Design method of high-efficiency broadband multilayer film blazed grating with constant focusing factor

Abstract

The invention relates to a method for designing a high-efficiency broadband multilayer film blazed grating with a constant focusing factor, and the method comprises the following steps: selecting a material combination of a non-periodic multilayer film according to a target wave band and the focusing factor of the broadband multilayer film grating, and determining a change relation of an incident angle with incident energy when the focusing factor is constant; determining a corresponding film thickness range of the broadband multilayer film grating under the target wave band and the focusing factor under each grating diffraction order, and matching according to the film thickness range to obtain a grating blaze angle for suppressing the non-working grating diffraction order; according to Bragg conditions of the multilayer film and the multilayer film grating, determining a target wave band and a film thickness range when the broadband multilayer film is optimized, and obtaining an optimized broadband multilayer film; and combining the optimized broadband multilayer film with a grating blazed angle for inhibiting a non-working diffraction order to obtain the high-efficiency broadband multilayer film blazed grating with a constant focusing factor in a target wave band. Compared with the prior art, the diffraction efficiency of the grating in the focusing factor constant mode is improved.

Description

Technical Field

[0001] The present invention relates to the field of diffraction grating design, and more particularly to a design method for a high-efficiency broadband multilayer blazed grating with a constant focusing factor. Background Art

[0002] X-rays cover a large number of elemental absorption edges. X-ray spectroscopy detection is an important experimental technique based on synchrotron radiation and free electron laser devices, providing a powerful detection means for the development of multiple disciplines such as astronomy, energy chemistry, life science, and environmental science. X-ray spectroscopy detection relies on optical systems such as monochromators and spectrometers, and the dispersive element is the core element in the system, and its diffraction efficiency has an important impact on the photon flux of the system. As a commonly used dispersive element, the single-layer film grating has now been widely used in soft X-ray monochromators and spectrometers. However, in the X-ray energy range above 1 keV, the diffraction efficiency of the traditional single-layer film grating is very low, only a few percent.

[0003] In synchrotron radiation light sources, the Constant Focusing Factor (C ff ) technology is widely applied in grating monochromator systems. The constant focusing factor mode is to adjust the combination of the incident angle and the exit angle so that the grating always works under constant focusing conditions, thereby keeping the position and focusing performance of the exit beam basically unchanged when scanning different wavelengths. This design method can simplify the mechanical adjustment requirements of the optical system during the wavelength scanning process, contribute to maintaining good beam quality and focusing performance within the entire wavelength range, and ensure the system stability. In addition, this mode can balance the energy resolution and the light flux, providing a better performance balance for synchrotron radiation experiments.

[0004] In recent years, multilayer film grating elements have been developed. By depositing periodic multilayer films on the grating substrate, the diffraction efficiency of the grating can be significantly improved. However, since the conventional periodic multilayer film grating needs to strictly satisfy the grating equation and the generalized Bragg condition to obtain high diffraction efficiency, the corresponding relationship between the incident photon energy and the incident angle of the periodic multilayer film grating is uniquely determined, so it cannot work efficiently in the constant focusing factor mode.

[0005] By combining aperiodic multilayer films with a grating, it is expected to obtain a broadband multilayer grating element with high diffraction efficiency under a wide spectrum. However, in the currently reported broadband multilayer grating design methods internationally, there is a lack of a design method for complex incident angle relationships, and the design method has significant limitations. For example, patent application CN105700134A discloses an X-ray broadband multilayer blazed grating design method, which cannot achieve a constant focusing factor and does not consider the differences in the Bragg conditions between the multilayer film and the grating. It is applicable to near-normal incidence conditions, but under grazing incidence conditions, the bandwidth of the multilayer film will be less than that of the multilayer grating, making it impossible to achieve precise optimization of the target band. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned existing technologies and provide a design method for a high-efficiency broadband multilayer blazed grating with a constant focusing factor, which improves the diffraction efficiency of the grating in the constant focusing factor mode.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A design method for a high-efficiency broadband multilayer blazed grating with a constant focusing factor, comprising the following steps:

