Design method and preparation method of film system of germanium substrate high-transmission wide-stop narrow-band filter

Abstract

This paper provides a method for designing and fabricating a high-transmittance, wide-cutoff, narrow-band filter system on a germanium substrate. The design method includes the following steps: Sa, S1 plane narrow-band master film design, including sub-steps: using four wavelengths (4257nm, 4513nm, 7994nm, and 10600nm) as the center wavelengths for optical film design, and applying the F-P cavity film stack formula: Sub / (LH)^32L(HL)^4 / AIR, where Sub is the germanium substrate, AIR represents air, L represents ZnS, and H represents Ge; generating a film structure with ZnS as the base layer, ZnS on the outermost layer, and alternating ZnS and Ge layers in the middle; optimizing the optimal film thickness; Sb, S2 plane interference dielectric film design, including sub-steps: using 550nm as the center wavelength for optical film design, and applying the film stack formula: Sub / 3.7(H2LK)^7. 6.1(K2LH)^8 / AIR, Sub is germanium substrate, AIR represents air, L represents ZnS, H represents Ge, K represents PbTe; a film structure is generated with ZnS as the base, ZnS on the outermost layer, ZnS and Ge alternating at both ends, and ZnS and PbTe alternating in the middle; the optimal film thickness is obtained by optimization.

Description

Technical Field

[0001] This disclosure relates to the field of infrared optical thin film technology, and more specifically to a design method and preparation method for a germanium substrate high-transmittance wide-cutoff narrow-band filter film system. Background Technology

[0002] Narrowband filters are commonly used in infrared measurement, temperature control, security systems, spectrometers, spectral imaging, and thermal radiation detection. With the rapid development of industrialization, industrial emissions have caused significant environmental damage, especially greenhouse gases such as CO2, N2O, NF3, CH4, and SF6, which are major contributors to global warming. Current detection devices utilize the characteristic that greenhouse gases absorb infrared light at their respective characteristic wavelengths, employing appropriate algorithms to calculate their concentrations, as shown in Table 1. The filters are designed with their respective characteristic wavelengths as the center wavelength. Four narrowband filters are assembled in a photoacoustic spectral detection system, capable of simultaneously monitoring four greenhouse gases: CO2, N2O, CH4, and SF6. Figure 1 As shown.

[0003] Table 1. Characteristic spectrum of greenhouse gases

[0004] gas components relative molecular weight Characteristic wavenumber / cm⁻¹ Characteristic wavelength / μm <![CDATA[CO2]]> 44 2349 4.257 <![CDATA[NO2]]> 44 2216 4.513 <![CDATA[CH4]]> 16 1251 7.994 <![CDATA[SF6]]> 146 948 10.6

[0005] Current narrowband filters require further improvement in design and fabrication. Summary of the Invention

[0006] 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 germanium substrate high transmittance wide cutoff narrow band filter film system, which enables the transmittance of the passband region of each wavelength designed and prepared for CO2 (characteristic wavelength 4257nm), N2O (characteristic wavelength 4513nm), CH4 (characteristic wavelength 7994nm), and SF6 (characteristic wavelength 10600nm) to meet the requirements, and the transmittance of the cutoff bandwidth outside the passband region to meet the requirements.

[0007] Another objective of this disclosure is to provide a design and fabrication method for a germanium substrate high-transmittance wide-cutoff narrow-band filter film system, which enables the germanium substrates designed and fabricated for CO2 (characteristic wavelength 4257nm), N2O (characteristic wavelength 4513nm), CH4 (characteristic wavelength 7994nm), and SF6 (characteristic wavelength 10600nm), along with the film systems on both sides, to meet the requirements of different application scenarios.

[0008] Another objective of this disclosure is to provide a design and fabrication method for a germanium substrate high-transmittance wide-cutoff narrow-band filter film system, which simplifies the production of CO2 (characteristic wavelength 4257nm), N2O (characteristic wavelength 4513nm), CH4 (characteristic wavelength 7994nm), and SF6 (characteristic wavelength 10600nm), helps to reduce costs, improve production efficiency, and especially facilitates large-scale production.

