GB1602893A

GB1602893A - Information storage and retrieval system

Info

Publication number: GB1602893A
Application number: GB11767/78A
Authority: GB
Original assignee: LASER FILE Inc
Current assignee: LASER FILE Inc
Priority date: 1977-03-24
Filing date: 1978-03-23
Publication date: 1981-11-18
Also published as: CA1115838A; AU3423278A; BR7801789A; FR2385170B1; AU520835B2; SE7803292L; FR2385170A1; JPS6244333B2; DE2812886A1; JPS53119005A; SE438929B; NL7803200A

Description

(54) INFORMATION STORAGE AND RETRIEVAL SYSTEM (71) We, LASER FILE. INC., a corporation organised under the laws of the State of California, United States of America, of5301 Beethoven Street, Los Angeles, California, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to information storage and retrieval systems.

A variety of file systems have been considered for storing many documents onto a high resolution material. Microfilm systems optically reduce the original and photograph it on a high resolution emulsion. Photographic systems of this type, including scanned photographic systems, require time-consuming wet photography. Thus new entries to the file take considerable time to be made available.

In addition portions of a photographic film storage medium cannot be separately addressed at different times because the development process normally encompasses the entire film. Thus new documents cannot be added to an existing photographic storage medium. Photographic storage appears bestsuited to applications where the entire plate is exposed in a single interval such as U.S.

Patent 3,198,880 "Photographic Disc Reproduction System for Television Signals" issued to P.M.G. Toulon on August 3, 1965.

One solution to the problem of having the stored information immediately available is described in U.S. Patent 3,314,073 "Laser Recorder with Vaporizable Film" issued to Carl H. Becker on October 20. 1964. In this system a thin thermally vaporizable film is coated onto a plastic substrate. An intense laser, focused on the coating, is used to vaporize the coating and produce arrays of transparent holes representing the information being stored. These can be immediately read out using light sources imaged at the holes.

This system, however, has a number of practical problems. Firstly, the large energies required to vaporize the film can only be realized by very expensive, high power lasers at the desired writing speeds. Secondly the strip format of the recording material, in the form of motion picture film, results in relatively slow accessing times to specific regions. Also the lack of an accurate tracking method results in relatively low resolution and thus inefficient use of the area in recording data.

Rapid accessing times can be achieved using the disc format where a radial motion is used to find the desired document and a circumferential motion is used to rapidly read it out. Disc recording is normally used in applications where the entire disc is written on in a single sequence. For example in the recording of television programs, as is done in the MCA Disco-Vision system, the entire disc is written at one time and copies are made from it. In document storage systems, however, where individual documents are added at different times, the disc presents serious tracking problems. If the disc is removed and then remounted, the resultant eccentricities of the tracks from a slightly off-center mounting can cause the tracks to cross and thus be destroyed. If large guard spaces are used to avoid track crossing, the storage area is used inefficiently and a limited number of documents can be stored.

In addition to eccentricities, various warping and distortions of the recording media can also cause the subsequently recorded tracks to cross with previously recorded tracks and thus destroy the stored information.

In the MCA Disco-Vision system, as with other disc recording systems, the information is recorded and played back at constant angular velocity. This makes inefficient use of the area of the disc and results in recording power problems. Much greater recording power is needed in the outer diameter parts of the disc because of the increased relative motion between the disc and the modulated recording light source. In addition, the inner diameters have resolution problems because the information is packed more closely together. A given data rate, at the reduced relative motion, results in greater packing density. A relatively large inner region of the disc is often unused because of this consideration.

According to one aspect of the present invention, there is provided apparatus for recording information as defined by claim 1 hereinafter.

According to another aspect of the present invention, there is provided a method of recording information as defined by claim 30 hereinafter.

Briefly, in a preferred embodiment of the invention, a recording medium is used consisting of a deformable film deposited on a disc-shaped substrate. A modulated light beam causes local redistribution of the material of the deformable film resulting in information storage. To insure that the recorded tracks do not overlap, yet have a high packing density, a tracking light beam is used, having a fixed radial distance with respect to the modulated light beam, so that the tracks are accurately recorded with respect to the previously recorded track. For optimum use of the area of the disc, and to provide constant recording power requirements, the disc is rotated so as to maintain a constant linear velocity of the modulated light beam with respect to the rotating disc.

