CN114496337A - Multilayer Laue lens and design method thereof - Google Patents

Abstract

The present application discloses a multilayer film Laue lens and a design method thereof. The lens includes a base layer and a diffractive structure disposed on the base layer. Each period includes a superimposed absorption layer and a spacer layer, and the thickness of the period gradually decreases from the direction close to the base layer to the direction away from the base layer; the cross-sectional depth of each of the absorption layer and the spacer layer is Optimal section depth*(1‑modification parameter Q), where Q is any value between 0.4‑1. According to the technical solutions provided in the embodiments of the present application, by modifying the multilayer Laue lens, the compensation for the structural error generated in the process of preparing the lens is realized by the modification, and in the case that other auxiliary optical elements are not required, The difference between the electric field at the exit surface of the ideal multilayer Laue lens is narrowed, so as to improve the focusing performance of the actually prepared multilayer Laue lens.

Description

Multilayer Laue lens and design method thereof

technical field

The present invention generally relates to the field of precision optical elements, in particular to a high-resolution X-ray microfocusing element, in particular to a multilayer Laue lens and a design method thereof.

Background technique

The X-ray band covers the resonance lines of most elements, has high element sensitivity, and has the characteristics of short wavelength and strong penetrability, which can realize non-destructive measurement of materials and biological cells. Therefore, X-ray microscopy is a biological, It is an important research tool in the fields of medicine, materials, physics and chemistry. The size of the X-ray converging spot is directly related to the resolution and sensitivity of microscopic analysis. Since the refractive index n of X-rays is close to 1, diffractive focusing elements are more convenient for X-ray focusing than reflective and refractive elements. Traditional zone plates can focus soft X-rays to a range of tens of nanometers, but in the hard X-ray band, a larger aspect ratio is required to achieve ideal focusing, and with the increase of X-ray energy, the required aspect ratio is higher. Large, traditional photolithography methods are difficult to produce zone plates that can focus to smaller spots.

In order to solve this problem, the Argonne laboratory in the United States proposed in 2004 that a multi-layer film with a zone plate structure was coated in reverse order on a flat substrate, and then sliced and polished to an ideal depth, which can obtain any aspect ratio. This new method, called Multilayer Laue Lens (MLL), can achieve focusing below 1 nm according to theoretical calculations, and is one of the most promising hard X-ray nanofocusing elements. In 2006, the Argonne National Laboratory in the United States used the WSi ₂ /Si material combination to prepare a 12.4-micron slanted multi-layer film Laue lens with a focusing efficiency of 44% at a 19.5KeV energy point, a spot size of 30nm, and a focusing focal length of 4.72mm; in 2012, Ray Conley and others in the United States completed the production of low-error multilayer films in the newly built high-precision coating laboratory, and carried out the stress-free micromachining technology of the diaphragm, realizing the preparation of practical micro lenses, one-dimensional The focusing spot is 11 nm. In 2015, Huang et al. prepared a wedge-shaped MLL with an aperture of 31 μm and a focal length of 3.2 mm. The 14.6 keV APS light source in the United States obtained a one-dimensional focused spot of 25.6 nm with a diffraction efficiency of 27%.

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 long-term plating will bring about a regular drift of the sputtering rate, both of which will affect the final sputtering rate. The prepared multilayer Laue lens brings structural errors, which make its structure deviate from the ideal structure, and then due to the influence of structural errors, the electric field on the exit surface of the actual multilayer Laue lens is different from that of the ideal multilayer Laue lens. The large deviation of the electric field on the exit surface will eventually affect its optical performance, reducing its diffraction efficiency and focusing resolution. Usually, additional optical elements such as phase shifters are needed to compensate, but this will increase the overall system performance. Commissioning work, and, is not conducive to the application of multilayer Laue lenses on different systems.

