Design method and preparation method of single-crystal calcium fluoride substrate 3.7-4.8 μm antireflection film

Abstract

Provided are a design method and a preparation method of a single-crystal calcium fluoride substrate 3.7-4.8 μm antireflection film. The design method of the single-crystal calcium fluoride substrate 3.7-4.8 μm antireflection film comprises: selecting 4 μm as a reference wavelength of optical film design 1 / 4 wavelength film thickness, using a film stack formula: Sub / 0.03Q / 0.3H / 0.4L / H / L / 0.15H / AIR, wherein Sub is a single-crystal calcium fluoride substrate, AIR represents air, H represents 1 / 4 wavelength thickness ZnS, and L represents 1 / 4 wavelength thickness YF3; Q represents 1 / 4 wavelength thickness Y2O3; a software is used to optimize the film thickness to obtain the optimal film thickness, and the optimized single-crystal calcium fluoride substrate 3.7-4.8 μm band transmittance meets the requirements; and the optimized film thickness is input into a control computer of a coating machine. The preparation method of the single-crystal calcium fluoride substrate 3.7-4.8 μm antireflection film comprises: S1, pre-coating cleaning and film preparation; S2, film system process parameter configuration; S3, vacuum baking and film pre-melting constant temperature; S4, ion source cleaning; S5, film layer coating and monitoring; S6, post-coating constant temperature keeping; S7, cooling and taking out; and S8, repeating steps S1 to S7 for second surface coating.

Description

Technical Field

[0001] This disclosure relates to the field of infrared coating technology, and more specifically to a design method and preparation method for a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate. Background Technology

[0002] Single-crystal calcium fluoride, as an excellent light-transmitting material, has wide applications in infrared optics. However, due to its high refractive index, its transmittance is insufficient in certain wavelength bands, limiting its application in some high-precision optical systems. Therefore, improving the transmittance of single-crystal calcium fluoride in the 3.7-4.8 μm wavelength band has become an urgent problem to be solved in the field of optical thin films. Summary of the Invention

[0003] In view of the problems existing in the background art, one object of this disclosure is to provide a design method and a preparation method for a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate, which enables the transmittance of the designed and prepared 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate to meet the requirements.

[0004] Another objective of this disclosure is to provide a design method and a preparation method for a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate, which can improve the adhesion and stability of the overall film system.

[0005] Therefore, a design method for a 3.7-4.8 μm antireflection film on a monocrystalline calcium fluoride substrate includes the following steps: Sa, selecting 4 μm as the reference wavelength for a 1 / 4 wavelength film thickness in optical film design, using the film stack formula: Sub / 0.03Q / 0.3H / 0.4L / H / L / 0.15H / AIR, where Sub is the monocrystalline calcium fluoride substrate, AIR represents air, H represents a 1 / 4 wavelength thickness of high-refractive-index material ZnS (zinc sulfide), L represents a 1 / 4 wavelength thickness of low-refractive-index material YF3 (yttrium fluoride), and Q represents a 1 / 4 wavelength thickness of the film layer substrate material Y2O3 (yttrium oxide); Sb, calculating and optimizing the film thickness using design software to obtain the optimal film thickness, the optimized monocrystalline calcium fluoride substrate in the 3.7-4.8 μm band transmittance meets the requirements; Sc, inputting the optimized film thickness into the control computer of the coating machine.

[0006] A method for preparing a 3.7-4.8 μm antireflection film on a monocrystalline calcium fluoride substrate includes the following steps: S1, cleaning the substrate and the product to be coated (used as a lens) and preparing three film materials: ZnS, YF3, and Y2O3; S2, configuring the film system process parameters, including the optimal film thickness, the vapor deposition mode of the film material, the deposition rate of the film material, and the use of ion source-assisted deposition. The film thickness in the film system process parameters is based on the aforementioned parameters stored in the control of the coating machine. S3. Optimal film thickness in the computer; S4. Place the cleaned lens into the fixture, hang the fixture with the lens in the cavity of the coating machine, vacuum bake, pre-melt the film material, degas, remove impurities, and maintain constant temperature; S5. Clean the lens with an ion source; S6. Film coating and monitoring: Apply the film to the first side of the lens according to the film system parameters and process configuration in step S2; S7. Maintain constant temperature after coating; S8. Cool down and remove the part; S9. Repeat steps S1 to S7 to apply the film to the second side of the lens.