[0009] Therefore, a method for designing a high-transmittance, wide-cutoff, narrow-band filter system on a germanium substrate includes the following steps: Sa, S1 plane narrow-band main film system design, including the sub-step: Sa1, using four wavelengths of 4257nm, 4513nm, 7994nm, and 10600nm as the center wavelengths for optical thin film design, and using the FP cavity film stack formula: Sub / (LH)^3 2L(HL)^4 / AIR, where Sub is the germanium substrate and AIR represents air. In the film stack formula: L represents a 1 / 4 wavelength thickness of low-refractive-index material ZnS (zinc sulfide); H represents a 1 / 4 wavelength thickness of high-refractive-index material Ge (germanium); Sa2, through the input film stack formula, a film structure is generated with ZnS as the base layer, ZnS on the outermost layer, and alternating ZnS and Ge layers in the middle, based on Sub / ZnS / Ge / ZnS / Ge…Ge / ZnS / Air; Sa3, the film thickness is optimized using thin film design software to obtain the optimal film thickness for the S1 surface. The transmittance of the passband region of each of the four wavelengths in the optimized S1 surface film structure meets the requirements; Sa4, the optimized optimal film thickness for the S1 surface is input into the control circuit of the coating machine. In the brain; Sb, S2 plane interference dielectric film system design, including sub-steps: Sb1, with 550nm as the center wavelength of the optical thin film design, using the film stack formula: Sub / 3.7(H2LK)^76.1(K2LH)^8 / AIR, where Sub is the germanium substrate, AIR represents air, in the film stack formula: L represents 1 / 4 wavelength thickness of low refractive index material ZnS (zinc sulfide); H represents 1 / 4 wavelength thickness of high refractive index material Ge (germanium); K represents 1 / 4 wavelength thickness of high refractive index material PbTe (lead telluride); Sb2, through the input film stack formula, generate Sub / ZnS / Ge / ZnS / Ge / ZnS / Ge / ZnS / PbTe…ZnS / PbTe / ZnS / Ge / ZnS / Ge / ZnS / Ge / ZnS / Ge / Zn The S / Air film structure consists of a ZnS base layer, ZnS on the outermost layer, alternating ZnS and Ge at both ends, and alternating ZnS and PbTe in the middle; Sb3, the film thickness is optimized using thin film design software to obtain the optimal film thickness for the S2 surface. The transmittance of the optimized S2 surface film structure in the passband region of each of the four wavelengths meets the requirements, and the transmittance in the cutoff bandwidth outside the passband region also meets the requirements; Sa4, the optimized optimal film thickness of the S2 surface is input into the control computer of the coating machine.

[0010] A method for preparing a germanium-based high-transmittance wide-cutoff narrow-band filter film system includes the following steps: Step 1, cleaning the germanium substrate (used as a lens) and the accompanying coating before deposition, and preparing three film materials: ZnS, Ge, and PbTe; Step 2, configuring the deposition process conditions and process documents, including deposition temperature, pre-deposition base vacuum, film thickness, film material evaporation mode, film material deposition rate, use of ion source-assisted deposition, and related parameters. The optimal film thickness is based on the design method for the germanium-based high-transmittance wide-cutoff narrow-band filter film system described above, stored in the control computer of the deposition machine. Step 1: Optimal film thickness for corresponding surfaces of S1 and S2; Step 2: Place the cleaned lens into the fixture, hang the fixture with the lens in it into the cavity of the coating machine, close the door, and evacuate for heating; Step 3: Pre-melting of the film material; Step 4: Cleaning the lens with an ion source; Step 5: Film coating and monitoring, according to the coating process conditions and process document configuration in Step 2, coat one of the S1 and S2 surfaces of the lens as the first surface; Step 6: Maintain constant temperature after coating; Step 7: Cool down and remove the part; Step 8: Repeat Steps 1 to 8, coat the other of the S1 and S2 surfaces of the lens as the second surface.

[0011] The beneficial effects of this disclosure are as follows.

[0012] In the design method of the germanium substrate high-transmittance wide-cutoff narrow-band filter according to the present disclosure, the film system design and optimization of the following structures not only ensure that the transmittance of the passband region of each of the four wavelengths in the film structure of the S1 surface meets the requirements, but also that the transmittance of the passband region of each of the four wavelengths in the film structure of the S2 surface meets the requirements, and that the transmittance of the cutoff bandwidth outside the passband region meets the requirements. Furthermore, considering the testing of the two-sided film system in the preparation process described later, such as the water bubble test, salt spray test, adhesion test, constant temperature and humidity test, low temperature test, and high temperature test, to meet the requirements of different application scenarios, the designed germanium substrate and the film system on both sides can be used in photoacoustic spectroscopy detection system devices to detect the composition and concentration of four greenhouse gases: CO2 (characteristic wavelength 4257nm), N2O (characteristic wavelength 4513nm), CH4 (characteristic wavelength 7994nm), and SF6 (characteristic wavelength 10600nm), so as to provide an important basis for evaluating the greenhouse effect and formulating corresponding energy conservation and emission reduction measures.

[0013] Furthermore, in the design method of the film system of the germanium substrate high transmittance wide cutoff narrow band filter according to the present disclosure, for the four wavelengths of 4257nm, 4513nm, 7994nm, and 10600nm, the same film layer structure can be generated in steps Sa2 and Sb2 without changing the type of film material. This greatly simplifies the preparation method (i.e., production process) for the four wavelengths described later, thereby helping to reduce the cost of the filter and improve the production efficiency of the filter, especially for large-scale production.

[0014] In the method for preparing a germanium substrate high-transmittance wide-cutoff narrow-band filter film system according to this disclosure, based on steps one to nine and the aforementioned design method for the germanium substrate high-transmittance wide-cutoff narrow-band filter film system, the optimal film thickness of the corresponding surfaces of the S1 and S2 surfaces stored in the control computer of the coating machine, as verified by subsequent tests, not only ensures that the prepared germanium substrate, along with the film system on both sides, has the required transmittance at its respective wavelength in the passband region of each of the four wavelengths and the required transmittance in the cutoff bandwidth outside the passband region, but also ensures that the prepared germanium substrate... The substrate and the films on both sides meet the requirements of various applications, including immersion testing, salt spray testing, adhesion testing, constant temperature and humidity testing, low temperature testing, and high temperature testing. This allows the germanium substrate product, along with the films on both sides, to be used in photoacoustic spectroscopy detection systems to detect the composition and concentration of four greenhouse gases: CO2 (characteristic wavelength 4257nm), N2O (characteristic wavelength 4513nm), CH4 (characteristic wavelength 7994nm), and SF6 (characteristic wavelength 10600nm). This provides an important basis for evaluating the greenhouse effect and formulating corresponding energy conservation and emission reduction measures.

