GB2070272A - Method and device for recording optical information - Google Patents

Abstract

The proposed method for recording optical information consists in that the image of an object (2) carrying optical information is projected in integrated light on a photothermoplastic recording medium (3). At the same time, an image pattern is produced by interfering beams. The interfering beams are controlled to obtain an overall picture of the projected image and the superimposed pattern; which is then recorded. The device for carrying out the above method comprises a system (1) for projecting the image of an object (2) on a photothermoplastic recording medium (3). In addition, the device comprises a laser (6) with a system of beam splitters and mirrors for initiating interfering beams, and a means for controlling the orientation and/or intensity of the interfering beams, which is coupled to the system of beam splitters and mirrors and optically associated with the photothermoplastic recording medium (3) via a device (5) for developing it. The invention can be used for recording holograms of moving objects and color images on black- and-white photographic materials. <IMAGE>

Description

SPECIFICATION Method and device for recording optical information The present invention relates to means for recording information, and more particularly to methods and devices for recording optical information .

The invention can be used for recording holograms of objects illuminated with incoherent light, for example, recording holograms of moving objects, as well as for recording color images on black-and-white photographic materials such as photothermoplastic recording media.

The invention is also applicable to image recognition systems, for example, data input and output units of computers, devices for obtaining three-dimensional and color images to be transmitted through TV channels and providing for long-term storage of the recorded information.

Known in the art is a method for recording optical information, consisting in projection of an image on the thermoplastic layer of a photothermoplastic recording medium with simultaneous display of a grid image by projecting a fringe pattern formed by two converging coherent beams on the recording medium.

A device can be easily made to record optical information by this method, which must comprise a system for projecting the object's image on a photothermoplastic recording medium, a device for charging the latter and a device for developing it, and a laser with a system of beam splitters and mirrors for initiating interfering beams.

However, such an approach does not permit recording color images on a photothermoplastic medium or recording holograms of moving objects illuminated with incoherent light.

Another method is known, whereby the image of an object carrying optical information is projected, in monochromatic light separated from integrated light, on a recording medium. A beam scattered by the object is split by means of a diffraction grating into two spatially coherent interfering beams which form a hologram.

The intensity of the interfering beams in this prior art method is not sufficiently high and is determined by that of the object's illumination and by the diffraction grating efficiency. If the object's configuration is more complex or in the case of moving objects, this method fails to provide for a contrasty fringe pattern. Besides, this method imposes stringent requirements on adjustment of the recording arrangement components. - Also known is a method for recording color images, wherein, to provide for spatial modulation, projected on a photographic material is a dot pattern continuously rotated at a constant angular speed.To avoid blurring of the dot pattern, the image is projected therethrough using a stroboscopic technique, the light being stroboscopically interrupted at intervals corresponding to the dot pattern being rotated through 30o. Placed across the light beam is an opaque disc with slots of different sizes, which serve as apertures. The disc is rotated smoothly and synchronously with the dot pattern so that at the moment a stroboscopic flash is produced, the beam hits an aperture whose size corresponds to the luminous flux intensity required for exposure in a particular color. Also placed across the beam, along with the disc and the dot pattern, is a filter of the corresponding color. The flash exposure at smooth rotation of the dot pattern enables the time interval between filter changes to be minimized.However, in order to avoid blurring of the rotating dot pattern, the exposure must take place within a very brief space of time, which will reduce the sensitivity of the recording system and require high beam power during exposure. Besides, such a method does not ensure high resolution.

The principal object of the invention is to provide a method for recording optical information with such beam control and such a device for carrying out this method as to enable recording, on a photothermoplastic recording medium, color images or holograms of objects illuminated with incoherent light.

Another object of the invention is to provide for recording of holograms of moving objects illuminated with integrated light.

Still another object of the invention is to enhance the sensitivity of recording.

Yet another object of the invention is to enable control of the image quality in the course of recording.

A further object of the invention is to simplify adjustment of the components in the device for carrying out the above method.

The invention resides in a method for recording optical information, consisting in that the image of an object carrying optical information is projected in integrated light on a photothermoplastic recording medium, an image pattern is produced at the same time by interfering beams, the resulting pattern is fixed, the interfering beams are controlled to obtain an overall picture of the projected image and the superimposed pattern, which has been recorded.

Preferably, in the case of recording color images, the interfering beams should be controlled by changing their mutual orientation, and the number of orientation changes should be taken equal to that of discriminated color components of the projected image.

To control the quality of the obtained overall picture of the projected image and the superimposed patter, said overall picture should preferably be visualized in the image plane by illumination with one of the interfer ing beams.