[0009] According to the target band and focusing factor of the broadband multilayer grating, select the material combination of the aperiodic multilayer film and determine the relationship between the incident angle and the incident energy when the focusing factor is constant;

[0010] Based on the Bragg condition of the multilayer grating, determine the film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and under the focusing factor according to the relationship between the incident angle and the incident energy when the focusing factor is constant;

[0011] According to the film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and under the focusing factor, match to obtain the grating blaze angle that suppresses the non-working grating diffraction orders;

[0012] According to the Bragg conditions of the multilayer film and the multilayer grating, determine the target band and film thickness range for optimizing the broadband multilayer film to obtain the optimized broadband multilayer film;

[0013] Combine the optimized broadband multilayer film with the grating blaze angle that suppresses the non-working diffraction orders to obtain a high-efficiency broadband multilayer blazed grating with a constant focusing factor in the target band.

[0014] Further, the material combination of the aperiodic multilayer film includes an absorption layer material and a spacer layer material.

[0015] Further, the relationship between the incident angle and the incident energy when the focusing factor is constant is:

[0016]

[0017] C ff = sin(θ n ) / sin(θ0)

[0018] where θ0 is the grazing incidence angle of the broadband multilayer grating, θ n is the grazing diffraction angle of the broadband multilayer grating, n is the grating diffraction order, λ is the incident light wavelength of the broadband multilayer grating, D is the grating period, and C ff is the focusing factor.

[0019] Furthermore, the film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and focusing factor is:

[0020]

[0021]

[0022] where d(z) is the thickness of each layer pair corresponding to the broadband multilayer grating at each order in the target band and focusing factor, θ0 is the grazing incidence angle of the broadband multilayer grating, is the average polarizability of the broadband multilayer, is the average polarizability of the absorber material A, is the average polarizability of the spacer material S, and γ is the proportion of the absorber layer thickness in the layer pair thickness.

[0023] Furthermore, the grating diffraction orders include the working grating diffraction order and the non - working grating diffraction order.

[0024] Furthermore, according to the film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and focusing factor, an effective film thickness that intersects with the film thickness - energy curve of the adjacent diffraction order is selected within the film thickness range at the working grating diffraction order, and the grating blaze angle for suppressing the non - working grating diffraction order is matched. The matching formula is:

[0025]

[0026] where α is the grating blaze angle for suppressing the non - working grating diffraction order, n is the grating diffraction order, D is the grating period, and d eff is the effective film thickness.

[0027] Furthermore, the film thickness range during the optimization of the broadband multilayer is:

[0028] d MS (z) = d(z)cosα

[0029] where dMS (z) is the thickness of each layer pair during the optimization of the broadband multilayer film, d(z) is the thickness of each layer pair of the broadband multilayer film grating corresponding to the target wavelength band and focusing factor at each order, and α is the grating blaze angle for suppressing the diffraction orders of non-working gratings.

[0030] Furthermore, the optimized broadband multilayer film has a uniform reflectivity. The incident angle relationships selected during the optimization of the broadband multilayer film include the grazing incident angle varying with wavelength and a constant incident angle.

[0031] The grazing incident angle varying with wavelength is:

[0032] θ MS (λ) = θ0(λ) + α

[0033] In the formula, θ MS (λ) is the grazing incident angle of the broadband multilayer film, θ0(λ) is the grazing incident angle corresponding to the broadband multilayer film grating at different wavelengths, and α is the grating blaze angle for suppressing the diffraction orders of non-working gratings;

[0034] The constant incident angle is:

[0035] θ MS (c) = θ0(λ max ) + α

[0036] In the formula, θ MS (c) is the constant incident angle, θ0(λ max ) is the grazing incident angle corresponding to the broadband multilayer film grating at the maximum wavelength, and α is the grating blaze angle for suppressing the diffraction orders of non-working gratings.

