Multilayer laue lens and method of designing the same

Abstract

The application discloses a multilayer film laue lens and a design method thereof. The lens comprises a substrate layer and a diffraction structure arranged on the substrate layer. The diffraction structure comprises a plurality of periods arranged in a stack. Each period comprises a stack of an absorption layer and a spacer layer. The thickness of the periods gradually decreases from the substrate layer to a direction away from the substrate layer. The cross-sectional depth of each absorption layer and spacer layer is an optimal cross-sectional depth*(1-modification parameter Q), wherein Q is any value between 0.4 and 1. According to the technical scheme provided by the embodiment of the application, the multilayer film laue lens is modified, the modification is used to compensate for the structural error generated in the preparation of the lens, the difference between the actual multilayer film laue lens and the ideal multilayer film laue lens is reduced without other auxiliary optical elements, and the focusing performance of the actual prepared multilayer film laue lens is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of precision optical elements, in particular to high-resolution X-ray micro-focusing elements, and more particularly to multilayer Laue lenses and methods for designing the same. BACKGROUND

[0002] The X-ray band covers the resonance lines of most elements, has high element sensitivity, and has the characteristics of short wavelength and strong penetration, so that non-invasive measurement of materials and biological cells can be achieved. Therefore, X-ray microscopy is an important research tool in the fields of biology, medicine, materials, physics and chemistry, and the size of the X-ray converging spot is directly related to the resolution and sensitivity of the microscopic analysis. Since the refractive index n of X-rays is close to 1, compared with reflective and refractive elements, the diffraction focusing element is more convenient to realize X-ray focusing. The traditional zone plate can converge soft X-rays to tens of nanometers, but in the hard X-ray band, a larger aspect ratio is needed to achieve ideal focusing, and as the X-ray energy increases, a larger aspect ratio is needed. It is difficult to manufacture a zone plate that can focus to a smaller spot using traditional photolithography methods.

[0003] In order to solve this problem, in 2004, the United States Argonne Laboratory proposed a multilayer film of a zone plate structure on a flat substrate, which was then sliced and polished to the desired depth. It can obtain any depth ratio. This new method is called multilayer Laue lens (MLL), which can obtain a focusing spot of less than 1 nm according to theoretical calculation, and is one of the most promising hard X-ray nanofocusing elements. In 2006, the United States Argonne National Laboratory used WSi2 / Si material combination to prepare a tilted multilayer Laue lens with a total thickness of 12.4 microns, with a focusing efficiency of 44% at 19.5KeV energy point, and a spot size of 30nm, and a focusing focal length of 4.72mm; In 2012, Ray Conley et al. in the United States completed the low-error multilayer film in a newly built high-precision coating laboratory, and developed a stress-free micro-machining technology for the film, realizing the preparation of a practical miniature lens, with a one-dimensional focusing spot of 11nm, and in 2015, Huang et al. prepared a wedge-shaped MLL with an aperture of 31μm and a focal length of 3.2mm, which was tested at the United States APS light source at 14.6keV to obtain a one-dimensional focusing spot of 25.6nm, with a diffraction efficiency of 27%.

[0004] However, in the actual preparation process, there is a certain difference between the actual sputtering rate and the calibrated sputtering rate due to the random error of the system, and the regular drift of the sputtering rate caused by long-time plating, both of which will bring structural errors to the final prepared multilayer film Laue lens, so that its structure deviates from the ideal structure, and then due to the influence of structural errors, the electric field on the exit surface of the actual multilayer film Laue lens deviates greatly from the electric field on the exit surface of the ideal multilayer film Laue lens, which ultimately affects its optical performance, reduces its diffraction efficiency and focusing resolution, and usually additional optical elements such as phase shifters are needed to compensate, but this will increase the debugging work of the whole system, and is not conducive to the application of multilayer film Laue lens in different systems. SUMMARY

[0005] In view of the above defects or deficiencies in the prior art, it is desirable to provide a multilayer film Laue lens and a design method thereof.