In a document storage and retrieval system the document is scanned with the resultant signal modulating the writing light beam. On readout, the readout light beam produces a recording signal which is applied to a printer.

For a more complete disclosure of the invention, reference can be made to the following detailed description of several illustrative embodiments thereof which is given in conjunction with the accompanying drawings, of which: Figure 1 is a schematic representation of an embodiment of the invention using a rotating disc; Figure 2 is a schematic representation of a tracking system; Figure 3 is a cross-sectional representation of an embodiment of the storage medium; and Figure 4 is a schematic representation of an embodiment of the storage medium using electrical energy for addressing.

It is often desired to store information from documents and subsequently read them out in an automatic fashion to replace manual files. A convenient method of storage is. the disc configuration shown in Fig. 1 where the data from the documents become tracks on the disc such as track 27 on disc 10.

The original document, not shown, is scanned on document scanner 14. This can be a conventional facsimile scanner having the document on a rotating drum or a flatbed structure. The resultant scanned signal, in an appropriate form, is used to modulate the light from laser 12. This appropriate form can be the analog signal itself, or preferably a frequency modulated form of the signal where different values of reflectance on the document represent different frequencies in the signal. Alternatively, the scanned signal can be a digital representation of the document information. In this form it is convenient to use various forms of bandwidth compression, if desired.

The scanned signal is applied to modulator 13 which modulates the light from laser 12.

The resultant modulated light beam 28, in reasonably collimated fashion is directed so as to be focused on the surface of disc 10. It goes through partially silvered mirror 22, is reflected by mirror 23, and goes through linear actuator 20 and pickup arm 26 to the recording region. Linear actuator 20 is used to move the pickup arm 26 radially with respect to rotating disc 10 while allowing the modulated light beam 28 to pass through.

The modulated light beam is reflected by mirror 24 onto air bearing assembly 25 which includes the objective lens. The air bearing maintains the objective lens at a fixed distance from the surface of disc 10 to ensure that the beam will be focused and produce a diffraction-limited spot.

Previous recording systems have used photographic emulsions. Although these are very sensitive, having modest light requirements, they result in a very limited and inconvenient system. The stored document information cannot be immediately read out since an awkward photographic development operation is required. Systems such as U.S. Patent 3,314,073 described in the description of prior art, have used a vaporizable film where the laser power renders the film into the gaseous state and removes the material.

These systems require very high laser powers and are thus awkward, expensive, and have limited data writing rates. In the system described here, a novel approach is used where the laser power causes a local deformation on a film by redistributing the material. Significantly reduced power is required since the material is not brought to the gaseous state. Also, since these redistributions are of a form which can be optically read out, the stored information is immediately available without any further processing. The size of the redistribution regions can be carefully controlled, using this reduced power, so as to provide high storage density.

Disc 10 consists of coating 31 on substrate 30. The coating can be a thin metalloid film such as a 400 Angstrom film of tellurium.

Coatings in the thickness range from 100 to 500 Angstroms would appear to be suitable.

The material should be such that, with modest energies, it is brought momentarily to the liquid state. In this state, through surface tension, the material redistributes itself in a manner which allows it to be subsequently read out.

The same configuration of Fig. 1 can be used for reading out the stored document and displaying it. Light beam 28 from laser 12 is now used in an unmodulated fashion with document scanner 14 and modulator 13 not functioning. This light beam, focused on recorded track 27 is selectively reflected by the redistributions of material on deformable film 31 to create a reflected light beam containing the document information. This light beam traverses the same path as the incident light beam, in the opposite direction.

Part of it is reflected by partially silvered mirror 22 and detected by detector 15. This detector can be a photocell which produces the recording signal 29. This signal can be applied to printer 16 which is a standard facsimile printer using any of a variety of techniques to convert signal 29 into variations of reflectance on a substrate. Some of the printing methods currently used include electrochemical, thermal, electrostatic, and mechanical. These are all commercially available. Alternatively, the signal can be applied to a television type display system where it can be viewed. An intermediate storage system can be used to store the recording signal so that it can be repeatedly applied to the display.