[0037] Furthermore, the target wavelength band during the optimization of the broadband multilayer film is:

[0038]

[0039]

[0040] In the formula, λ MS is the target wavelength band during the optimization of the broadband multilayer film, d MS (z) is the thickness of each layer pair during the optimization of the broadband multilayer film, θ MS is the incident angle of the broadband multilayer film, is the average polarizability of the broadband multilayer film, is the average polarizability of the absorbing layer material A, is the average polarizability of the spacer layer material S, and γ is the proportion of the absorbing layer thickness in the layer pair thickness.

[0041] Furthermore, the target spectral energy range of the high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor in the target band is between 0.1 - 10 keV, the film pair thickness is between 1 - 20 nm, and the range of the grazing incidence angle of the grating is:

[0042] θ c <θ<90°

[0043] where θ is the grazing incidence angle of the grating, and θ c is the critical angle of total reflection, and its value matches the average polarizability of the broadband multilayer thin film.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. According to the target band and focusing factor of the broadband multilayer thin-film grating, the present invention selects the material combination of the aperiodic multilayer thin film and determines the relationship between the incident angle and the incident energy when the focusing factor is constant, determines the corresponding film thickness range of the broadband multilayer thin-film grating at the target band and focusing factor under each grating diffraction order, and matches the blazed angle of the grating that suppresses the non-working grating diffraction order according to this film thickness range; according to the Bragg conditions of the multilayer thin film and the multilayer thin-film grating, the target band and film thickness range during the optimization of the broadband multilayer thin film are determined, and the optimized broadband multilayer thin film is obtained. By combining the optimized broadband multilayer thin film with the grating, a broadband multilayer thin-film grating dispersion element with both a constant focusing factor and high efficiency can be obtained. Compared with the traditional single-layer thin-film grating that can operate in the constant focusing factor mode, the diffraction efficiency is significantly improved.

[0046] 2. According to the corresponding film thickness range of the broadband multilayer thin-film grating at the target band and focusing factor under each grating diffraction order, the present invention matches the blazed angle of the grating that suppresses the non-working grating diffraction order according to this film thickness range, which can effectively suppress the excitation of non-working diffraction orders, and thus obtain a higher broadband diffraction efficiency at the target diffraction order. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a schematic structural diagram of the present invention;

[0048] Figure 2 is a schematic structural diagram of the high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor;

[0049] Figure 3 is the energy-focusing factor and energy-incident angle relationship curves of the conventional periodic multilayer thin-film grating and the broadband multilayer thin-film grating;

[0050] Figure 4 is the energy-film thickness relationship curves of the multilayer thin film with the incident angle varying with the wavelength and at a constant incident angle, and the energy-film thickness relationship curves of the multilayer thin-film grating at each diffraction order under a constant focusing factor;

[0051] Figure 5 The thickness distribution curves of each layer and the diffraction efficiencies of each order of the broadband multilayer grating G1. Among them, (5a) is the thickness distribution curve of each layer of the broadband multilayer grating G1, and (5b) is the reflectivity of the multilayer M1 when the incident angle is constant at 1.35° and the diffraction efficiencies of each order of the multilayer grating G1 when the focusing factor is constant at 2.52;

[0052] Figure 6 The thickness distribution curves of each layer and the diffraction efficiencies of each order of the broadband multilayer grating G2. Among them, (6a) is the thickness distribution curve of each layer of the broadband multilayer grating G2, and (6b) is the reflectivity of the multilayer M2 under the incident angle relationship that varies with the wavelength and the diffraction efficiencies of each order of the multilayer grating G2 when the focusing factor is constant at 2.52. Specific implementation mode

[0053] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented on the premise of the technical solution of the present invention, and gives detailed implementation manners and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0054] Embodiment 1

[0055] This embodiment provides a design method for a high-efficiency broadband multilayer blazed grating with a constant focusing factor. The structure of the high-efficiency broadband multilayer blazed grating designed by the method provided in this embodiment is as Figure 2 shown. The broadband multilayer blazed grating is formed by alternately depositing two materials on a grating substrate. Among them, θ0 is the grazing incidence angle of the grating, the Z-axis is the depth direction of the multilayer film, and θ n is the grazing angle of the grating, D is the grating period, α is the blaze angle, d is the thickness of each film pair from the top to the substrate, and d MS is the film thickness of the multilayer film structure.