SUMMARY OF THE INVENTION

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

In a first aspect, there is provided a multi-layer Laue lens, comprising a base layer and a diffractive structure disposed on the base layer, the diffractive structure comprising a plurality of periods arranged in a stack, each of the periods comprising a stack. placed absorber and spacer layers,

The thickness of the period gradually decreases from the direction close to the base layer to the direction away from the base layer;

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

In a second aspect, a method for designing the above-mentioned multilayer Laue lens is provided, comprising the following steps:

determining a diffractive structure, the depth of the diffractive structure is an optimal cross-sectional depth, and the optimal cross-sectional depth corresponds to an optimal electric field distribution;

forming an actual diffraction structure on the base layer, and the electric field distribution of the formed actual diffraction structure is the actual electric field distribution;

Modify the absorbing layer and the spacer layer in the diffractive structure, and calculate 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 the set range. , determine the modification parameter Q;

The exit surface of the diffractive structure is etched according to the modification parameter Q, and the etching depth is the optimum section depth*modification parameter Q.

According to the technical solutions provided in the embodiments of the present application, the multi-layer Laue lens is modified to compensate for the error generated in the prepared lens structure by modifying the shape. In the case of no other auxiliary optical elements, the difference between the lens and the lens can be reduced. The difference between the electric field at the exit surface of the ideal multilayer Laue lens can improve the focusing performance of the actually prepared multilayer Laue lens.

Description of drawings

Other features, objects and advantages of the present application will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

1 is a schematic diagram of the structure of a multilayer Laue lens in the prior art;

FIG. 2 is a schematic structural diagram of an ideal multilayer Laue lens and an actually prepared multilayer Laue lens;

3 is a schematic view of the structure of the multilayer Laue lens in this embodiment;

FIG. 4 is the outgoing electric field of the multilayer Laue lens at the optimum cross-sectional depth in this embodiment;

Figure 5 shows the intensity distribution near the focal point of the multilayer Laue lens provided in this embodiment when focusing is achieved; Figure a is an ideal structure multilayer Laue lens, and Figure b is an actual structure multilayer Laue lens with errors Erlenmeyer lens, Figure c shows the actual structure of the multi-layer film Laue lens after modification;

6 is a schematic diagram comparing the normalized electric field intensity curve at the focal plane of the multilayer Laue lens in the present embodiment and the ideal situation;

FIG. 7 is a modified embodiment of the multilayer Laue lens provided in this example.

Detailed ways

The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the related invention, but not to limit the invention. In addition, it should be noted that, for the convenience of description, only the parts related to the invention are shown in the drawings.

It should be noted that the embodiments in the present application and the features of the embodiments may be combined with each other in the case of no conflict. The present application will be described in detail below with reference to the accompanying drawings and in conjunction with the embodiments.

Laue lens is a linear 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 the base layer, and the structure formed by plating is a diffraction structure. , as shown in Figure 1, the material with high atomic number forms the absorption layer, the material with low atomic number forms the spacer layer, and an absorption layer and a spacer layer adjacent to it are used as a film layer period; in this Laue lens structure is formed A coordinate system, in which the diffraction structure formed has an incident surface and an exit surface, the length of the diffraction structure along the Z axis is the depth of the section, and Dn shown in the figure refers to the thickness of different periods, and the layer at the maximum position of the X axis is The outermost layer of the diffractive structure, the thickness of the outermost structure is Drout, rn indicates the position radius of the _nth film layer, and each lens structure has a theoretically calculated number of film layers during preparation, and the film thickness , and the cross-sectional depth of the film layer, the theoretically calculated cross-sectional depth is the optimal cross-sectional depth. According to the above theoretical parameters, the corresponding multilayer Laue lens is prepared. 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 long-term plating will It brings about the regular drift of the sputtering rate, and produces structural errors on the prepared multilayer Laue lens, forming an actual structure as shown in Figure 2. In the actual structure, there will be various film layers that are not gradually The reduced regular arrangement affects its optical performance.