Previous disc recording systems have used constant angular velocity, with the motor speed remaining constant. This results in increased writing power requirements at the outer radii of the disc where the linear velocity is greatest. In addition, the area of the disc is inefficiently used since the data is excessively packed together at the inner radii. Usually only a limited area of the disc is used in these systems. In Fig. 2, these problems are solved by recording and playing back with a constant linear velocity.

On recording, a radial indicating signal 21 is derived from linear actuator 20 which indicates the radial position of the objective lens assembly 25. This radial indicating signal is applied to motor speed control 19 which controls motor 11 such that the product of the radius and the motor speed remain a constant. This provides constant linear velocity of the focused modulated light beam with respect to the surface of the disc 10.

On playback, recording signal 29 is applied to the data rate monitor 17. This monitor measures the data rate of this signal 29 and applies an error signal 18 to motor speed control 19 so as to keep the data rate constant. A constant data rate corresponds to constant linear velocity if the track has been recorded at constant linear velocity.

The data rate monitor can simply measure the bit rate if a digital format is used. If a frequency modulated format is used the data rate monitor can measure the frequency during the synchronization pulse regions where the frequency should be a constant.

Alternatively, if a buffered system is used with the printer 16, the data rate monitor can measure the status of the buffer.

Figure 1 shows an embodiment where the recording and playback are conveniently used in a single system. In some applications it may be more convenient to use separate systems. For example, a disc containing a number of stored documents could be used with a number of readout systems where these documents are printed out or displayed. The readout-only system normally requires a lower power light source and no light modulator and is thus less expensive.

In many existing systems all of the information is written onto the disc at a single time interval without ever removing the disc and replacing it. In these, the registration of each newly written track with respect to the previously recorded tracks is reasonably accurate since there is no problem of concentricity. However, even in these systems, subtle warpage or other distortions of the disc between recording periods can cause problems. The newly recorded tracks can overlap previously recorded tracks, thus destroying information. This problem is avoided by increasing track spacing, thus reducing the storage capability.

This tracking problem is particularly aggravated in systems where the disc is removed and then replaced, as would be the case in the desirable versatile arrangements.

Here the eccentricity caused by the replaced disc not being exactly centered again can cause the tracks to cross and destroy information. If guard bands are placed between recording intervals, much of the information storage capacity is lost.

This problem is solved by the unique approach illustrated in Fig. 2. Here the focused modulated light beam 42 is referenced to a previously recorded track 41 so as to insure that the tracks maintain the desired spacing independent of eccentricity or distor tion. Initially a reference track is written on the outer periphery of the disc. This can be done using a lead screw to radially drive a light source while the disc is being rotated. A tracking light source, positioned a fixed radial distance with respect to the modulated light source, is used to track the reference track and thus position the writiting beam.

As new tracks are written, the tracking beam tracks those to accurately position the focused modulated light beam with respect to the previously recorded track.

In Fig. 2, the modulated light beam 28 is produced by an argon laser source 12 and modulator 13. This beam is transmitted through dichroic mirrors 51 and 43. These mirrors are transmissive to the shorter wavelength of the argon laser and reflective or partially reflective to the longer wavelength of the helium neon laser 46 which is the source of the tracking light beam 52. The modulated light beam 28 is then reflected off controllable mirror 24 and focused by objective lens 40 onto the surface of rotating disc 10 to produce foCused modulated light beam 42.

