A high-efficiency broadband long-wave spectrometric film with oblique incidence

Abstract

The application provides a kind of oblique incidence high-efficiency broadband long-wave light splitting film, the working angle of the light splitting film is 45°, the equivalent relationship of double-sided design and single-sided design under oblique incidence is established by numerical calculation, the target values of 45° single-sided transmittance and reflectivity are set, three kinds of refractive index alternating design methods are used for film system matching, the film system structure design optimization is completed, then the same film system is coated on the two sides of long-wave infrared substrate respectively, and the preparation of the light splitting film is realized. The purpose of the application is to realize the high-efficiency splitting of long-wave infrared window in the wavelength range of 7-12 μm with transmittance / reflectivity of 1:1 under 45° oblique incidence. The light splitting film has stable performance, small surface shape change and is suitable for optical systems such as imaging and detection.

Description

Technical Field

[0001] The present invention belongs to the field of thin film optical technology, and in particular relates to an oblique incidence high-efficiency broadband long-wavelength spectroscopic film technology, specifically a spectroscopic film that can achieve high-efficiency spectroscopic performance with a transmittance / reflectivity of 1:1 in the infrared window within the 7μm-12μm band at an incident angle of 45°. Background Art

[0002] Infrared optical systems play an important role in detection, remote sensing, laser applications and other fields. For multi-band composite optical test platforms, conventional single-wavelength spectroscopic films cannot meet the requirements of use, and a broadband spectroscopic solution must be adopted to reduce the complexity of the optical system, which places higher demands on the optical components in the optical system. Taking the surface shape change of optical components as an example, it will cause distortion of the transmitted light beam, which in severe cases will affect the practical application of precision optical components in optical systems. With the development of optical technology, optical systems have higher requirements for the performance of long-wave infrared spectroscopic films. We hope to have simple design and preparation while meeting high performance requirements such as small surface shape changes, high efficiency and reliability.

[0003] The most common design for existing beamsplitting films is to provide beam splitting on one side and broadband antireflection on the other. This requires the design and optimization of two film systems, and the structures of both the beamsplitting and broadband antireflection films are relatively complex. Furthermore, due to the significant structural differences between the two film systems, stress mismatches on both sides of the substrate can easily lead to significant surface shape variations, which in turn can cause distortion of the transmitted beam in the laser system. Furthermore, the choice of substrate material can significantly impact the performance of the optical system. KBr is commonly used as the substrate for long-wavelength broadband beamsplitting films, but this material is prone to moisture absorption and has poor environmental stability. In contrast, Ge and ZnSe substrates offer excellent mechanical strength and stability.

[0004] To address these issues, the present invention utilizes Ge and ZnSe, low-absorption, high-transparency long-wave infrared window substrates. Numerical calculations establish the equivalence between double-sided and single-sided designs under oblique incidence. Target values ​​for single-sided transmittance and reflectance at 45° are set, and a design method employing alternating high, medium, and low refractive indices is employed to optimize the film system design. The same film system is then deposited on both sides of the infrared window substrate to fabricate the spectroscopic film. This spectroscopic film offers advantages such as simple design, stable performance, and minimal surface shape variation. Summary of the Invention

[0005] The purpose of the present invention is to provide an oblique-incidence high-efficiency broadband long-wavelength spectroscopic film, particularly a film that can achieve a high-efficiency spectroscopic function with a transmittance / reflectivity of 1:1 in the long-wave infrared window within the 7μm-12μm band by optimizing a specific film structure design under a 45° incident angle and then coating the same film system on both sides of the substrate. The film has the advantages of simple design, stable performance, and small surface shape change.