Referring to FIG. 3 , the present embodiment provides a multilayer Laue lens, which includes a base layer 10 and a diffractive structure 20 disposed on the base layer 10 . The diffractive structure 20 includes a plurality of periods arranged in layers, Each said period includes a superimposed absorber layer and a spacer layer,

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;

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

The multilayer Laue lens provided in this embodiment includes a base layer 10 and a diffractive structure 20 disposed on the base layer 10. The diffractive structure 20 includes multiple layers of absorbing layers and spacer layers, and the period thickness of the diffractive structure 20 is gradually increased. Decrease, the cross-sectional depth of the absorption layer and the spacer layer in the diffractive structure 20, that is, the length of the diffractive structure 20 on the Z axis, is the optimal cross-sectional depth*(1-modification parameter Q), where Q is the current The degree to which the layer structure is etched, Q is generally any value between 0.4-1, and 1 means no etching at all; by modifying the corresponding absorption layer and spacer layer, and adjusting the cross-sectional depth, to achieve the The prepared lens structure produces error compensation, and without the need for other auxiliary optical elements, the difference between it and the electric field at the exit surface 2 of the ideal multilayer Laue lens is reduced, thereby improving the actually prepared multilayer Laue lens. The focusing performance of the lens.

Further, the optimal cross-sectional depth is the depth of the diffraction structure 20 corresponding to the maximum diffraction efficiency of the multilayer Laue lens.

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

First, 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 1;

According to the wavelength λ of the incident light, the focal length f of the -1st-order diffracted light of the lens and the number of film layers, the curve η-1(Z) of the -1st-order diffraction efficiency changing with the section depth Z is calculated to obtain the optimal section depth Zopt;

Among them, the thickness of each film layer involved is calculated by the following formula:

D _n = _fλ /rn ;

Wherein, D _n is the periodic thickness of the nth film layer, f is the focal length of the lens-1 order diffracted light, and λ is the wavelength of the incident light;

Among them, the position radius r _n of the nth film layer is calculated by the following formula:

rn =nfλ+ _n ² λ ² /4.

Further, the thicknesses of the absorption layer and the spacer layer in each of the periods are the same.

The above-mentioned diffraction structure 20 includes a plurality of periods, and in each film layer period, the thicknesses of the _two layer structures are the same, wherein the material of the absorption layer can be WSi or Nb, and the material of the spacer layer can be Si or Al, wherein The material with the larger absorption coefficient is used as the absorption layer, and the absorption coefficient of the opposite spacer layer is smaller than that of the absorption layer.

Further, the diffractive structure 20 includes an incident surface 1 and an exit surface 2 disposed 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.

Further, the error between the actual electric field distribution of the exit surface 2 of the multilayer Laue lens and the optimal electric field distribution is within a set range.

As shown in FIG. 3 , in the lens structure provided in this embodiment, each layer structure of the exit surface 2 is not on the same plane, which is mainly to realize that the actual electric field distribution of the exit surface 2 of the multilayer Laue lens is in the optimal electric field distribution The error between them is small, and the error is adjusted to an acceptable range. Therefore, only the exit surface 2 of the lens structure needs to be adjusted. Therefore, the final structure shown in Figure 2 is formed. The end face of the incident surface 1 of the lens structure is formed. It is located on the same plane, and usually the end face is 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 to ensure that the actual electric field distribution of the exit surface 2 is the same as the maximum. The error between the optimal electric field distribution is within the set range.

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

determining a diffractive structure, the depth of the diffractive structure is an optimal cross-sectional depth, and the optimal cross-sectional depth corresponds to an optimal electric field distribution;

An actual diffraction structure is formed on the base layer 10, and the electric field distribution of the formed actual diffraction structure is an actual electric field distribution;

Modify the absorption layer and the spacer layer in the actual diffraction structure, and calculate the actual electric field distribution of the exit surface 2 after modification, until the error between the actual electric field distribution and the optimal electric field distribution is set Within the range, determine the modification parameter Q;

The exit surface 2 of the actual diffractive structure is etched according to the modification parameter Q, and the etching depth is the optimal section depth*modification parameter Q.