The tracking light beam 52 is reflected from dichroic mirror 51 and is partially transmitted by the partially reflective dichroic mirror 43. It is then also reflected off controllable mirror 24, at a slightly different angle, and focused by lens 40 to produce a focused tracking beam at track 41 which is displaced a fixed radial distance from the focused modulated light beam 42. The light reflected from track 41 traverses the same optical path in the opposite direction and is partially reflected off partially reflecting dichroic mirror 43. This reflected beam is focused by lens 50 onto adjacent photocells 48 and 49. Their outputs are applied to difference amplifier 47. This amplifier subtracts the two photocell outputs to form error signal 53. This signal will be zero when the two outputs are equal which corresponds to the focused tracking beam being exactly on the previously recorded track 41. If it is off on either side, either photocell 48 or 49 will have a greater output, generating a positive or negative error signal 53. This error signal is coupled to the mirror actuator system 45 which drives rotator 44 and thus pivots mirror 24 in response to signal 53. The mirror actuator system 45 can be a servo-amplifier with rotator 44 a servo-motor. As mirror 24 rotates the focused tracking light beam is brought onto the center of previously recorded track 41 and the focused modulated light beam 42 is simultaneously moved to remain a fixed radial distance from the focused tracking light beam. Thus the focused modulated light beam is kept a fixed radial distance from the previously recorded track.

The mirror 24, rotator 44 and objective lens holder 25 are all supported by pickup arm 26 of Fig. 1. This pickup arm is moved radially by linear actuator 20 which provides the coarse radial motions which brings the tracking system into the vicinity of the correct track. The rotating tracking mirror 24 has a range of a number of tracks so that the coarse radial position provided by linear actuator 20 needn't be very accurate.

The tracking light system can also be used in the readout mode without using the modulated light beam 28 from the argon laser 12. As the focused tracking light beam tracks the previously recorded tracks it is providing a readout of these tracks in addition to a tracking error signal 53. For example the output of either photocell, such as 48 as shown, can be used for the recording signal 29 which is then applied to the display system or printer 16. Alternatively, the sum of the two photocells 48 and 49 can be used for recording signal 29.

Assembly 25 in Figs. 1 and 2 contains the objective lens 40 which must be kept a fixed distance from the surface of disc 10. This can be accomplished by an air bearing system such as the one described in U.S. Patent 3,947,888 "Hydrodynamic Bearing Head Providing Constant Spacing" issued to Manfred H. Jarsen on March 30, 1976.

As shown in Fig. 3, a number of methods may be used to redistribute the material in deformable film 31. Referring to the upper layers only and ignoring the lower layers, the incident energy causes the material in film 31 to become momentarily liquified. Due to phenomena such as surface tension the material redistributes itself in a new configuration which can be subsequently read out.

With sufficient incident power the material in deformable film 31 will redistribute itself so as to form a void 33. This can be read out in a number of ways. For example, the variation in light transmission can be measured by transmission a focused readout beam through the film to a photocell on the other side of the substrate. Generally, however, it is more convenient to have the readout beam measure variations in reflected light as shown in Figs. 1 and 2.

The variations in reflection can be enhanced by the use of an additional antireflection coating 32 placed between the deformable film 31 and the light source.

Firstly, however, this film has an important function in the writing operation by matching the modulated light beam to the deformable film 31. Anti-reflection coating 32 can provide matching by being a quarter wave thick at the writing wavelength and having a refractive index which is the geometric mean of that of free space and that of the deformable film. Alternatively it can be a more complex multilayer coating. The film will thus minimize the reflections of the modu lated light beam so that most of the energy goes into deformable film 31.

The coating 31 can serve a variety of functions in the reflective readout mode. For example it can minimize the reflections of the readout beam from the film, and result in large reflections in the vicinity of voids 33 because the coating 32 is intentionally not matched to the substrate material 30. Alternatively, when using a readout wavelength different from that of the writing beam, a relatively large reflection can be obtained at the metal film and a small reflection at the void since, at the readout wavelength, the coating 32 is better matched to the substrate 30 than the deformable film 31. Here the readout signal will have the opposite polarity since it will decrease in the written regions.

The power requirements are further diminished by having the modulated light beam liquefy only the upper portion of the film. Here the material will redistribute itself in the forms shown in 34 and 35. In 34 the material has redistributed itself into a concave region and in 35 it has become a concave diffuse region because of the material used. These are also read out due to their varying reflectivity. This variation is due to combinations of effects. One effect is the partial destruction of the matching between anti-reflection coating 32 and the deformable film 31 due to the small separation. This causes increased reflections at the exposed regions. Another effect is the spreading of the reflected light caused by the concavity 34.

