JPS6080801A - Pattern generator of fresnel zone plate - Google Patents

Abstract

PURPOSE:To form an interference pattern of a Fresnel zone plate for X-ray imaging by bisecting the luminous flux from one spot light source with a beam splitter, reflecting respectively the split beams with spherical mirrors and condensing the beams to different two points on the common optical axis of both spherical mirrors which are optically superposed. CONSTITUTION:The laser beam from a laser light source 1 is condensed to a point P to form a divergent luminous flux which is then bisected by a beam splitter 3. The luminous flux reflected by the splitter 3 is made incident to a concave spherical mirror M by which the luminous flux is reflected to condense at the point O. The luminous flux transmitted through the splitter 3 is reflected by a concave spherical mirror M' and is corrected in spherical aberration by an aberration correcting lens L. The corrected flux is reflected by the splitter 3 and is condensed at the point I. The point I is on the optical axis of the mirror M together with the point O and the recording carrier F for the interference pattern is set at the intermediate of the point O and the point I and said pattern is recorded thereto.

Description

Detailed Description of the Invention B) Industrial Application Field The present invention relates to an apparatus for manufacturing a Fresnel zone plate used as an imaging element, and particularly relates to an apparatus for manufacturing a Fresnel zone plate suitable as an imaging element in the X-ray region. .

(b) Prior Art Although convergence means using refraction cannot be applied to X-rays, it is possible to converge or image them using diffraction. For this reason, it is difficult to fabricate a tube for X-rays. 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 was devised. The wavelength of the light used for holography is several thousand years, and when the target X and I wavelengths are set to about 100A, the focal length of the light used for holography is several meters.
Even if a zone plate is made with a distance of m, the focal length for the target X-ray will be about 200 mm. Therefore, when recording a Fresnel zone plate with a focal length of about 200 mm for the target X-ray and a practical diameter of about 2 to 3 mm using visible light holography, the light beams that cause interference are It is necessary to converge at a medium-sized aperture angle, and the spherical aberration of the holographic optical system becomes a major obstacle.

(c) Purpose The present invention provides a Fresnel zone pattern generator in which the spherical aberration of a holographic optical system for recording the pattern of a Fresnel zone plate for X-ray imaging is sufficiently corrected.

B) Structure The present invention splits the spherical wave light beams emitted from - point light sources into two directions with a beam sinter, and reflects the two divided light beams with spherical mirrors to optically overlap the two slopes. This is a Fresnel zone pattern generation device in which light is focused on two different points on a common optical axis of a mirror, and an interference pattern recording carrier is placed at an appropriate position on the same optical axis.

(E) Embodiments Before explaining the embodiments, a general explanation will be given. In Figure 1, F is the Fresnel zone plate and A is its optical axis. Let 0 and 1 points be placed on both sides of the zone plate F on the optical axis A, and let the distances from the center of the zone plate to these points be u and v. Consider a circle with radius rn from the optical axis on zone plate F, and let S be the distance from the 0 and 1 points to the circumference of this circle.

When t, u 1 V = 8 + t - nλ n is an integer and the light is focused on one point, and the 1 point and the 0 point are in the relationship of conjugate points of the imaging system. The focal length 1 of such a zone plate is l / u3
, 1/v3 or more, the following relationship holds true: 111 uvf, f=nJ... (1). When such a zone plate is used for light with a wavelength of λ1, the focal length f1 is calculated from equation (1) as follows: When intertwined, it becomes 1.25 mm.

The principle of creating a zone plate using holography is as shown in Figure 1. Point light sources that emit light that can interfere with each other are placed at points 0 and 1, respectively, to form an interference pattern on plate F, and this is recorded. It is. The wavelength of the light used at this time is λ
If so, a zone plate that satisfies equation (1) can be obtained. Therefore, using 400OA light, 100
When trying to make a zone plate with a focal length of 50 mm for X-rays A, if u = v in equation (1), then u
=v=2.5mm, and the outer diameter of the zone plate is 3m.
When m, the opening angle of the luminous flux becomes nearly 60°.

The present invention splits the light beam from one point light source into two with a beam splitter, focuses each of the two divided light beams with a spherical mirror to create an image of the light source, and converts these images into the 0 point and 1 point mentioned above. This is to form an interference pattern.

FIG. 2 shows an embodiment of the invention. 1 is a laser light source (output light wavelength 4t16A), and 2 is a condenser lens that focuses the laser beam on point P. h is a pinhole placed at point P. As the condensing lens 2, an objective lens of a microscope is used. The laser beam focused on point P is P
It diverges from a point as a spherical wave. This diverging light beam is split into two by the beam splitter 3. Of the two divided beams, the one reflected by the beam splitter enters a concave spherical mirror M, is reflected by the mirror, and is condensed at a zero point. The 0 point and the P point are located symmetrically with respect to the reflecting surface of the beam splitter, and the center of curvature of the spherical mirror M is made to coincide with the 0 point.

