JPH05100615A - Method and device for hologram reproduction - Google Patents

Abstract

PURPOSE:To reproduce a hologram consisting of modulated equal-interval linear interference fringes with high precision by using two plane waves. CONSTITUTION:The plane wave for reproduction and the conjugate plane wave which is conjugate to it are made incident on the hologram H consisting of the equal-interval linear interference fringes which are modulated with a recording wave front and the diffracted reproduction wave front and conjugate wave front are made to interfere with each other, thereby optically reproducing the hologram H. In this case, the plane wave for reproduction and the conjugate plane wave are generated with symmetrical diffracted light beams of (+ or -1)th order generated by a linear diffraction grating 1. Light of unnecessary diffraction order from the diffraction grating 1 is removed by a spatial filter 7 and light other than the reproduction wave front and conjugate wave front from the hologram H is removed by a spatial filter 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hologram reproducing method and a reproducing apparatus, and more particularly to a hologram suitable for highly accurate reproduction of a hologram such as an electron beam hologram in which wavefronts are recorded by modulating linearly spaced interference fringes. The present invention relates to a reproduction method and a reproduction device.

[0002]

2. Description of the Related Art In an electron beam hologram, as shown schematically in FIG. 5, a sample is arranged on one side of the optical axis, a plane electron wave is made incident along the optical axis, and the electron wave is once made by an objective electron lens. After focusing, the image is formed, and the electron biprism is placed between this focusing point and the image plane, and the wave passing through the sample on one side of the optical axis is the object wave and the wave passing the opposite side of the optical axis. Is used as a reference wave and is made to interfere as an image hologram.
Actually, in order to reproduce the hologram by light, an electron beam hologram is obtained by enlarging and recording this interference fringe with an electronic lens. Such an electron beam hologram has a form in which straight-interval linear interference fringes are modulated by object information.

To reproduce a wavefront recorded from a hologram in which linearly spaced interference fringes with equal intervals are modulated by object information like this electron hologram, the plane wave for reproduction is used as shown in FIG. Then, a conjugate plane wave that is conjugate with each other is made incident at an angle 2θ with respect to the optical axis, and a reproduction plane wave reproduces a reproduction wavefront along the optical axis and a conjugate plane wave reproduces a conjugate wavefront along the optical axis. , The other 0th-order light is removed, and the reproduction wavefront traveling along the optical axis and the conjugate wavefront are interfered with each other to reproduce the recording wavefront as interference fringes whose phase is doubled.

By the way, in order to reproduce the recording wavefront by amplifying the phase as shown in FIG. 3, the arrangement as shown in FIG. 4 has conventionally been adopted (Applied Optics Vol. 26, No. 2 (1987)). p
p.377-382). That is, using a Twyman-Green type interferometer consisting of reflecting mirrors A and B and a beam splitter,
Both or one of the reflecting mirrors A and B is tilted by a slight angle, and the incident laser light is divided into two lights forming an angle equal to the angle 2θ formed by the reproducing plane wave and the conjugate plane wave in FIG. According to the principle of FIG. 3, a reproduction wavefront that advances along the optical axis and its conjugate wavefront are obtained. At this time, in order to remove other 0th-order light and diffracted light, a lens L1 is placed after the hologram, and a spatial filter is placed on the focal plane on the rear side of the hologram to reproduce a reproduction wavefront and its conjugate wavefront. Only the light is allowed to pass, and both wavefronts that have passed through the spatial filter are collimated again by the lens L2, a TV camera is arranged at a position conjugate with the hologram to cause interference between both wavefronts, and the interference fringe information is stored in the image memory. , The image is processed by the computer to obtain the shape of the recorded wavefront. On this occasion,
Phase modulation interferometry is used to accurately obtain the recorded wavefront phase distribution (see, for example, "Introduction to Applied Optical Optical Measurement" by Toyohiko Yatagai, pages 131 to 135 (published by Maruzen Co., Ltd.), Therefore, one of the plane waves for reproduction or the conjugate plane wave is phase-modulated between 0 and 2π,
A PZT (piezoelectric element) is attached to the back surface of one of the reflecting mirrors A, and the reflecting mirror A is moved back and forth by a minute distance according to a signal from the PZT driver.

[0005]

As described above, a plane mirror forming two angles is generated by using a reflecting mirror (a beam splitter is also included in the reflecting mirror), and it is composed of linearly spaced interference fringes. When reproducing a hologram, there are some problems, and it is not easy to reproduce the recorded wavefront with high accuracy. First, the reflecting mirror has unevenness of at least about λ / 30, and it is difficult to obtain a good plane wave. Furthermore, when a reflecting mirror is used, the divided optical paths spatially follow different paths, so that the fluctuation of air has a great influence. Furthermore, since a plurality of reflecting mirrors are usually arranged separately, they are weak against vibration. Further, the influence of the aberration of the light source system and the intermediate optical system is large. Further, since the reflecting mirror is moved back and forth to perform phase modulation, it is necessary to increase the modulation accuracy.