[0056] This embodiment provides a design method for a high-efficiency broadband multilayer blazed grating with a constant focusing factor as Figure 1 shown, including the following steps:

[0057] S1. According to the target wavelength band and focusing factor of the broadband multilayer grating, select the material combination of the aperiodic multilayer film and determine the relationship between the incident angle and the incident energy when the focusing factor is constant.

[0058] The material combination of the aperiodic multilayer film includes an absorption layer material and a spacer layer material.

[0059] The relationship between the incident angle and the incident energy when the focusing factor is constant is:

[0060]

[0061] C ff = sin(θ n ) / sin(θ0)

[0062] In the formula, θ0 is the grazing incidence angle of the broadband multilayer grating, θ n is the grazing diffraction angle of the broadband multilayer grating, n is the grating diffraction order, λ is the incident light wavelength of the broadband multilayer grating, D is the grating period, and C ff is the focusing factor.

[0063] In this embodiment, a broadband multilayer blazed grating with a constant focusing factor C ff = 2.52 is designed for the 2 - 3 keV band. The Cr / C material combination is selected, where Cr is the absorption layer and C is the spacer layer. The proportion γ of the absorption layer thickness in the film pair thickness is 0.4. To obtain a higher resolution, a grating with a line density of 2400 l / mm is selected, that is, the grating period D = 416.67 nm, and the grating diffraction order n = -1. According to the variation relationship of the incident angle with the incident energy when the focusing factor is constant, the energy - incident angle curve under the constant focusing factor C ff = 2.52 is as shown by the black solid line in Figure 3 , which is significantly different from the working incident angle of the conventional periodic multilayer grating with a focusing factor of 2.52 at 2.5 keV shown by the gray solid line in Figure 3 . Although the conventional periodic multilayer grating can obtain a high diffraction efficiency, as shown by the gray dashed line in Figure 3 , its focusing factor C ff significantly changes from 2.09 to 3.06 at 2 - 3 keV.

[0064] S2. Based on the Bragg condition of the multilayer grating, determine the film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and under the focusing factor according to the variation relationship of the incident angle with the incident energy when the focusing factor is constant.

[0065] The film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and under the focusing factor is:

[0066]

[0067]

[0068] In the formula, d(z) is the thickness of each layer of film pair corresponding to the broadband multilayer grating at each order in the target band and under the focusing factor, θ0 is the grazing incidence angle of the broadband multilayer grating, is the average polarizability of the broadband multilayer film, is the average polarizability of the absorption layer material A, is the average polarizability of the spacer layer material S, and γ is the proportion of the absorber layer thickness in the film pair thickness.

[0069] Based on the Bragg condition of the multilayer film grating, the energy-thickness curves at each order can be determined, as Figure 4 shown by the solid lines 1 and 2 in the figure. The thickness range corresponding to the broadband multilayer film grating operating at the n=-1 order in the 2-3 keV energy range with C ff =2.52 is 9.16-6.85 nm, Figure 4 and the gray area in the figure is the effective working area.

[0070] S3. According to the thickness range corresponding to the broadband multilayer film grating at each grating diffraction order in the target band and focusing factor, the grating blaze angle for suppressing the non-working grating diffraction order is matched.

[0071] The grating diffraction orders include the working grating diffraction order and the non-working grating diffraction order.