[0006] In a first aspect, a multilayer film Laue lens is provided, comprising a substrate layer and a diffraction structure arranged on the substrate layer, the diffraction structure comprising a plurality of periods arranged in stacks, each of the periods comprising a stack of an absorbing layer and a spacer layer,

[0007] The thickness of the period gradually decreases from the direction close to the substrate layer to the direction away from the substrate layer;

[0008] The cross-sectional depth of each of the absorbing layer and the spacer layer is the optimal cross-sectional depth*(1-shape modification parameter Q), wherein Q is any value between 0.4 and 1.

[0009] In a second aspect, a design method of the above multilayer film Laue lens is provided, comprising the following steps:

[0010] Determining a diffraction structure, the depth of the diffraction structure being the optimal cross-sectional depth, the optimal cross-sectional depth corresponding to an optimal electric field distribution;

[0011] Forming an actual diffraction structure on the substrate layer, the electric field distribution of the formed actual diffraction structure being an actual electric field distribution;

[0012] Shape modifying the absorbing layer and the spacer layer in the diffraction structure, and calculating the actual electric field distribution of the exit surface after shape modification, until the error between the actual electric field distribution and the optimal electric field distribution is within a set range, to determine the shape modification parameter Q;

[0013] According to the shape modification parameter Q, etching the exit surface of the diffraction structure, the etching depth being the optimal cross-sectional depth*shape modification parameter Q.

[0014] According to the technical scheme provided in the embodiment of the present application, the multi-layer Laue lens is shaped, the shaping is used to compensate for the error of the prepared lens structure, the difference between the multi-layer Laue lens and the ideal multi-layer Laue lens is reduced without other auxiliary optical elements, and thus the focusing performance of the multi-layer Laue lens prepared in practice is improved. BRIEF DESCRIPTION OF DRAWINGS

[0015] Other features, objects, and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments thereof, taken in conjunction with the accompanying drawings:

[0016] Figure 1 A multi-layer Laue lens structure in the prior art is shown in the figure;

[0017] Figure 2 A multi-layer Laue lens structure in the prior art is shown in the figure;

[0018] Figure 3 A multi-layer Laue lens structure in the prior art is shown in the figure;

[0019] Figure 4 The exit electric field of the multi-layer Laue lens in the embodiment at the best cross-sectional depth is shown in the figure;

[0020] Figure 5 The intensity distribution near the focal point when the multi-layer Laue lens provided in the embodiment is used to focus is shown in the figure; wherein figure a is an ideal multi-layer Laue lens, figure b is an actual multi-layer Laue lens with error, and figure c is a multi-layer Laue lens after shaping;

[0021] Figure 6 The normalized electric field intensity curve of the multi-layer Laue lens in the embodiment at the focal plane is shown in the figure;

[0022] Figure 7 The shaping implementation of the multi-layer Laue lens provided in the embodiment is shown in the figure. DETAILED DESCRIPTION

[0023] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and are not a limitation on the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for ease of description.

[0024] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and embodiments.

[0025] Laue lens is a linear wave zone plate with a multi-layer film structure. The existing Laue lens is generally formed by alternately plating two materials with different atomic numbers on the surface of a base layer. The plating structure is a diffraction structure, as shown in Figure 1 , the material with high atomic number forms an absorption layer, and the material with low atomic number forms a spacer layer. One absorption layer and one spacer layer adjacent thereto form a film layer period. A coordinate system is formed in the Laue lens structure. The diffraction structure has an incident surface and an exit surface. The length of the diffraction structure along the Z axis is the cross-sectional depth. Dn in the figure indicates the thickness of different periods. The layer at the maximum position of the X axis is the outermost layer of the diffraction structure. The thickness of the outermost layer structure is Drout, r n indicates the position radius of the nth layer film layer. Each lens structure has a theoretically calculated number of film layers, film layer thickness, and film layer cross-sectional depth when prepared. The theoretically calculated cross-sectional depth is the optimal cross-sectional depth. According to the above theoretical parameters, the corresponding multi-layer film Laue lens is prepared. Due to the difference between the actual sputtering rate and the calibrated sputtering rate caused by system random errors, and the regular drift of the sputtering rate caused by long-term plating, structural errors are generated in the prepared multi-layer film Laue lens, and the actual structure is as shown in Figure 2 . In the actual structure, each film layer is not arranged according to the rule of gradually decreasing thickness, which affects the optical performance.