The present invention has been made in view of such a situation, and an object thereof is to make a hologram composed of modulated linearly spaced interference fringes such as an electron beam hologram highly precise by using two plane waves. It is to provide a reproducing method and an apparatus therefor.

[0007]

According to the hologram reproducing method of the present invention which achieves the above-mentioned object, a reproducing plane wave and a conjugate plane wave conjugate therewith are made incident on a hologram composed of linearly spaced interference fringes modulated by a recording wavefront. In the method of optically reproducing a hologram by causing the diffracted reproduction wavefront and the conjugate wavefront to interfere with each other, the reproduction plane wave and the conjugate plane wave conjugated to the reproduction plane wave are generated by light of a predetermined diffraction order symmetrical to the linear diffraction grating. The method is characterized by

In the hologram reproducing apparatus of the present invention, a reproducing plane wave and a conjugate plane wave conjugate therewith are made incident on a hologram composed of linearly spaced interference fringes which are modulated by a recording wavefront, and conjugate with the diffracted reproducing wavefront. A device for optically reproducing a hologram by interfering wavefronts, which comprises a linear diffraction grating and a light source device for making parallel light incident on the diffraction grating, and a predetermined symmetric order among diffracted light diffracted by the diffraction grating. It is characterized by including an optical system for selecting the two light beams and emitting them so as to intersect with each other at a predetermined angle on the hologram.

In this case, by providing a means for moving the diffraction grating along the plane in a direction intersecting with the grating, the recording wavefront can be measured with high accuracy by the phase modulation interferometry. This device can be used for inspection of a linear diffraction grating.

According to another hologram reproducing apparatus of the present invention, a reproducing plane wave and a conjugate plane wave conjugated to the reproducing plane wave are made incident on a hologram composed of linearly spaced interference fringes which are modulated by a recording wavefront to obtain a diffracted reproducing wavefront. An apparatus for optically reproducing a hologram by causing a conjugate wavefront to interfere with each other is provided with a linear diffraction grating that emits only two lights of a predetermined symmetrical diffraction order and a light source device that makes parallel light incident on the diffraction grating. It is characterized in that it is provided with means for holding the hologram close to or in close contact with the exit surface of the grating.

[0011]

In the hologram reproducing method and reproducing apparatus of the present invention, since two plane waves for reproduction are generated by using the diffraction grating without using the reflecting mirror, the influence on the plane wave by the incompleteness of the diffraction grating is affected. Is considerably smaller than that of a reflecting mirror, and more accurate wavefront reproduction is possible. Further, since the two plane waves follow almost the same optical path, there is almost no influence of air fluctuation, and since only one diffraction grating is used for dividing the optical path, it is resistant to external vibration.
Further, the influence of the aberration of the reproduction optical system is removed. Further, also in the phase modulation, the division accuracy of the modulation is considerably improved as compared with the conventional case.

[0012]

Embodiments of the hologram reproducing method of the present invention and an apparatus therefor will be described below with reference to the drawings. FIG. 1 is an optical path diagram of a hologram reproducing apparatus according to an embodiment of the present invention. The most important point of this apparatus is that a linear diffraction grating 1 is used to generate two symmetrical diffracted light beams. Is used as a plane wave and a conjugate plane wave (FIG. 3) for reproducing the hologram H. In FIG. 1, the intensity of the light from the stabilized laser 2 is adjusted by the ND filter 3,
After passing through the mirror 4, a collimator 5 forms a plane wave having an expanded beam diameter, which is incident on the diffraction grating 1. The incident light is diffracted by the diffraction grating 1 into ± 1st order, ± 2nd order, etc. in addition to the 0th order, but is once condensed by the lens 6 in order to select a predetermined symmetrical order, usually ± 1st order. A spatial filter 7 that passes only the ± first-order light is arranged on the light collecting surface (rear focal surface). The two lights that have passed through the spatial filter 7 are reflected by the lens 8 at the rear focal plane at a predetermined angle 2θ.
(FIG. 3) is converted into two plane waves intersecting with each other with the optical axis sandwiched therebetween. A hologram H composed of modulated linear interference fringes at equal intervals is arranged at this position, and the reproduced wavefront reproduced by the plane wave incident on the hologram H and the conjugate plane wave and the conjugate wavefront thereof travel along the optical axis. Zero-order light generated at this time,
Since the high-order diffracted light forms an angle with the optical axis, the diffracted light is once condensed on the rear focal plane by the lens 9 arranged at the position of the focal length after the hologram H, and the optical axis is at that position. A special (spatial) filter 10 that cuts light other than light traveling along is arranged to pass only the reproduced wavefront and its conjugate plane wave, and both wavefronts passing through the special filter 10 are collimated again by the lens 11 to form the hologram H. The two-dimensional detector 12 is arranged at a conjugate position to cause both wavefronts to interfere with each other, and the interference fringe information is stored in the image memory 1.
3 and the image is processed by the computer 14 to obtain the shape of the recorded wavefront. At this time, in order to accurately obtain the phase distribution of the recorded wavefront, the above-mentioned phase modulation interferometry is used. To this end, the diffraction grating 1 is moved by the diffraction grating moving mechanism and the control unit 15 in the direction intersecting the grating on the surface, phase modulation in the opposite direction is applied to both wavefronts, and interference patterns having different phase states are obtained. An accurate wavefront phase distribution can be obtained from different interference patterns (see the above reference). The phase modulation by the movement of the diffraction grating 1 is such that when the diffraction grating 1 is moved by a half pitch, the phase of the + 1st order wave advances by π and the phase of the −1st order wave delays by π.
It is understood that when both waves are made to interfere, the same effect as advancing one wave by 2π is obtained. In the above arrangement, the diffraction grating 1, the hologram H, and the two-dimensional detector 12 are arranged in mutually conjugate positions.