[0072] According to the thickness range corresponding to the broadband multilayer film grating at each grating diffraction order in the target band and focusing factor, an effective thickness that intersects with the thickness-energy curve of the adjacent diffraction order is selected within the thickness range at the working grating diffraction order, and the grating blaze angle for suppressing the non-working grating diffraction order is matched. The matching formula is:

[0073]

[0074] In the formula, α is the grating blaze angle for suppressing the non-working grating diffraction order, n is the grating diffraction order, D is the grating period, and d eff is the effective thickness.

[0075] Through the energy-thickness curves of the broadband multilayer film grating at each order as Figure 4 shown in the figure, within the thickness range at the working order n=-1, that is, within the gray effective working area, an effective thickness d eff =6.91 nm that intersects with the thickness-energy curve of the adjacent order n=-2 is selected, as Figure 4 shown by the dashed line 3 in the figure. Through the matching formula, the calculated grating blaze angle α=0.95° for suppressing other non-working diffraction orders is obtained.

[0076] S4. According to the Bragg conditions of the multilayer film and the multilayer film grating, the target band and thickness range for optimizing the broadband multilayer film are determined to obtain the optimized broadband multilayer film.

[0077] The thickness range for optimizing the broadband multilayer film is:

[0078] d MS (z)=d(z)cosα

[0079] In the formula, d MS (z) is the thickness of each layer pair during the optimization of the broadband multilayer film, d(z) is the thickness of each layer pair corresponding to the broadband multilayer film grating at the target wavelength band and focusing factor at each order, and α is the grating blaze angle for suppressing the diffraction orders of non-working gratings.

[0080] The target wavelength band during the optimization of the broadband multilayer film is:

[0081]

[0082]

[0083] In the formula, λ MS is the target wavelength band during the optimization of the broadband multilayer film, d MS (z) is the thickness of each layer pair during the optimization of the broadband multilayer film, θ MS is the incident angle of the broadband multilayer film, is the average polarizability of the broadband multilayer film, is the average polarizability of the absorbing layer material A, is the average polarizability of the spacer layer material S, and γ is the proportion of the absorbing layer thickness in the layer pair thickness.

[0084] The incident angle relationships selected during the optimization of the broadband multilayer film include the grazing incident angle varying with wavelength and the constant incident angle.

[0085] The grazing incident angle varying with wavelength is:

[0086] θ MS (λ) = θ0(λ) + α

[0087] In the formula, θ MS (λ) is the grazing incident angle of the broadband multilayer film, θ0(λ) is the grazing incident angle corresponding to the broadband multilayer film grating at different wavelengths, and α is the grating blaze angle for suppressing the diffraction orders of non-working gratings;

[0088] The constant incident angle is:

[0089] θ MS (c) = θ0(λ max ) + α

[0090] In the formula, θ MS (c) is the constant incident angle, θ0(λ max ) is the grazing incident angle corresponding to the broadband multilayer film grating at the maximum wavelength, and α is the grating blaze angle for suppressing the diffraction orders of non-working gratings.

[0091] The optimized broadband multilayer film has a uniform reflectivity under the selected incident angle relationships.

[0092] S5. Combine the optimized broadband multilayer film with the grating blaze angle that suppresses non-working diffraction orders to obtain a high-efficiency broadband multilayer film blazed grating with a constant focusing factor in the target band.

[0093] According to the Bragg formulas of the multilayer film and the multilayer film grating, select a constant incident angle. The energy-thickness curve of the broadband multilayer film at a constant multilayer film incident angle of 2.30° is as Figure 4 shown by the gray dotted line 4 in. The optimized target band of the multilayer film corresponding to the gray dotted line 4 within the working thickness range is 0.506 - 0.632 nm, and the corresponding energy range is 1.96 - 2.45 keV. Set the layer distribution within the working thickness range as the initial film system, and optimize the aperiodic multilayer film structure with the uniform reflectivity as the target and the thickness of each layer as the variable value. The broadband multilayer film M1 can be obtained. Its reflectivity at a constant incident angle of 2.30° is as Figure 5 shown by the dotted line 1 in (5b) of. The average diffraction efficiency is 26.5% at 1.96 - 2.45 keV.