[0026] Please refer to Figure 3 , the embodiment provides a multi-layer film Laue lens, which comprises a base layer 10 and a diffraction structure 20 arranged on the base layer 10. The diffraction structure 20 comprises a plurality of periods arranged in layers, each of the periods comprises an absorption layer and a spacer layer arranged in layers,

[0027] The thickness of the period gradually decreases from the direction close to the base layer 10 to the direction away from the base layer 10.

[0028] The cross-sectional depth of each absorption layer and spacer layer is the optimal cross-sectional depth *(1-modification parameter Q), wherein Q is any value between 0.4 and 1.

[0029] The multilayer film laue lens provided by the embodiment comprises a substrate layer 10 and a diffraction structure 20 arranged on the substrate layer 10, the diffraction structure 20 comprises a plurality of absorption layers and interval layers, the period thickness of the diffraction structure 20 gradually decreases, and the cross-sectional depth of the absorption layers and the interval layers in the diffraction structure 20, that is, the length of the diffraction structure 20 on the Z axis, is the optimal cross-sectional depth *(1-modification parameter Q), wherein Q is the degree of etching for the current layer structure, Q is generally any value between 0.4 and 1, and 1 is complete non-etching; the cross-sectional depth is adjusted by modifying the corresponding absorption layers and interval layers to compensate for the error of the prepared lens structure, the difference between the actual prepared multilayer film laue lens and the ideal multilayer film laue lens exit surface 2 electric field is reduced without other auxiliary optical elements, and thus the focusing performance of the actual prepared multilayer film laue lens is improved.

[0030] Further, the optimal cross-sectional depth is the depth of the diffraction structure 20 corresponding to the maximum diffraction efficiency of the multilayer film laue lens.

[0031] The optimal cross-sectional depth in the above embodiment is the depth of the diffraction structure 20 corresponding to the maximum diffraction efficiency of the lens, and specifically, the optimal cross-sectional depth Zopt with the maximum efficiency can be selected according to the efficiency curve of the negative first-order diffraction efficiency with the depth, and the specific steps will be described in detail below.

[0032] First, the total thickness of the film layers of the lens, the period thickness Drout of the outermost film layer, and the total number of film layers are determined according to the application requirements of the lens.

[0033] The period thickness of each film layer at the incident surface 1 is determined.

[0034] The curve η-1(Z) of the first-order diffraction efficiency with the cross-sectional depth Z is calculated according to the wavelength λ of the incident light, the focal length f of the first-order diffraction light of the lens, and the number of film layers, and the optimal cross-sectional depth Zopt is obtained.

[0035] Wherein, the thickness of each film layer is calculated by the following formula:

[0036] D n = fλ / r n ;

[0037] Wherein, D n is the period thickness of the nth film layer, f is the focal length of the first-order diffraction light of the lens, and λ is the wavelength of the incident light.

[0038] Wherein, the position radius r n of the nth film layer is calculated by the following formula:

[0039] r n = nfλ + n 2λ 2 / 4.

[0040] Furthermore, the absorption layer and the spacer layer in each period have the same thickness.

[0041] The above-mentioned diffraction structure 20 includes multiple periods. Within each film layer period, the thickness of the two layer structures is the same. The material of the absorption layer can be WSi2 or Nb, and the material of the spacer layer can be Si or Al. The material with a larger absorption coefficient serves as the absorption layer, and the absorption coefficient of the relative spacer layer is smaller than the absorption coefficient of the absorption layer.

[0042] Furthermore, the diffraction structure 20 includes an incident surface 1 and an exit surface 2 that are arranged opposite to each other, and the end surfaces of the plurality of absorption layers and the spacer layers at the incident surface 1 are located on the same plane.

