide) with a thickness of 1 / 4 wavelength;

[0057] K represents the low refractive index material YbF3 (ytterbium fluoride) with a thickness of 1 / 4 wavelength;

[0058] Sb, through the input film stack formula, generates a film structure of 75 layers on the S1 surface and 12 layers on the S2 surface. The S1 surface is ZnSe as the base, ZnSe as the outermost protective layer, and Ge and ZnSe alternate in the middle. The S2 surface is Ge / ZnSe / Ge / ZnSe / Ge / ZnSe / YbF3 / ZnSe / Ge / ZnSe / YbF3 / ZnSe;

[0059] Sc, the film thickness is optimized by thin film design software TFCalc to obtain the best film thickness. The optimized film structure has a cutoff in the 2-5.9μm band and a transmittance in the 6.3-14μm band to reach the target.

[0060] In step Sc, the film thickness of the S1 surface and the S2 surface is as follows,

[0061]

[0062]

[0063]

[0064] Sd, the optimized best film thickness is input into the control computer of the coating machine, the coating machine is Leybold ARES1350.

[0065] Part II: Preparation method of high-transmittance filter film with 2-5.9μm cutoff and 6.3-14μm cutoff on germanium substrate

[0066] The preparation method of the germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film adopts the following steps:

[0067] Step 1: Clean the germanium substrate product and accompanying plating sheet as the lens before plating, and prepare the three film materials of ZnSe, Ge, and YbF3. The product is a 50mm×10mm round wafer, and the accompanying plating sheet is a 25mm×2mm round wafer. The lens is polished with alumina polishing liquid and then ultrasonically cleaned with pure water. The alumina polishing liquid uses a 0.1μm polycrystalline diamond liquid from Nanjing Henry Precision Optics Co., Ltd.;

[0068] Step 2, configuration of coating process conditions and process files, including coating temperature, background vacuum before coating, film thickness, film material evaporation mode, film material deposition rate, use and parameters of ion source assisted deposition, wherein the film thickness is based on the optimal film thickness stored in the control computer of the coating machine in the design method of the germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film in the first part;

[0069] In step 2,

[0070] The coating temperature is 150°C;

[0071] The background vacuum before plating is 1.5×10 -3 Pa;

[0072] The film thickness in the configuration of the coating process conditions and process files is based on the optimal film thickness stored in the control computer of the coating machine as described in the design method of the germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film in the first part;

[0073] The evaporation mode of the film materials is: ZnSe and YbF3 are evaporated by resistance heating, and Ge is evaporated by electron beam heating;

[0074] The deposition rate of the film material is: The deposition rate of the ZnSe film layer is The deposition rate of the YbF3 film is The deposition rate of the Ge film is

[0075] The use of ion source assisted deposition is: the ion source is turned on for evaporation of ZnSe film and YbF3 film, and the ion source is not turned on for evaporation of Ge film;

[0076] The ion source is a Hall source, and the parameters of the ion source are: neutralization current 1A, neutralization gas flow rate 10sccm, anode voltage 120V, anode current 2A, no oxygen is added during the whole process, and the proportion of argon in the neutralization gas is 100%;

[0077] Step 3: Put the cleaned lens into the fixture, hang the fixture with the lens into the chamber of the coating machine, close the door and vacuumize to 5×10 -2 Pa, then the coating machine chamber starts heating to 150°C and then maintains it for 40 minutes;

[0078] Step 4: Pre-melt the film material. When the vacuum reaches 5.0×10 -3 The three film materials were pre-melted at Pa. After the pre-melting of the film materials was completed, the temperature of the cavity of the coating machine reached 150°C and was kept constant for 10 minutes.

[0079] In step 4, the pre-melting process uses electron beam heating and resistance heating.

[0080] For ZnSe film material, the current of resistance heating is 740mA;

[0081] For Ge film material, the current of electron beam heating is 265mA;

[0082] For YbF3 film material, the current of resistance heating is 880mA;

[0083] Step 5: Clean the ion source and draw vacuum to make the vacuum degree of the chamber reach 5.0×10 -3 Pa, start ion source cleaning, the ion source is a Hall source, the ion source parameters are: neutralization current 1A, neutralization gas flow 10sccm, anode voltage 120V, anode current 2A, argon gas in the neutralization gas ratio is 100%, cleaning time 5min;

[0084] Step 6: Coating and monitoring: Coating the S2 surface of the lens is performed according to the coating process conditions and process file configuration of step 2.

[0085] In step 6, when coating each film layer, no gas is introduced from outside the coating machine into the cavity of the coating machine, and the cavity of the coating machine is kept evacuated, and the coating temperature is kept at 150° C.;

[0086] Each film layer is coated at a chamber temperature of 150°C in the coating machine;

[0087] The crystal oscillator method is used to monitor the film thickness using the corresponding crystal oscillator of the multiple crystal oscillators of the crystal controller. After the ion source is cleaned, the crystal controller controls the corresponding operation of the new crystal oscillator of the multiple crystal oscillators, and the crystal oscillator frequency is 5990Hz.

