A wide spectrum infrared transmission filter window with cutoff for ultraviolet and visible light

Abstract

The present invention discloses a wide-spectrum infrared transmission filter window that cuts off ultraviolet and visible light. The window substrate is a zinc selenide crystal, and a broadband cutoff film is designed on one side of the substrate. The main film system adopts a long-wave filter-type film structure, with zinc selenide and ytterbium fluoride as high and low refractive index materials, respectively. Two cutoff film stacks are used to achieve broadband cutoff, and matching layers are added at both ends of the main film system. The infrared band transmittance is improved by optimizing the matching layers; a wide-spectrum anti-reflection film is designed on the other side of the substrate. The optical thin film preparation process of the filter window adopts appropriate deposition temperature, deposition rate, and ion-assisted deposition processes. The window can prevent light in a wide band of 0.20μm to 0.80μm from passing through, and allows light in a wide band of 0.92μm to 15.50μm to pass through and reach the infrared detector response area through the subsequent optical path. The filter window of the present invention has stable performance and good reliability, and is suitable for spectral selection in infrared imaging systems.

Description

Technical Field

[0001] The present invention relates to optical thin film technology, specifically to a wide-spectrum infrared transmission filter window that cuts off ultraviolet and visible light. By preparing a cutoff film with a spectral selection function on one side of a zinc selenide substrate and a wide-spectrum anti-reflection film on the other side of the substrate, the window can cut off light in a wide wavelength band of 0.20μm to 0.80μm and transmit light in a wide spectral band of 0.92μm to 15.50μm. Technical Background

[0002] Infrared imaging spectrometers are one of the primary detection payloads on Earth observation satellites. In multi-channel infrared remote sensing imaging spectrometers, filters are typically used to selectively transmit the desired infrared light to the detector's response area. By designing a wide-spectrum infrared transmission filter window that cuts off ultraviolet and visible light, initial spectral selection can be performed on light within a wide spectral band from ultraviolet, visible to mid- and long-wave infrared. This cuts off light from 0.20μm to 0.80μm, while allowing light from 0.92μm to 15.50μm to enter the subsequent optical path.

[0003] Because the filter window requires excellent stability and reliability, and a wide light transmission range, especially good light transmittance from the near-infrared to the long-wave infrared, factors such as environmental stability, light transmission range, and mechanical strength were comprehensively considered. Zinc selenide crystals with good infrared transmittance, mechanical strength, and stability were selected as the substrate material. The film layer was designed using zinc selenide and ytterbium fluoride, which have low absorption from the visible near-infrared to the mid- and long-wave infrared bands and good environmental stability. Summary of the Invention

[0004] The purpose of the present invention is to provide a wide spectrum infrared transmission filter window that cuts off ultraviolet and visible light, and performs spectral selection on the 0.20μm to 15.50μm infrared wide spectrum to meet the spectral selection requirements in infrared imaging systems.

[0005] The technical solution of the present invention is: preparing a front cut-off filter film on one side of a zinc selenide substrate, and preparing a wide-spectrum anti-reflection film on the other side of the substrate.

[0006] The main film system for the front cutoff film utilizes a longpass filter-like structure, with zinc selenide and ytterbium fluoride as the high and low refractive index materials, respectively. The cutoff band is broadband, and the film system utilizes a dual-cutoff stack. Matching layers are added to both ends of the cutoff film system as the initial film system. By optimizing the matching layers to improve infrared transmittance, a usable film system is obtained that meets spectral requirements and facilitates film thickness monitoring. A broadband anti-reflection coating is applied to the other side of the zinc selenide substrate.

[0007] According to the above analysis, the implementation of the filter window includes the following steps:

[0008] 1. Structure of the membrane system

[0009] The membrane structure of the cut-off membrane (1) is:

[0010] Base / W1(0.56N1.12L0.56N) a (0.43N0.86L0.43N) b W2 / air Wherein: W1 is the front matching layer, and its structure is: k1Nk2Lk3N; W2 is the back matching layer, and its structure is: p1Np2Lp3Np4Lp5N; the index a is the first cutoff stack period number, and a takes the value of 7 or 6; the index b is the second cutoff stack period number, and b takes the value of 6 or 5; k1, k2, k3, p1, p2, p3, p4, and p5 are the optical thickness coefficients of each film layer.