[0043] Furthermore, the error between the actual electric field distribution of the exit surface 2 of the multi-layer Laue lens and the optimal electric field distribution is within a set range.

[0044] like Figure 3 As shown, the various layers of the exit surface 2 of the lens structure provided in this embodiment are not on the same plane. This is mainly to achieve a smaller error between the actual electric field distribution of the exit surface 2 of the multi-layer Laue lens and the optimal electric field distribution, and to adjust the error to an acceptable range. Therefore, only the exit surface 2 of the lens structure needs to be adjusted, so that the final result is as shown in FIG. Figure 2 In the structure shown, the end faces of the incident surface 1 of the lens structure are located on the same plane, and usually the end faces are perpendicular to the base layer 10. Since the cross-sectional depths of different layer structures are not the same, the end faces of the exit surface 2 are also not on the same plane, ensuring that the error between the actual electric field distribution of the exit surface 2 and the optimal electric field distribution is within a set range.

[0045] This embodiment also provides a method for designing a multilayer Laue lens, comprising the following steps:

[0046] Determining a diffraction structure, wherein the depth of the diffraction structure is an optimal cross-sectional depth, and the optimal cross-sectional depth corresponds to an optimal electric field distribution;

[0047] forming a real diffraction structure on the base layer 10, wherein the electric field distribution of the real diffraction structure is a real electric field distribution;

[0048] The absorption layer and the spacer layer in the actual diffraction structure are modified, and the actual electric field distribution of the exit surface 2 after modification is calculated until the error between the actual electric field distribution and the optimal electric field distribution is within a set range, and the modification parameter Q is determined;

[0049] The exit surface 2 of the actual diffraction structure is etched according to the shaping parameter Q, and the etching depth is the optimal cross-sectional depth*the shaping parameter Q.

[0050] The preparation method provided in this embodiment first determines the corresponding diffraction structure. The determined diffraction structure has an optimal cross-sectional depth. The electric field distribution on the exit surface corresponding to the optimal cross-sectional depth is the optimal electric field distribution, which is the theoretical goal that the prepared lens structure needs to achieve.

[0051] According to the theoretically determined diffraction structure, the corresponding actual diffraction structure is prepared on the substrate 10. The prepared lens structure has a certain systematic random deviation between the actual sputtering rate and the calibrated sputtering rate, and long-term plating will cause a regular drift of the sputtering rate. The multilayer film Laue lens finally prepared will have a certain error. Figure 4 As shown, Figure 4 is the output electric field of the multilayer Laue lens at the optimal cross-sectional depth, where the black line represents the ideal case and the gray line represents the case under the actual structure. Therefore, it is necessary to measure the actual prepared lens structure and compare the measured actual electric field distribution with the theoretical electric field distribution, that is, the optimal electric field distribution. The gap between the actual electric field distribution and the theoretical electric field distribution can be narrowed by adjusting the prepared lens structure.

[0052] Optionally, modifying the absorption layer and the spacer layer in the actual diffraction structure includes:

[0053] Divide the actual diffraction structure into N parts with equal spacing or equal number of film layers, each part of the actual diffraction structure corresponds to one of the shaping parameters Q;

[0054] N shaping parameters are optimized simultaneously.

[0055] The multilayer Laue lens prepared in practice Figure 2 The X direction in the image is subdivided into N parts with equal spacing or equal film layers. A shaping parameter Q is set for each structure, and the range of variation of this shaping parameter is 0.4-1. Due to the strong electric field coupling between different layer structures, simple manual optimization of a single substructure cannot fully consider all coupling factors, which will introduce some unexpected changes to the output electric field of adjacent substructures and fail to achieve the optimal effect. Therefore, a genetic algorithm is used to simultaneously optimize the N shaping parameters. Ultimately, the output electric field of the modified multilayer Laue lens at zopt is approximately the same as the output electric field of the ideal multilayer Laue lens at the optimal depth Zopt.