[0015] Similarly, in the method for preparing a germanium substrate high-transmittance wide-cutoff narrow-band filter film system according to the present disclosure, for four wavelengths of 4257nm, 4513nm, 7994nm, and 10600nm, with the film material type remaining unchanged, based on the optimal film thickness (and the same film structure) of the corresponding surfaces of the S1 and S2 surfaces stored in the control computer of the coating machine in the aforementioned design method for the germanium substrate high-transmittance wide-cutoff narrow-band filter film system, the preparation method (i.e., production process) for the four wavelengths described later is greatly simplified, thereby helping to reduce the cost of the filter and improve the production efficiency of the filter, especially for large-scale production. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a photoacoustic spectroscopy detection system that uses four narrowband filters to simultaneously monitor four greenhouse gases: CO2, CH4, N2O, and SF6.

[0017] Figure 2 The spectrum is for the center wavelength of 4257nm, where (a) is the spectrum of the main film system on the S1 side of the design method, (b) is the spectrum of the cutoff film system on the S2 side of the design method, and (c) is the measured spectrum of the film system on both sides of the substrate of the preparation method.

[0018] Figure 3 The spectrum is for the center wavelength of 4513nm, where (a) is the spectrum of the main film system on the S1 side of the design method, (b) is the spectrum of the cutoff film system on the S2 side of the design method, and (c) is the measured spectrum of the film system on both sides of the substrate of the preparation method.

[0019] Figure 4 The spectrum is for the center wavelength of 7994nm, where (a) is the spectrum of the main film system on the S1 side of the design method, (b) is the spectrum of the cutoff film system on the S2 side of the design method, and (c) is the measured spectrum of the film system on both sides of the substrate of the preparation method.

[0020] Figure 5 The spectrum is for the center wavelength of 10600nm, where (a) is the spectrum of the main film system on the S1 side of the design method, (b) is the spectrum of the cutoff film system on the S2 side of the design method, and (c) is the measured spectrum of the film system on both sides of the substrate of the preparation method. Detailed Implementation

[0021] It is 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.

[0022] [Design Methods for High-Transmittance, Wide-Cutoff, Narrow-Band Filter Systems on Germanium Substrates]

[0023] The design method for a germanium substrate high-transmittance, wide-cutoff, narrow-band filter film system according to this disclosure includes the following steps:

[0024] Sa,S1 plane narrow-band master film system design, including sub-steps:

[0025] Sa1 uses four wavelengths—4257nm, 4513nm, 7994nm, and 10600nm—as the center wavelengths for optical thin film design, employing the FP cavity film stack formula: Sub / (LH)^3 2L

[0026] (HL)^4 / AIR, where Sub is the germanium substrate and AIR represents air, in the film stack formula:

[0027] L represents ZnS (zinc sulfide), a low-refractive-index material with a thickness of 1 / 4 wavelength;

[0028] H represents Ge (germanium), a high-refractive-index material with a thickness of 1 / 4 wavelength;

[0029] Sa2, through the input film stack formula, generates a film structure with ZnS as the base layer, ZnS on the outermost layer, and alternating ZnS and Ge in the middle layer, consisting of Sub / ZnS / Ge / ZnS / Ge…Ge / ZnS / Air.

[0030] Sa3, the film thickness is optimized using thin film design software to obtain the optimal film thickness of the S1 surface. The transmittance of the passband region of each of the four wavelengths of the optimized film structure of the S1 surface meets the requirements.

[0031] Sa4 inputs the optimal film thickness of the optimized S1 surface into the control computer of the coating machine;

[0032] Design of Sb, S2 plane interference dielectric film system, including sub-steps:

[0033] Sb1, with 550nm as the center wavelength for optical thin film design, uses the film stack formula: Sub /

[0034] 3.7(H2LK)^7 6.1(K2LH)^8 / AIR, where Sub is the germanium substrate and AIR represents air, in the film stack formula:

[0035] L represents ZnS (zinc sulfide), a low-refractive-index material with a thickness of 1 / 4 wavelength;

[0036] H represents Ge (germanium), a high-refractive-index material with a thickness of 1 / 4 wavelength;

[0037] K represents PbTe (lead telluride), a high-refractive-index material with a thickness of 1 / 4 wavelength;

[0038] Sb2, through the input membrane stack formula, generates Sub / ZnS / Ge / ZnS / Ge / ZnS / Ge / ZnS / PbTe…ZnS / PbTe / ZnS / Ge / ZnS / Ge / ZnS / Ge / ZnS

[0039] The film structure is as follows: / Ge / ZnS / Air, with ZnS as the base layer, ZnS on the outermost layer, ZnS and Ge alternating at both ends, and ZnS and PbTe alternating in the middle.

[0040] Sb3, the film thickness is optimized using thin film design software to obtain the optimal film thickness of the S2 surface. The transmittance of the passband region of each of the four wavelengths of the optimized S2 surface film structure meets the requirements, and the transmittance in the cutoff bandwidth other than the passband region also meets the requirements.

[0041] Sa4 inputs the optimal film thickness of the optimized S2 surface into the control computer of the coating machine.

