Shallow slot deep broadband all-dielectric reflection grating for middle and long wave infrared and preparation method thereof

Abstract

The application discloses a kind of middle-long wave infrared shallow slot deep broadband all-dielectric reflection grating and preparation method thereof, belong to the technical field of infrared optical device.The grating is composed of bottom grating film and top shallow slot deep diffraction grating, bottom grating film and top shallow slot deep diffraction grating cooperate and modulate Bloch mode reflection phase, and the diffraction efficiency of-1 level is higher than 99% in 3-14 μm wave band range.Preparation method includes: sequentially depositing functional film layer on substrate, and forming shallow slot deep grating structure by patterning etching.The application adopts the design of all-dielectric shallow slot deep grating, avoids the preparation difficulty of middle-long wave infrared diffraction grating, and has the performance of wide angular spectrum, ultra-wide band, high diffraction efficiency and high damage threshold.The application provides a solution to the preparation condition limitation of middle-long wave diffraction grating, accelerates the application of diffraction grating in middle-long wave infrared, and promotes the development of middle-long wave infrared high-energy laser spectrum beam combination system, ultra-short laser pulse compression and spectrometer system.

Description

Technical Field

[0001] The present invention relates to a medium- and long-wave infrared reflective diffraction grating in the application fields of high-energy lasers and spectrometers, in particular to a medium- and long-wave infrared shallow-groove deep-broadband all-dielectric reflective grating. Technical Background

[0002] As a "window to the atmosphere", the mid- and long-wave infrared covers the absorption spectra of a variety of molecules. Lasers in this band have important application value in infrared spectroscopy, infrared medical treatment, infrared countermeasures, atmospheric monitoring, infrared remote sensing, industrial gas detection and other fields. Diffraction gratings are core components in optical systems such as high-energy laser systems and spectrometers, and directly determine the performance of the entire optical system. However, most of the current research on diffraction gratings focuses on the short-wave infrared band, and research on mid- and long-wave infrared diffraction grating technology is relatively lacking. So far, some diffraction gratings used in the mid- and long-wave infrared are based on metal coating structures. However, due to the inherent absorption characteristics of metal gratings, not only is the highest diffraction efficiency limited to below 95%, but in 2014, the highest diffraction efficiency of gratings prepared by gold and alumina coatings at Pennsylvania State University in the United States was 92%, and the theoretical maximum value was only 94.2% [Prior technology 1: Chen TB, Liu B, McCoy JA, et al. Optical Materials Express, 2024, 14(5): 1336-1348.]. In addition, the heat absorbed by the metal greatly reduces the laser damage threshold, making it difficult for the final laser output power to reach a high level, and the service life of the diffraction grating is also severely limited.

[0003] In the application of short-wave infrared, diffraction gratings are usually designed with lossless all-dielectric materials to improve diffraction efficiency (>99%) and high laser damage threshold. There are also some studies on medium- and long-wave infrared dielectric gratings. However, in the medium- and long-wave infrared bands, due to the wavelength effect, the dielectric film thickness and the dielectric grating groove depth will increase. Since the grating design groove depth is relatively deep, it is limited by current process conditions and cannot be actually prepared. Many studies remain at the theoretical and design stages. In 2022, the Changchun Institute of Optics and Precision Mechanics used Si and SiO2 as the top grating material for the first time to design a high diffraction efficiency reflective all-dielectric grating for 4.7 microns [Prior Art 2: Wang Y, Fu X, Chen Y, et al. Micromachines, 2022, 13(4): 632.]. The ratio of the working grating groove depth to the wavelength is 0.123, which is comparable to that of short-wave gratings and falls within the design range of conventional gratings. If extended to the long-wave band, the design will fail due to the difficulty of preparation. In 2024, Tongji University designed an all-dielectric reflective diffraction grating for the 9.3-9.6 μm band using germanium as the top grating material [Prior Art 3: Zhou S, Dong S, He T, et al. Micromachines, 2024, 15(4): 538.] However, due to the grating groove depth of 2.5 μm, the existing preparation process cannot meet the preparation requirements of this grating. Although there are also studies on sample preparation [Prior Art 4: Zhu J, Zhou S, He T, et al. Nanophotonics, 2025(0).], this work is based on non-periodic gratings, and the processing tolerance is very small, resulting in low diffraction efficiency and narrow bandwidth in actual testing, which cannot meet the application requirements of high-energy lasers and other fields.