[0056] The N is 65%-70% of the number of film layers. The film layer with a smaller thickness has a greater contribution to the focusing effect in the multi-film Laue lens. Therefore, in order to save the process step of shaping, only the film layer structure with a greater effect is shaped, and generally 65%-70% of the number of film layers, preferably 70% of the number of film layers is set from the outermost film layer of the lens. The N can be set at equal intervals or equal number of film layers, and preferably equal film layers, each film layer is calculated and shaped.

[0057] After the N shaping parameters are simultaneously optimized by the genetic algorithm, the error between the actual electric field distribution after shaping and the optimal electric field distribution is within the set range. Since the etching accuracy in the prior art is generally 50 nanometers, the error between the actual electric field distribution and the optimal electric field distribution is preferably set to ±0.1π according to the etching accuracy. According to the development of etching accuracy, the error between the actual electric field distribution and the optimal electric field distribution can be further reduced.

[0058] Subsequently, the exit surface 2 of the actual diffraction structure is etched according to the shaping parameters calculated by the genetic algorithm, including:

[0059] According to the number N of the actual diffraction structure and the shaping parameter Q corresponding to N, the exit surface 2 of the actual diffraction structure is etched.

[0060] The etching of the actual diffraction structure is related to the number of the actual diffraction structure divided above, and each part of the actual diffraction structure corresponds to a shaping parameter Q. The corresponding film layer of the corresponding part is etched on the exit surface 2 of the actual diffraction structure, and the etching depth is the optimal cross-sectional depth*shaping parameter Q.

[0061] At this point, the multi-film Laue lens after etching above compensates for the change of the exit surface 2 electric field caused by the structure error without other auxiliary optical elements, thereby improving the focusing performance of the actual prepared multi-film Laue lens.

[0062] Optionally, the determining the diffraction structure comprises the following steps:

[0063] According to the application requirements of the lens, the total thickness of the film layer of the lens, the period thickness Drout of the outermost film layer, and the total number of film layers are determined.

[0064] The period thickness of each film layer at the entrance surface 1 is determined.

[0065] According to the wavelength λ of the incident light, the focal length f of the-1 order diffraction light of the lens, and the number of film layers, the curve η-1(Z) of the-1 order diffraction efficiency changing with the cross-sectional depth Z is calculated, and the optimal cross-sectional depth Zopt is obtained.

[0066] In the above steps, firstly, the diffraction structure needs to be determined, and the total thickness of the film layers of the lens, the period thickness Drout of the outermost film layer and the total number of the film layers are determined according to the application requirements of the lens;

[0067] The thickness of the outermost layer is determined by the following formula:

[0068] Δ = 1.22Drout, wherein Δ is the spatial resolution required to be achieved by the lens;

[0069] The total number of the film layers is determined by the following formula:

[0070] N max = fλ / (4*Drout 2 );

[0071] The total thickness can be obtained by the total number of the layers;

[0072] Subsequently, the period thickness of each film layer at the incident surface 1 is determined, including the following steps:

[0073] The position radius r n of the nth film layer is obtained by the following formula:

[0074] r n = nfλ + n 2 λ 2 / 4;

[0075] Wherein n is the number of the film layers from the substrate outward, f is the focal length of the -1 order diffracted light of the lens, and λ is the wavelength of the incident light;

[0076] The period thickness D n of the nth film layer is obtained based on the position radius of the nth film layer:

[0077] D n = fλ / r n ;

[0078] Subsequently, the Takagi-Taupin theory in the diffraction dynamics is used to calculate the curve η-1 of the -1 order diffraction efficiency changing with the depth Z, and according to the calculated efficiency curve η-1, the optimal cross-sectional depth Zopt with the maximum efficiency is selected, and the exit electric field Eopt of the ideal type multilayer film Laue lens at the optimal cross-sectional depth Zopt is calculated; subsequently, the actual lens is prepared according to the optimal cross-sectional depth value Zopt.

[0079] The preferred embodiment in this example gives a specific implementation, assuming the incident light energy E = 20 keV, the required focusing resolution is 25 nm, the focal length is selected as 3 mm, at this time the total film thickness should be 10 μm, according to the film plating capacity and resolution requirements, the outermost layer thickness is selected as 10 nm, according to the calculation, the total film layer number is 500 layers.