[0042] In the design method of the germanium substrate high-transmittance wide-cutoff narrow-band filter according to the present disclosure, the film system design and optimization of the following structures not only ensure that the transmittance of the passband region of each of the four wavelengths in the film structure of the S1 surface meets the requirements, but also that the transmittance of the passband region of each of the four wavelengths in the film structure of the S2 surface meets the requirements, and that the transmittance of the cutoff bandwidth outside the passband region meets the requirements. Furthermore, considering the testing of the two-sided film system in the preparation process described later, such as the water bubble test, salt spray test, adhesion test, constant temperature and humidity test, low temperature test, and high temperature test, to meet the requirements of different application scenarios, the designed germanium substrate and the film system on both sides can be used in photoacoustic spectroscopy detection system devices to detect the composition and concentration of four greenhouse gases: CO2 (characteristic wavelength 4257nm), N2O (characteristic wavelength 4513nm), CH4 (characteristic wavelength 7994nm), and SF6 (characteristic wavelength 10600nm), so as to provide an important basis for evaluating the greenhouse effect and formulating corresponding energy conservation and emission reduction measures.

[0043] Furthermore, in the design method of the film system of the germanium substrate high transmittance wide cutoff narrow band filter according to the present disclosure, for the four wavelengths of 4257nm, 4513nm, 7994nm, and 10600nm, the same film layer structure can be generated in steps Sa2 and Sb2 without changing the type of film material. This greatly simplifies the preparation method (i.e., production process) for the four wavelengths described later, thereby helping to reduce the cost of the filter and improve the production efficiency of the filter, especially for large-scale production.

[0044] In one example, the optimal film thickness in sub-step Sa3 is:

[0045]

[0046] In sub-step Sb3, the optimal film thickness is:

[0047]

[0048]

[0049] In one example, in substep Sa3,

[0050]

[0051] In sub-step Sb3

[0052]

[0053] In one example, in steps Sa and Sb, the software is designed as TFCalc or Essential Macleod.

[0054] [Preparation method of germanium substrate high transmittance wide cutoff narrow band filter film system]

[0055] The method for preparing a germanium substrate high-transmittance wide-cutoff narrow-band filter film system according to this disclosure includes the following steps:

[0056] Step 1: Before plating, the germanium substrate product and the accompanying plating sheet are cleaned and prepared with three types of film materials: ZnS, Ge, and PbTe.

[0057] Step 2, configuration of coating process conditions and process documents. The configuration of coating process conditions and process documents includes coating temperature, pre-coating base vacuum, film thickness, vapor deposition mode of film material, deposition rate of film material, use and parameters of ion source assisted deposition. Among them, the optimal film thickness is based on the optimal film thickness of the corresponding surface of S1 surface and S2 surface stored in the control computer of the coating machine as described in the design method of the film system of germanium substrate high transmittance wide cutoff narrow band filter.

[0058] Step 3: Place the cleaned lenses into the tooling fixture, hang the tooling fixture with the lenses in it into the cavity of the coating machine, close the door, and evacuate and heat.

[0059] Step four: Pre-melting of the film material;

[0060] Step 5: Clean the lenses with an ion source;

[0061] Step 6, coating and monitoring: According to the coating process conditions and process document configuration in Step 2, the coating is applied to one of the S1 and S2 surfaces of the lens as the first surface.

[0062] Step 7: Maintain constant temperature after coating is completed;

[0063] Step 8: Cool down and remove the item;

[0064] Step nine: Repeat steps one through eight, and apply the coating to the other side of the lens, S1 or S2, as the second side.

[0065] In the method for preparing a germanium substrate high-transmittance wide-cutoff narrow-band filter film system according to this disclosure, based on steps one to nine and the aforementioned design method for the germanium substrate high-transmittance wide-cutoff narrow-band filter film system, the optimal film thickness of the corresponding surfaces of the S1 and S2 surfaces stored in the control computer of the coating machine, as verified by subsequent tests, not only ensures that the prepared germanium substrate, along with the film system on both sides, has the required transmittance at its respective wavelength in the passband region of each of the four wavelengths and the required transmittance in the cutoff bandwidth outside the passband region, but also ensures that the prepared germanium substrate... The substrate and the films on both sides meet the requirements of various applications, including immersion testing, salt spray testing, adhesion testing, constant temperature and humidity testing, low temperature testing, and high temperature testing. This allows the germanium substrate product, along with the films on both sides, to be used in photoacoustic spectroscopy detection systems to detect the composition and concentration of four greenhouse gases: CO2 (characteristic wavelength 4257nm), N2O (characteristic wavelength 4513nm), CH4 (characteristic wavelength 7994nm), and SF6 (characteristic wavelength 10600nm). This provides an important basis for evaluating the greenhouse effect and formulating corresponding energy conservation and emission reduction measures.

[0066] Similarly, in the method for preparing a germanium substrate high-transmittance wide-cutoff narrow-band filter film system according to the present disclosure, for four wavelengths of 4257nm, 4513nm, 7994nm, and 10600nm, with the film material type remaining unchanged, based on the optimal film thickness (and the same film structure) of the corresponding surfaces of the S1 and S2 surfaces stored in the control computer of the coating machine in the aforementioned design method for the germanium substrate high-transmittance wide-cutoff narrow-band filter film system, the preparation method (i.e., production process) for the four wavelengths described later is greatly simplified, thereby helping to reduce the cost of the filter and improve the production efficiency of the filter, especially for large-scale production.