[0011] The film system structure of the wide spectrum anti-reflection film (3) is: substrate / 3.67N0.26L3.63N0.38L1.46N0.85L1.21N0.87L1.13N1.35L0.53N4.72L0.32N5.16L0.33N / air, wherein: N represents a zinc selenide film layer with an optical thickness of λ0 / 4, L represents an ytterbium fluoride film layer with an optical thickness of λ0 / 4, λ0 is a center wavelength, and the numbers 3.67, 0.26, 3.63, 0.38, 1.46, 0.85, 1.21, 0.87, 1.13, 1.35, 0.53, 4.72, 0.32, 5.16, and 0.33 are optical thickness coefficients of each film layer.

[0012] 2. Film preparation method

[0013] All film layers were deposited using thermal evaporation under high vacuum conditions in a chamber-type vacuum coating system equipped with a diffusion pump system. Before depositing the first film layer, the ZnSe substrate was bombarded with an ion beam. Electron beam evaporation was used for L, and resistance heating evaporation was used for N. Ion beam-assisted deposition was used for some film layers using a Mark II ion source. Specific parameters were: anode voltage of 130V to 150V, cathode current of 14A to 16A. Test results from the film materials showed that the films exhibited excellent durability when the substrate temperature was controlled at 200°C. However, at higher temperatures, ZnSe reverse evaporation was severe, hindering deposition. At lower temperatures, cracks were easily formed when depositing thick YbF films.

[0014] The beneficial effects of the present invention are as follows:

[0015] 1. The present invention provides a wide spectrum infrared transmission filter window that cuts off ultraviolet and visible light, which is of great significance for spectrum selection.

[0016] 2. The present invention adopts a specific process to reduce the absorption of the thin film material in the long-wave region, ensure the transmittance in a wide spectrum from near-infrared to long-wave infrared transmission region, and improve spatial reliability.

[0017] 3. The technical solution of the present invention is reasonable and feasible, the product performance is stable, and it can be applied to infrared imaging spectrometer systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The schematic diagram of the film structure of the window is shown in the figure:

[0019] 1—front cutoff filter;

[0020] 2—ZnSe substrate;

[0021] 3—Broad spectrum anti-reflection film

[0022] Figure 2 This is the measured transmittance spectrum curve of the window.

[0023] Figure 3 This is the measured transmittance spectrum curve of the window. DETAILED DESCRIPTION

[0024] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] The substrate material is zinc selenide crystal.

[0026] Based on technical requirements, a cutoff film was fabricated on one side of a zinc selenide substrate and a wide-spectrum anti-reflection film on the other. The cutoff film design required consideration of both the cutoff bandwidth within the specified range and the transmission across a wide spectrum from the near-infrared to the long-wave infrared. The primary film system for the cutoff film employed a long-wavepass filter structure, with matching layers added on both sides to form the initial film system. A usable film system was achieved by locally optimizing the thickness of individual key layers. The wide-spectrum anti-reflection film designed on the backside of the substrate followed the same principles.

[0027] (1) When the number of membrane stack cycles a=7, b=5,

[0028] The film system was optimized and adjusted by software, and the thickness of some key layers was controlled. The resulting film system was: substrate / 5.45N0.75L0.55N (0.56N1.12L0.56N) 7 (0.43N0.86L0.43N) 5 0.27N1.07L1.34N1.58L0.35N / air;

[0029] (2) When the number of membrane stack cycles a=7, b=6,

[0030] The film system is optimized and adjusted by software, while the thickness of a few key layers is controlled and the film layer with an optical thickness coefficient of 0 is removed. The resulting film system is: substrate / 3.38N0.64L0.73N (0.56N1.12L0.56N) 7 (0.43N0.86L0.43N) 6 0.17N 3.75L0.31N / air;