[0007] The beneficial effects of this disclosure are as follows.

[0008] In the design and preparation method of the 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to the present disclosure, by using three film materials, namely Y2O3, ZnS, and YF3, with ZnS and YF3 as high and low refractive index materials, Y2O3 as the underlayer material, and ZnS and YF3 forming alternating second to sixth layers, the transmittance of the designed 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate can meet the requirements.

[0009] In the design and preparation method of the 3.7-4.8 μm antireflection film on a monocrystalline calcium fluoride substrate according to the present disclosure, Y2O3 is selected as the underlayer material in combination with the monocrystalline calcium fluoride substrate. When the film system composed of the three film materials Y2O3, ZnS and YF3 and the monocrystalline calcium fluoride substrate meet the requirements of 3.7-4.8 μm transmittance, the adhesion and stability of the overall film system can be improved. Attached Figure Description

[0010] Figure 1 This is a schematic structural diagram of the optimized membrane stack design based on the design method of the 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate disclosed herein.

[0011] Figure 2 This is a transmittance curve of the membrane stack design optimization diagram of the 3.7-4.8μm antireflection film on a single-crystal calcium fluoride substrate in Example 1.

[0012] Figure 3This is a graph showing the transmittance in the 3.7-4.8μm wavelength range of the substrate with 3.7-4.8μm antireflection films deposited on both sides in Example 1. Detailed Implementation

[0013] It will be understood that the disclosed embodiments are merely examples of this disclosure, which can be implemented in various forms. Therefore, the specific details disclosed herein should not be construed as limiting, but are intended only as the basis for the claims and as an illustrative basis to teach those skilled in the art how to implement this disclosure in various ways.

[0014] [Design method for 3.7-4.8 μm antireflection films on monocrystalline calcium fluoride substrates]

[0015] The design method for a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to this disclosure includes the following steps:

[0016] Sa, 4μm is selected as the reference wavelength for 1 / 4 wavelength film thickness in optical thin film design, using the film stack formula:

[0017] Sub / 0.03Q / 0.3H / 0.4L / H / L / 0.15H / AIR,

[0018] Wherein, Sub represents a single-crystal calcium fluoride substrate, AIR represents air, H represents a 1 / 4 wavelength thick high-refractive-index material ZnS (zinc sulfide), L represents a 1 / 4 wavelength thick low-refractive-index material YF3 (yttrium fluoride), and Q represents a 1 / 4 wavelength thick film underlay material Y2O3 (yttrium oxide).

[0019] Sb, by using design software to calculate and optimize the film thickness, the optimal film thickness was obtained, and the transmittance of the optimized single-crystal calcium fluoride substrate in the 3.7-4.8μm band met the requirements;

[0020] Sc inputs the optimized film thickness into the control computer of the coating machine.

[0021] In the design method of the 3.7-4.8 μm antireflection film on a monocrystalline calcium fluoride substrate according to the present disclosure, by using three film materials, namely Y2O3, ZnS and YF3, with ZnS and YF3 as high and low refractive index materials, Y2O3 as the underlayer material, and ZnS and YF3 forming alternating second to sixth layers, the transmittance of the designed 3.7-4.8 μm antireflection film on a monocrystalline calcium fluoride substrate can meet the requirements.

[0022] In the design method of the 3.7-4.8μm antireflection film on the monocrystalline calcium fluoride substrate according to the present disclosure, Y2O3 is selected as the underlayer material by combining it with the monocrystalline calcium fluoride substrate. When the film system composed of the three film materials Y2O3, ZnS and YF3 and the monocrystalline calcium fluoride substrate meet the requirements of 3.7-4.8μm transmittance, the adhesion and stability of the overall film system can be improved.