[0067] In one example, in step one, the product is a (25.4±0.1)mm×(1±0.05)mm disc, and the accompanying plate is a (25±0.1)mm×(1±0.1)mm disc.

[0068] The cleaning in step one ensures a clean lens surface, which is beneficial for the adhesion and bonding of the coating. In one example, the lens is polished with an alumina polishing slurry, followed by ultrasonic cleaning with pure water. Specifically, the alumina polishing slurry used is a 0.1μm polycrystalline diamond slurry from Nanjing Hengrui Precision Optics Co., Ltd.

[0069] In one example, in step two, the coating temperature is 150±2℃; the pre-coating base vacuum is (1.0±0.1)×10⁻⁶. -3Pa; the film thickness in the coating process conditions and process documentation configuration is based on the optimal film thickness of the corresponding surface stored in the control computer of the coating machine, as described in the aforementioned design method for a germanium substrate high-transmittance wide-cutoff narrow-band filter film system; the film deposition mode is: ZnS and PbTe are evaporated using resistance heating, and Ge is evaporated using electron beam heating; the film deposition rate is: the deposition rate of the ZnS film is... The deposition rate of the Ge film is The deposition rate of the PbTe film is The use of ion source-assisted deposition is as follows: the ion source is not turned on for all film layers.

[0070] In one example, in step two, the coating machine is a Leybold ARES1350.

[0071] In one example, in step three, a vacuum is first drawn to 5 × 10⁻⁶. -2 Pa, after which the cavity of the coating machine is heated. This prevents the germanium substrate from oxidizing under humid and hot conditions.

[0072] Step four involves pre-melting the membrane material to remove gas and impurities, ensuring the purity of the membrane material. In step four, when the vacuum reaches (4.0-5.0)×10⁻⁶... -3 At step Pa, the film material undergoes pre-melting treatment. After pre-melting, the temperature of the cavity of the coating machine reaches 150℃ and is maintained at a constant temperature for 10 minutes. Specifically, for example, in step four, the pre-melting treatment uses both electron beam heating and resistance heating. For ZnS film material, the resistance heating current is 720-760mA; for Ge film material, the electron beam heating current is 260-290mA; and for PbTe film material, the resistance heating current is 420-460mA.

[0073] Step five, ion source cleaning, removes the surface oxide layer and attached particles from the germanium substrate, resulting in a cleaner substrate surface and increased film adhesion. In one example, in step five, the cavity vacuum reaches (1.0 ± 0.1) × 10⁻⁶. -3 Pa, start the ion source to perform ion cleaning on the lens. The ion source is a Hall source. The ion source parameters are: neutralization current 0.6±0.01A, neutralization gas flow rate 8±0.1sccm, anode voltage 130±2V, anode current 1±0.01A. No oxygen is supplied throughout the process. The argon ratio is 100%. The cleaning time is 300±2s.

[0074] In one example, in step six, when depositing each film layer, no protective gas is introduced from outside the coating machine, but the internal cavity of the coating machine is evacuated, and the coating temperature is maintained at 150°C; each film layer is deposited at a temperature of 150°C in the cavity of the coating machine; the film thickness is monitored by using the crystal oscillator method with the corresponding crystal oscillators of multiple crystal oscillators of the crystal controller; after ion source cleaning, the crystal controller controls the new crystal oscillator among the multiple crystal oscillators to work accordingly, and the crystal oscillator frequency is not less than 5850Hz.

[0075] In one example, in step seven, the cavity is kept at 150±2°C for 30 minutes after plating is completed.

[0076] In one example, in step eight, after step seven is completed, the temperature is first lowered to 130±2℃ at 1℃ / min and held for 5min, then lowered to 110±2℃ at 1℃ / min and held for 5min, and finally lowered to below 80±2℃ at 1℃ / min, and the door is opened to retrieve the item.

[0077] [test]

[0078] Example 1

[0079] Part 1: Design Methods for High-Transmittance Wide-Cutoff Narrow-Band Filter Systems on Germanium Substrates

[0080] The design method for a germanium substrate high-transmittance wide-cutoff narrow-band filter film system adopts the following steps:

[0081] The Sa,S1 plane narrow-band main film system design adopts the following sub-steps:

[0082] Sa1 uses four wavelengths—4257nm, 4513nm, 7994nm, and 10600nm—as the center wavelengths for optical thin film design. In TFCalc, the FP cavity film stack formula is used:

[0083] Sub / (LH)^3 2L(HL)^4 / AIR, where Sub represents the germanium substrate and AIR represents air, in the film stack formula:

[0084] L represents ZnS (zinc sulfide), a low-refractive-index material with a thickness of 1 / 4 wavelength;

[0085] H represents Ge (germanium), a high-refractive-index material with a thickness of 1 / 4 wavelength;

[0086] Sa2, through the input film stack formula, generates a film structure with ZnS as the base layer, ZnS on the outermost layer, and alternating ZnS and Ge in the middle layer, consisting of Sub / ZnS / Ge / ZnS / Ge…Ge / ZnS / Air.

[0087] Sa3: The film thickness was optimized using the thin film design software TFCalc to obtain the optimal film thickness for the S1 surface. The transmittance of the passband region of each of the four wavelengths in the optimized S1 surface film structure meets the requirements.