Therefore, the point P is also the center of curvature of the spherical mirror M in red optical terms. Therefore, the laser beam focused on the zero point is completely focused without aberration. The light beam that has passed through the beam splitter 3 is reflected by the concave spherical mirror M1, and then reflected by the beam splitter 3 and condensed at one point. The 1 point and the 0 point are on the optical axis of the spherical mirror M, and the 1 point and the P point are in a conjugate relationship with respect to the spherical mirror M1, but they are located at positions slightly shifted from the center of curvature of the spherical mirror M1. Therefore, if only the spherical mirror M+ is used, the light beam condensed to one point will have spherical aberration. The lens L corrects this spherical aberration. The record carrier F of the interference pattern is set at an intermediate position between the 0 point and the 1 point.

In the above embodiment, the opening angle of the light beam condensed to the 0 point is the spherical mirror M
The aperture angle is set so that the aperture angle of the light beam condensed at one point is also equal to that of the light beam condensed at 0 point, and in order to obtain a large aperture angle, a beam splitter and a spherical mirror M are used. , M' becomes large, which is disadvantageous in terms of construction. Third
The embodiment shown in the figure is an embodiment that improves this point. The dimensions marked in the figure indicate the size of the device in mm. The laser beam is focused on the pp point by the condensing lens 2, and the spherical wave light diverging from the P point is split into 2 by the beam splitter 3.
The configuration in which the light beam is divided into light beams, incident on two concave spherical mirrors M and M', and reflected is the same as in the above embodiment. The P point and the 01 point are symmetrical with respect to the beam splitter 3 and are made to coincide with the center of curvature of the concave spherical mirror M. The light reflected by the spherical mirror M is focused on the 0° point without aberration, but by the abrasive lens Ll whose conjugate points are the 01 point and the 0 point)
, 01 point is also focused without aberration on the 0 point near the mirror M, and the opening angle of the light beam is expanded from α·1 to α. The abranatic lens L'' uses the well-known abranatic point on the spherical refractive surface, and has the 0 point and the Ql
It is completely aberration-free with respect to. beam sp.

The light beam that has passed through the liter 3 is focused at one point by an optical system consisting of a concave spherical mirror M', a lens L, and a lens L1.

The light reflected by M+ passes through lens L and is focused on point 1, but since point 1 and point 1 are not abrasive points with respect to lens Ll, aberrations appear at point 1, but lens Ll is for correcting the aberration of the light beam converging at one point. The interference pattern record carrier is set between 0 and 1 points.

In addition, the abrasive point of lens Ll is ■l.

A correction lens may also be placed in front of the spherical mirror M by placing it between 01 and 01, and between 0 and 0.

(f) Effect As described above, in the device of the present invention, light that diverges from the center of curvature of a spherical mirror is focused on the center of curvature without aberration, and light that diverges from near the center of curvature is focused on other lights near the center of curvature. This method takes advantage of the fact that light is focused on a point and has little aberration, making it easy to correct aberrations.It is possible to obtain an aberration-free focusing point with a large aperture angle using a simple optical system, making it relatively It became possible to make Fresnel zone plates as X-ray imaging elements with large diameters.

[Brief Description of the Drawings] Fig. 1 is an explanatory diagram of a Fresnel zone plate, Fig. 2 is a plan view of an apparatus according to an embodiment of the present invention, and Fig. 3 is a plan view of another embodiment of the present invention. . l...Laser light source, 2...Condenser lens, 3...
...Beam splitter, M, M+...Concave spherical mirror, L
...Aberration correction lens, L'...abranatic lens. Agent Patent Attorney Hiroshi Agata

Claims (2)

[Claims] (1) The light diverging from the point light source is divided into two beams by a beam splitter, and one of the divided beams is optically reflected by a concave spherical mirror having a center of curvature at the point light source, which is different from the point light source. A pattern generating device for a Fresnel zone plate, wherein the other divided light beam is reflected and focused near the focal point on the optical axis of the concave spherical mirror by another concave spherical mirror. (2) Using an abranatic lens, in which one of the direct convergence points of the concave spherical surface or a point near it is one of the abranatic points, the two convergence points are set on the line connecting the concave spherical surface. 2. The Fresnel zone plate pattern generating device according to claim 1, wherein the divergence angle of the condensed light beam is expanded by bringing the condensed light beam closer to the side.