[0004] Based on this, due to the stringent requirements on the preparation conditions of the mid- and long-wave infrared all-dielectric deep-groove deep diffraction grating, the current mainstream diffraction grating used in the mid- and long-wave infrared band is still the metal-coated grating. There is currently no report on the successful preparation of mid- and long-wave high-efficiency infrared all-dielectric diffraction grating. The design of shallow-groove deep diffraction grating can circumvent the shortcomings of the process and accelerate the preparation and application of the mid- and long-wave infrared diffraction grating. Summary of the Invention

[0005] The purpose of the present invention is to circumvent the difficulties in designing and preparing medium-wave infrared all-dielectric diffraction gratings, provide a broadband all-dielectric shallow-groove deep-reflective diffraction grating for the medium and long-wave infrared, and a preparation method thereof, thereby filling the research gap in medium and long-wave all-dielectric diffraction gratings. The diffraction grating has a shallow-groove deep grating structure that is easy to prepare, uses all-dielectric materials, has the characteristics of low absorption and high laser damage threshold, has a -1 order diffraction efficiency in the operating band greater than 99%, and has a large operating angular spectrum range. Therefore, the diffraction grating has important practical value in medium and long-wave infrared high-power spectral beam combining technology and chirped pulse amplification and compression technology. In addition, this type of diffraction grating can also be used in spectrometers.

[0006] The technical solution of the present invention is to provide a shallow-groove deep broadband all-dielectric reflective grating for mid- and long-wave infrared, which is composed of a bottom grating film and a top shallow-groove deep diffraction grating. The bottom grating film and the top shallow-groove deep diffraction grating jointly modulate the reflection phase of the Bloch mode propagating in the grating, achieving a -1 order diffraction efficiency higher than 99% within the effective working band of 3-14μm.

[0007] The top shallow groove deep diffraction grating has a grating ridge structure profile that is determined by a single amplitude grating profile function y(x; d,Λ,α,β)=d(1-{1-[sin 2 (πx / Λ)] α} β ), wherein α and β are real numbers and α≥1, β≥1, Λ and d are grating period and groove depth respectively, and 14 μm>Λ>1.5 μm, 1 μm>d>50 nm, the grating duty cycle f is 0.2-0.8, and the ratio of the groove depth d to the operating wavelength λ is less than 0.05;

[0008] The top shallow groove deep diffraction grating adopts a low-absorption, high-refractive-index dielectric material, preferably a single layer of germanium (Ge) or a multilayer structure of alternately deposited germanium and ytterbium fluoride (Ge / YbF3).

[0009] The bottom grating film is composed of a multilayer dielectric structure with low expansion, high thermal conductivity and low absorption. Its reflectivity is higher than 99% within the incident angle range of 0-89° and the effective working band range of 3-14μm. Its layered structure includes a substrate, a high-reflection film stack, a phase matching layer and an etching residual layer from bottom to top.

[0010] The substrate is made of a low expansion, high thermal conductivity material, preferably fused quartz, diamond or silicon carbide.

[0011] The highly reflective film stack is a multilayer film structure comprising two or more materials. The optical thickness of a single film layer does not exceed one-quarter of the operating wavelength, providing a reflectivity higher than 99%. The film system structure is preferably, but not limited to, the following structures:

[0012] Regular periodic film system: high refractive index material layers and low refractive index material layers are alternately composed with a fixed period and thickness;

[0013] Irregular film system: It is composed of alternating layers of high refractive index material and low refractive index material, in which the thickness of at least some of the material layers varies non-periodically;

[0014] Composite film system: comprising a regular periodic film system and at least one medium refractive index material layer, wherein the medium refractive index material layer is combined with the regular periodic film system in one of the following ways:

[0015] Insertion type: embedding a medium refractive index material layer in a regular periodic sequence;

[0016] Terminal type: adding a medium refractive index material layer at the end of the regular periodic stack;

[0017] Hybrid: Multiple layers of medium refractive index material are inserted into a periodic sequence according to a predetermined pattern;

[0018] The high refractive index material is preferably germanium (Ge) or silicon (Si), the low refractive index material is preferably silicon dioxide (SiO2) or ytterbium fluoride (YbF3), and the medium refractive index material is preferably zinc selenide (ZnSe) or zinc sulfide (ZnS).

[0019] The phase matching layer is a one-layer or multi-layer structure that modulates the reflection phase of the top shallow groove deep diffraction grating. The material is preferably at least one of germanium (Ge), silicon dioxide (SiO2), ytterbium fluoride (YbF3), barium fluoride (BaF2) or zinc selenide (ZnSe), and the thickness of each layer is less than 1.5μm.