[0006] The technical solution provided by the present invention is as follows:

[0007] The invention discloses an oblique-incidence high-efficiency broadband long-wavelength spectroscopic film. The film is characterized by setting target values ​​for transmittance and reflectance of a 45° single-sided design based on the equivalent relationship between a double-sided design and a single-sided design under oblique incidence, adopting a design method of alternating high, medium and low refractive indices for film system matching, completing design optimization based on an initial film system structure, and achieving a long-wavelength infrared window with a transmittance / reflectance ratio of 1:1 in the 7μm-12μm band under 45° oblique incidence. The initial film system structure is expressed as G / (a1Ha2Ma3L)^n a1H / A, where G is a substrate, H, M and L are materials of high, medium and low refractive index with an optical thickness of λ / 4, respectively, n is the number of film layer periods, a1, a2 and a3 are film layer thickness coefficients of the high, medium and low materials, respectively, and A is an air layer.

[0008] The film layer period number n is selected in the range of 1 to 10, and the film layer thickness coefficients a1, a2, and a3 are between 0.1 and 5.

[0009] The long-wave infrared window substrate is Ge or ZnSe.

[0010] The high refractive index material is Ge or PbTe.

[0011] The medium refractive index material is ZnS or ZnSe.

[0012] The low refractive index material is YF3, YbF3 or SrF2.

[0013] Compared with the prior art, the present invention has the following technical effects:

[0014] 1. Compared with the existing common design of splitting film, which has one side for splitting and the other side for broadband anti-reflection, it is necessary to design and optimize two film systems, and the film system structure is relatively complex. The present invention establishes the equivalent relationship between double-sided design and single-sided design under oblique incidence through numerical calculation, sets the target values ​​of single-sided transmittance and reflectance, and only needs to design and optimize one film system structure.

[0015] 2. The conventional solution of splitting light on one side and broadband anti-reflection on the other side is prone to cause significant changes in the substrate surface shape due to the large difference in the film structure of the two sides. The present invention reduces the complexity of the design while reducing the change in the substrate surface shape. It has the advantages of simple design, stable performance, and small surface shape change. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic structural diagram of an oblique-incidence high-efficiency broadband long-wavelength spectroscopic film according to the present invention.

[0017] Figure 2 This is a graph showing how the single-side transmittance and reflectance change with the incident angle in Example 1.

[0018] Figure 3 This is the optimal film structure of Example 1.

[0019] Figure 4 Spectral curves of double-sided transmittance and reflectance at an incident angle of 45° in Example 1.

[0020] Figure 5 This is a graph showing how the single-side transmittance and reflectance change with the incident angle in Example 2.

[0021] Figure 6 This is the optimal film structure of Example 2.

[0022] Figure 7 This is the double-sided transmittance and reflectance spectral curve at an incident angle of 45° in Example 2. DETAILED DESCRIPTION

[0023] The specific examples of the present invention are described in detail below with reference to the accompanying drawings.

[0024] Figure 1 The present invention discloses a high-efficiency, broadband, long-wavelength spectroscopic film for oblique incidence. Numerical calculations establish the equivalent relationship between double-sided and single-sided designs under oblique incidence. Target values ​​for single-sided transmittance and reflectance at 45° are set. A design method employing alternating high, medium, and low refractive indices is employed to match the film system. Design optimization is achieved based on the initial film system structure. The same film system is then deposited on both sides of a ZnSe substrate to fabricate the spectroscopic film. The initial film system structure is expressed as G / (a1Ha2Ma3L)^n a1H / A, where G represents the substrate, H, M, and L represent high, medium, and low refractive index materials with optical thicknesses of λ / 4, respectively. n represents the number of periods, a1, a2, and a3 represent the film thickness coefficients for the high, medium, and low materials, respectively. A represents the air layer.

[0025] Example 1

[0026] The design specifications of the infrared window film required by Example 1 are: achieving a range of 7 μm-12 μm, an incident angle of 45°, and a splitting ratio T:R=1:1 on the ZnSe window.

[0027] The specific design steps are as follows:

[0028] 1. According to the spectral characteristics of the target band, select long-wavelength broadband high-transmittance coating materials, high refractive index material Ge, medium refractive index material ZnS, and low refractive index material YbF3. The initial film structure is G / (HML)^2H / A, where H represents Ge with an optical thickness of one-quarter wavelength, M represents ZnS with an optical thickness of one-quarter wavelength, and L represents YbF3 with an optical thickness of one-quarter wavelength. The refractive index parameters of high refractive index material Ge, medium refractive index material ZnS, and low refractive index material YbF3 are all calculated by the Sellmeier formula The specific parameters are shown in Table 1.