[0023] In one example, in step Sb, for each of the two sides of the single-crystal calcium fluoride substrate, the optimal film thickness is as follows: the thickness of the first Y₂O₃ film is 15±3 nm, the thickness of the second ZnS film is 144.89±3 nm, the thickness of the third YF₃ film is 268.44±3 nm, the thickness of the fourth ZnS film is 500.47±3 nm, the thickness of the fifth YF₃ film is 671.43±3 nm, and the thickness of the sixth ZnS film is 65±5 nm. Figure 1 As shown, the overall thickness of the six-layer film structure formed on each of the two sides of the single-crystal calcium fluoride substrate is 1665.23 ± 20 nm.

[0024] Accordingly, in one example, in step Sb, the average transmittance of the optimized monocrystalline calcium fluoride substrate in the 3.7–4.8 μm band is greater than 99.5%.

[0025] In step Sb, the design software can be, but is not limited to, TFCalc, Essential Macleod, OptiLayer, Filmstar, Filmaster, and Autofilm.

[0026] [Preparation method of 3.7-4.8 μm antireflection film on single-crystal calcium fluoride substrate]

[0027] The method for preparing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to this disclosure includes the following steps:

[0028] S1. Before plating, the accompanying film and product, which serve as the monocrystalline calcium fluoride substrate for the lens, are cleaned and the three film materials ZnS, YF3, and Y2O3 are prepared.

[0029] S2, membrane system process parameter configuration, which includes the optimal membrane thickness, the vapor deposition mode of the membrane material, the deposition rate of the membrane material, and the use of ion source-assisted deposition. The membrane thickness in the membrane system process parameters is based on the optimal membrane thickness stored in the control computer of the coating machine.

[0030] S3, the cleaned lens is placed into the tooling fixture, the tooling fixture with the lens is hung into the cavity of the coating machine, vacuum baking, pre-melting of the film material, degassing, impurity removal and constant temperature.

[0031] S4, Ion source cleaning of lenses;

[0032] S5, Coating and monitoring: Coating is performed on the first surface of the lens according to the coating system parameters and process configuration in step S2.

[0033] S6, constant temperature maintenance after plating;

[0034] S7, cool down before picking up the part;

[0035] S8. Repeat steps S1 to S7 to apply a coating to the second surface of the lens.

[0036] In the method for preparing a 3.7-4.8 μm antireflective film on a monocrystalline calcium fluoride substrate according to the present disclosure, the thickness of the film layer in the film system process parameters of steps S1 to S8 and step S2 is the optimal film thickness stored in the control computer of the coating machine based on the aforementioned design method for a 3.7-4.8 μm antireflective film on a monocrystalline calcium fluoride substrate according to the present disclosure, so that the transmittance of the prepared 3.7-4.8 μm antireflective film on a monocrystalline calcium fluoride substrate meets the requirements.

[0037] Similarly, in the preparation method of the 3.7-4.8 μm antireflection film on the monocrystalline calcium fluoride substrate disclosed herein, Y2O3 is selected as the underlayer material by combining it with the monocrystalline calcium fluoride substrate. When the film system composed of the three film materials Y2O3, ZnS and YF3 and the monocrystalline calcium fluoride substrate meet the requirements of 3.7-4.8 μm transmittance, the adhesion and stability of the overall film system can be improved.

[0038] The cleaning in step S1 helps improve the surface condition of the first and second surfaces of the lens, and helps enhance the adhesion between the coating structure on each surface and the corresponding surface of the lens. For example, the lens surface can be cleaned using ultrasonic cleaning or manual wiping. For example, the thickness of the coating is 1.0 mm.