[0020] The etching residual layer and the top shallow groove deep diffraction grating are made of the same material to increase the preparation tolerance of the grating, and the thickness is less than 1.5 μm.

[0021] The present invention also provides a method for preparing a medium- and long-wave infrared shallow groove deep broadband all-dielectric reflective grating, which mainly comprises the following steps:

[0022] (1) depositing a high-reflection film stack, a phase matching layer, an etching residual layer, and a grating layer to be etched on a grating substrate in sequence;

[0023] (2) forming a photoresist patterned mask structure on the surface of the grating layer to be etched;

[0024] (3) etching using the mask structure as a barrier layer until the target groove depth is reached to form a top-layer shallow groove deep diffraction grating;

[0025] (4) Residual photoresist mask is removed to obtain a reflective diffraction grating consisting of a bottom grating film containing a substrate, a high-reflection film stack, a phase matching layer, an etched residual layer, and a top shallow-groove deep diffraction grating. The grating has a first-order diffraction efficiency exceeding 99% in the 3-14 μm band.

[0026] Compared with the prior art, the present invention has the following beneficial technical effects:

[0027] The groove depth of the top diffraction grating structure of the present invention is preferably less than 1 μm, and the ratio of the groove depth to the used wavelength is controlled below 0.05, which avoids the difficulties in the preparation of medium and long wave infrared and accelerates the application of diffraction gratings in medium and long wave infrared.

[0028] The diffraction grating of the present invention adopts low-loss all-dielectric material, overcomes the absorption characteristics of the material, and has a high damage threshold and high diffraction efficiency.

[0029] The -1 order diffraction efficiency of the present invention within the use band is higher than 99%, and the invention has a larger use angular spectrum range.

[0030] The invention has the characteristics of broadband, high diffraction efficiency and easy preparation, and has important practical prospects in the fields of medium- and long-wave infrared high-energy laser spectral beam combining, pulse compression and spectrometers. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural cross-sectional view of the present invention for the medium and long wave infrared shallow groove deep broadband all-dielectric reflection grating.

[0032] Figure 2 It is a cross-sectional view of the design structure of Example 1 and Example 2.

[0033] Figure 3 This is a graph showing the relationship between the reflectivity of the bottom grating film of Example 1 and the wavelength and incident angle under TE polarization incidence conditions in the operating band within the range of 4300nm to 4600nm.

[0034] Figure 4 This is a graph showing the relationship between the phase difference between two Bloch modes propagating in the grating at the central wavelength and the grating groove depth in Example 1.

[0035] Figure 5 This is a graph showing the relationship between the diffraction efficiency of the diffraction grating and the wavelength under the TE polarization incident condition in the wavelength range of 4300nm to 4600nm used in Example 1.

[0036] Figure 6 This is a graph showing the relationship between the reflectivity of the bottom grating film of Example 2 and the wavelength and incident angle under the condition of TE polarization incidence in the operating band within the range of 8300nm to 8700nm.

[0037] Figure 7This is a graph showing the relationship between the phase difference between two Bloch modes propagating in the grating at the central wavelength and the grating groove depth in Example 2.

[0038] Figure 8 This is a graph showing the relationship between the diffraction efficiency of the diffraction grating and the wavelength under the TE polarization incident condition in the wavelength range of 8300nm to 8700nm used in Example 2.

[0039] Figure 9 This is a graph showing the relationship between the reflectivity of the bottom grating film of Example 3 and the wavelength and incident angle under the condition of TE polarization incidence in the operating band within the range of 12000nm to 12500nm.

[0040] Figure 10 This is a graph showing the relationship between the phase difference between two Bloch modes propagating in the grating at the central wavelength and the grating groove depth in Example 3.

[0041] Figure 11 This is a graph showing the relationship between the diffraction efficiency of the diffraction grating and the wavelength under the TE polarization incident condition in the wavelength range of 12000nm to 12500nm used in Example 3.

[0042] Figure 12 It is a cross-sectional view of the design structure of Example 4.

[0043] Figure 13 This is a graph showing the relationship between the reflectivity of the bottom grating film of Example 4 and the wavelength and incident angle under the condition of TM polarized incidence in the operating band within the range of 8300nm to 8700nm.

[0044] Figure 14 This is a graph showing the relationship between the phase difference between two Bloch modes propagating in the grating at the central wavelength and the grating groove depth in Example 4.

[0045] Figure 15 This is a graph showing the relationship between the diffraction efficiency of the diffraction grating and the wavelength under the condition of TM polarization incidence in the wavelength range of 8300nm to 8700nm used in Example 4. DETAILED DESCRIPTION

[0046] The following further illustrates the embodiments of the present invention in conjunction with the examples and drawings, but this should not limit the scope of protection of the present invention.