[0029] Table 1: Refractive index parameters of high, medium and low refractive index materials in Example 1

[0030] <![CDATA[A1]]> <![CDATA[B1]]> <![CDATA[A2]]> <![CDATA[B2]]> Ge 14.9647 0.291572 -0.0155259 203.543 ZnS 3.98348 0.0387852 40.955 15956.9 <![CDATA[YbF3]]> 1.39173 -0.000332655 98.1245 13801.9

[0031] 2. At oblique incidence, the relationship between single-side transmittance and reflectance without obvious absorption is T 单 =1-R 单 , the relationship between the double-sided transmittance and the single-sided transmittance is T 双 =|T 单 | 2 , and the double-sided reflectivity can be expressed as R 双 =1-T 双 . According to the indicator requirement of the splitting ratio T:R=1:1 under 45° oblique incidence, it can be known that the target value of transmittance and reflectance after double-sided coating is 50%. Combined with the principle of multilayer film characteristics in reference materials such as "Modern Optical Films and Technologies", and through computer-assisted numerical calculations, the relationship between the single-side transmittance, reflectance and oblique incident angle at different incident angles is obtained, as shown in Table 2, and the change graphs of single-side transmittance and reflectance with incident angle are drawn accordingly, as shown in Table 2. Figure 2 shown.

[0032] Table 2: Relationship between single-side transmittance, reflectivity and oblique incidence angle in Example 1

[0033] 0° 15° 30° 45° 60° 75° <![CDATA[T 单 ]]> 66.66％ 66.68％ 66.48％ 65.53％ 62.45％ 56.21％ <![CDATA[R 单 ]]> 33.34％ 33.32％ 33.52％ 34.47％ 37.55％ 43.79％

[0034] 3. According to Table 2 or Figure 2The relationship between single-side transmittance and reflectance as a function of incident angle was determined. At an incident angle of 45°, the target transmittance in the 7μm-12μm mid-infrared band was 65.53% or the reflectance was 34.47%. The initial film structure was optimized using the simplex and simulated annealing parameters optimization algorithms in the film design software.

[0035] 4. The best design result is obtained through optimization, specifically G / 0.56H1.72M0.54L2.30H0.60M0.39L1.33H / A. The optimal membrane structure is as follows Figure 3 As shown in Figure 1, the number of film layers is 7, and the total film thickness is 1320nm. At an incident angle of 45°, the double-sided transmittance / reflectance spectrum curve of the ZnSe window film is as follows: Figure 4 shown.

[0036] Comparative Example 1

[0037] The difference between this comparative example and Example 1 is that the two film surfaces adopt 50% splitting and 100% high transmittance design schemes respectively. Optimization obtained the best design result. The 50% splitting film system structure is specifically G / 0.66H0.62M1.65L1.25H2.19M1.46L1.55H0.74M0.43L3.76H / A, with 10 film layers and a total film thickness of 2820nm. The 100% high transmittance film system structure is specifically G / 1.48H0.58M0.44L6.61H0.99M0.1L1.36H2.98M2.46L0.1H0.1M2.46L / A, with 12 film layers and a total film thickness of 3946nm. Compared with Example 1, the structures of the two film systems in this solution are more complex and have greater differences. The film thickness is 2 to 3 times the film thickness in Example 1, which can easily lead to larger surface shape changes and film quality problems.

[0038] Example 2

[0039] The design specifications of the infrared window film required by Example 2 are: achieving a range of 7 μm-12 μm on the Ge window, an incident angle of 45°, and a splitting ratio T:R=1:1.