The preparation method provided in this embodiment first determines the corresponding diffraction structure, the determined diffraction mechanism has an optimal cross-sectional depth, and the electric field distribution of the exit surface corresponding to the corresponding optimal cross-sectional depth is the optimal electric field distribution, which is required for the prepared lens structure. the theoretical goals to be achieved;

According to the theoretically determined diffraction structure, the corresponding actual diffraction structure is prepared on the base layer 10. The prepared lens structure has a certain systematic random deviation between the actual sputtering rate and the calibrated sputtering rate, and the long-term plating will lead to Due to the regular drift of the sputtering rate, there will be a certain error in the finally prepared multilayer Laue lens, as shown in Figure 4. Figure 4 shows the exit of the multilayer Laue lens at the optimal cross-sectional depth. Electric field, in which the black line is the ideal case, and the gray line is the case under the actual structure. Therefore, it is necessary to measure the actually prepared lens structure, and compare the actual electric field distribution obtained by measurement with the theoretical electric field distribution, that is, the optimal electric field The distribution maps were compared, and the gap between the actual electric field distribution and the theoretical electric field distribution was narrowed by adjusting the prepared lens structure.

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

Divide the actual diffractive structure into N parts with equal spacing or the same number of film layers, and each part of the actual diffractive structure corresponds to one of the modification parameters Q;

Simultaneously optimize the N modification parameters.

The actually prepared multilayer Laue lens is subdivided into N parts along the X direction in Figure 2 with equal spacing or equal film layers, and a modification parameter Q is set for each part of the structure. The variation range of the parameters is 0.4-1. Due to the strong electric field coupling between different layer structures, it is impossible to consider all coupling factors when simply optimizing a single sub-structure, and it will introduce some outgoing electric fields to adjacent sub-structures. Unexpected changes cannot achieve the most ideal effect. Therefore, the genetic algorithm is used to optimize the N modification parameters at the same time, and finally the modified multilayer Laue lens has the output electric field at zopt and the ideal multilayer film. The Laue lens exits the electric field approximately the same at the optimum depth Zopt.

Wherein, the N is 65%-70% of the number of film layers. In the multilayer Laue lens, the film layer that contributes more to the focusing effect is in the film layer with the smaller thickness. Therefore, in order to save the process steps of modification, only the structure of the film layer with the larger effect is modified. 65%-70% of the number of film layers, preferably starting from the outermost film layer of the lens, and setting N of 70% of the number of film layers; where N can be set at equal intervals, or it can be equal to the number of film layers The setting of the film can preferably be set as the film layer, and each film layer is used as a copy for calculation and modification;

After the genetic algorithm is used to optimize the N modification parameters at the same time, the modification parameter Q is determined, and the error between the actual electric field distribution after modification and the optimal electric field distribution is determined to be within the set range. The etching accuracy is generally 50 nanometers. According to the etching accuracy, the error between the actual electric field distribution and the optimal electric field distribution is preferably set to ±0.1π. According to the development of the etching accuracy, the difference between the actual electric field distribution and the optimal electric field distribution is The error between can be further reduced;

Then, the exit surface 2 of the actual diffraction structure is etched according to the modification parameters calculated by the genetic algorithm, including:

The exit surface 2 of the actual diffractive structure is etched one by one according to the number N of the actual diffractive structures and the modification parameter Q corresponding to N.

The etching of the actual diffraction structure is related to the fraction of the actual diffraction structure. The layer is etched, and the depth of the etching is optimal cross-section depth * modification parameter Q.

So far, the above etched multi-layer Laue lens can compensate for the electric field change of the exit surface 2 caused by its structural error without the need for other auxiliary optical components, thereby improving the actual production of the multi-layer Laue lens obtained. Focus on performance.

Optionally, the determining of the diffraction structure includes 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 1;

According to the wavelength λ of the incident light, the focal length f of the -1st-order diffracted light of the lens and the number of film layers, the curve η-1(Z) of the -1st-order diffraction efficiency changing with the section depth Z is calculated to obtain the optimal section depth Zopt.