[0047] See also Figure 1 , Figure 1This is a structural cross-sectional diagram of the mid- and long-wave infrared shallow-groove deep broadband all-dielectric reflective diffraction grating of the present invention. As can be seen from the figure, the mid- and long-wave infrared broadband all-dielectric reflective diffraction grating of the present invention is composed of a bottom grating film 1 and a top shallow-groove deep diffraction grating 2. The bottom grating film and the top shallow-groove deep diffraction grating jointly modulate the Bloch mode reflection phase propagating in the grating, achieving a -1 order diffraction efficiency of higher than 99% within the effective working band of 3-14μm.

[0048] The top shallow groove deep diffraction grating has a grating ridge structure profile that is determined by a single amplitude grating profile function y(x; d,Λ,α,β)=d(1-{1-[sin 2 (πx / Λ)] α} β ), wherein α and β are real numbers and α≥1, β≥1, Λ and d are grating period and groove depth respectively, and 14 μm>Λ>1.5 μm, 1 μm>d>50 nm, the grating duty cycle f is 0.2-0.8, and the ratio of the groove depth d to the operating wavelength λ is less than 0.05;

[0049] The top shallow groove deep diffraction grating is made of low absorption, high refractive index dielectric material, including but not limited to Ge single layer or Ge / SiO2 multilayer combination structure.

[0050] The bottom grating film 1 is composed of a multilayer dielectric structure with low expansion, high thermal conductivity, and low absorption. The reflectivity is higher than 99% within an incident angle range of 0-89° and an ultra-wide bandwidth. The structure includes, from bottom to top, a substrate 3, a high-reflection film stack 4, a phase matching layer 5, and an etched residual layer 6.

[0051] The substrate 3 is made of a material with low expansion and high thermal conductivity, preferably fused quartz, diamond or silicon carbide.

[0052] The highly reflective film stack 4 is a multilayer film structure, comprising two or more materials. The optical thickness of a single film does not exceed one-quarter of the operating wavelength, providing a reflectivity higher than 99%. The film system structure is preferably, but not limited to, the following structures:

[0053] Regular periodic film system: high refractive index material layers and low refractive index material layers are alternately composed with a fixed period and thickness;

[0054] Irregular film system: It is composed of alternating layers of high refractive index material and low refractive index material, in which the thickness of at least some of the material layers varies non-periodically;

[0055] Composite film system: comprising a regular periodic film system and at least one medium refractive index material layer, wherein the medium refractive index material layer is combined with the regular periodic film system in one of the following ways:

[0056] Insertion type: embedding a medium refractive index material layer in a regular periodic sequence;

[0057] Terminal type: adding a medium refractive index material layer at the end of the regular periodic stack;

[0058] Hybrid: Multiple layers of medium refractive index material are inserted into a periodic sequence according to a predetermined pattern;

[0059] The high refractive index material is preferably Ge or Si, the low refractive index material is preferably SiO2 or YbF3, and the medium refractive index material is preferably ZnSe or ZnS.

[0060] The phase matching layer is a one-layer or multi-layer structure that modulates the reflection phase of the top shallow groove deep diffraction grating. The material is preferably at least one of Ge, SiO2, YbF3, BaF2 or ZnSe, and the thickness of each layer is less than 1.5μm.

[0061] The etching residual layer and the top shallow groove deep diffraction grating are made of the same material to increase the preparation tolerance of the grating, and the thickness is less than 1.5 μm.

[0062] The above-mentioned method for preparing a shallow-groove, deep, broadband all-dielectric reflective grating for the medium and long-wave infrared comprises first depositing a high-reflection film stack 4, a phase-matching layer 5, an etching residual layer 6, and a grating layer to be etched on a grating substrate 3 in sequence, then forming a photoresist patterned mask structure on the surface of the grating layer to be etched, and then etching with the mask structure as a barrier layer until the target groove depth is reached to form a top shallow-groove, deep diffraction grating 2; finally, removing the residual photoresist mask to obtain a reflective diffraction grating consisting of a bottom grating film 1 containing a substrate 3, a high-reflection film stack 4, a phase-matching layer 5, and an etching residual layer 6, and a top shallow-groove, deep diffraction grating 2, wherein the grating has a -1 order diffraction efficiency exceeding 99% in the 3-14 μm band.