[0088] Step 7: After plating, keep the cavity at 150°C for 40 minutes;

[0089] Step 8: After step S7 is completed, the temperature is first lowered to 120°C at 1°C / min and held for 5 minutes, then lowered to 90°C at 1°C / min and held for 5 minutes, and then lowered to 60°C at 1°C / min, and the door is opened to take out the items;

[0090] Step nine, repeat steps one to eight to perform film coating on the S2 surface of the lens.

[0091] Figure 1 This is a transmittance curve designed by the design method of the germanium substrate 2-5.9μm band cutoff 6.3-14μm high transmittance filter film of Example 1. Figure 1 It can be seen that the average transmittance of the germanium substrate and the films on both sides is less than 1% in the 2-5.9 μm band, and the average transmittance in the 6.3-14 μm band is greater than 88%.

[0092] Figure 2 The transmittance curve of the accompanying plate after the coating is completed is the method for preparing the high-transmittance filter film with a 2-5.9 μm band cutoff of 6.3-14 μm on the germanium substrate of Example 1. Figure 1 It can be seen that the average transmittance of the accompanying plate together with the films on both sides in the 2-5.9 μm band is less than 1%, and the average transmittance in the 6.3-14 μm band is 88.4% (ie, greater than 88%).

[0093] The accompanying plating sheet of Example 1 and the film systems on both sides were subjected to the following overall performance test.

[0094] Water bubble test: Take tap water to conduct a water bubble test for 2 hours to observe whether the film layer on each surface falls off or cracks.

[0095] Adhesion test: Use your hands to stick 3M tape on each side and pull the tape in the direction opposite to the sticking end to see if the film layer is pulled up.

[0096] The accompanying plating sheet of Example 1 together with the films on both sides passed the blister test and the adhesion test.

[0097] Figure 3 This is the preparation method of the germanium substrate 2-5.9μm band cutoff 6.3-14μm high-transmittance filter film of Example 1. After the coating is completed, the accompanying coating sheet and the film system on both sides are photographed before and after the adhesion test and before and after the blister test.

[0098] The above detailed description is used to describe multiple exemplary embodiments, but this document is not intended to be limited to the explicitly disclosed combinations. Therefore, unless otherwise stated, the various features disclosed herein can be combined together to form multiple additional combinations that are not shown for the sake of simplicity.

Claims

1. A method for designing a high-transmittance filter film with a germanium substrate and a wavelength range of 2-5.9 μm and a cutoff of 6.3-14 μm, characterized in that: Includes steps: Sa, the film system design uses 550nm as the reference wavelength for the 1 / 4 wavelength thickness of the optical thin film design, and uses the film stack expression: Sub / S1 film stack 2.1(L2HL)^10, 2.8(L2HL)^10, 3.6(L2HL)^9, 4.5(L2HL)^9 / S2 film stack .42(L2HLKL)^3, .59(K2LK)^1AIR, where Sub is the germanium substrate and AIR represents air. In the film stack expression: H represents the high refractive index material Ge (germanium) with a thickness of 1 / 4 wavelength; L represents the low refractive index material ZnSe (zinc selenide) with a thickness of 1 / 4 wavelength; K represents the low refractive index material YbF3 (ytterbium fluoride) with a thickness of 1 / 4 wavelength; Sb, through the input film stack formula, generates a film structure of 75 layers on the S1 surface and 12 layers on the S2 surface. The S1 surface is ZnSe as the base, ZnSe as the outermost protective layer, and Ge and ZnSe alternate in the middle. The S2 surface is Ge / ZnSe / Ge / ZnSe / Ge / ZnSe / YbF3 / ZnSe / Ge / ZnSe / YbF3 / ZnSe; Sc, the film thickness is optimized through the thin film design software to obtain the best film thickness. The optimized film structure has a cutoff of 6.3-14μm in the 2-5.9μm band and achieves the target transmittance; Sd, input the optimized best film thickness into the control computer of the coating machine.

2. The design method of the germanium substrate 2-5.9 μm band cutoff 6.3-14 μm high transmittance filter film according to claim 1, characterized in that: In step Sc, the optimal film thickness of the S1 surface and the S2 surface is as follows, In step Sc, the average transmittance of the optimized film structure in the 2-5.9 μm band is less than 1%, and the average transmittance in the 6.3-14 μm band is greater than 88%.