With such an arrangement, when reproducing the hologram H composed of linearly spaced interference fringes modulated by an object, compared with the conventional example shown in FIG. 4, the hologram is reproduced without using a reflecting mirror. Since two plane waves are generated, the influence is only due to the imperfections of the diffraction grating and is not affected by the unevenness of the reflecting mirror. The effect of the imperfections of the diffraction grating on the plane wave is about one-third that of the reflecting mirror. Moreover, the imperfections of the diffraction grating 1 can be removed by spatial filtering by the spatial filter 7. Further, when a reflecting mirror is used, the divided optical paths follow spatially different paths, and the influence of air fluctuations is large. However, in the case of FIG. 1, almost the same optical paths are traced, so the influence of air fluctuations is large. Almost never. Also, 1 for the optical path division
Since it uses only one diffraction grating, it is strong against external vibration.
Further, in the case of FIG. 1, since the two plane waves incident on the hologram H intersect at the same position as the division position, even if the illumination systems 2 to 5 of the diffraction grating 1 have aberrations, the reproduction wavefront and its conjugate wavefront are generated. Will be affected by the aberration in the same direction,
The interference removes the effects of aberrations. Further, even if there are axially symmetric aberrations in the optical systems 6 and 8 between the diffraction grating 1 and the hologram H, the two plane waves incident on the hologram H are affected in the same manner, and thus the influence of the aberrations is also manifested. Absent.
Further, also in the phase modulation, since the pitch of the diffraction grating 1 is about 50 to 500 times the wavelength, the division accuracy of the modulation becomes considerably higher than that of the conventional case.

In the case of FIG. 1, if a zoom lens (variable magnification lens) is used as the lens 6, the diffraction grating 1 does not have to be changed even when the hologram H to be reproduced has a different interference fringe pitch. That is, in this way, the magnification of the lens 6 is changed and the hologram H
This is because it is possible to match the angle formed by the two wavefronts incident on the angle with the angle peculiar to the hologram H. Note that this has the same technical meaning as adjusting the grating pitch of an image formed on the hologram H of the diffraction grating 1 to the pitch of the interference fringes of the hologram H by changing the magnification corresponding to the focal length of the lens 6. Is. Actually, the grating pitch of the image of the diffraction grating 1 and the pitch of the interference fringes of the hologram H do not necessarily have to match exactly, and even if there is some deviation, there is no problem in measurement. Since the interference pattern has interference fringes of a spatial frequency corresponding to the deviation as a background, it is sufficient to remove the interference fringes by image processing.

In the above description, the apparatus of FIG. 1 is premised on being used to reproduce the phase information recorded in, for example, an electron beam hologram, but it can also be used to inspect a diffraction grating. .. In this case, the inspected diffraction grating is arranged as the hologram H.

In the case of FIG. 1, the reproducing plane wave and the conjugate plane wave are made to enter the hologram H from both sides with the optical axis interposed therebetween to amplify and phase the interference, based on the principle shown in FIG. The plane wave for use and the plane wave traveling along the optical axis may be incident on the hologram H, and the phase of the wavefront may be detected by causing the reproduced wavefront and the plane wave transmitted through the hologram H along the optical axis to interfere with each other. In this case, the 0th-order light and the + 1st-order light transmitted through the diffraction grating 1 are selected by the spatial filter 7 and used. In this case, the recording wavefront is obtained by causing interference without phase amplification.

