JPS6031101A - X-ray imaging element - Google Patents

Abstract

PURPOSE:To reduce an aberration in case a titled zone plate is used by a shorter wavelength than a wavelength used for a holography by recording an interference fringe by the holography on a curve surface which is curved symmetrically in its rotation. CONSTITUTION:In case a Fresnel zone plate is made by an interference on a plane plate P of two optical waves of luminous flux W1 and W2, it is the same as what is called a hologram of a point image, and if a wavelength is the same as a wavelength of a recording light source in case of condensing a light from a point O to I, the focal position is constant with regard to any annular zone, and a point image of non-aberration is obtained in a position of I. In case the Fresnel zone plate prepared in this way is used by other wavelength than a wavelength of a recording light source, a large aberration is generated and it does not become practical, therefore, the aberration is corrected by forming a hologram of a point image on the spherical surface. That is, in case a relative relation of the recording light source is constant, the aberration can be corrected by forming the zone plate to a spherical surface, therefore, the Fresnel zone is improved remarkably by forming it on a curved surface.

Description

[Detailed description of the invention] (b) Industrial application field related to what was done.

(b) Conventional technology Although convergence means using refraction cannot be applied to X-rays, it is possible to converge or image them using diffraction. For this reason, a Fresnel zone plate for X-rays was considered, but the spacing between the concentric circles is very small, making it difficult to fabricate mechanically. An annular drawing method using electron beam exposure has also been considered, but it is difficult to make one of a practical size. Therefore, a method of recording interference fringes using holography has been considered, but this would involve using light with a very long wavelength as the wavelength of light used for holography. However, when a zone plate recorded using light with such a long wavelength was used at a wavelength different from that used for holography, the imaging aberration was large, and its performance as an X-ray focusing device was extremely low. .

(c) Purpose The present invention aims to reduce aberrations when a Fresnel zone plate recorded by holography is used at a wavelength shorter than the wavelength used for holography.

(d) Configuration In order to achieve the above object, the present invention provides a Fresnel zone plate in which interference fringes are recorded by holography on a rotationally symmetrically curved curved surface.

As shown in Figure 1, point 0 and point 1 are taken on the axis perpendicular to the flat plate P, and the dimensional relationships are determined as shown in the diagram, u, V, S, and t. n is an integer)...
...(1) If we form a concentric zone with a radius rn that satisfies the relationship 2, that is, a Fresnel zone, the light emitted from the point O will be focused on the dot, and 1/n3. If we ignore higher-order terms of 1/v3 or higher, we get:

This shows that the Fresnel zone plate has the same effect as a convex lens, and its focal length is n2 f=□・・・・・・・・・・・・・・・(3)n
It is expressed as λ (n is an integer and rn is the radius of the nth ring zone).

Figure 2 A is a schematic diagram of recording and reproducing when such a Fresnel zone plate is created by interference on a plane plate P of two light waves, a light beam W1 diverging from 0 point and a light beam W2 converging to one point. The plate is the same as a so-called point image hologram. In the Fresnel zone plate made in this way, the light from point 0 is
If the wavelength is the same as that of the recording light source, the focal position will be constant with respect to the annular zones and, and an aberration-free point image will be obtained at the position of ■. However, when the Fresnel zone play 1- created in this way is used at a wavelength λ1 in the X-ray region, which is different from the wavelength of the recording light source, the focal length is λ fλ'--f...・・・・・・・・・・・・
・・・・・・・・・・・・(4) λ1 The relational expression for imaging corresponding to equation (2) is −1−=□
・・・・・・・・・・・・・・・・・・・・・(5)u
l v l fλ1 , but large aberrations also occur, making the arrangement impractical. The present invention attempts to solve these problems by forming a point image hologram shown in FIG. 2 on a spherical surface. For example, He-C
Even when recording with a 44'+-6A d laser and using this at a wavelength of 100A in the soft X-ray region, it is possible to provide a large Fresnel zone plate with sufficient aberration correction for practical use. .

(E) Example wavelength λ at a distance of 200 mm from the Fresnel zone plate
' = 100 There is a point light source A, which is 200mm
Let us consider the case where the light is focused on a point (strictly speaking, 200.42949 □). In equation (5), U“−v1=
Since it is 200 mm, fλ'=lOOmm.

Now, if we try to create this using the 4416X wavelength of the He-cd laser, the focal length of λ-4416A from equation (4) is f = 2.26449 mm L, so in equation (1), u = 3. If it is .89622mm, ■
-5°16785mm.

Figure 3 is a diagram showing this recording condition. When the hologram surface is a flat surface or several spherical surfaces, the reproduced image of λ' = 10OA under the conditions shown in Figure 4 is as shown in Figure 5. Aberration curves are shown. In this figure, Rf is the radius of curvature of the plate surface, and the sign of Rf means that the result is the same no matter which direction the curved surface faces. Further, the horizontal axis shows the distance from the center of the zone plate, and the vertical axis shows the amount of lateral aberration.

(F) Effect As is clear from FIG. 5, when the relative relationship between the recording light sources is constant, it is possible to significantly correct aberrations by making the zone plate spherical.

The present invention is characterized in that the aberrations that occur when a Fresnel zone plate made at a wavelength of λ is used at a wavelength of λ1 are significantly improved by forming the Fresnel zone on a curved surface.

In this example, a spherical surface with the center of curvature at U and V gives good results, but of course it is not limited to this.
It is also possible to have a convex spherical surface or a concave spherical surface.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram explaining the principle of a Fresnel zone plate, Figure 2 A is a side view showing the relationship between the light flux and the plate when creating a Fresnel zone plate by interference of two light waves, and Figure 2 B is a schematic diagram explaining the principle of a Fresnel zone plate. FIG. 3 is a side view illustrating the image formation state of the Fresnel zone plate produced, FIG. 3 is a side view illustrating the relationship between the luminous flux and the grating when producing a Fresnel zone plate according to an embodiment of the present invention, and FIG. 4 is the above-mentioned FIG. 5 is a side view showing the positional relationship between a light source and an image point when the resulting zone plate is used for X-rays, and FIG. 5 is an aberration curve showing the effects of the present invention. P... Plate, 0... Light source, ■... Convergence point agent Patent attorney Hiroshi Agata 7-

Claims (1)

[Claims] A Fresnel zone plate that records concentric interference fringes formed on a curved surface with the same axis as the axis of rotational symmetry by the interference of three beams on the same axis.