[0039] In one example, in step S2, the film thickness in the film system process parameters is based on the optimal film thickness stored in the control computer of the coating machine, i.e., for each of the two sides of the single-crystal calcium fluoride substrate, the optimal film thickness is: the thickness of the first Y2O3 film is 15±3nm, the thickness of the second ZnS film is 144.89±3nm, the thickness of the third YF3 film is 268.44±3nm, the thickness of the fourth ZnS film is 500.47±3nm, the thickness of the fifth YF3 film is 671.43±3nm, and the thickness of the sixth ZnS film is 65±5nm; the evaporation mode of the film material is that Y2O3 is evaporated by electron beam heating, and ZnS and YF3 are evaporated by resistance heating; the deposition rate of the film material is: the deposition rate of the Y2O3 film is... The deposition rate of the ZnS film is The deposition rate of the YF3 film is The use of ion source-assisted deposition means that all film layers are deposited using ion source-assisted deposition. Using ion source-assisted deposition results in denser and more uniform film layers.

[0040] Furthermore, in one example, the ion source parameters for depositing the Y₂O₃ film are: neutralization current 0.5A, neutralization gas flow rate 8 sccm, anode voltage 180V, anode current 1.8A, argon flow rate in the neutralization gas 20%, and oxygen flow rate in the neutralization gas 80%; the ion source parameters for depositing all the ZnS film are: neutralization current 0.5A, neutralization gas flow rate 8 sccm, anode voltage 120V, anode current 1.2A, and argon flow rate in the neutralization gas 100%; the ion source parameters for depositing all the YF₃ film are: neutralization current 0.5A, neutralization gas flow rate 8 sccm, anode voltage 100V, anode current 1A, and argon flow rate in the neutralization gas 100%.

[0041] The baking in step S3 prepares the temperature for the pre-melting of the film material. Pre-melting releases gases and removes impurities from the film material, ensuring its purity and reducing adverse factors affecting film quality during the coating process in step S5. Furthermore, baking also heats the lens. Specifically, in step S3, the temperature of the coating machine cavity is set to 180°C; when the vacuum reaches (4.0-6.0)×10... -3 The film material is pre-melted at Pa. After the film material is pre-melted, the temperature of the cavity of the coating machine reaches 180℃ and is maintained at a constant temperature for 10 minutes.

[0042] Step S4, ion source cleaning, utilizes ion bombardment to clean the surface microstructure of the lens, eliminating the oxide layer and making the lens surface cleaner, which is beneficial for the firm adhesion and growth of the film. Specifically, in one example, in step S4, when the vacuum degree reaches (0.9-1.0)×10 -3 When Pa, start the ion source of the vacuum coating machine and set the ion cleaning parameters of the ion source as follows: neutralization current 0.8-1.0A, neutralization gas flow rate 8-10sccm, anode voltage 200-220V, anode current 2-2.5A, argon gas flow rate in the neutralization gas is 100%, and cleaning time is 5-8min.

[0043] In one example, in step S5, argon gas is introduced and a vacuum is drawn during the deposition of each film layer to maintain a constant vacuum, with the constant vacuum level set to be no less than 5.0 × 10⁻⁶. -3Pa; The first Y2O3 film layer was deposited by vapor deposition at a temperature of 180°C in the coating machine chamber. After the first Y2O3 film layer was deposited, the temperature of the coating machine chamber was lowered to 150°C and held for 5 minutes. Then, the second to sixth film layers were deposited by vapor deposition at the same temperature of 150°C in the coating machine chamber. Depositing the first film layer at 180°C improves the adhesion and stability of the overall film system. In one example, a crystal oscillator method was used to monitor the film thickness using multiple crystal oscillators of a crystal controller. After ion source cleaning, the crystal controller controlled the replacement crystal oscillator among the multiple crystal oscillators to operate accordingly, with a crystal frequency of not less than 5.7MHz.

[0044] In one example, in step S6, after the deposition is completed, the cavity is kept at a constant temperature of 150°C for 5 minutes to allow the film structure to release internal stress.

[0045] In one example, in step S7, the door is opened and the item is retrieved after the temperature drops below 90°C.