It is advisable that the interfering beams be controlled during hologram recording by using one of the interfering beams as a reference, while the image visualized by the other interfering beams be used as an object beam, and a hologram resulting from the interference of both beams be recorded.

The intensity ratio of the interfering beams should preferably be changed.

The invention also resides in that a device for carrying out the above method for recording optical information, comprising a system for projecting the image of an object on a photothermoplastic recording medium, a device for charging the recording medium and a device for developing it, and a laser with a system of beam splitters and mirrors for initiating interfering beams, according to the invention, additionally comprises a means for controlling the orientation and/or intensity of the interfering beams, coupled to the system of beam splitters and mirrors and optically associated with the photothermoplastic recording medium via the device for developing it.

Preferably, the means for controlling orientation should incorporate a modulator made as an opaque disc with curved slots shifted relative to each other by 2m/n angularly and by R/n radially, where R is the disc radius and n is the number of discriminated color components, "n" beam splitters being arranged between the photothermoplastic recording medium and the opaque disc and "n-1 "beam splitters being arranged between the laser and the opaque disc.

Another photothermoplastic recording medium should preferably be arranged in the image plane with device for charging and developing it, in which the means for controlling the orientation and/or intensity of the interfering beams also includes a beam splitter and a mirror arranged so that separated from the main laser beam is a portion with the required intensity, which is directed onto the additional photo-thermoplastic recording medium and used as a reference beam in hologram recording.

Such an embodiment of the method and device for recording optical information permits high-resolution recording, on a photothermoplastic medium, color images or holograms of objects illuminated with incoherent light. The proposed method and device enable the interference beams to be controlled by adjusting their intensity and/or orientation.

The intensity control provides for the necessary ratio between the reference and object beams in hologram recording and while recording the fringe pattern.

It should be noted that in the case of color image recording high spatial frequency carriers are attained, which are independent of the resolution of the optical elements. Since during smooth synchronous rotation of the discs there is practically no time interval between filter and pattern changes and the illumination is continuous rather than stroboscopic, the proposed device also permits increasing the recording sensitivity.

The invention will now be described in greater detail with reference to a specific embodiment thereof, taken in conjunction with the accompanying drawings, wherein: Figure 1 shows a device for carrying out the method for recording optical information according to the invention; Figure 2 shows a modulator according to the invention; The method for recording optical information resides in that the image of an object carrying optical information is projected in integrated light on a photothermoplastic recording medium. At the same time, an image pattern is produced by interfering beams which are controlled to obtain an overall picture of the projected image and the superimposed pattern, which is then recorded.

In color image recording, the interfering beams are controlled by changing their mutual orientation, and the number of orientation changes is taken equal to that of discriminated color components of the projected image.

To control the quality of the resulting overall picture of the projected image and the superimposed pattern, the overall picture is visualized in the image plane by illumination with one of the interfering beams.

The interfering beams are controlled during hologram recording by using one of the interfering beams as a reference, while the image visualized by the other interfering beam is used as an object beam. Then, the hologram resulting from the interference of both beams is recorded.

Therewith, the intensity ratio of the interfering beams is changed.

For a better understanding of the proposed method, the following examples of its practical embodiment are given by way of illustration.

Example 1 Color images were recorded on a photothermoplastic recording medium consisting of a photosensitive layer and a thermoplastic storage layer. The image of an object was succes sively projected on the recording medium throughout a blue, yellow and red filters. The projected image was irised in accordance with the luminous flux through each filter to provide for the same spectral response of the semiconductor layer in the selected regions of the spectrum.

At the same time, a fringe pattern was projected on the recording medium, the orientation whereof was alternately changed through 120 in accordance with the filter.

The laser beam was split into three compo nents with intensities decreasing to 10-7 J/cm2, each being then successively directed onto the recording medium along a path providing for a pattern orientation required for a given color.

The multiple change of the filters and pattern orientations within an exposure ensures recording of the overall picture of the object and its color componenrs which are contained in the patterns.

Example 2 A color image was recorded using the recording medium and procedure of Example 1.

To control the quality of the color components of the object's image, recorded on the medium, the object was illuminated with a fullintensity laser beam. A screen was placed near the first diffraction maximum from each pattern to determine the quality of the resulting image.

Example 3 An object's hologram was recorded. The object illuminated with incoherent light was projected on a recording medium. At the same time, an image pattern was projected on the medium as a spatial frequency close to the optimal value for the given thermoplastic layer thickness. The image pattern was formed by converging two laser beam components at an angle corresponding to the selected spatial frequency. The overall picture was recorded on the medium.