3. A method for preparing a germanium-based 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film, characterized in that: Includes steps: Step 1: Clean the germanium substrate and accompanying plating sheet before plating, and prepare the three film materials of ZnSe, Ge and YbF3; Step 2, configuration of coating process conditions and process files, including coating temperature, background vacuum before coating, film thickness, evaporation mode of film material, deposition rate of film material, use and parameters of ion source assisted deposition, wherein the film thickness is based on the optimal film thickness stored in the control computer of the coating machine according to any one of claims 1-2; Step 3: Put the cleaned lens into the fixture, hang the fixture with the lens into the cavity of the coating machine, close the door, and vacuum and heat; Step 4: pre-melting the film material; Step 5, ion source cleaning; Step 6: coating and monitoring the film layer, coating the film layer on the S2 surface of the lens according to the coating process conditions and configuration of the process file in step 2; Step 7: After coating, keep the temperature constant; Step 8, cooling down and picking up the items; Step nine, repeat steps one to eight to perform film coating on the S2 surface of the lens.

4. The method for preparing a germanium-based 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film according to claim 3, characterized in that: In step one, The product is a (50±0.1)mm×(10±0.1)mm round disc, and the accompanying plating sheet is a (25±0.1)mm×(2±0.1)mm round disc; The lenses are polished with aluminum oxide polishing liquid and then cleaned with ultrasonic pure water; The alumina polishing liquid adopts the 0.1μm polycrystalline diamond liquid produced by Nanjing Henry Precision Optics Co., Ltd.

5. The method for preparing a germanium-based 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film according to claim 3, characterized in that: In step 2, The coating temperature is 150±2℃; The background vacuum before plating is (1.5±0.1)×10 -3 Pa; The coating process conditions and the film thickness in the configuration of the process file are based on The optimum film thickness stored in the control computer of the coating machine according to claim 2; The evaporation mode of the film materials is: ZnSe and YbF3 are evaporated by resistance heating, and Ge is evaporated by electron beam heating; The deposition rate of the film material is: The deposition rate of the ZnSe film layer is The deposition rate of the YbF3 film is The deposition rate of the Ge film is The use of ion source assisted deposition is: the ion source is turned on for evaporation of ZnSe film and YbF3 film, and the ion source is not turned on for evaporation of Ge film; The ion source is a Hall source, and the parameters of the ion source are: neutralization current 1±0.01A, neutralization gas flow rate 10±0.01sccm, anode voltage 120±2V, anode current 2±0.01A, no oxygen is added during the whole process, and the proportion of argon in the neutralization gas is 100%; The coating machine is Leybold ARES1350.

6. The method for preparing a germanium-based 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film according to claim 3, characterized in that: In step 3, first vacuum the sample to 5×10 -2 Pa, then the cavity of the coating machine starts heating to 150°C and then maintains it for 40 minutes.

7. The method for preparing a germanium-based 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film according to claim 3, characterized in that: In step 4, when the vacuum reaches (4.0-5.0)×10 -3 The three film materials were pre-melted at Pa. After the pre-melting of the film materials was completed, the temperature of the cavity of the coating machine reached 150°C and was kept constant for 10 minutes. In step 4, the pre-melting process uses electron beam heating and resistance heating. For ZnSe film material, the current of resistance heating is 720-760mA; For Ge film material, the current of electron beam heating is 260-290mA; For YbF3 film material, the current of resistance heating is 860-900mA.

8. The method for preparing a germanium-based 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film according to claim 3, characterized in that: In step 5, the vacuum is drawn to make the vacuum degree of the chamber reach 5.0×10 -3 Pa, start ion source cleaning, the ion source is a Hall source, the parameters of the ion source are: neutralization current 1±0.01A, neutralization gas flow rate 10±0.01sccm, anode voltage 120±2V, anode current 2±0.01A, the proportion of argon in the neutralization gas is 100%, and the cleaning time is 5min.

9. The method for preparing a germanium-based 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film according to claim 3, characterized in that: In step six, When coating each film layer, do not introduce any gas from outside the coating machine into the coating machine cavity and keep the coating machine cavity evacuated, and keep the coating temperature at 150±2℃; Each film layer is coated at a chamber temperature of 150±2℃ in the coating machine; The crystal oscillator method is used to monitor the film thickness using the corresponding crystal oscillator pieces of the multiple crystal oscillator pieces of the crystal controller. After the ion source is cleaned, the crystal controller controls the corresponding operation of the new crystal oscillator pieces among the multiple crystal oscillator pieces, and the crystal oscillator frequency is not less than 5850Hz.

10. The method for preparing a germanium-based 2-5.9 μm band cutoff 6.3-14 μm high-transmittance filter film according to claim 3, characterized in that: In step seven, the cavity is kept at 150°C for 40 minutes after plating is completed; In step eight, after step S7 is completed, the temperature is first lowered to 120°C at 1°C / min and held for 5 minutes, then lowered to 90°C at 1°C / min and held for 5 minutes, and then lowered to below 60°C at 1°C / min, and the door is opened to take out the items.

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