[0046] [test]

[0047] Example 1

[0048] Part 1: Design Methods for 3.7-4.8 μm Antireflection Films on Monocrystalline Calcium Fluoride Substrates

[0049] The design method for the 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate in Example 1 follows these steps:

[0050] Sa, 4μm is selected as the reference wavelength for 1 / 4 wavelength film thickness in optical thin film design, using the film stack formula:

[0051] Sub / 0.03Q / 0.3H / 0.4L / H / L / 0.15H / AIR,

[0052] Wherein, Sub represents a single-crystal calcium fluoride substrate, AIR represents air, H represents a 1 / 4 wavelength thick high-refractive-index material ZnS (zinc sulfide), L represents a 1 / 4 wavelength thick low-refractive-index material YF3 (yttrium fluoride), and Q represents a 1 / 4 wavelength thick film underlay material Y2O3 (yttrium oxide).

[0053] Sb, by using design software to calculate and optimize the film thickness, the optimal film thickness was obtained, and the transmittance of the optimized single-crystal calcium fluoride substrate in the 3.7-4.8μm band met the requirements;

[0054] Sc inputs the optimized film thickness into the control computer of the coating machine;

[0055] In step Sb, the optimal film thickness for each of the two sides of the single-crystal calcium fluoride substrate is:

[0056] The thickness of the first Y2O3 film is 15 nm.

[0057] The thickness of the second ZnS film is 144.89 nm.

[0058] The thickness of the third YF3 film is 268.44 nm.

[0059] The thickness of the fourth ZnS film is 500.47 nm.

[0060] The fifth YF3 film has a thickness of 671.43 nm.

[0061] The thickness of the sixth ZnS film is 65 nm;

[0062] In step Sb, the design software is TFCalc.

[0063] Part 2: Preparation method of 3.7-4.8 μm antireflection film on single-crystal calcium fluoride substrate

[0064] The preparation method of the 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate in Example 1 adopts the following steps:

[0065] S1. Before plating, ultrasonic cleaning is used to clean the substrate and product of the monocrystalline calcium fluoride substrate used as the lens, and to prepare three types of film materials: ZnS, YF3, and Y2O3. The thickness of the substrate is 1.0mm.

[0066] S2, the vacuum coating machine is a Hall ion source vacuum coating machine with a neutralizer manufactured and sold by Chengdu Xiwoke Vacuum Technology Co., Ltd. The Hall ion source with the neutralizer was purchased from Boton Optoelectronics Technology Co., Ltd. The film system process parameters are configured, including the optimal film thickness, film material evaporation mode, film material deposition rate, and the use of ion source-assisted deposition. The film thickness in the film system process parameters is based on the optimal film thickness stored in the control computer of the coating machine in the first part mentioned above. The film material evaporation mode is electron beam heating evaporation for Y2O3, and resistance heating evaporation for ZnS and YF3. The film deposition rate is: the deposition rate of the Y2O3 film is... The deposition rate of the ZnS film is The deposition rate of the YF3 film is The use of ion source-assisted deposition was as follows: ion source-assisted deposition was used for all film layers; the ion source parameters for depositing the Y2O3 film were: neutralization current 0.5A, neutralization gas flow rate 8sccm, anode voltage 180V, anode current 1.8A, argon flow rate in the neutralization gas 20%, and oxygen flow rate in the neutralization gas 80%; the ion source parameters for depositing all ZnS films were: neutralization current 0.5A, neutralization gas flow rate 8sccm, anode voltage 120V, anode current 1.2A, and argon flow rate in the neutralization gas 100%; the ion source parameters for depositing all YF3 films were: neutralization current 0.5A, neutralization gas flow rate 8sccm, anode voltage 100V, anode current 1A, and argon flow rate in the neutralization gas 100%.

[0067] S3. The cleaned lenses are placed into the fixture, and the fixture with the lenses is then hung into the cavity of the coating machine. Vacuum baking, pre-melting of the coating material, degassing, impurity removal, and temperature control are then performed. The temperature of the coating machine cavity is set to 180℃. When the vacuum reaches 4.0×10... -3 When Pa, the film material is pre-melted. After the film material is pre-melted, the temperature of the cavity of the coating machine reaches 180℃ and is kept constant for 10 minutes.