[0088] In sub-step Sa3, the optimal film thickness is:

[0089]

[0090] In sub-step Sa3

[0091]

[0092] Sa4 inputs the optimal film thickness of the S1 surface into the control computer of the coating machine, which is a Leybold ARES1350.

[0093] The design of Sb, S2 plane interference dielectric film system adopts the following sub-steps:

[0094] Sb1, with 550nm as the center wavelength for optical thin film design, is represented in TFCalc using the film stack formula: Sub / 3.7(H2LK)^7 6.1(K2LH)^8 / AIR, where Sub represents the germanium substrate and AIR represents air.

[0095] L represents ZnS (zinc sulfide), a low-refractive-index material with a thickness of 1 / 4 wavelength;

[0096] H represents Ge (germanium), a high-refractive-index material with a thickness of 1 / 4 wavelength;

[0097] K represents PbTe (lead telluride), a high-refractive-index material with a thickness of 1 / 4 wavelength;

[0098] Sb2, through the input film stack formula, generates a film structure with Sub / ZnS / Ge / ZnS / Ge / ZnS / Ge / ZnS / PbTe…ZnS / PbTe / ZnS / Ge / ZnS / Ge / ZnS / Ge / ZnS / Ge / ZnS / Air as the base layer, ZnS on the outermost layer, alternating ZnS and Ge at both ends, and alternating ZnS and PbTe in the middle;

[0099] The thickness of the Sb3 film was optimized using the thin film design software TFCalc to obtain the optimal film thickness for the S2 surface. The optimized S2 surface film structure achieved acceptable transmittance in the passband region of each of the four wavelengths and acceptable transmittance in the cutoff bandwidth outside the passband region.

[0100] In sub-step Sb3, the optimal film thickness is:

[0101]

[0102]

[0103] In sub-step Sb3

[0104]

[0105] Sa4, the optimal film thickness of the optimized S2 surface is input into the control computer of the coating machine, which is the Leybold ARES1350.

[0106] Part 2: Preparation method of germanium substrate high-transmittance wide-cutoff narrow-band filter film system

[0107] The preparation method of the germanium substrate high-transmittance wide-cutoff narrow-band filter film system adopts the following steps:

[0108] Step 1: Before plating, the germanium substrate product and the substrate to be plated are cleaned and the three coating materials ZnS, Ge and PbTe are prepared. The product is a 25.4mm×1mm disc and the substrate to be plated is a 25mm×1mm disc. The lens is polished with alumina polishing slurry and then ultrasonically cleaned with pure water. The alumina polishing slurry used is 0.1μm polycrystalline diamond slurry from Nanjing Hengrui Precision Optics Co., Ltd.

[0109] Step two involves configuring the coating process conditions and process documents. This includes configuring the coating temperature, pre-deposition base vacuum, film thickness, vapor deposition mode of the film material, deposition rate of the film material, and the use and parameters of ion source-assisted deposition. The optimal film thickness is based on the optimal film thickness of the corresponding surfaces of the S1 and S2 surfaces stored in the coating machine's control computer, as described in the design method for the germanium substrate high-transmittance wide-cutoff narrow-band filter in Part One, with a selected characteristic wavelength of 10600 nm.

[0110] In step two,

[0111] The coating temperature is 150℃;

[0112] The base vacuum before plating is 1.0 × 10⁻⁶. -3 Pa;

[0113] The film thickness in the coating process conditions and process document configuration is based on the optimal film thickness of the corresponding surface stored in the control computer of the coating machine, as described in the design method of the film system of high transmittance wide cutoff narrow band filter on germanium substrate in Part 1, and the selected characteristic wavelength is 10600nm.

[0114] The evaporation mode of the film material is as follows: ZnS and PbTe are evaporated using resistance heating, and Ge is evaporated using electron beam heating.

[0115] The deposition rate of the film material is: the deposition rate of the ZnS film layer is The deposition rate of the Ge film is The deposition rate of the PbTe film is

[0116] The use of ion source-assisted deposition is as follows: the ion source is not turned on for all film layers;

[0117] Step 3: Place the cleaned lenses into the fixture, hang the fixture with the lenses inside the coating machine cavity, close the door, and first evacuate to 5×10. -2 Pa, then the cavity of the coating machine is heated;

[0118] Step four, pre-melting of the membrane material, when the vacuum reaches 4.5 × 10 -3 At Pa, the film material is pre-melted. After the film material is pre-melted, the temperature of the coating machine cavity reaches 150℃ and is maintained at a constant temperature for 10 minutes.

[0119] In step four, the pre-melting process employs both electron beam heating and resistance heating.

[0120] For ZnS film material, the resistance heating current is 740mA;

[0121] For Ge film materials, the electron beam heating current is 265mA;

[0122] For PbTe film material, the resistance heating current is 440mA;

[0123] Step 5: Clean the lenses with the ion source until the cavity vacuum reaches 1.0 × 10⁻⁶. -3 Pa, start the ion source to perform ion cleaning on the lens. The ion source is a Hall source. The ion source parameters are: neutralization current 0.6A, neutralization gas flow rate 8sccm, anode voltage 130V, anode current 1A. No oxygen is supplied throughout the process. Argon ratio is 100%. The cleaning time is 300s.

[0124] Step Six: Coating and Monitoring. Following the coating process conditions and process documentation from Step Two, coat the lens onto one of the S1 or S2 surfaces as the first surface.