[0063] Figure 1 This is a cross-sectional diagram of the structure of the shallow-groove, deep-band, all-dielectric reflective diffraction grating used in the mid- and long-wave infrared (WIR) spectrum. For TE-polarized incident light, the electric field vector's vibration direction is perpendicular to the plane of incidence, while for TM-polarized incident light, the electric field vector's vibration direction lies within the plane of incidence. As can be seen, both the incident medium above the grating and the medium within the grating grooves are air. When light enters the grating surface from air, the top shallow-groove, deep-diffraction grating layer and the bottom grating film modulate the Bloch mode phase, resulting in highly efficient emission of diffracted light.

[0064] The present invention uses simplified mode theory to calculate the effective refractive index of the Bloch mode propagating within the grating. The transmission phase of the Bloch mode and the transmission phase difference between the two Bloch modes supporting propagation within the grating are calculated using a transmission matrix. When the transmission phase difference between the two Bloch modes supporting propagation within the grating is close to π (the difference from π is less than 0.5π), the designed grating meets the high diffraction efficiency condition. Furthermore, the present invention uses rigorous coupled-wave theory to calculate the -1 order diffraction efficiency of a mid- and long-wave infrared broadband all-dielectric reflective diffraction grating. Using a genetic algorithm, the structural parameters of the bottom grating film and the top shallow-groove deep diffraction grating of the mid- and long-wave infrared shallow-groove deep broadband all-dielectric reflective diffraction grating are optimized. The conclusion is that for shallow-groove deep gratings, high -1 order diffraction efficiency of incident light can be achieved within a larger processing tolerance, a larger range of incident angles, and a wider bandwidth.

[0065] Example 1:

[0066] In such Figure 2 In the grating structure shown, 2 is a top shallow-groove deep diffraction grating, the grating period Λ is 3333.3nm, the grating groove depth d is 115nm, the grating duty cycle f is 0.382, the etched residual layer 6 has a thickness d1 of 30nm and is made of germanium, the phase matching layer 5 has a thickness d2 of 346nm and is made of silicon dioxide, and the high reflective structure composed of the grating substrate 3 and the periodic film system 4 is S|(HL) m H, H and L are respectively the high refractive index material layer and the low refractive index material layer, S is the grating substrate layer, the material is fused silica, the periodic film system high refractive index material is Ge, the thickness is 278.1nm, the periodic film system low refractive index material is SiO2, the thickness is 794.6nm, m is the number of film periods and m=3; the coupling output angle θ=41.87° (corresponding to the Littrow angle at a central wavelength of 4450nm). Figure 3 As shown in FIG, the reflectivity of the grating film before etching is higher than 99% within the operating bandwidth within the angular spectrum range of 0-89°. Figure 4 As shown in , the phase difference between the two Bloch modes propagating in the grating has a value close to π when the groove depth is shallow, and the corresponding groove depth is basically consistent with the designed grating groove depth. Figure 5 As shown, in the wavelength range of 4300nm to 4600nm, the minimum value of the -1 order diffraction efficiency of the grating TE polarization exceeds 99.5%, and the peak value of the diffraction efficiency exceeds 99.9%.

[0067] Preparation of the above-mentioned medium- and long-wave infrared shallow groove deep broadband all-dielectric reflective diffraction grating. First, a high-reflection film stack 4, a phase matching layer 5, an etching residue layer 6, and a grating layer to be etched are sequentially deposited on a grating substrate 1 with dimensions of 50mm*50mm*1.5mm using electron beam evaporation and ion-assisted deposition techniques. A layer of 600nm thick photoresist is spin-coated on the surface of the deposited film layer at a speed of 3800 rpm using a spin coating device. The layer is then baked at 100°C for 2 minutes. The coated photoresist is then exposed using a holographic interference exposure method with an exposure power of 110μW. The exposed sample was exposed for 300 seconds, and then developed with a 1.6% sodium hydroxide solution to obtain a photoresist mask structure. Subsequently, a reactive ion beam etcher was used to perform etching using the photoresist mask structure as a barrier layer until the target groove depth was reached, forming a top shallow-groove deep diffraction grating 2. Finally, the residual photoresist mask was removed to obtain a reflective diffraction grating consisting of a bottom grating film 1 containing a substrate 3, a highly reflective film stack 4, a phase matching layer 5, and an etched residual layer 6, and a top shallow-groove deep diffraction grating 2.