[0031] (3) When the number of membrane stack cycles a=6, b=5,

[0032] The film system was optimized and adjusted by software, and the thickness of some key layers was controlled at the same time. The obtained film system was: substrate / 4.65N0.39L0.69N (0.56N1.12L0.56N) 6 (0.43N0.86L0.43N) 5 0.31N0.52L0.39N3.93L0.28N / air;

[0033] (4) When the number of membrane stack cycles a=6, b=6,

[0034] The film system is optimized and adjusted through software, while the thickness of a few key layers is controlled and the film layer with an optical thickness coefficient of 0 is removed. The resulting film system is: substrate / 2.76N0.77L0.61N (0.56N1.12L0.56N) 6 (0.43N0.86L0.43N) 6 0.28N4.35L0.53N / air;

[0035] Taking into account the certain absorption of ytterbium fluoride in the long-wave infrared, the total thickness of the film layer, and the technical index requirements, the cutoff film on one side of the zinc selenide substrate was actually produced using the film system in 2. Combined with the anti-reflection film system on the other side of the zinc selenide substrate, the final complete film system is: n0 / 0.31N3.75L0.17N (0.43N0.86L0.43N) 6 (0.56N1.12L0.56N) 7 0.73N0.64L3.38N / n s / 3.67N0.26L3.63N0.38L1.46N0.85L1.21N0.87L1.13N1.35L0.53N4.72L0.32N5.16L0.33N / n0Where: n s is a zinc selenide substrate, n0 is air, N represents a zinc selenide film layer with an optical thickness of λ0 / 4, L represents an ytterbium fluoride film layer with an optical thickness of λ0 / 4, λ0 is the center wavelength, indices 7 and 6 are the cutoff stack periods, and the numbers before N and L are the optical thickness coefficients of each film layer.

[0036] In this embodiment, the film system of the filter window is developed at a substrate temperature of 200° C., using resistance evaporation and electron beam evaporation to deposit high and low refractive index materials, and ion beam assisted deposition of local film layers.

[0037] The filter window of the present technical solution has an average transmittance of 0.3% in the cutoff band of 0.20μm to 0.80μm, and a maximum transmittance of no more than 3%. The average transmittance in the band of 0.92μm to 2.50μm is 84%, the average transmittance in the band of 2.5μm to 5.0μm is 91%, the average transmittance in the band of 5.0μm to 9.5μm is 89%, the average transmittance in the band of 9.5μm to 13.0μm is 91%, and the average transmittance in the band of 13.0 to 15.5μm is 87.5%, which can meet the spectral selection requirements of the infrared imaging spectrometer system.

Claims

1. A wide-spectrum infrared transmission filter window that cuts off ultraviolet and visible light, comprising a front-cut filter film (1) with a spectrum selection function prepared on one side of a zinc selenide substrate (2), and a wide-spectrum anti-reflection film (3) prepared on the other side of the zinc selenide substrate (2), characterized in that: The film structure of the front cut-off filter (1) is: Base / W1(0.56N1.12L0.56N) a (0.43N0.86L0.43N) b W2 / Air W1 is the front matching layer, and its structure is: k1Nk2Lk3N, W2 is the post-matching layer, and its structure is: p1Np2Lp3Np4Lp5N, Where: index a is the first cutoff stack period number, a is 7 or 6; index b is the second cutoff stack period number, b is 6 or 5; N represents a zinc selenide film layer with an optical thickness of λ0 / 4, L represents an ytterbium fluoride film layer with an optical thickness of λ0 / 4, λ0 is the center wavelength, k1, k2, k3, p1, p2, p3, p4, and p5 are matching layer optical thickness coefficients; When a=7, b=6, the front matching layer is: 3.38N0.64L0.73N, and the rear matching layer is: 0.17N3.75L0.31N; When a=7, b=5, the front matching layer is: 5.45N0.75L0.55N, and the rear matching layer is: 0.27N1.07L1.34N1.58L0.35N; When a=6, b=6, the front matching layer is: 2.76N0.77L0.61N, and the rear matching layer is: 0.28N4.35L0.53N; When a=6 and b=5, the front matching layer is: 4.65N0.39L0.69N, and the rear matching layer is: 0.31N0.52L0.39N 3.93L0.28N.

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