Large-aperture double-sided focusing type Kinform lens and design method thereof

Abstract

The invention discloses a large-aperture double-sided focusing type Kinform lens and a design method thereof. Comprising N lenses located on the same optical axis, the aperture of the nth lens # imgabs0 # n is equal to 2-N, A1 is the aperture of the first lens, yn is the length of the nth lens, q (n-1) 22 is the emergent focal length of the emergent surface of the (n-1) th lens, the incident surfaces and the emergent surfaces of all the lenses except the incident surface of the first lens are all OVAL surface types, and q is a positive integer. The surface type of the incident surface of the first lens is # imgabs1 # imgabs2 # f is the focal length of the incident surface of the first lens, and delta is the difference between the refractive index of the first lens and the refractive index of air. The defects caused by divergence of the rear surface of the lens are overcome, and the total length of the lens group can be shortened.

Description

Technical Field

[0001] The invention belongs to the field of optical technology and relates to a large-aperture double-sided focusing Kinoform lens and a design method thereof. Background Art

[0002] At present, in many fields such as information, energy, materials, and military, the demand for small-size spots is gradually becoming more and more significant, that is, the diffraction-limited nano-focusing of X-rays has become a current research hotspot. According to rough statistics, the best focusing method at present is to use diffraction and reflection elements such as MLL and KB mirrors for focusing, which can push the spot size to within 10nm, while the best CRL for refractive elements can push the spot size to about 47nm.

[0003] The Kinoform lenses proposed and produced by Evans-Lutterodt, Aristov V and others are based on the removal of concave-planar lenses. The lens with a diffraction effect caused by the thick material achieves the focusing effect (where m is a positive integer, λ is the wavelength of the X-ray, and δ is the difference in the real part of the refractive index of the medium material and the vacuum), such as Figure 1 However, when using this traditional Kinoform lens, only the refraction of the left surface is considered and the right surface is ignored during design. This approximation will cause certain errors and affect the focusing efficiency.

[0004] The known OVAL surface type is a refocusing lens surface type derived by John P. Sutter et al. in 2017, such as Figure 2 As shown, this surface type can realize X-ray refocusing, and Formula 1 is the surface equation (where δ=n1-n2, n1 is the real part of the refractive index of the incident medium, n2 is the real part of the refractive index of the exiting medium, q1 and q2 are the focal lengths before and after refocusing respectively).

[0005]

[0006] In 2022, Xu Yuanze and others proposed the OK lens based on the traditional Kinoform lens and the OVAL surface shape. The OK lens uses the method of successively reducing lenses to improve the focusing performance of the lens, but the lens still does not make up for the defects caused by the divergence of the rear surface. Summary of the invention

[0007] In view of the problems existing in the prior art, the purpose of the present invention is to provide a large-aperture double-sided focusing Kinoform lens and a design method. Based on the OK lens, the present invention optimizes its rear surface to compensate for the defects caused by the divergence of the rear surface, shorten the total length of the lens group, reduce absorption, and facilitate processing.

[0008] The technical solution of the present invention is:

[0009] A large-aperture double-sided focusing Kinoform lens, characterized in that it comprises N lenses located on the same optical axis, wherein the aperture of the nth lens arranged along the light incident direction is The distance between the vertex of the incident surface of the nth lens surface and the vertex of the incident surface of the n-1th lens surface is y n ,y n is the length of the nth lens, n = 2 ~ N, A1 is the aperture of the first lens, q (n-1)22 is the exit focal length of the exit surface of the n-1th lens. Except for the incident surface of the first lens, the incident surface and the exit surface of each lens are OVAL surface type. A rectangular coordinate system is established with the vertex of the first lens as the origin O and the optical axis as the y-axis. Then the surface type of the incident surface of the first lens is f is the focal length of the incident surface of the first lens, and δ is the difference between the refractive index of the first lens and the refractive index of air.

[0010] Furthermore, q n21 is the incident focal length of the nth lens exit surface, q n12 is the exit focal length of the incident surface of the nth lens, and m is the step number of the lens.

[0011] Furthermore, the incident surface and the exit surface of the step at the top of each lens are symmetrical.

[0012] Furthermore, the length of the lens is An integer multiple of .

[0013] Furthermore, the material of the lens is SU8, the incident light is an X-ray with an energy of 20 KeV, and the aperture A0 of the first lens is 200 μm.

[0014] A design method for a large-aperture double-sided focusing Kinoform lens, the steps of which include:

[0015] 1) Design N lenses on the same optical axis;

[0016] 2) Establish a rectangular coordinate system with the vertex of the first lens as the origin O and the optical axis as the y-axis, then the shape of the incident surface of the first lens is f is the focal length of the incident surface of the first lens, δ is the difference between the refractive index of the first lens and the refractive index of air, and the aperture of the first lens is A0;

[0017] 3) Designing the exit surface of the first lens and the remaining lenses according to the refocusing model, so that the incident surface and the exit surface of each lens except the incident surface of the first lens are all OVAL surface types; wherein the aperture of the nth lens arranged along the incident direction of light is The distance between the vertex of the incident surface of the nth lens surface and the vertex of the incident surface of the n-1th lens surface is y n ,y n is the length of the nth lens.