[0068] S4, Ion source cleaning of lenses, when the vacuum degree reaches 1.0×10 -3 At Pa, start the ion source of the vacuum coating machine and set the ion cleaning parameters of the ion source as follows: neutralization current 1.0A, neutralization gas flow rate 10sccm, anode voltage 220V, anode current 2A, argon gas flow rate in the neutralization gas is 100%, and cleaning time is 8min.

[0069] S5, Coating and Monitoring: Following the coating parameters and process configuration of step S2, coating is performed on the first surface of the lens. During the coating process, argon gas is introduced and a vacuum is drawn to maintain a constant flow vacuum. The constant vacuum level is set to 5.0 × 10⁻⁶. -3 Pa, the first Y2O3 film layer was vapor-deposited at a temperature of 180°C in the coating machine chamber. After the first Y2O3 film layer was vapor-deposited, the temperature of the coating machine chamber was cooled to 150°C and held for 5 minutes. Then, the second to sixth film layers were vapor-deposited at a temperature of 150°C in the coating machine chamber. The film thickness was monitored by using the crystal oscillator method with the corresponding crystal oscillators of the multiple crystal oscillators in the crystal controller. After the ion source was cleaned, the crystal controller controlled the newly replaced crystal oscillators in the multiple crystal oscillators to work. The crystal oscillator frequency was 6MHz.

[0070] S6, after plating, keep the cavity at a constant temperature of 180℃ for 5 minutes;

[0071] S7, wait for the temperature to drop to 90℃ before opening the door to retrieve the item;

[0072] S8. Repeat steps S1 to S7 to apply a coating to the second surface of the lens.

[0073] Comparative Example 1

[0074] Except for omitting the deposition of the innermost Y2O3 layer (i.e., the first film layer) and the innermost Y2O3 layer in the first and second parts, the rest is the same as in Example 1.

[0075] Comparative Example 2

[0076] Except for step S5 in the second part, where the first Y2O3 film layer is vapor-deposited at a temperature of 150°C in the cavity of the coating machine, the rest is the same as in Example 1.

[0077] Figure 3 This is a graph showing the transmittance in the 3.7-4.8 μm wavelength range of the substrate with 3.7-4.8 μm antireflection films deposited on both sides in Example 1. From... Figure 3 It can be seen that the average transmittance of the prepared single-crystal calcium fluoride substrate in the 3.7-4.8μm band is greater than 99.5%.

[0078] In accordance with GJB2485A-2019, the following tests were performed on both sides of Example 1, Comparative Example 1 and Comparative Example 2 after coating.

[0079] Water immersion test: Take tap water and conduct a water immersion test for 2 hours. Observe whether the film layer on each surface has fallen off from the substrate and whether the film layer on each surface has cracked.

[0080] Salt spray test: Neutral salt spray test for 48 hours, observe whether the film layer on each surface of the substrate peels off, and observe whether the film layer on each surface of the substrate cracks.

[0081] Adhesion test: Apply 3M tape to each side of the coated sheet by hand and pull the tape in the opposite direction to the adhesive end. Observe whether the film layer is pulled up.

[0082] Thermal shock test: The film is subjected to thermal shock in the range of -40℃ to 85℃ for 24 hours in a high and low temperature chamber. Observe whether the film layer on each surface of the substrate is peeled off and whether the film layer on each surface of the substrate is cracked.

[0083] Constant temperature and humidity test: In a constant temperature and humidity chamber, at 50℃ and 95% relative humidity for 48 hours, observe whether the film layer on each surface of the substrate peels off and whether the film layer on each surface of the substrate cracks.

[0084] Low temperature test: In a low temperature chamber, at -40℃ for 48 hours, observe whether the film layer on each surface of the substrate peels off and whether the film layer on each surface of the substrate cracks.

[0085] High temperature test: In a high temperature chamber, at 85℃ for 48 hours, observe whether the film layer on each surface of the substrate peels off and whether the film layer on each surface of the substrate cracks.