[0068] Example 2:

[0069] In such Figure 2 In the grating structure shown, in this embodiment 2, the grating layer has a grating period Λ of 6250 nm, a grating groove depth d of 226.8 nm, a grating duty cycle f of 0.35, a thickness d1 of the etched residual layer 6 of 25.9 nm, and a material thereof is germanium. The thickness d2 of the phase matching layer 5 is 891.4 nm, and a material thereof is ytterbium fluoride. The high reflective structure formed by the grating substrate 3 and the periodic film system 4 is S|(HL). m H, H and L are high refractive index material layer and low refractive index material layer respectively, S is the grating substrate layer, the material is fused silica, the periodic film system high refractive index material is germanium, the thickness is 673nm, the periodic film system low refractive index material is ytterbium fluoride, the thickness is 900nm, m is the number of film periods and m=3; the coupling output angle θ=37.25° (corresponding to the Littrow angle at the central wavelength of 8500nm). Figure 6 As shown in FIG, the reflectivity of the grating film before etching is higher than 99% within the operating bandwidth within the angular spectrum range of 0-89°. Figure 7 As shown in , the phase difference between the two Bloch modes propagating in the grating has a value close to π when the groove depth is shallow, and the corresponding groove depth is basically consistent with the designed grating groove depth. Figure 8 As shown, in the wavelength range of 8300nm to 8700nm, the minimum value of the -1 order diffraction efficiency of the grating TE polarization exceeds 99.4%, and the peak value of the diffraction efficiency exceeds 99.7%.

[0070] Preparation of the above-mentioned medium- and long-wave infrared shallow groove deep broadband all-dielectric reflective diffraction grating. First, a high-reflection film stack 4, a phase matching layer 5, an etching residue layer 6, and a grating layer to be etched are sequentially deposited on a grating substrate 1 with dimensions of 50mm*50mm*1.5mm using electron beam evaporation and ion-assisted deposition techniques. A layer of 600nm thick photoresist is spin-coated on the surface of the deposited film layer at a speed of 3800 rpm using a spin coating device. The layer is then baked at 100°C for 2 minutes. The coated photoresist is then exposed using a holographic interference exposure method with an exposure power of 110μW. The exposed sample was exposed for 300 seconds, and then developed with a 1.6% sodium hydroxide solution to obtain a photoresist mask structure. Subsequently, a reactive ion beam etcher was used to perform etching using the photoresist mask structure as a barrier layer until the target groove depth was reached, forming a top shallow-groove deep diffraction grating 2. Finally, the residual photoresist mask was removed to obtain a reflective diffraction grating consisting of a bottom grating film 1 containing a substrate 3, a highly reflective film stack 4, a phase matching layer 5, and an etched residual layer 6, and a top shallow-groove deep diffraction grating 2.

[0071] Example 3:

[0072] In such Figure 2 In the grating structure shown, in this embodiment 2, the grating layer has a grating period Λ of 8696 nm, a grating groove depth d of 320.3 nm, a grating duty cycle f of 0.3045, a thickness d1 of the etched residual layer 6 of 50 nm, and a material of germanium; a thickness d2 of the phase matching layer 5 of 1200 nm, and a material of barium fluoride; and a high reflective structure composed of the grating substrate 3 and the periodic film system 4 is S|(HL). m H, H and L are respectively the high refractive index material layer and the low refractive index material layer, S is the grating base layer, the material is fused silica, the periodic film system high refractive index material is germanium, the thickness is 1103.8nm, the periodic film system low refractive index material is barium fluoride, the thickness is 1400nm, m is the number of film periods and m=3; the coupling output angle θ=44.77° (corresponding to the Littrow angle at a central wavelength of 12250nm). Figure 9 As shown in FIG, the reflectivity of the grating film before etching is higher than 99% within the operating bandwidth within the angular spectrum range of 0-89°. Figure 10 As shown in , the phase difference between the two Bloch modes propagating in the grating has a value close to π when the groove depth is shallow, and the corresponding groove depth is basically consistent with the designed grating groove depth. Figure 11 As shown, in the wavelength range of 12000nm to 12500nm, the minimum value of the -1 order diffraction efficiency of the grating TE polarization exceeds 99.67%, and the peak value of the diffraction efficiency exceeds 99.79%.