[0018] This design discloses a large-aperture double-sided focusing Kinoform lens. Figure 3 As shown in the figure, the lens group consists of 34 single-piece mirrors (the light beam propagates from left to right, and the aperture on the right is smaller than that on the left). Its initial aperture size is 200μm, which can converge a parallel X-ray beam with an energy of 20Kev to a position with a focal length of 10cm. The curved surface of the lens mainly adopts the OVAL surface type. Therefore, the lens is subsequently simplified to the OKp lens.

[0019] Compared with the traditional OK (OVAL-Kinofrom) lens, the OKp lens adopts the method of double refraction (taking into account the refraction of X-rays through all surfaces of the lens) to reduce the lens length to achieve the effect of reducing absorption, and makes up for the defects caused by the divergence of the rear surface of the traditional OK lens; compared with the traditional double-sided focusing CRL lens, the OKp lens can focus on a smaller spot and has a higher light intensity; by simulating the OKp lens with an aperture of 200μm through BPM, a better focusing effect can be obtained, and the spot size (FWHM) at the focal plane is about 25nm (focal length is 10cm), and the focal spot is smaller when the focal length is 5cm.

[0020] The advantages of the present invention are as follows:

[0021] 1. The lens of the present invention can reduce absorption. Without considering the processing limit size, the lens was simulated using BPM, and the results showed that the peak light intensity was greatly improved.

[0022] 2. This lens makes up for the defects caused by the uncontrollable divergence of the rear surface and shortens the size of the focused spot.

[0023] 3. The lens adopts double-sided focusing, which can greatly shorten the total length of the lens group and achieve focusing of a larger aperture spot. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of a single OK lens.

[0025] Figure 2 Schematic diagram of OVAL surface refocusing.

[0026] Figure 3 Schematic diagram of OKp lens.

[0027] Figure 4 This is a comparison chart between a single OK lens and an OKp lens.

[0028] Figure 5 This is an explanatory diagram of the first surface.

[0029] Figure 6 Schematic diagram of OKp lens focusing. DETAILED DESCRIPTION

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

[0031] The refractive index of the material for X-rays is 1-δ+iβ. Known data show that in the medium and low energy range, SU8 has better refraction and absorption. For 20Kev energy X-rays, δ=1.21854487E-06; β=8.3084406E-10. Therefore, this design is a double-sided focusing lens made of SU8. Figure 3 As shown in the figure (this figure is an ideal OKp lens). The comparison between this lens and the OK lens is shown in Figure 4 As shown, the dark blue and green parts together constitute a schematic diagram of the OKp single-piece lens, and the dark blue and light blue parts together constitute a schematic diagram of the single-piece OK lens (for better contrast, the overlapping parts are drawn in dark blue, and the different parts are green and light blue respectively). From the lens structure, it can be seen that the absorption effect of the single-piece lens on the light beam is similar, but the focusing ability of the OKp lens can reach twice the effect, so shortening the length of the lens reduces the overall absorption and makes up for the defects caused by the divergence of the back surface of the OK lens.

[0032] Figure 6 This is a schematic diagram of the focusing of an ideal OKp. It can be seen from the figure that two OKp lenses can focus the light beam four times, which is approximately the effect that can only be achieved by four traditional OK lenses. The refraction of all curved surfaces in the lens is also considered, which makes up for the defect that the OK lens only considers curved surfaces.

[0033] The large-aperture double-sided focusing Kinoform lens of the present invention comprises a plurality of lenses located on the same optical axis, wherein the initial aperture is 200 μm, the aperture of the nth lens is And the distance between the vertex of the left surface of the nth lens and the vertex of the left surface of the n-1th lens is y n ,y n It is also the length of the nth lens, n=2~N, where N is the total number of lenses.

[0034] The surface types of all curved surfaces except the left surface of the first lens (including the left surface and the right surface of each lens) are OVAL surface types.

[0035] N=34, that is, 34 lenses are used to make the focal length of the lens 10 cm. To make the focal spot smaller, the focal length can be reduced, that is, the number of lenses can be increased, and vice versa.