The intensity of the laser beam components was increased and the component was used for reconstructing the object's image at the first diffraction maximum. At the same time, the second laser beam component with an intensity reduced to that of the luminous flux forming the image at the first diffraction maximum was directed to the hologram plane as a reference beam. The object's hologram was obtained as a result of interference of the beam component reconstructing the image pattern at the first diffraction maximum and the second, reference component, the intensities of both components being equal in the recording plane.

Referring now to Fig. 1, the device for recording optical information by the above method comprises a system 1 for projecting the image of an object 2 on a photothermoplastic recording medium 3, a device 4 for charging the medium 3 and a device 5 for developing it. In addition, the device comprises a laser 6 with a system of beam splitters and mirrors for initiating interfering beams.

The beam of the laser 6 is split, with the aid of the beam splitters 7 and 8, into beams equal in number to the discriminated color components of the image (Fig. 1 shows three beams). Each of these beams passes successively through a modulator 9.

The modulator 9 (Fig. 2) is essentially an opaque disc 9, with curved slots 92 shifted relative to each other by 27run angularly and by R/n radially, where R is the disc radius and n is the number of discriminated color components. Therewith, in the system 1 (Fig.

1), "n" beam splitters and mirrors are arranged between the recorded medium 3 and the modulator 9, and "n-1" beam splitters are arranged between the laser 6 and the modulator 9.

The modulator 9 is actuated by an electric motor 10 through a transmission 11. The beams are reflected by mirrors 12, 13, 14, 1 5 and directed onto beam splitters 16, 1 7 and 18. The beam splitters 16, 17 and 18 split each of the three beams into two beams of equal intensity. The beam splitters 16, 1 7, 18 and mirrors 19, 20, 21 are arranged so that the resulting pairs of beams lie in planes forming 120 angles.

The paired beams are projected on the recording medium 3 from the side of the developing device 5.

The device 5 includes a source 22 of regulated voltage and a heater element 23.

The heater element 23 is made transparent.

This permits, at the same time with the projection of interference fringes shifted relative to one another through 1 20D on the recording medium 3, projection of the object 2 illuminated with integrated light by means of the system 1 incorporating a lens 24 arranged in the focal plane whereof are a disc 25 with filters and a disc 26 with apertures. The system 1 also includes a lens 27 for projecting the object 2 on the recording medium 3 through the charging device 4.

The latter incorporates a high-voltage source 28 whose positive terminal is coupled to a glow-discharge electrode 29, while the negative terminal is coupled to the recording medium 3.

The discs 25 and 26 rotate synchronously with the modulator 9 so that each time the interference fringes have a new orientation, the image of the object 2 is projected through a particular color filter.

The means for controlling the orientation of the interfering beams includes the modulator 9, beam splitters 7, 8, 16, 1 7 and 18, mirrors 12, 13, 14, 15, 19, 20 and 21, three beam splitters 1 6, 1 7 and 1 8 being arranged between the recording medium 3 and the modulator 3, while the other two beam splitters 7 and 8 are arranged between the laser 6 and the modulator 9.

Simultaneous loading and development of the recording medium 3 during projection of the fringe pattern with synchronous change of the colour filters permits recording color images of the object 2 illuminated with integrated light on the medium 3.

The device also enables recording of holograms of the object 2. To this end, in the proposed device, the beam splitter 7 is inserted between the laser 6 and the modulator 9 so that it can move relative to the laser beam and be completely removed therefrom during hologram recording. The modulator 9 is, in turn, registered in a position enabling passage of the laser beam.

In addition, the proposed device comprises a beam splitter 30 and a mirror 31 which provide for intensity and orientation control of the interfering beams. The beam splitter 30 is positioned so that separated from the laser beam is a portion with the required intensity, which is directed by the mirror 31 onto a second photothermoplastic recording medium 32 and is used as a reference beam in hologram recording. The other portion of the laser beam, which has passed through the beam splitter 30, is incident upon the mirror 1 5 and, after having been reflected by the lasser, creates interfering beams with the aid of the beam splitter 1 6 and mirror 1 9. These beams create interference fringes in the plane of the recording medium 3.

At the same time, while a fringe pattern is being created, projected on the recording medium 3 with the aid of the system 1 is the image of the object 2 in integrated light.

The fixed position of the disc 26 with the disc 25 being removed provides for passage of the integrated light toward the recording medium 3.

In the case of a moving object, the disc 26 rotates stroboscopically interrupting the integrated light from the object 2 to the recording medium 3. In this case, the modulator 9 remains stationary providing for passage of the laser beam.