In the above steps, the first thing that needs to be determined is the diffraction structure, and the total film thickness of the lens, the periodic thickness Drout of the outermost film layer and the total number of film layers are determined according to the application requirements of the lens;

The outermost layer thickness is determined by the following formula:

Δ=1.22Drout, where Δ is the spatial resolution required by the lens;

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

N _max =fλ/(4*Drout ² );

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

Then determining the periodic thickness of each film layer at the incident surface 1 includes the following steps:

The position radius rn of the _nth film layer is obtained by the following formula:

r _n =nfλ+n ² λ ² /4;

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

The periodic thickness D _n of the n-th film layer is obtained based on the position radius of the n-th film layer:

D _n = _fλ /rn ;

Then, using the Takagi-Taupin theory in diffraction dynamics, the curve η-1 of the -1st-order diffraction efficiency changing with the depth Z was calculated; The outgoing electric field Eopt of the ideal multilayer Laue lens at the optimal cross-sectional depth Zopt; then the actual lens is fabricated according to the optimal cross-sectional depth value Zopt.

A specific implementation is preferably given in this embodiment, assuming that the incident light energy E=20keV, the required focusing resolution is 25nm, the selected focal length is 3mm, and the total film thickness at this time should be 10μm. According to the resolution requirements, the thickness of the outermost layer is selected to be 10nm. According to the calculation, the total number of film layers is 500 layers.

Determine the diffractive structure according to the company in the above steps;

Using the Takagi-Taupin theory, calculate the curve η-1(z) of the negative first-order diffraction efficiency as a function of depth z;

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

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

The multi-layer Laue lens of the actual structure is subdivided into a certain number of substructures along the X direction, the subdivision number is set to 350, and each layer is subdivided and etched in the Z direction;

Let the modification parameter be Q, and the variation range is 0.4-1, where 1 is the complete etching. Due to the strong electric field coupling between different substructures, it is impossible to consider all coupling factors when simply optimizing a single substructure, which will introduce some unexpected changes to the outgoing electric field of adjacent substructures, which cannot achieve the best possible results. Therefore, the genetic algorithm is used to optimize the N modification parameters at the same time. The optimal optimization result is shown in Figure 7, which indicates the parameters that need to be modified for each layer structure. The abscissa is the number of layers, and the ordinate is the number of layers. is the modification parameter.

After the optimization, Kirchhoff-Fresnel diffraction integration is used to obtain the light intensity distribution on the image plane. After the modification is obtained, the focusing resolution of the lens is 26 nm, and the ideal focusing resolution is 25 nm. The focusing resolution is 39 nm, as shown in Figure 5 and Figure 6. The normalized distribution curves of the electric field intensity at the three focal planes in Figure 6 are the theoretical ideal case, the actual preparation according to the calculated parameters, and the actual Laue lens structure after The structure after modification and etching, wherein, the structure provided in the above-mentioned embodiment after modification and etching is relatively close to the curve under the theoretical ideal situation;

Among them, after the Laue lens of the present application is modified, the focusing resolution is approximately the same as that of the ideal type, which is far better than the focusing resolution of the Laue lens under the actual structure, indicating that the single-order diffraction Laue lens of the present application can be With the help of any additional optical elements, the difference of the electric field on the exit surface 2 caused by the structural error in the actual situation can be effectively compensated.

It should be understood that the terms "center", "portrait", "horizontal", "top", "bottom", "front", "rear", "left", "right", "vertical" "," "horizontal", "top", "bottom", "inside", "outside", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description , rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be construed as a limitation to the present invention; the orientation terms "inside and outside" refer to the The inside and outside of the silhouette. In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature defined as "first" or "second" may expressly or implicitly include one or more of that feature.