[0094] The target spectral energy range of the high-efficiency broadband multilayer film blazed grating with a constant focusing factor in the target band is between 0.1 - 10 keV, the film pair thickness is between 1 - 20 nm, and the range of the grating grazing incident angle is:

[0095] θ c <θ<90°

[0096] where θ is the grating grazing incident angle, and θ c is the critical angle of total reflection, and its value matches the average polarizability of the broadband multilayer film.

[0097] After the broadband multilayer film M1 is matched with the blaze angle α = 0.95°, the broadband multilayer film grating G1 is obtained. The thickness distribution curve of each layer of G1 is as Figure 5 shown in (5a) of. (The first layer is the top layer far from the substrate, and the topmost material is Cr); The diffraction efficiencies of each order of G1 at a constant focusing factor C ff = 2.52 are as Figure 5 shown by the curves 2 - 4 in (5b) of. The average diffraction efficiency of the -1 order reaches 29.5% at 2 - 3 keV, and the diffraction efficiencies of the 0 order and the -2 order are both at a relatively low level.

[0098] According to the Bragg formulas of the multilayer film and the multilayer film grating, select the grazing incident angle that changes with the wavelength. The energy-thickness curve of the broadband multilayer film at a multilayer film incident angle changing from 2.30° to 2.05° with energy is as Figure 4As shown by the black dashed line 5 in , the optimized target energy of the multilayer film corresponding to the black dashed line 5 within the working film thickness range is 1.95 - 2.68 keV, and the width multilayer film M2 is optimized. Under the incident angle relationship varying with wavelength, its reflectivity under the energy - incident angle relationship is as Figure 6 shown by the dashed line 1 in (6b) of . The average efficiency at 1.95 - 2.68 keV is 30.0%. After matching the blaze angle α = 0.95°, the width multilayer film grating G2 is obtained. The thickness distribution curve of each film layer of G2 is as Figure 6 shown in (6a) of (the first layer is the top layer away from the substrate, and the topmost material is Cr); The diffraction efficiency of G2 under the constant focusing factor C ff = 2.52 is as Figure 6 shown by the curves 2 - 4 in (6b) of . The diffraction efficiencies of its 0th order and - 2nd order are both at a relatively low level, and the average efficiency reaches 29.8% at 2 - 3 keV. The width multilayer film gratings obtained through the above two ideas can achieve an average diffraction efficiency of nearly 30% within the 2 - 3 keV broad spectral range.

[0099] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A design method for a high-efficiency broadband multilayer blazed grating with a constant focusing factor, characterized in that, It includes the following steps: According to the target band and focusing factor of the broadband multilayer grating, select the material combination of the aperiodic multilayer and determine the relationship between the incident angle and the incident energy when the focusing factor is constant; Based on the Bragg condition of the multilayer grating, determine the film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and under the focusing factor according to the relationship between the incident angle and the incident energy when the focusing factor is constant; According to the film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and under the focusing factor, match to obtain the grating blaze angle for suppressing the diffraction orders of non-working gratings; According to the Bragg conditions of the multilayer and the multilayer grating, determine the target band and film thickness range during the optimization of the broadband multilayer to obtain the optimized broadband multilayer; Combine the optimized broadband multilayer with the grating blaze angle for suppressing the diffraction orders of non-working gratings to obtain a high-efficiency broadband multilayer grating with a constant focusing factor in the target band; 2. The design method of a high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor according to claim 1, characterized in that The material combination of the aperiodic multilayer includes an absorption layer material and a spacer layer material; 3. The design method of a high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor according to claim 1, characterized in that, The focusing factor C ff When it is constant, the relationship between the incident angle and the incident energy is as follows: C ff = sin(θ n ) / sin(θ0) where θ0 is the grazing incidence angle of the broadband multilayer grating, θ n is the grazing diffraction angle of the broadband multilayer grating, n is the diffraction order of the grating, λ is the incident light wavelength of the broadband multilayer grating, D is the grating period, and C ff is the focusing factor.