This can cause an effective increase or decrease in reflectivity depending on the remainder of the optical system. The lens action of the concavity can cause the reflected beam to be more or less concentration on the receiving photocell as determined by the optics. The diffuse region 35 will, in general, cause a spreading of the light beam without lens action. This effect alone will result in an effective decrease in reflectivity.

It is important to note that the particular mode of operation is determined by the power level of the modulated light beam. To maintain this at its proper value, the newly written track can be immediately read out with the resultant signal used to control the power of the modulated light beam. The readout should be done at some information independent portion of the track, such as a portion corresponding to a synchronization region, which should always produce the same readout signal.

The ability to use the anti-reflection coating 32, with its many advantages is a result of the novel recording scheme used where the film material is redistributed by the modulated light beam. In the prior art, where high powers are used to vaporize the material, this coating could not be used since it does not permit the escape of the vaporized material.

As shown in Fig. 3, both sides of the disc can be used. An additional deformable film 31 and anti-reflection coating 32 is deposited on the underside of the substrate 30. This can be separately written on and read out in the same manner previously described to double the storage capacity of each disc.

In the systems discussed thus far the writing modulated light beam itself caused the redistribution of material in the deformable film 31. An alternate embodiment is shown in Fig. 4 where the modulated light beam acts as a control of another energy source which contributes to the process of redistributing the material in deformable film 31. Here a photoconductor 60 and a transparent conductor 61 are deposited on the deformable film 31. If desired, these coatings can also have some of the antireflection properties of coating 32 previously described. In addition, substrate 30 is made of conductive material. A power source 62 is connected between the transparent conductor 61 and the conducting substrate 30. The modulated light beam 28, as before, is focused by objective lens 40 to form a focused spot 42 in the region of the photoconductive coating 60 and the deformable film 31. This focused modulated light beam changes the photoconductor from an insulator to a conductor, thus completing the electrical path in the vicinity of the focused light beam 42. This electrical energy is then applied to that region of deformable film 31 and contributes to the process of redistributing the material of the film to create the writing action.

Although most of the embodiments illustrated used readout in the reflection mode, light transmission can also be used where the readout beam and photocell pickup are on opposite sides of the disc. This mode, however, is limited to the redistribution arrangement 33 of Fig. 3 where a void is created. It is also limited to recording to information on one side of the substrate 30.

Formats other than the disc format illustrated can be used with this system. The deformable film can be used in a rotating drum configuration with the light sources appropriately translated along the axis of the drum. Alternatively the deformable film can be used in a flat bed format (using a stationary plate) where the light beams are mechanically or electro-optically scanned across the stationary deformable film. In all of the formats the tracking while writing can be accomplished by referencing to a previously recorded track as was described for the disc format.

The systems as described used the signal from a scanned document to modulate the writing light beam to produce the redistributions of material on the deformable film. The information used to modulate the light beam can, of course, be any signal source. One important application is the storage of digital information. Thus modulator 13 in Fig. 1 can be driven by a digital signal derived from a computer. The signal 29 read out by detector 15 will then be the desired digital information.

The track format on disc 10 will generally be a spiral so that continuous information can be recorded. In some applications, however, it may be convenient to use a concentric ring format. In this case the linear actuator 20, rather than moving continuously, moves in radial steps following each revolution of disc 10.

Under some conditions disc 10 in Figs. 1 and 2 may be subject to excessive vibration.

Under those circumstances air bearing assembly 25 may not be able to adequately follow these variations, especially when they occur at a relatively high frequency. This problem is solved by the use of a forced air system, not shown, on the underside of the disc 10. This forced air can be derived from an annular array of apertures positioned under the disc. The air creates a force proportional to position which both reduces the amplitude and frequency of the vibration. In addition, it provides a viscous force which damps the vibration. These effects bring the variations within the range of air bearing assembly 25.