[0040] The specific steps are as follows:

[0041] 1. According to the spectral characteristics of the target band, select long-wavelength broadband high-transmittance coating materials, high refractive index material Ge, medium refractive index material ZnS, and low refractive index material YbF3. The initial film structure is G / (HML)^2H / A, where H represents Ge with an optical thickness of one-quarter wavelength, M represents ZnS with an optical thickness of one-quarter wavelength, and L represents YbF3 with an optical thickness of one-quarter wavelength. The refractive index parameters of high refractive index material Ge, medium refractive index material ZnS, and low refractive index material YbF3 are all based on the Sellmeier formula. The specific parameters are shown in Table 3:

[0042] Table 3: Refractive index parameters of high, medium and low refractive index materials in Example 2

[0043] <![CDATA[A1]]> <![CDATA[B1]]> <![CDATA[A2]]> <![CDATA[B2]]> Ge 14.9647 0.291572 -0.0155259 203.543 ZnS 3.98348 0.0387852 40.955 15956.9 <![CDATA[YbF3]]> 1.39173 -0.000332655 98.1245 13801.9

[0044] 2. At oblique incidence, the relationship between single-side transmittance and reflectance without obvious absorption is T 单 =1-R 单 , the relationship between the double-sided transmittance and the single-sided transmittance is T 双 =|T 单 | 2 , and the double-sided reflectivity can be expressed as R 双 =1-T 双 . According to the indicator requirement of the splitting ratio T:R=1:1 under 45° inclined incidence, it can be known that the target value of transmittance and reflectance after double-sided coating is 50%. Combined with the principle of multilayer film characteristics in reference materials such as "Modern Optical Films and Technologies", and through computer-assisted numerical calculations, the relationship between the single-side transmittance, reflectance and oblique incident angle at different incident angles is obtained, as shown in Table 4, and the change graphs of single-side transmittance and reflectance with incident angle are drawn accordingly, as shown in Table 4. Figure 4 shown.

[0045] Table 4: Relationship between single-side transmittance, reflectivity and oblique incidence angle in Example 2

[0046] 0° 15° 30° 45° 60° 75° <![CDATA[T 单 ]]> 67.96％ 67.94％ 67.79％ 66.87％ 63.80％ 61.39％ <![CDATA[R 单 ]]> 32.04％ 32.06％ 32.21％ 33.13％ 36.20％ 38.61％

[0047] 3. According to Table 2 or Figure 2 The relationship between single-side transmittance and reflectance as a function of incident angle was determined. At an incident angle of 45°, the target transmittance in the 7μm-12μm mid-infrared band was 66.87% or the reflectance was 33.13%. The initial film structure was optimized using the simplex and simulated annealing parameters optimization algorithms in the film design software.

[0048] 4. The best design result is obtained through optimization, specifically G / 0.99H0.22M0.15L3.73H0.32M0.32L3.50H / A. The optimal membrane structure is as follows Figure 6 As shown, the number of film layers is 7. At an incident angle of 45°, the double-sided transmittance / reflectance spectrum curve of the Ge window film is as follows Figure 7 shown.

[0049] The above description is only a preferred example of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An oblique-incidence high-efficiency broadband long-wavelength spectroscopic film, characterized in that: Based on the equivalence between double-sided and single-sided designs under oblique incidence, target values ​​for transmittance and reflectance of the 45° single-sided design were set. A design method of alternating high, medium, and low refractive indices was used to match the film system. Based on the initial film system structure, design optimization was completed to achieve efficient spectral splitting with a transmittance / reflectance ratio of 1:1 in the 7μm-12μm band for the long-wave infrared window under 45° oblique incidence. The initial film system structure expression is G / (a1Ha2Ma3L)^n a1H / A, wherein G is the substrate, H, M, and L are high, medium, and low refractive index materials with optical thickness of λ / 4, respectively, n is the number of film layers, a1, a2, and a3 are thickness coefficients of the high, medium, and low film layers, respectively, and A is the air layer; the film system structure is G / 0.56H1.72M0.54L2.30H0.60M0.39L1.33H / A or G / 0.99H0.22M0.15L3.73H0.32M0.32L3.50H / A; the long-wave infrared window substrate is Ge or ZnSe; the high refractive index material is Ge or PbTe; the medium refractive index material is ZnS or ZnSe; and the low refractive index material is YF3, YbF3, or SrF2.

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