[0086] Table 1 shows the transmittance of Example 1 and Comparative Examples 1-2, as well as the results of various tests.

[0087] Table 1. Transmittance of Example 1 and Comparative Examples 1-2, and results of various tests.

[0088]

[0089]

[0090] As can be seen from Comparative Example 1 and Example 1, Comparative Example 1 did not use Y2O3 as the base layer for the bottom film layer, and the adhesion test failed, and the firmness did not meet the acceptance standard of GJB2485A-2019.

[0091] As can be seen from Comparative Example 2 and Example 1, the deposition temperature of the Y2O3 film in Comparative Example 2 was lower than that in Example 1, and it failed both the salt spray test and the constant temperature and humidity test. This indicates that the long-term damp heat and salt spray environment cannot maintain the durability of the film. The temperature increase in Example 1 (under ion source assisted deposition) can effectively optimize the growth conditions of the film, making the Y2O3 film layer bond more firmly with the substrate, thereby ensuring the overall stability of the film layer.

[0092] Several exemplary embodiments have been described in detail above, but this document is not intended to limit itself to the explicitly disclosed combinations. Therefore, unless otherwise stated, the various features disclosed herein can be combined to form several other combinations, which are not shown for simplicity.

Claims

1. A method for designing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate, characterized in that, Including the following steps: Sa, 4μm is selected as the reference wavelength for 1 / 4 wavelength film thickness in optical thin film design, using the film stack formula: Sub / 0.03Q / 0.3H / 0.4L / H / L / 0.15H / AIR, Wherein, Sub represents a single-crystal calcium fluoride substrate, AIR represents air, H represents a 1 / 4 wavelength thick high-refractive-index material ZnS (zinc sulfide), L represents a 1 / 4 wavelength thick low-refractive-index material YF3 (yttrium fluoride), and Q represents a 1 / 4 wavelength thick film underlay material Y2O3 (yttrium oxide). Sb, by using design software to calculate and optimize the film thickness, the optimal film thickness was obtained, and the transmittance of the optimized single-crystal calcium fluoride substrate in the 3.7-4.8μm band met the requirements; Sc inputs the optimized film thickness into the control computer of the coating machine; In step Sb, for each of the two sides of the monocrystalline calcium fluoride substrate, the optimal film thickness is: The thickness of the first Y2O3 film is 15±3 nm. The thickness of the second ZnS film is 144.89±3 nm. The thickness of the third YF3 film is 268.44±3 nm. The thickness of the fourth ZnS film is 500.47 ± 3 nm. The thickness of the fifth YF3 film is 671.43±3 nm. The thickness of the sixth ZnS film is 65±5 nm; In step Sb, the average transmittance of the optimized monocrystalline calcium fluoride substrate in the 3.7-4.8 μm band is greater than 99.5%.

2. The design method for a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to claim 1, characterized in that, In step Sb, the design software is TFCalc, Essential Macleod, OptiLayer, Filmstar, Filmaster, and Autofilm.

3. A method for preparing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate, characterized in that, Including the following steps: S1. Before plating, the accompanying film and product, which serve as the monocrystalline calcium fluoride substrate for the lens, are cleaned and the three film materials ZnS, YF3, and Y2O3 are prepared. S2, membrane system process parameter configuration, the membrane system process parameter configuration includes the optimal membrane thickness, the vapor deposition mode of the membrane material, the deposition rate of the membrane material, and the use of ion source assisted deposition. The membrane thickness in the membrane system process parameters is based on the optimal membrane thickness stored in the control computer of the coating machine according to the design method of the 3.7-4.8μm antireflection film on the monocrystalline calcium fluoride substrate according to any one of claims 1-2. S3, the cleaned lens is placed into the tooling fixture, the tooling fixture with the lens is hung into the cavity of the coating machine, vacuum baking, pre-melting of the film material, degassing, impurity removal and constant temperature. S4, Ion source cleaning of lenses; S5, Coating and monitoring: Coating is performed on the first surface of the lens according to the coating system parameters and process configuration in step S2. S6, constant temperature maintenance after plating; S7, cool down before picking up the part; S8. Repeat steps S1 to S7 to apply a coating to the second surface of the lens.

