JPS6032841B2 - How to make a zone plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a method of optically fabricating zone plates.

A zone plate is a light-shielding plate in which only odd or even numbered zones among a large number of zones are transparent, and when the zones are Fresnel zones, they are especially called Fresnel zone plates.

In the case of a Fresnel zone plate, the transmittance of light within one annular zone is almost uniform, and when the zone plate is scanned outward from the center with a narrow light beam, the intensity of the transmitted light changes in a rectangular waveform. A Fresnel zone plate with such properties is created by drawing a large ring zone using calculated values and photographing it in a reduced size. Therefore, the number of rings in a Fresnel zone plate is about 100.
It is very difficult to make a Fresnel zone plate with 2000 to 3000 ring zones. Therefore, in recent years, especially since the technology of holography has advanced, it has become common to produce zone plates by recording interference fringes caused by plane waves and spherical waves having the same optical axis on a photosensitive material. When a zone plate manufactured by this method is scanned outward from the center with a narrow beam, the intensity of the transmitted light changes sinusoidally. Therefore, a zone plate made by this method is called a hologram zone plate to distinguish it from a Fresnel zone plate. The number of annular zones in the hologram zone plate can easily be 1000 or more.

Hologram zone plates are superior to Fresnel zone plates in some respects, such as their size, but most of the Fresnel zone plates currently made have a main ring zone and a center point other than the main ring zone. These spurious ring zones overlap, and this spurious ring zone finally forms a harmful point image.

Spurious annular zones occur due to reflection from the back surface of a semi-transparent mirror used to align plane waves and spherical waves so that their optical axes coincide, and are unavoidable as long as the semi-transparent mirror is thick. Therefore, it was considered to use a Wollaston prism type beam splitter instead of a semi-transparent mirror, but large Wollaston prisms are actually very difficult to obtain. The purpose of this invention is to improve the conventional optical zone plate manufacturing method as described above,
To provide a method for inexpensively manufacturing a hologram zone plate without spurious ring zones.

The principle of the invention is as follows.

Interference fringes caused by interference between a first spherical wave having an arbitrary radius of curvature and a reference wave are first recorded on a recording material, and then a second spherical surface having the same optical axis as the first spherical wave but a different radius of curvature is recorded. A hologram is produced by recording interference fringes caused by interference between a wave and a reference wave having the same properties as the reference wave on the photosensitive material, and two spherical waves having different radii of curvature are simultaneously reproduced from the hologram. If the concentric striped pattern formed by interference is recorded on a recording material, a zone plate without overlapping spurious ring zones can be produced. Therefore, the feature of the method for manufacturing a zone plate according to the present invention is that interference fringes caused by interference between a first spherical wave having an arbitrary radius of curvature and a reference wave are first recorded on a recording material, and then the first spherical wave and the light A hologram is produced by superimposing and recording interference fringes on the photosensitive material due to interference between a second spherical wave having the same axis but a different radius of curvature and a reference wave having the same properties as the reference wave, and simultaneously reproducing from the hologram. The point is that two spherical waves having different radii of curvature interfere with each other to form a zero-circle striped pattern on the recording material.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an optical device conventionally used for optically manufacturing a zone plate, in which 101 is a coherent light generating blind pupil such as a laser device, and 102 is a coherent light generating device. A coherent light beam emitted from 101, 103 a beam splitter for splitting the coherent light beam 102 into two directions, 104, 105 an inverted telescope type optical system for expanding the diameter of the coherent light beam, 106, 107 108 is a reflecting mirror, 108 is a lens for converting a coherent light beam whose diameter has been expanded into a spherical wave with an arbitrary radius of curvature, 109 is a semi-transparent mirror, 1 10
is a recording material. In this optical device, the main interference fringes are expanded by an inverted telescope type optical system 104, reflected by a reflecting mirror 106, and coherent light 1 transmitted through a semi-transparent mirror 109.
1 1 and is expanded by the inverted telescope type optical system 105, and the reflecting mirror 1
07, the radius of curvature is changed by the lens 108, and the coherent light 1121 is reflected from the front surface 1091 of the semi-transparent mirror 109, but the coherent light that is reflected from the back surface 1092 of the semi-transparent mirror 109, e.g. 112
2 also interferes with the coherent light 111 to form interference fringes, so when a zone plate is manufactured using this optical rhombus pupil, a zone plate with spurious annular zones superimposed on the main annular zone is created as shown in Figure 2. can. FIG. 3 is a diagram showing the configuration of an embodiment of an optical device for manufacturing a hologram in the zone plate manufacturing method according to the present invention, in which 301 is a coherent light generator, and 302 is a coherent light generator 301 that emits light. 303 is a beam splitter for splitting the coherent light beam 302 into two directions, 304 and 305 are inverted telescope type optical systems for expanding the diameter of the coherent light beam, and 306, 307, and 308 are reflecting mirrors. , 309 is a lens that can be moved along the optical axis to convert the diameter-expanded coherent light beam into a spherical wave with an arbitrary radius of curvature;
310 is a recording material.

In this optical equipment, interference fringes are first recorded on the recording material 310' when the lens 309 is placed at an appropriate position.
Next, without moving anything other than lens 309, lens 30
9 is moved along the optical axis to change the radius of curvature of the coherent light that reaches the recording material 310. Interference fringes are recorded on the recording material 310. A hologram is completed by subjecting the recording material on which the two interference fringes have been recorded in this way to a normal development and fixing process. As shown in FIG. 4, when the hologram produced in this way is illuminated with coherent light whose diameter is expanded by the inverted telescope type optical system 403 of the coherent light beam 402 emitted from the coherent light generator 401, the hologram 404 Two spherical waves 405 and 406 are reproduced, and the spherical waves 405 and 406 interfere to form the same D circular striped pattern.

Then, this concentric cotton pattern is recorded on a recording material 407 and subjected to normal development and fixing processing to complete a zone plate. The zone plate made in this way has
Since no semi-transparent mirror is used after the diameter of the coherent light beam is expanded, there are no spurious rings. As described in detail above, according to the present invention, a zone plate without spurious annular zones can be manufactured easily and inexpensively.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of an optical setup conventionally used to optically manufacture a zone plate, and Figure 2 is a diagram showing the configuration of an optical setup used to optically manufacture a zone plate.
A diagram showing an example of a zone plate with a spurious annular zone manufactured using the optical apparatus shown in the figure. FIG. FIG. 4 is an embodiment of an optical device for reproducing a wavefront forming a zero-circle stripe pattern from a hologram produced by the optical device shown in FIG. 3 and recording the concentric stripe pattern. FIG. In the figure, 101, 301, 401 are coherent light generating bags, 102, 302, 402 are coherent light beams, 103, 303 are beam splitters, 104, 1
05, 304, 305, 403 are inverted telescope type optical systems, 1
06, 107, 306, 307, 308 are reflecting mirrors, 10
8,309 Shins, 109 semi-transparent mirror, 110,31
0,407 is recording material, 404 is E. grams, 405,
406 is a spherical wave. O figure 2 figure O 3 figure O 4 figure

Claims (1)

[Claims] 1 First, interference fringes caused by interference between a first spherical wave having an arbitrary radius of curvature and a reference wave are recorded on a recording material, and then a second spherical wave having the same optical axis as the first spherical wave but a different radius of curvature is recorded. A hologram is produced by superimposing and recording interference fringes caused by interference between a spherical wave and a reference wave having the same properties as the reference wave on the photosensitive material, and two spherical surfaces with different radii of curvature are simultaneously reproduced from the hologram. A method for manufacturing a zone plate, characterized in that a concentric striped pattern formed by interference of waves is recorded on a recording material.