[0080] According to the company in the above steps, determine the diffraction structure;

[0081] Using Takagi-Taupin theory, calculate the curve η-1(z) of the negative 1st order diffraction efficiency varying with depth z;

[0082] According to the diffraction curve η-1(z), select the optimal depth Zopt=6 μm with the maximum efficiency;

[0083] According to the optimal depth Zopt, calculate the electric field distribution of the ideal structure multilayer film Laue lens exit surface 2, denoted as Eopt; according to the actual measured structure, calculate the electric field distribution of the actual structure multilayer film Laue lens exit surface 2 according to the same method, denoted as Eopt'.

[0084] Subdivide the actual structure multilayer film Laue lens along the X direction into a certain number of substructures, the subdivision number is set to 350, subdivide according to each layer structure, and etch in the Z direction;

[0085] Set the modification parameter as Q, the change range is 0.4-1, wherein 1 is complete etching. Due to the strong electric field coupling between different substructures, when artificially simply optimizing a single substructure, all coupling factors cannot be considered, which will introduce some unexpected changes to the exit electric field of the adjacent substructure, and the ideal effect cannot be achieved, therefore, the genetic algorithm is used to optimize N modification parameters at the same time, and the optimization result is preferably as shown in Figure 7 , wherein the modification parameter required for each layer structure is indicated, the horizontal coordinate is the layer number, and the vertical coordinate is the modification parameter.

[0086] After optimization, the light intensity distribution on the image plane is obtained by using Kirchhoff-Fresnel diffraction integral, the focusing resolution of the modified lens is 26 nm, the ideal focusing resolution is 25 nm, and the focusing resolution under the actual structure is 39 nm, see Figure 5 and Figure 6 , Figure 6 , wherein the three electric field intensity normalized distribution curves at the focal plane are respectively under the theoretical ideal condition, according to the actual preparation of the calculation parameters, and the structure after modification and etching of the actual Laue lens structure, wherein the structure after modification and etching is close to the curve under the theoretical ideal condition in the above embodiment;

[0087] Wherein, the focusing resolution of the Laue lens of the present application is similar to the ideal type after the modification, and is much better than the focusing resolution of the Laue lens under the actual structure, which shows that the single-stage diffraction Laue lens of the present application can effectively compensate the difference of the electric field on the exit surface 2 caused by the structure error under the actual condition without the help of any additional optical element.

[0088] It should be noted that, the above-mentioned terms such as "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application; the orientation terms "inner" and "outer" refer to the inner and outer of the contour of each component itself. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" can explicitly or implicitly include one or more of the features.

[0089] For the convenience of description, spatial relative terms such as "over", "above", "upper surface", "upper", and the like can be used herein to describe the spatial positional relationship of one device or feature with respect to other devices or features as shown in the drawings. It should be understood that the spatial relative terms are intended to include different orientations in use or operation in addition to the orientation of the devices described in the drawings. For example, if the devices in the drawings are inverted, the device described as "above" or "over" other devices or structures will be positioned "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below" orientations. The device can also be positioned at 90 degrees or in other orientations in other different ways, and the spatial relative descriptions used herein are interpreted accordingly.

[0090] It should be noted that, unless otherwise explicitly specified and limited, the terms "mount", "connect", "connection" should be understood broadly, for example, can be fixedly connected, can also be detachably connected, or integrally connected; can be mechanically connected, can also be electrically connected; can be directly connected, can also be indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0091] The above description is only the preferred embodiment of the present application and the explanation of the technical principles. It should be understood by those skilled in the art that the scope of the protection of the present application is not limited to the technical solutions formed by the specific combinations of the above technical features. It should also cover other technical solutions formed by the combinations of the above technical features or their equivalent features without departing from the concept of the present application. For example, the technical solutions formed by the mutual replacements of the above features and the technical features disclosed in the present application (but not limited to) with similar functions.