The overall picture of the projected image and interference fringes (superimposed pattern) is recorded on the medium 3. At the same time, one of the interfering beams reflected from the beam splitter 1 6 is used to read out the recorded overall picture. Since the element 23 is transparent, the reconstructed object's image is observed at the first diffraction maxima. This permits controlling the quality of the resulting overall picture of the projected image and the superimposed fringe pattern during recording. The reconstructed image is used as a reference beam when a hologram is recorded on the medium 32.

In the case of color image recording on the photothermoplastic recording medium 3, the proposed device operates as follows: the image of the object 2 illuminated with integrated light is projected by the system 1 on the thermoplastic layer of the photothermoplastic recording medium 3 through the discs 25 and 26 which are synchronously rotated by the motor 1 0. To alter the time interval between filter and aperture changes and during rotation of the discs 25 and 26, both discs are arranged in the focal plane of the lens 24 of the projecting system 1. The lens 27 of the projecting system 1 produces an image of the object 2 in the plane of the recording medium 3 after the light has been modulated by the discs 25 and 26.

The image of the object 2, projected on the recording medium 3, receives three fringe patterns turned relative to one another in the recording medium plane through 120 (2n/3, n = 3) and projected on the recording medium 3 through the transparent heater element 23.

The fringes forming patterns result from incorporation in the proposed device of the laser 6 and the means for controlling the orientation of interfering beams. In this arrangement, the beam of the laser 6 is split by the beam splitters 7 and 8 into three beams. The beams thus produced plus the beam reflected by the mirror 1 2 pass successively through the modulator 9 rotating synchronously with the discs 25 and 26.

Having passed through the modulator 9, the coherent beams successively reach the mirrors 13, 14 and 1 5. Reflected from these mirrors, each beam is split by the beam splitters 16, 1 7 and 1 8 into two beams of equal intensity. The resulting pairs of beams are directed by the beam splitters 16, 17, 1 8 and mirrors 19, 20 and 21 to the recording medium 3 through the transparent heater element 23 of the developing device 5.The beam splitters 16, 17, 18 and mirrors 19, 20, 21 are spatially arranged in such a manner that the resulting pairs of coherent beams lie in plates mutually oriented at 120 angles (2sir/3). Each pair of interfering beams successively creates in the plane of the recording medium 3 fringe patterns at 120 to one another. The fringe frequency depends on the angle between the interfering beams and can easily be changed within a broad range by varying the distance between the beam splitters 16, 17, 18 and repective mirrors 19, 20, 21. Each time the orientation of the interfering beams projected on the recording medium 3 through the transparent heater element 23 changes, the image of the object 2 is projected on the thermoplastic layer of the medium 3 through a respective colour filter and aperture. A simultaneous change in the orien- a tation of the interference fringes and filters is achieved by synchronous rotation of the discs 25 and 26 and the modulator 9. The overall picture produced on the recording medium 3 by the interference fringes and the object's image which has passed through the beam splitters and apertures is recorded on the recording medium in the form of a phase structure with simultaneous projection of the image and fringe pattern, charging of the recording medium 3 from the glow-discharge electrode 29 and thermal developement thereof by the transparent heater element 23.

The overall picture recorded on the medium 3 represents fringe patterns oriented at 120 angles relative to one another. Each of the fringe patterns is modulated in depth and density by the intensity of the object's image which has passed through the color filter and aperture corresponding to a respective fringe pattern orientation.

The color image recorded in this manner on the recording medium 3 can be reconstructed by any appropriate method and means (for example, by the method disclosed in British Patent No. 1,272,031).

The use of fringe patterns in the proposed device and changes in their orientation synchronously with the filters by the orientation control means permit continuous recording of the overall picture, which provides for better sensitivity as compared with prior art devices.

The use of the orientation control means also enables the resolution of the proposed device to be substantially enhanced as compared with the known devices.

The herein-disclosed device permits visual monitoring of the recorded quality in the course of recording and holography of moving objects. For this purpose, the beam splitter 7 is arranged between the laser 6 and the modulator 9 so that it can move with respect to the laser beam.

In hologram recording, the beam splitter 7 is withdrawn from the path of the laser beam and replaced by a beam splitter 34. The latter is made in such a manner that appropriate positioning thereof enables separation from the main laser of a portion with the required intensity. This laser beam portion is directed by the mirror 31 to the additional photothermoplastic recording medium 32 provided with its own charging and developing devices. To enable passage of the integrated light from the object 2 the disc is removed. The motor 10 stops at a position whereat the disc 26 with apertures lets through the image of the object 2, projected by the system 1, while the curved slor 92 of the modulator 9 passes the main laser beam.