[0125] In step six,

[0126] When depositing each film layer, no protective gas is introduced from outside the coating machine, but the internal cavity of the coating machine is evacuated and the coating temperature is maintained at 150°C.

[0127] Each film layer is deposited at a temperature of 150°C in the cavity of the coating machine;

[0128] 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 new crystal oscillator in the multiple crystal oscillators to work accordingly. The crystal oscillator frequency is 5990Hz.

[0129] Step 7: After plating is completed, keep the cavity at 150℃ for 30 minutes;

[0130] Step 8: After step 7 is completed, first lower the temperature to 130℃ at 1℃ / min and hold for 5 minutes, then lower the temperature to 110℃ at 1℃ / min and hold for 5 minutes, and finally lower the temperature to 80℃ at 1℃ / min, then open the door and take out the part.

[0131] Step nine: Repeat steps one through eight, and apply the coating to the other side of the lens, S1 or S2, as the second side.

[0132] Comparative Example 1

[0133] Except for step two, when depositing ZnS and Ge films, the ion source is turned on, the ion source is a Hall source, and the ion source parameters are: neutralization current 0.6A, neutralization gas flow rate 8sccm, anode voltage 130V, anode current 1A, no oxygen is supplied throughout the process, and the argon ratio is 100%, the rest is the same as in Example 1.

[0134] Comparative Example 2

[0135] Except for replacing the ZnS (zinc sulfide) film material with ZnSe (zinc selenide) in steps one, two, and four (i.e., only the film material is replaced), the rest is the same as in Example 1.

[0136] Comparative Example 3

[0137] Except for replacing the film material Ge (germanium) with the film material PbTe (lead telluride) in steps one, two, and four (i.e., only the film material is replaced), the rest is the same as in Example 1.

[0138] Comparative Example 4

[0139] Except for the coating temperature of 180°C in step two, the temperature of the cavity of the coating machine reaching 180°C in step four, the coating temperature being maintained at 180°C in step six, and the coating of each film layer being completed at a temperature of 180°C in the cavity of the coating machine, the rest is the same as in Example 1.

[0140] Comparative Example 5

[0141] Except for the base vacuum of 3×10 in step two before plating. -3 Pa, the cavity vacuum level in step five reaches 3×10 -3 Except for Pa, the rest is the same as in Example 1.

[0142] Comparative Example 6

[0143] Except for the deposition rate of the PbTe film in step two, which is Except for the above, the rest is the same as in Example 1.

[0144] Example 2

[0145] Except for the characteristic wavelength of 7994nm selected in step two, the rest is the same as in Example 1.

[0146] Example 3

[0147] Except for the characteristic wavelength of 4513nm selected in step two, the rest is the same as in Example 1.

[0148] Example 4

[0149] Except for the characteristic wavelength of 4257nm selected in step two, the rest is the same as in Example 1.

[0150] Figure 2 The spectrum is for the center wavelength of 4257nm, where (a) is the spectrum of the main film system on the S1 side of the design method, (b) is the spectrum of the cutoff film system on the S2 side of the design method, and (c) is the measured spectrum of the film system on both sides of the substrate of the preparation method (corresponding to Example 4).

[0151] Figure 3 The spectrum is for the center wavelength of 4513nm, where (a) is the spectrum of the main film system on the S1 side of the design method, (b) is the spectrum of the cutoff film system on the S2 side of the design method, and (c) is the measured spectrum of the film system on both sides of the substrate of the preparation method (corresponding to Example 3).

[0152] Figure 4 The spectrum is for the center wavelength of 7994nm, where (a) is the spectrum of the main film system on the S1 side of the design method, (b) is the spectrum of the cutoff film system on the S2 side of the design method, and (c) is the measured spectrum of the film system on both sides of the substrate of the preparation method (corresponding to Example 2).

[0153] Figure 5 The spectrum is for the center wavelength of 10600nm, where (a) is the spectrum of the main film system on the S1 side of the design method, (b) is the spectrum of the cutoff film system on the S2 side of the design method, and (c) is the measured spectrum of the film system on both sides of the substrate of the preparation method (corresponding to Example 1).

[0154] Example 1: The coating sheets of Comparative Examples 1-6 and Examples 2-4, along with the film systems on both sides, were subjected to the following overall performance tests.

[0155] Water immersion test: Take tap water and conduct a water immersion test for 2 hours, and observe whether the film layer on each surface is peeled off or whether the film layer on each surface is cracked.

[0156] Salt spray test: Neutral salt spray test for 24 hours, observe whether the film layer on each surface peels off or cracks.

[0157] Adhesion test: Apply 3M tape by hand and pull the tape in the opposite direction to the adhesive end on each side to observe whether the film layer is pulled up.

[0158] Constant temperature and humidity test: In a constant temperature and humidity chamber, at 50℃ and 95% relative humidity for 24 hours, observe whether the film layer on each surface peels off or cracks.

[0159] Low temperature test: In a low temperature chamber, at -40℃ for 24 hours, observe whether the film layer on each surface peels off or cracks.

[0160] High temperature test: In a high temperature chamber, at 85℃ for 24 hours, observe whether the film layer on each surface peels off or cracks.

[0161] Table 1 shows the peak transmittance, half-peak bandwidth, cutoff depth (transmittance T of cutoff bandwidth) of the substrates of Examples 1, Comparative Examples 1-6 and Examples 2-4, along with the corresponding characteristic wavelengths on both sides, as well as the results of their respective tests.

