Large aperture bifocal kinoform lens and design method

Abstract

The application discloses a large-aperture double-surface focusing Kinoform lens and a design method. n The application discloses a large-aperture double-surface focusing Kinoform lens and a design method. (n‑1)22 The application discloses a large-aperture double-surface focusing Kinoform lens and a design method. The application discloses a large-aperture double-surface focusing Kinoform lens and a design method. The application discloses a large-aperture double-surface focusing Kinoform lens and a design method. The application discloses a large-aperture double-surface focusing Kinoform lens and a design method.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optics and relates to a large-aperture double-surface focusing Kinoform lens and a design method. BACKGROUND

[0002] At present, in many fields such as information, energy, materials and military, the demand for small-size light spots is gradually significant, that is, X-ray diffraction limit nanofocusing has become a current research hotspot. According to rough statistics, the current best focusing approach is to use MLL and KB mirror and other diffraction and reflection elements for focusing, which can push the light spot size to within 10 nm, and the current best CRL for refractive elements can push the light spot size to about 47 nm.

[0003] Evans-Lutterodt Aristov V and others proposed and made Kinoform lenses, which are all based on the Kinoform lens removing thickness material to cause diffraction effect to achieve focusing effect (wherein m is a positive integer, λ is the X-ray wavelength, and δ is the real part difference of the refractive index of the medium material and vacuum), as shown in the formula 2. However, when using this traditional Kinoform lens, only the left surface refraction is considered and the right surface is ignored during design, which will cause certain errors and affect the focusing efficiency. Figure 1

[0004] It is known that the OVAL surface type is a refocusing lens surface type derived by John P. Sutter and others in 2017, as shown in the formula 3. This surface type can realize X-ray refocusing, and the formula 1 is a curved surface equation (wherein 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 exit medium, q1 and q2 are the focal lengths before and after refocusing, respectively). Figure 2

[0005]

[0006] Xu Yuanze and others proposed an OK lens based on the traditional Kinoform lens and the OVAL surface type in 2022. The OK lens uses a lens reduction method in turn to improve the focusing performance of the lens, but the lens still does not compensate for the defects caused by the divergence of the rear surface. SUMMARY

[0007] In view of the problems in the prior art, the purpose of the present application is to provide a large-aperture double-surface focusing Kinoform lens and a design method. The present application optimizes the rear surface of the OK lens to compensate for the defects caused by the divergence of the rear surface, shortens the total length of the lens group, reduces absorption, and facilitates processing.

[0008] The technical scheme of the present application is:​​

[0009] A large aperture double-sided focusing Kinoform lens, characterized in that it comprises N lenses on the same optical axis, wherein the aperture of the nth lens arranged along the light incident direction is A n and the distance between the incident surface vertex of the nth lens and the incident surface vertex of the (n-1)th lens 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-1)th lens, the incident surface and the exit surface of each lens except the incident surface of the first lens are OVAL surface types, and 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] Further, q n21 is the incident focal length of the exit surface of the nth lens, 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] Further, the incident surface and the exit surface of the step at the top of each lens are symmetrical.

[0012] Further, the length of the lens is an integer multiple of .

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

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

[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 surface type 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 A0 is the aperture of the first lens;

[0017] 3) Design 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 OVAL surface types; wherein the aperture of the nth lens arranged along the light incident direction is A And the distance between the vertex of the incident surface of the nth lens and the vertex of the incident surface of the (n-1)th lens is y. n y n Let be the length of the nth lens.

[0018] This design discloses a large-aperture, double-sided focusing Kinoform lens, which, as... Figure 3 As shown, the lens group consists of 34 monolithic mirrors (the 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 focus a parallel X-ray beam with an energy of 20Kev to a position with a focal length of 10cm. The curved surface of this lens mainly adopts the OVAL surface type. Therefore, this lens is later simplified as the OKp lens.

[0019] Compared to traditional OK (OVAL-Kinofrom) lenses, the OKp lens employs birefringence (considering the refraction of X-rays through all surfaces of the lens) to reduce lens length and thus lower absorption. It also overcomes the drawbacks caused by the divergence effect of the rear surface of traditional OK lenses. Compared to traditional double-focusing CRL lenses, the OKp lens can focus to a smaller spot size with higher light intensity. Simulations using BPM on a 200μm aperture OKp lens demonstrate good focusing performance, with a focal plane spot size (FWHM) of approximately 25nm (at a focal length of 10cm), and an even smaller spot size at a focal length of 5cm.

[0020] The advantages of this invention are as follows:

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

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

[0023] 3. This lens uses double-sided focusing, which can greatly shorten the total length of the lens group and achieve a larger aperture light spot focusing. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of a single OK lens.

[0025] Figure 2 This is a schematic diagram of OVAL surface refocusing.