In FIG. 1, the optical systems 6 to 8 are arranged between the diffraction grating 1 and the hologram H in order to extract diffracted light of two predetermined orders from the diffraction grating 1. When using, for example, one that diffracts only the ± 1st order light as 1, the optical systems 6 to 8 can be omitted. The optical path diagram in that case is as shown in FIG. In this case, the hologram H may be brought into close contact with the diffraction grating 1 and arranged on the front focal plane of the lens 9.

1 and 2, the spatial filtering optical system including the lenses 9 and 11 and the special filter 10 is used to extract the two wavefronts diffracted from the hologram H in the optical axis direction. , Instead of this,
It is also possible to dispose a lens at a relatively distant position, pass only two wavefronts traveling along the optical axis through the aperture, and form a hologram surface on the detection surface of the two-dimensional detector 12 by this lens.

Although the hologram reproducing method and reproducing apparatus of the present invention have been described above based on some embodiments, the present invention can be modified in various ways. Further, the hologram to be reproduced is not limited to the electron beam hologram, but may be an X-ray hologram or a normal optical hologram.

[0020]

As described above, according to the hologram reproducing method and reproducing apparatus of the present invention, since two plane waves for reproduction are generated by using the diffraction grating without using the reflecting mirror, the diffraction grating The effect of the imperfections on the plane wave is about one-third as compared with the case of the reflecting mirror, and the wavefront can be reproduced with higher accuracy. In addition, since the two plane waves follow almost the same optical path, there is almost no effect of air fluctuations, and since only one diffraction grating is used for dividing the optical path,
It is strong against external vibration. Further, the influence of the aberration of the reproduction optical system is removed. Further, also in the phase modulation, the division accuracy of the modulation is considerably improved as compared with the conventional case.

[Brief description of drawings]

FIG. 1 is an optical path diagram of a hologram reproducing device according to an embodiment of the present invention.

FIG. 2 is an optical path diagram of a hologram reproducing device according to another embodiment.

FIG. 3 is a diagram for explaining the principle of the reproducing method which is the basis of the present invention.

FIG. 4 is an optical path diagram of a conventional hologram reproducing device.

FIG. 5 is a schematic diagram showing a schematic configuration of an electron beam hologram imaging apparatus.

[Explanation of symbols]

 H ... Hologram 1 ... Linear diffraction grating 2 ... Stabilized laser 3 ... ND filter 4 ... Mirror 5 ... Collimator 6 ... Lens 7 ... Spatial filter 8 ... Lens 9 ... Lens 10 ... Special (spatial) filter 11 ... Lens 12 ... Two-dimensional Detector 13 ... Image memory 14 ... Computer 15 ... Diffraction grating moving mechanism and control unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Ishizuka 14-48 Matsufudai, Higashimatsuyama City, Saitama Prefecture (72) Inventor Akira Tonomura 2-19-5 Kaedeoka, Hatoyama Town, Hiki-gun, Saitama Prefecture

Claims (5)

[Claims] 1. A hologram is formed by injecting a reproducing plane wave and a conjugate plane wave conjugate with the hologram into a hologram composed of linearly spaced interference fringes modulated by a recording wavefront, and causing the diffracted reproduction wavefront and the conjugate wavefront to interfere with each other. In the method for optically reproducing, a hologram reproducing method characterized in that the reproducing plane wave and a conjugate plane wave conjugate therewith are generated by light of a predetermined diffraction order symmetrical with respect to a linear diffraction grating. 2. A hologram is formed by injecting a reproducing plane wave and a conjugate plane wave conjugate with the hologram into a hologram composed of equal-interval linear interference fringes modulated by a recording wavefront, and causing the diffracted reproduction wavefront and the conjugate wavefront to interfere with each other. A device for optically reproducing includes a linear diffraction grating and a light source device for making parallel light incident on the diffraction grating, and selects two lights of a predetermined symmetry order from diffracted lights diffracted by the diffraction grating. A hologram reproducing apparatus comprising an optical system that emits light so as to intersect a hologram at a predetermined angle. 3. The hologram reproducing apparatus according to claim 2, further comprising means for moving the diffraction grating along a plane thereof in a direction intersecting with the grating. 4. The hologram reproducing apparatus according to claim 2, which is used for inspecting a linear diffraction grating. 5. A hologram is formed by injecting a reproducing plane wave and a conjugate plane wave which is conjugate to the hologram into a hologram composed of linearly spaced interference fringes modulated by a recording wavefront, and causing the diffracted reproduction wavefront and the conjugate wavefront to interfere with each other. An apparatus for optically reproducing includes a linear diffraction grating that emits only two lights of a predetermined symmetric diffraction order and a light source device that makes parallel light incident on the diffraction grating, and is close to or in close contact with the exit surface of the diffraction grating. And a hologram holding device for holding a hologram.