Claims

1. A multilayer Laue lens, characterized in that: The invention comprises a base layer and a diffraction structure arranged on the base layer, wherein the diffraction structure comprises a plurality of periods of stacked layers, and each period comprises a stacked absorption layer and a spacer layer. The thickness of the period gradually decreases from close to the base layer to away from the base layer; The cross-sectional depth of each of the absorption layer and the spacer layer is the optimal cross-sectional depth*(1-modification parameter Q), Wherein, determining the diffraction structure includes the following steps: Determine the total thickness of the lens film, the periodic thickness Drout of the outermost film layer, and the total number of film layers according to the application requirements of the lens; determine the periodic thickness of each film layer at the incident surface; According to the wavelength λ of the incident light, the focal length f of the -1 order diffraction light of the lens and the number of film layers, the curve η-1(Z) showing the change of -1 order diffraction efficiency with cross-sectional depth Z is calculated to obtain the optimal cross-sectional depth Zopt; The optimal cross-sectional depth corresponds to the optimal electric field distribution, and an actual diffraction structure is formed on the substrate layer. The electric field distribution of the actual diffraction structure formed is the actual electric field distribution. The absorption layer and the spacer layer in the actual diffraction structure are shaped, and the actual electric field distribution of the exit surface after shaping is calculated until the error between the actual electric field distribution and the optimal electric field distribution is within the set range, and the shaping parameter Q is determined.

2. The multi-layer Laue lens according to claim 1, wherein: The optimal cross-sectional depth is the diffraction structure depth corresponding to the maximum diffraction efficiency of the multilayer Laue lens.

3. The multi-layer Laue lens according to claim 1, wherein: The absorption layer and the spacer layer in each period have the same thickness.

4. The multi-layer Laue lens according to claim 1, wherein: The diffraction structure includes an incident surface and an exit surface that are oppositely arranged, and the end surfaces of the plurality of absorption layers and the spacer layer at the incident surface are located on the same plane.

5. The multi-layer Laue lens according to claim 1, wherein: The error between the actual electric field distribution on the exit surface of the multi-layer Laue lens and the optimal electric field distribution is within a set range.

6. A method for designing a multilayer Laue lens according to any one of claims 1 to 5, characterized in that: The following steps are involved: Determining a diffraction structure, wherein the depth of the diffraction structure is an optimal cross-sectional depth, and the optimal cross-sectional depth corresponds to an optimal electric field distribution; forming a real diffraction structure on the base layer, wherein the electric field distribution of the real diffraction structure is a real electric field distribution, Modifying the absorption layer and the spacer layer in the actual diffraction structure, and calculating the actual electric field distribution of the exit surface after modification, until the error between the actual electric field distribution and the optimal electric field distribution is within a set range, and determining the modification parameter Q; The exit surface of the actual diffraction structure is etched according to the shaping parameter Q, and the etching depth is the optimal cross-sectional depth*the shaping parameter Q.

7. The design method according to claim 6, characterized in that: The modifying of the absorption layer and the spacer layer in the actual diffraction structure includes: Divide the actual diffraction structure into N parts with equal spacing or equal number of film layers, each part of the actual diffraction structure corresponds to one of the shaping parameters Q; N shaping parameters are optimized simultaneously.

8. The design method according to claim 7, characterized in that: When modifying the membrane layer structure having a greater effect, the number of membrane layers is selected to be 65%-70%.

9. The design method according to claim 6, characterized in that: The etching of the exit surface of the actual diffraction structure according to the shaping parameter Q comprises: The exit surface of the actual diffraction structure is etched portion by portion according to the number N of the actual diffraction structure and the shaping parameter Q corresponding to N.

10. The design method according to claim 6, characterized in that: Determining the diffraction structure comprises the following steps: Determine the total film thickness of the lens, the periodic thickness Drout of the outermost film layer, and the total number of film layers according to the application requirements of the lens; Determine the periodic thickness of each film layer at the incident surface; According to the wavelength λ of the incident light, the focal length f of the -1st order diffraction light of the lens and the number of film layers, the curve η-1(Z) showing the change of -1st order diffraction efficiency with cross-sectional depth Z is calculated to obtain the optimal cross-sectional depth Zopt.

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