WHAT WE CLAIM IS:- 1. Apparatus for recording information comprising: a deformable film; means for producing a modulated light beam representing information to be recorded and for focusing the modulated light beam onto the deformable film with an intensity which is sufficient to result in a redistribution of the material of the deformable film without consequential vaporisation thereof, the redistribution being optically readable by a readout light beam; and means for producing relative movement between the deformable film and the path of the modulated light beam to produce a pattern of recorded information 2. Apparatus according to claim 1, wherein the film is provided on a substrate in the form of a disc and the means for producing relative movement includes means for rotating the disc.

3. Apparatus according to claim 2, wherein the means for rotating the disc provides constant linear velocity between the focused modulated light beam and the rotating disc.

4. Apparatus according to claim 2, wherein the means for producing relative movement further includes means for radially translating the modulated light beam with respect to the rotating disc.

5. Apparatus according to claim 4, wherein the means for radially translating the modulated light beam with respect to the rotating disc includes means for optically tracking a previously recorded track on the disc and radially translating the modulated light beam with respect to the previously recorded track.

6. Apparatus according to claim 5, wherein the means for optically tracking a previously recorded track includes a tracking light beam focused at a fixed radial displacement with respect to the modulated light beam, means for detecting the radial position of the tracking light beam with respect to the radial position of the previously recorded track and producing an error signal, and means for radially translating both the tracking light beam and modulated light beam in response to the error signal.

7. Apparatus according to claim 1, wherein the deformable film material is metalloid.

8. Apparatus according to claim 7, wherein the metalloid film is tellurium.

9. Apparatus according to claim 1, wherein the deformable film is between 100 and 500 Angstroms thick.

10. Apparatus according to claim 1, wherein the redistribution of the material of the deformable film can result in a void in the film in the region exposed to the modulated light beam.

11. Apparatus according to claim 1, wherein the redistribution of the material of the deformable film can result in a local concavity in the film in the region exposed to the modulated light beam.

12. Apparatus according to claim 1, wherein the redistribution of the material of the deformable film can result in a local diffuse structure in the film in the region exposed to the modulated light beam.

13. Apparatus according to claim 1, including an anti-reflection coating on the illumination side of the deformable

Claims

**WARNING** start of CLMS field may overlap end of DESC **. can, of course, be any signal source. One important application is the storage of digital information. Thus modulator 13 in Fig. 1 can be driven by a digital signal derived from a computer. The signal 29 read out by detector 15 will then be the desired digital information. The track format on disc 10 will generally be a spiral so that continuous information can be recorded. In some applications, however, it may be convenient to use a concentric ring format. In this case the linear actuator 20, rather than moving continuously, moves in radial steps following each revolution of disc 10. Under some conditions disc 10 in Figs. 1 and 2 may be subject to excessive vibration. Under those circumstances air bearing assembly 25 may not be able to adequately follow these variations, especially when they occur at a relatively high frequency. This problem is solved by the use of a forced air system, not shown, on the underside of the disc 10. This forced air can be derived from an annular array of apertures positioned under the disc. The air creates a force proportional to position which both reduces the amplitude and frequency of the vibration. In addition, it provides a viscous force which damps the vibration. These effects bring the variations within the range of air bearing assembly 25. WHAT WE CLAIM IS:-

1. Apparatus for recording information comprising: a deformable film; means for producing a modulated light beam representing information to be recorded and for focusing the modulated light beam onto the deformable film with an intensity which is sufficient to result in a redistribution of the material of the deformable film without consequential vaporisation thereof, the redistribution being optically readable by a readout light beam; and means for producing relative movement between the deformable film and the path of the modulated light beam to produce a pattern of recorded information

2. Apparatus according to claim 1, wherein the film is provided on a substrate in the form of a disc and the means for producing relative movement includes means for rotating the disc.

8. Apparatus according to claim 7, wherein the metalloid film is tellurium.

13. Apparatus according to claim 1, including an anti-reflection coating on the illumination side of the deformable film whereby the modulated light beam is efficiently coupled to the deformable film.