[0026] Figure 3 This is a schematic diagram of an OKp lens.

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

[0028] Figure 5 is the cross section of the first surface of the lens.

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

[0030] The application will be further described in conjunction with the accompanying drawings, the examples are used to explain the application, and are not used to limit the scope of the application.

[0031] The refractive index of the material for X-ray is 1-d+iβ, and the known data shows that the refractive absorption of SU8 is good in the medium and low energy region, and for the X-ray of 20Kev energy, d=1.21854487E-06; β=8.3084406E-10. Therefore, the design is a double-side focusing lens made of SU8 base, Figure 3 is shown (the diagram is ideal OKp lens). The comparison diagram of the lens and OK lens is shown in Figure 4 , wherein the dark blue and green parts together constitute the OKp single lens diagram, and the dark blue and light blue parts together constitute the single OK lens diagram (in order to better compare, the overlapping part is drawn with dark blue, and the different parts are green and light blue respectively). As can be seen from the lens structure, the absorption effect of the single lens on the light beam is close, but the focusing ability of the OKp lens can reach twice the effect, thus shortening the length of the lens and reducing the overall absorption, and making up for the defects caused by the rear surface divergence of the OK lens.

[0032] Figure 6 is the focusing diagram of the ideal OKp, and as can be seen from the diagram, two OKp lenses can focus the light beam 4 times, which is close to the effect of the traditional 4-piece OK lens. And the refraction of all the curved surfaces in the lens makes up for the defects of the OK lens considering only the curved surface.

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

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

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

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

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

[0038] As shown in Figure 5 , the parallel X-ray beam is incident from the left side of the air to the left surface of the first lens, and it is assumed that the curved surface will focus the parallel light beam to point F, and the left side is air refractive index n1=1; the right side is medium refractive index n2=1-δ; it is assumed that the focal length is OF, i.e. f; the point y(x) on the surface. According to the equal path principle, it is known that According to the relationship, the surface (1-δ) can be obtained 2 x 2 +(δ 2 -2δ)y 2 -2fy(δ 2 -δ)=0, which is an elliptical equation. The relationship between y and x is solved by separating variables (Another solution is discarded according to the lens surface, z≤0).

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

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

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

[0042] 4. In designing the lens aperture size, the OKp lens also uses the transfer equation of the OK lens. The aperture relationship of the nth lens and the n+1th lens is wherein y n represents the length of the nth lens, y n-1denotes the length of the (n-1)th lens, Figure 6 as shown.

[0043] 5. Where the length of each lens, i.e. the distance from the left plane of a single lens to the right plane of the same lens, is designed to be This length can also be a value that is an integer multiple of the length of the other lenses.

[0044] Although specific embodiments of the application have been disclosed herein in detail, this was done by way of example for purposes of illustration only. It is to be understood that various substitutions, alterations, and changes can be made to the specific embodiments described without departing from the spirit and scope of the application. Accordingly, the scope of the application should be judged in terms of the claims which follow.

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 direction of light incidence is... And the distance between the vertex of the incident surface of the nth lens and the vertex of the incident surface of the (n-1)th lens is y. n y n Let A1 be the length of the nth lens, where n = 2 to N, and A1 be the aperture of the 1st lens. (n-1)22 Let be the exit focal length of the (n-1)th lens exit surface. Excluding the incident surface of the first lens, the incident and exit surfaces of all the lenses are of OVAL shape. 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, 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 Let q be the incident focal length of the nth lens exit surface. n12 λ is the exit focal length of the nth lens incident surface, m is the step number of the lens, and λ is the incident light wavelength.

3. The large-aperture double-sided focusing Kinoform lens according to claim 2, characterized in that, The incident and exit surfaces of the steps 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 The integer multiple of λ, where λ is the wavelength of the incident light.

5. The large-aperture double-sided focusing Kinoform lens according to claim 1, characterized in that, The lens is made of SU8, the incident light is 20 KeV X-rays, and the aperture of the first lens is A1 = 200 μm.

6. A design method for a large-aperture double-sided focusing Kinoform lens as described in claim 1, comprising the following steps: 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 surface 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 A1. 3) Based on the refocusing model, design the exit surface of the first lens and the remaining lenses, so that the entrance and exit surfaces of all lenses except the entrance surface of the first lens are of OVAL type; wherein the aperture of the nth lens arranged along the light incident direction is... And the distance between the vertex of the incident surface of the nth lens and the vertex of the incident surface of the (n-1)th lens is y. n y n Let be the length of the nth lens.

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

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

9. The method according to claim 6, characterized in that, The length of the lens is The integer multiple of λ, where λ is the wavelength of the incident light.

10. The method according to claim 6, characterized in that, The lens is made of SU8, the incident light is 20 KeV X-rays, and the aperture of the first lens is A1 = 200 μm.

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