[0073] Preparation of the above-mentioned medium- and long-wave infrared shallow groove deep broadband all-dielectric reflective diffraction grating. First, a high-reflection film stack 4, a phase matching layer 5, an etching residue layer 6, and a grating layer to be etched are sequentially deposited on a grating substrate 1 with dimensions of 50mm*50mm*1.5mm using electron beam evaporation and ion-assisted deposition techniques. A layer of 600nm thick photoresist is spin-coated on the surface of the deposited film layer at a speed of 3800 rpm using a spin coating device. The layer is then baked at 100°C for 2 minutes. The coated photoresist is then exposed using a holographic interference exposure method with an exposure power of 110μW. The exposed sample was exposed for 300 seconds, and then developed with a 1.6% sodium hydroxide solution to obtain a photoresist mask structure. Subsequently, a reactive ion beam etcher was used to perform etching using the photoresist mask structure as a barrier layer until the target groove depth was reached, forming a top shallow-groove deep diffraction grating 2. Finally, the residual photoresist mask was removed to obtain a reflective diffraction grating consisting of a bottom grating film 1 containing a substrate 3, a highly reflective film stack 4, a phase matching layer 5, and an etched residual layer 6, and a top shallow-groove deep diffraction grating 2.

[0074] Example 4:

[0075] In such Figure 12 In the grating structure shown, in Example 2, the grating layer has a grating period Λ of 5586.7 nm, a grating groove depth d of 394 nm, a grating duty cycle f of 0.837, an etched residual layer 6 with a thickness d1 of 882.1 nm and made of germanium, a first phase matching layer 51 made of ytterbium fluoride with a thickness d2 of 750.18 nm, a second phase matching layer 52 made of zinc selenide with a thickness d3 of 100 nm, and a high reflective structure formed by the grating substrate 3 and the periodic film system 4 is S|BHB (LBHB). m , H and L are respectively a high refractive index material layer and a low refractive index material layer, B is a medium refractive index material layer with a refractive index between the high refractive index material and the low refractive index material, the material is zinc selenide, the thickness is 100nm, S is the grating base layer, the material is fused silica, the periodic film system high refractive index material is germanium, the thickness is 617.8nm, the periodic film system low refractive index material is ytterbium fluoride, the thickness is 1000nm, m is the film period number and m=3; the coupling output angle θ=50°. Figure 13 As shown in FIG, the reflectivity of the grating film before etching is higher than 99% within the operating bandwidth within the angular spectrum range of 0-89°. Figure 14 As shown in , the phase difference between the two Bloch modes propagating in the grating has a value close to π when the groove depth is shallow, and the corresponding groove depth is basically consistent with the designed grating groove depth. Figure 15 As shown, in the wavelength range of 8300nm to 8700nm, when TM polarization is incident, the highest diffraction efficiency within the used bandwidth is 99.47%, and the bandwidth average diffraction efficiency is 99.52%.

[0076] Preparation of the above-mentioned medium- and long-wave infrared shallow groove deep broadband all-dielectric reflective diffraction grating. First, a high-reflection film stack 4, a phase matching layer 5, an etching residue layer 6, and a grating layer to be etched are sequentially deposited on a grating substrate 1 with dimensions of 50mm*50mm*1.5mm using electron beam evaporation and ion-assisted deposition techniques. A layer of 600nm thick photoresist is spin-coated on the surface of the deposited film layer at a speed of 3800 rpm using a spin coating device. The layer is then baked at 100°C for 2 minutes. The coated photoresist is then exposed using a holographic interference exposure method with an exposure power of 110μW. The exposed sample was exposed for 300 seconds, and then developed with a 1.6% sodium hydroxide solution to obtain a photoresist mask structure. Subsequently, a reactive ion beam etcher was used to perform etching using the photoresist mask structure as a barrier layer until the target groove depth was reached, forming a top shallow-groove deep diffraction grating 2. Finally, the residual photoresist mask was removed to obtain a reflective diffraction grating consisting of a bottom grating film 1 containing a substrate 3, a highly reflective film stack 4, a phase matching layer 5, and an etched residual layer 6, and a top shallow-groove deep diffraction grating 2.

[0077] In summary, the present invention is used for a shallow-groove, deep-band, all-dielectric reflective diffraction grating for the mid- and long-wave infrared. It adopts a shallow-groove, deep grating and an all-dielectric structure, and has the characteristics of ultra-wideband, high diffraction efficiency, and high damage threshold. It circumvents the difficulties in preparing mid-infrared diffraction gratings and accelerates the application of diffraction gratings in the mid-infrared band. In particular, it can meet the requirements of high-energy laser systems and spectrometer systems for diffraction gratings with high laser damage thresholds and broadband and high diffraction efficiency.