[0162] Table 1 shows the peak transmittance, half-peak bandwidth, cutoff depth (transmittance T of cutoff bandwidth) of the substrates in Examples 1, Comparative Examples 1-6, and Examples 2-4, along with the corresponding characteristic wavelengths on both sides, and the results of their respective tests.

[0163]

[0164]

[0165] 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 preparing a film system of a germanium substrate high-transmittance wide-cutoff narrow-band filter, characterized in that, Including the following steps: Step 1: Before plating, the germanium substrate product and the accompanying plating sheet are cleaned and prepared with three types of film materials: ZnS, Ge, and PbTe. Step two involves configuring the coating process conditions and process documents. This includes configuring the coating temperature, pre-coating base vacuum, film thickness, film deposition mode, film deposition rate, and the use and parameters of ion source-assisted deposition. The optimal film thickness is based on the optimal film thickness of the corresponding surfaces of the S1 and S2 planes stored in the coating machine's control computer. For the S1 surface, the optimal film thickness is: For S2, the optimal film thickness is: Step 3: Place the cleaned lenses into the tooling fixture, hang the tooling fixture with the lenses in it into the cavity of the coating machine, close the door, and evacuate and heat. Step four: Pre-melting of the film material; Step 5: Clean the lenses with an ion source; Step 6, coating and monitoring: According to the coating process conditions and process document configuration in Step 2, the coating is applied to one of the S1 and S2 surfaces of the lens as the first surface. Step 7: Maintain constant temperature after coating is completed; Step 8: Cool down and remove the item; Step nine: Repeat steps one through eight, and apply the coating to the other side of the lens, S1 or S2, as the second side.

2. The method for preparing the film system of a germanium substrate high-transmittance wide-cutoff narrow-band filter according to claim 1, characterized in that, In step one, The product is a (25.4±0.1)mm×(1±0.05)mm round piece, and the accompanying plate is a (25±0.1)mm×(1±0.1)mm round piece; The lenses are polished with aluminum oxide polishing solution and then ultrasonically cleaned with pure water. The alumina polishing slurry used is the 0.1μm polycrystalline diamond slurry from Nanjing Hengrui Precision Optics Co., Ltd.

3. The method for preparing the film system of a germanium substrate high-transmittance wide-cutoff narrow-band filter according to claim 1, characterized in that, In step two, The coating temperature is 150±2°C; The base vacuum before plating was (1.0±0.1)×10 -3 Pa; The evaporation mode of the film material is as follows: ZnS and PbTe are evaporated using resistance heating, and Ge is evaporated using electron beam heating. The deposition rates of the films are as follows: the deposition rate of the ZnS film is 5 ± 0.2 Å / s, the deposition rate of the Ge film is 3 ± 0.2 Å / s, and the deposition rate of the PbTe film is 3 ± 0.2 Å / s. The use of ion source-assisted deposition is as follows: the ion source is not turned on for all film layers; The coating machine is a Leybold ARES1350.

4. The method for preparing the film system of a germanium substrate high-transmittance wide-cutoff narrow-band filter according to claim 1, characterized in that, In step three, a vacuum is first drawn to 5×10. -2 Pa, then the cavity of the coating machine is heated.

5. The method for preparing the film system of a germanium substrate high-transmittance wide-cutoff narrow-band filter according to claim 1, characterized in that, In step four, when the vacuum reaches (4.0-5.0)×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 150°C and is kept constant for 10 minutes. In step four, the pre-melting process employs both electron beam heating and resistance heating. For ZnS film materials, the resistance heating current is 720-760mA; For Ge film materials, the electron beam heating current is 260-290mA; For PbTe film materials, the resistance heating current is 420-460mA.

6. The method for preparing the film system of a germanium substrate high-transmittance wide-cutoff narrow-band filter according to claim 1, characterized in that, In step five, The cavity vacuum level reaches (1.0±0.1)×10 -3 Pa, start the ion source to perform ion cleaning on the lens. The ion source is a Hall source. The ion source parameters are: neutralization current 0.6±0.01A, neutralization gas flow rate 8±0.1sccm, anode voltage 130±2V, anode current 1±0.01A. No oxygen is supplied throughout the process. The argon ratio is 100%. The cleaning time is 300±2s.

7. The method for preparing the film system of a germanium substrate high-transmittance wide-cutoff narrow-band filter according to claim 1, characterized in that, In step six, When depositing each film layer, no protective gas is introduced from outside the coating machine, but the internal cavity of the coating machine is evacuated and the coating temperature is maintained at 150°C. Each film layer is deposited at a temperature of 150°C in the cavity of the coating machine; 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 new crystal oscillator in the multiple crystal oscillators to work accordingly, and the crystal oscillator frequency is not less than 5850Hz.

8. The method for preparing the film system of a germanium substrate high-transmittance wide-cutoff narrow-band filter according to claim 1, characterized in that, In step seven, after the plating is completed, the cavity is kept at 150±2°C for 30 minutes; In step eight, after step seven is completed, the temperature is first lowered to 130±2°C at a rate of 1°C / min and held for 5 minutes, then lowered to 110±2°C at a rate of 1°C / min and held for 5 minutes, and finally lowered to below 80±2°C at a rate of 1°C / min, and the door is opened to retrieve the item.

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