4. The design method of a high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor according to claim 1, characterized in that, The film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and under the focusing factor is: In the formula, d(z) is the thickness of each layer pair of the broadband multilayer grating at each order corresponding to the target band and the focusing factor, and θ0 is the grazing incidence angle of the broadband multilayer grating. is the average polarizability of the broadband multilayer. is the average polarizability of the absorbing layer material A. is the average polarizability of the spacer layer material S, and γ is the proportion of the absorbing layer thickness in the layer pair thickness.

5. The design method of a high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor according to claim 1, characterized in that, The grating diffraction orders include the diffraction orders of working gratings and non-working gratings; 6. The design method of a high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor according to claim 5, characterized in that According to the film thickness range corresponding to the broadband multilayer grating at each grating diffraction order in the target band and under the focusing factor, select an effective film thickness within the film thickness range at the diffraction order of the working grating that has an intersection with the film thickness-energy curve of the adjacent diffraction order, and match to obtain the grating blaze angle for suppressing the diffraction orders of the non-working gratings. The matching formula is: Where α is the grating blaze angle for suppressing the diffraction orders of the non-working grating, n is the grating diffraction order, D is the grating period, and d eff is the effective film thickness.

7. The design method of a high-efficiency broadband multilayer blazed grating with a constant focusing factor according to claim 6, characterized in that The film thickness range during the optimization of the broadband multilayer is: d MS (z) = d(z) cos α where d MS (z) is the thickness of each layer pair during the optimization of the broadband multilayer film, d(z) is the thickness of each layer pair corresponding to the broadband multilayer film grating at each order under the target wavelength band and focusing factor, and α is the grating blaze angle for suppressing the diffraction orders of non-working gratings.

8. The design method of a high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor according to claim 1, characterized in that The optimized broadband multilayer has a uniform reflectivity. The incident angle relationships selected during the optimization of the broadband multilayer include a grazing incident angle that varies with wavelength and a constant incident angle; The grazing incident angle that varies with wavelength is: θ MS (λ) = θ0(λ) + α where θ MS (λ) is the grazing incidence angle of the broadband multilayer film, θ0(λ) is the grazing incidence angle corresponding to the broadband multilayer film grating at different wavelengths, and α is the grating blaze angle for suppressing the diffraction orders of non-working gratings; The constant incident angle is: θ MS (c) = θ0(λ max ) + α where θ MS (c) is the constant incident angle, θ0(λ max ) is the grazing incident angle corresponding to the width multilayer grating at the maximum wavelength, and α is the grating blaze angle for suppressing the diffraction orders of non-working gratings.

9. The design method of a high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor according to claim 1, characterized in that The target band during the optimization of the broadband multilayer is: where λ MS is the target wavelength band during the optimization of broadband multilayer films, d MS (z) is the thickness of each layer pair during the optimization of broadband multilayer films, θ MS is the grazing incidence angle of the broadband multilayer film, is the average polarizability of the broadband multilayer film, is the average polarizability of the absorption layer material A, is the average polarizability of the spacer layer material S, and γ is the proportion of the absorption layer thickness in the layer pair thickness.

10. The design method of a high-efficiency broadband multilayer thin-film blazed grating with a constant focusing factor according to claim 1, wherein The target spectral energy range of the high-efficiency broadband multilayer grating with a constant focusing factor in the target band is between 0.1 - 10 keV, the film pair thickness is between 1 - 20 nm, and the range of the grating grazing incident angle is: θ c <θ<90° where θ is the grazing incidence angle of the grating, and θ c is the critical angle of total reflection, and its value matches the average polarizability of the broadband multilayer film.

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