4. The method for preparing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to claim 1, characterized in that, In step S1, Cleaning is performed using ultrasonic cleaning and manual wiping. The thickness of the plating sheet is 1.0 mm.

5. The method for preparing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to claim 1, characterized in that, In step S2, The film thickness in the membrane process parameters is based on the optimal film thickness stored in the control computer of the coating machine, which is determined by the design method of the 3.7-4.8 μm antireflection film on a monocrystalline calcium fluoride substrate according to claim 2. The evaporation mode of the film material is that Y2O3 is evaporated by electron beam heating, while ZnS and YF3 are evaporated by resistance heating. The deposition rate of the film material is: the deposition rate of the Y2O3 film layer is The deposition rate of the ZnS film is The deposition rate of the YF3 film is The use of ion source-assisted deposition is as follows: ion source-assisted deposition is used for the deposition of all film layers.

6. The method for preparing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to claim 5, characterized in that, The ion source parameters for depositing the Y2O3 film were: neutralization current 0.5A, neutralization gas flow rate 8sccm, anode voltage 180V, anode current 1.8A, argon flow rate in the neutralization gas 20%, and oxygen flow rate in the neutralization gas 80%. The ion source parameters for depositing all ZnS films were: neutralization current 0.5A, neutralization gas flow rate 8sccm, anode voltage 120V, anode current 1.2A, and argon gas flow rate in the neutralization gas 100%. The ion source parameters for depositing all YF3 films were: neutralization current 0.5A, neutralization gas flow rate 8sccm, anode voltage 100V, anode current 1A, and argon gas flow rate in the neutralization gas 100%.

7. The method for preparing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to claim 3, characterized in that, In step S3, The temperature of the coating machine's cavity is set to 180℃; When the vacuum reaches (4.0-6.0)×10 -3 The film material is pre-melted at Pa. After the film material is pre-melted, the temperature of the cavity of the coating machine reaches 180℃ and is maintained at a constant temperature for 10 minutes.

8. The method for preparing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to claim 3, characterized in that, In step S4, When the vacuum degree reaches (0.9-1.0)×10 -3 At Pa, the ion source of the vacuum coating machine is started. The ion cleaning parameters for the ion source are set as follows: neutralization current 0.8-1.0A, neutralization gas flow rate 8-10 sccm, anode voltage 200-220V, anode current 2-2.5A, argon gas flow rate in the neutralization gas is 100%, and cleaning time is 5-8 min.

9. The method for preparing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to claim 3, characterized in that, In step S5, Argon gas is introduced and a vacuum is drawn during the deposition of each film layer to maintain a constant vacuum in a flow-through manner. The constant vacuum level is set to be no less than 5.0 × 10⁻⁶. -3 Pa; The first Y2O3 film layer was deposited by vapor deposition at a temperature of 180°C in the coating machine chamber. After the first Y2O3 film layer was deposited by vapor deposition, the temperature of the coating machine chamber was cooled down to 150°C and held for 5 minutes. Then the second to sixth film layers were deposited by vapor deposition at a temperature of 150°C in the coating machine chamber. The crystal oscillator method is used to monitor the film thickness by using the corresponding crystal oscillators of multiple crystal oscillators in the crystal controller. After cleaning with the ion source, the crystal controller controls the corresponding operation of the replaced crystal oscillator among the multiple crystal oscillators. The crystal oscillator frequency is not less than 5.7MHz.

10. The method for preparing a 3.7-4.8 μm antireflection film on a single-crystal calcium fluoride substrate according to claim 3, characterized in that, In step S6, after the plating is completed, the cavity is kept at a constant temperature of 150°C for 5 minutes; In step S7, the door is opened and the item is retrieved once the temperature drops below 90°C.

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