Claims

1. A shallow-groove, deep-band, all-dielectric reflective grating for mid- and long-wave infrared, characterized in that: The invention is composed of a bottom grating film (1) and a top shallow groove deep diffraction grating (2), wherein the bottom grating film (1) and the top shallow groove deep diffraction grating (2) jointly modulate the reflection phase of the Bloch mode propagating in the grating, and achieve a -1 order diffraction efficiency higher than 99% within the effective working band of 3-14 μm; The top shallow groove deep diffraction grating (2) adopts a low absorption, high refractive index dielectric material, and its grating ridge structure profile is composed of a single amplitude grating profile function Description, where and is a real number and , and The grating period and groove depth are 14 μm and >1.5μm, 1μm > >50nm, grating duty cycle The groove depth is 0.2-0.8 The ratio to the working wavelength λ is less than 0.05; The bottom grating film (1) is composed of a multilayer dielectric structure with low expansion, high thermal conductivity and low absorption, and has a reflectivity higher than 99% within an incident angle of 0-89° and an effective working band of 3-14 μm. The layered structure comprises, from bottom to top, a substrate (3), a high-reflection film stack (4), a phase matching layer (5) and an etching residual layer (6).

2. The shallow groove deep broadband all-dielectric reflective grating for mid- and long-wave infrared according to claim 1, characterized in that: The top shallow groove deep diffraction grating (2) structure is selected from a Ge single layer structure or a Ge / YbF3 alternately deposited multilayer structure.

3. The shallow groove deep broadband all-dielectric reflective grating for mid- and long-wave infrared according to claim 1, characterized in that: The substrate (3) is made of a low expansion, high thermal conductivity material.

4. The shallow-groove, deep-band, all-dielectric reflective grating for mid- and long-wave infrared according to claim 3, characterized in that: The low expansion, high thermal conductivity material is selected from fused silica, diamond or silicon carbide.

5. The shallow groove deep broadband all-dielectric reflection grating for mid- and long-wave infrared according to claim 1, characterized in that: The high reflective film stack (4) is a multilayer film structure, comprising two or more materials, the optical thickness of a single film does not exceed one quarter of the working wavelength, and provides a reflectivity higher than 99%, and the film system structure is selected from one of the following structures: a regular periodic film system: a high refractive index material layer and a low refractive index material layer are alternately composed with a fixed period and thickness; an irregular film system: a high refractive index material layer and a low refractive index material layer are alternately composed, wherein the thickness of at least some of the material layers is non-periodic; a composite film system: comprising a regular periodic film system and at least one medium refractive index material layer, wherein the medium refractive index material layer is combined with the regular periodic film system in one of the following ways: Insertion type: embedding a medium refractive index material layer in a regular periodic sequence; Terminal type: adding a medium refractive index material layer at the end of the regular periodic stack; Hybrid: Multiple layers of medium refractive index material are inserted in a periodic sequence according to a predetermined pattern.

6. The shallow groove deep broadband all-dielectric reflective grating for mid- and long-wave infrared according to claim 5, characterized in that: The high refractive index material is selected from Ge or Si, the low refractive index material is selected from SiO2 or YbF3, and the medium refractive index material is selected from ZnSe or ZnS.

7. The shallow groove deep broadband all-dielectric reflection grating for mid- and long-wave infrared according to claim 1, characterized in that: The phase matching layer (5) is a one-layer or multi-layer structure, modulating the reflection phase of the top shallow groove deep diffraction grating, and the thickness of a single layer is less than 1.5 μm.

8. The shallow groove deep broadband all-dielectric reflective grating for mid- and long-wave infrared according to claim 7, characterized in that: The phase matching layer (5) is made of a material selected from Ge, SiO2, YbF3, BaF2 or ZnSe.

9. The shallow groove deep broadband all-dielectric reflective grating for mid- and long-wave infrared according to claim 1, characterized in that: The etching residual layer (6) and the top shallow groove deep diffraction grating (2) are made of the same material, and are used to increase the preparation tolerance of the grating, and the thickness is less than 1.5 μm.

10. A method for preparing a shallow groove, deep broadband all-dielectric reflective grating for mid- and long-wave infrared according to any one of claims 1 to 9, characterized in that: The main steps include: S1: depositing a high-reflection film stack (4), a phase matching layer (5), an etching residual layer (6), and a grating layer to be etched on a grating substrate (3) in sequence; S2: forming a photoresist patterned mask structure on the surface of the grating layer to be etched; S3: etching with the mask structure as a barrier layer until the target groove depth is reached, thereby forming a top-layer shallow groove deep diffraction grating (2); S4: Residual photoresist mask is removed to obtain a reflective diffraction grating consisting of a bottom grating film (1) containing a substrate (3), a high-reflection film stack (4), a phase matching layer (5), an etched residual layer (6), and a top shallow-groove deep diffraction grating (2). The grating has a first-order diffraction efficiency exceeding 99% in the 3-14 μm band.

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