For ease of description, spatially relative terms, such as "on", "over", "on the surface", "above", etc., may be used herein to describe what is shown in the figures. The spatial positional relationship of one device or feature shown to other devices or features. It should be understood that spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" or "over" other devices or features would then be oriented "below" or "over" the other devices or features under other devices or constructions". Thus, the exemplary term "above" can encompass both an orientation of "above" and "below." The device may also be otherwise oriented, rotated 90 degrees or at other orientations, and the spatially relative descriptions used herein interpreted accordingly.

It should be noted that, unless otherwise expressly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it may be a fixed connection, a detachable connection, or an integral connection; It can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal communication between the two elements or the interaction relationship between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific situations.

The above description is only a preferred embodiment of the present application and an illustration of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solution formed by the specific combination of the above technical features, and should also cover the above technical features without departing from the inventive concept. Other technical solutions formed by any combination of its equivalent features. For example, a technical solution is formed by replacing the above-mentioned features with the technical features disclosed in this application (but not limited to) with similar functions.

Claims (10)

1. A multilayer film Laue lens comprising a substrate layer and a diffractive structure disposed on the substrate layer, the diffractive structure comprising a plurality of periods arranged in a stack, each period comprising an absorbing layer and a spacer layer in a stack,

the thickness of the period is gradually reduced from the direction close to the substrate layer to the direction far away from the substrate layer;

the cross-sectional depth of each of the absorber and spacer layers is an optimum cross-sectional depth (1-modification parameter Q), wherein Q is any value between 0.4 and 1.

2. The multilayer film laue lens of claim 1, wherein the optimal cross-sectional depth is a depth of a diffraction structure corresponding to a maximum value of a diffraction efficiency of the multilayer film laue lens.

3. The multilayer film laue lens of claim 1, wherein the absorber layer and the spacer layer thickness in each of the periods are the same.

4. The multilayer film laue lens of claim 1, wherein the diffractive structure comprises oppositely disposed entrance and exit faces, and wherein the end faces of the plurality of absorbing layers and the spacer layer at the entrance face lie in the same plane.

5. The multilayer film laue lens of claim 1, wherein an error between an actual electric field distribution and an optimal electric field distribution of an exit surface of the multilayer film laue lens is within a set range.

6. A method of designing a multilayer film Laue lens as claimed in any one of claims 1 to 5, comprising the steps of:

determining a diffraction structure, wherein the depth of the diffraction structure is an optimal section depth, and the optimal section depth corresponds to an optimal electric field distribution;

forming an actual diffraction structure on the base layer, the electric field distribution of the actual diffraction structure being formed as an actual electric field distribution,

modifying the shape of the absorption layer and the spacing layer in the actual diffraction structure, calculating the actual electric field distribution of the modified emergent surface until the error between the actual electric field distribution and the optimal electric field distribution is within a set range, and determining a modification parameter Q;

and etching the emergent surface of the actual diffraction structure according to the shape modification parameter Q, wherein the etching depth is the optimal section depth.

7. The design method of claim 6, wherein the shaping the absorption layer and the spacer layer in the actual diffractive structure comprises:

dividing the actual diffraction structure into N parts with equal intervals or equal film quantity, wherein each part of the actual diffraction structure corresponds to one shape modification parameter Q;

and optimizing the N modification parameters simultaneously.

8. The design method of claim 7, wherein N is 65% -70% of the number of film layers.

9. The design method of claim 6, wherein the etching the exit surface of the actual diffraction structure according to the modification parameter Q comprises:

and etching the emergent surface of the actual diffraction structure in parts by parts according to the part N of the actual diffraction structure and the shape modification parameter Q corresponding to the part N.

10. The design method of claim 6, wherein said determining a diffractive structure comprises the steps of:

determining the total film thickness, the periodic thickness Drout of the outermost film layer and the total film layer number of the lens according to the application requirement of the lens;

determining the periodic thickness of each film layer at the incident surface;

and calculating a curve eta-1 (Z) of the-1 st order diffraction efficiency changing with the section depth Z according to the wavelength lambda of the incident light, the focal length f of the lens-1 st order diffraction light and the number of film layers to obtain the optimal section depth Zopt.

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