14. Apparatus according to claim 13, wherein the anti-reflection coating is not matched to the substrate at the wavelength of the readout light beam whereby regions of the deformable film containing voids result in increased reflections of the readout light beam.

15. Apparatus according to claim 13, wherein the anti-reflection coating at the wavelength of the readout light beam results in a greater reflection at the deformable film than at the substrate whereby regions of the deformable film containing voids result in decreased reflections of the readout light beam.

16. Apparatus according to any one of claims 1 to 6, wherein the information used

to modulate the modulated light beam is derived by scanning a document and using the resultant scanned signal.

17. Apparatus according to claim 1, wherein the information used to modulate the modulated light beam is binary digital information.

18. Apparatus according to claim 1, wherein the energy required to redistribute the material in the deformable film is derived directly from the modulated light beam.

19. Apparatus according to claim 1, wherein the modulated light beam controls a secondary source of energy which redistributes the material in the deformable film in the region of the focused modulated light beam.

20. Apparatus according to claim 19, wherein the film is on a substrate which is conductive and there is: a photoconductive layer deposited on the deformable film on the light addressed side of the film; a transparent conductor deposited on the photoconductive layer; and a source of electrical energy connected between the conducting substrate and the transparent conductor whereby light from the modulated light beam renders the photoconductor conductive in the region of the focused modulated light beam resulting in electrical power being applied to that region of the deformable film so as to redistribute the material in the film.

21. Apparatus according to claim 1, wherein the film is on a substrate and there is a second deformable film on the side of the substrate opposite to that of the first said deformable film whereby information may be stored on both sides of the substrate.

22. Apparatus according to claim 16, wherein means are provided for so scanning the document as to produce the scanned signal in a manner representing the variations in reflectance of the document.

23. Apparatus for retrieving stored information, comprising a deformable film in which information is stored as redistribution of the material of a deformable film produced by apparatus according to claim 1, means for optically reading out the redistributions of the material in the deformable film to produce a recording signal; and means for utilizing the recording signal to display the information.

24. Apparatus according to claim 23, wherein the means for displaying the information includes a printer which utilizes the recording signal to vary the reflectivity of a substrate whereby an image of the information is reproduced.

25. Apparatus according to claim 23, wherein the means for optically reading out the redistributions includes: a readout beam focused on a recorded track of the deformable film; means for moving the recorded track with respect to the readout beam; and a photocell for measuring the variations in reflected light from the redistributions of material on the recorded track of the deformable film to produce the recording signal.

26. Apparatus according to claim 25, including means for optically tracking the recorded track whereby the readout beam remains positioned on the recorded track.

27. Apparatus according to claim 25, wherein the information is stored on a disc and the means for moving the recorded track with respect to the readout beam includes means for rotating the disc so as to provide constant linear velocity between the readout beam and the disc.

28. Apparatus according to claim 27, wherein the means for rotating the disc so as to provide constant linear velocity between the readout beam and the disc includes means for measuring the data rate of the recording signal and varying and the rotational speed of the disc so as to keep the measured data rate approximately constant.

29. Apparatus according to claim 6, wherein the said detecting means includes two adjacent photocells whose output difference is the error signal.

30. A method for recording information comprising the steps of: modulating a light beam with the information to be recorded; focusing the modulated light beam on a deformable film; redistributing the material of the deformable film in the region of the focused modulated light beam without consequentially vaporising the said material; and producing relative movement between the deformable film and the focused modulated light beam.

31. A method according to claim 30, wherein the deformable film is on a disc and the step of producing relative movement comprises the steps of rotating the disc and radially translating the focused modulated light beam with respect to the disc.

32. A method according to claim 31, wherein the step of radially translating the focused modulated light beam includes the steps of the tracking a previously recorded track and translating the focused modulated light beam with respect to the previously recorded track.

33. A method according to claim 30 and including the step of scanning a document to obtain the information to be used in modulating the light beam.

34. Apparatus for recording information, substantially as described hereinbefore with reference to any one of the accompanying drawings.

35. A method of recording and/or retrieving information, substantially as de scribed hereinbefore with reference to any one of the accompanying drawings.