[0036] The OKp lens surface design method is as follows, and the steps include:

[0037] 1. First calculate the left surface of the first lens (parallel light incidence does not meet the OVAL surface condition):

[0038] like Figure 5 As shown, a parallel X-ray beam is incident from the air on the left side to the left surface of the first lens. Assuming that the curved surface will focus the parallel beam to point F, the refractive index of air on the left side is n1 = 1; the refractive index of the medium on the right side is n2 = 1-δ; assuming the focal length is OF, that is, f; point y(x) on the surface. According to the principle of equal optical path, we know According to this relationship, the surface type (1-δ) can be obtained 2 x 2 +(δ 2 -2δ)y 2 -2fy(δ 2 -δ)=0, this surface is an ellipse equation. Solve the relationship between y and x by separating the variables (According to the lens surface shape, we can know that z≤0, so we discard the other solution).

[0039] The aperture A1 of the first lens is 200 μm.

[0040] 2. The remaining lenses all conform to the refocusing model, so the left plane is a traditional OVAL surface, where the relationship between y and x can be obtained by solving formula (1).

[0041] 3. Figure 6 is a schematic diagram of the focusing of the n-1th lens and the nth lens, where q1 (incident focal length) and q2 (exit focal length) of the left plane of the n-1th lens are represented by q (n-1)11 ,q (n-1)12 Indicates that q1 and q2 on the right plane are represented by q (n-1)21 ,q (n-1)22 Indicates that the apertures on the left and right planes are equal, using A n Indicates that, and the first step on the far right is symmetrical, then Where m represents the number of steps of the lens, q (n-1)22 It can also be derived using Formula 1.

[0042] 4. When designing the lens aperture, the OKp lens also uses the transfer equation of the OK lens. The aperture relationship between the nth lens and the n+1th lens is: where y n represents the length of the nth lens, y n-1represents the length of the n-1th lens, Figure 6 shown.

[0043] 5. When designing the lens, the length of each lens is the length of the left plane of the single lens. The length can also be other A value that is an integer multiple of .

[0044] Although the specific embodiments of the present invention are disclosed for the purpose of illustration, the purpose is to help understand the content of the present invention and implement it accordingly, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the best embodiment, and the scope of the present invention is subject to the scope defined in the claims.

Claims

1. A large-aperture double-sided focusing Kinoform lens, characterized in that: It includes N lenses located on the same optical axis, wherein the aperture of the nth lens arranged along the incident direction of light is The distance between the vertex of the incident surface of the nth lens surface and the vertex of the incident surface of the n-1th lens surface is y n ,y n is the length of the nth lens, n = 2 ~ N, A1 is the aperture of the first lens, q (n-1)22 is the exit focal length of the exit surface of the n-1th lens. Except for the incident surface of the first lens, the incident surface and the exit surface of each lens are OVAL surface type. A rectangular coordinate system is established with the vertex of the first lens as the origin O and the optical axis as the y-axis. Then the surface type of the incident surface of the first lens is f is the focal length of the incident surface of the first lens, and δ is the difference between the refractive index of the first lens and the refractive index of air.

2. The large-aperture double-sided focusing Kinoform lens according to claim 1, characterized in that: q n21 is the incident focal length of the nth lens exit surface, q n12 is the exit focal length of the incident surface of the nth lens, and m is the step number of the lens.

3. The large-aperture double-sided focusing Kinoform lens according to claim 2, characterized in that: The incident surface and the exit surface of the step at the top of each lens are symmetrical.

4. The large-aperture double-sided focusing Kinoform lens according to claim 1, characterized in that: The length of the lens is An integer multiple of .

5. The large-aperture double-sided focusing Kinoform lens according to claim 1, characterized in that: The material of the lens is SU8, the incident light is an X-ray with an energy of 20 KeV, and the aperture A0 of the first lens is 200 μm.

6. A method for designing the large-aperture double-sided focusing Kinoform lens according to claim 1, comprising the steps of: 1) Design N lenses on the same optical axis; 2) Establish a rectangular coordinate system with the vertex of the first lens as the origin O and the optical axis as the y-axis, then the shape of the incident surface of the first lens is f is the focal length of the incident surface of the first lens, δ is the difference between the refractive index of the first lens and the refractive index of air, and the aperture of the first lens is A0; 3) Designing the exit surface of the first lens and the remaining lenses according to the refocusing model, so that the incident surface and the exit surface of each lens except the incident surface of the first lens are all OVAL surface types; wherein the aperture of the nth lens arranged along the incident direction of light is The distance between the vertex of the incident surface of the nth lens surface and the vertex of the incident surface of the n-1th lens surface is y n ,y n is the length of the nth lens.

7. The method according to claim 6, characterized in that q n21 is the incident focal length of the nth lens exit surface, q n12 is the exit focal length of the incident surface of the nth lens, and m is the step number of the lens.

8. The method according to claim 7, characterized in that The incident surface and the exit surface of the step at the top of each lens are symmetrical.

9. The method according to claim 6, characterized in that The length of the lens is An integer multiple of .

10. The method according to claim 6, characterized in that The material of the lens is SU8, the incident light is an X-ray with an energy of 20 KeV, and the aperture A1 of the first lens is 200 μm.

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