A hologram of the object 2 is recorded as follows.

Projected on the thermoplastic layer of the recording medium 3 by the system 1 is the image of the object 2 illuminated with integrated light. At the same time, a fringe pattern is projected from the side of the heater element 23 on the recording medium 3. The fringe pattern is formed as follows. The beam from the laser 6 passes through the beam splitter 30, reaches the mirror 15, is reflected thereby and split by the beam splitter 1 6 into two coherent beams. These beams are directed by the mirror 1 9 onto the photothermoplastic recording medium 3. The coherent beams interfere to produce fringes in the recording medium plane.Simultaneous projection of the fringe pattern and the image of the object 2 on the recording medium 3, charging of the latter by the glow-discharge electrode 29 and thermal development thereof permit the overall picture to be recorded on the medium 3 in the form of a phase structure. The recorded overall picture represents a diffraction grating modulated in depth and density by the intensity of the image of the object 2.

To reconstruct and visualize the object in the course of recording use is made of one of the interference beams, for example, the beam reflected from the beam splitter 1 6.

This beam diffracts on the diffraction grating modulated by the integrated image of the object 2 and creates a coherent image of the latter at first diffraction maxima. During holography of the object, one of the beams diffracted at the first diffraction maxima is used as an object beam and directed onto the additional photothermoplastic recording medium 32. As a reference beam, the recording medium 32 receives the above-mentioned laser beam portion reflected from the beam splitter 30. The object's hologram is recorded on the medium 32 with simultaneous charging and development thereof, immediately after the fringe pattern formed on the recording.

medium 3.

Such an embodiment of the device for recording optical information permits reconstruction of the image of the object 2 in monochromatic light passing through the recording medium 3, which improves the resolution of the device and provides for stability of the reconstructed image in space, hence, renders the requirements to the orientation of the reference beam less stringent.

The proposed method and device for recording optical information permit recording holograms and color images of objects illuminated with incoherent light, as well as controlling the quality of the image in the course of its recording. In addition, holograms of moving objects may be recorded. The device features high resolution and sensitivity.

Claims (10)

CLAIMS:

1. A method for recording optical information, consisting in that the image of an object carrying optical information is projected in integrated light on a photothermoplastic recording medium, an image pattern is produced at the same time by interfering beams, the resulting pattern is fixed, the interfering beams are controlled to obtain an overall picture of the projected image and the superimposed pattern, which is then recorded.

2. A method as claimed in claim 1, wherein, in the case of recording color images, the interfering beams are controlled by changing their mutual orientation, and the number of orientation changes is taken equal to that of discriminated color components of the projected image.

3. A method as claimed in claim 1, wherein to control the quality of the obtained overall picture of the projected image and the superimposed pattern said overall picture is visualized in the image plane by illumination with one of the interfering beams.

4. A method as claimed in claim 3, wherein the interfering beams are controlled during hologram recording by using one of the interfering beams as a reference in the image plane, while the image visualized by the other interfering beam is used as an object beam, and a hologram resulting from the interference of both beams is recorded.

5. A method as claimed in any one of claims 3 and 4, wherein the intensity ratio of the interfering beams is changed.

6. A device for carring out the method of claim 1, comprising a system for projecting the image of an object on a photothermoplastic recording medium, a device for charging the recording medium and a device for developing it, a laser with a system of beam splitters and mirrors for initiating interfering beams, and a means for controlling the orientation and/or intensity of the interfering beams, coupled to the system of beam splitters and mirrors and optically associated with the photothermoplastic recording medium via the device for developing it.

7. A device as claimed in claim 6, wherein the means for orientation control incorporates a modulator which is essentially an opaque disc with curved slots shiifted relative to each other by 2iron angularly and by R/n radially, where R is the disc radius and n is the number of discriminated color components of the projected image, "n" beam splitters being arranged between the photothermoplastic recording medium and the opaque disc and "n-1" beam splitters being arranged between the laser and the opaque disc.

8. A device as claimed in claim 6, comprising another photothermoplastic recording medium arranged in the image plane with devices for charging and developing it, in which the means for controlling the orientation and/or intensity of the interfering beams also includes a beam splitter and a mirror arranged so that separated from the main laser beam is a portion with the required intensity, which is directed onto the photothermoplastic recording medium and used as a reference beam in hologram recording.

9. A method for recording optical information, substantially as described herein above and illustrated in examples.

10. A device for recording optical information, substantially as described hereinabove with reference to the accompanying drawings.