NL8100766A - DEVICE AND METHOD FOR STORING INFORMATION ON A VIDEO DISC. - Google Patents

Description

E 4789-21

P&C

Device and method for storing information on a video disc.

The invention relates to the storage of information on an information carrier and. in particular writing video information on a video disc.

Systems have been developed for recording signals at 5 video frequencies on discs, tapes and other carriers. In such systems, optical recording on photosensitive carriers, electron beam recording on thermoplastic carriers, and other methods have been employed to obtain an immediately reproducible recording of video information.

The prior art can generally be divided into systems using photographic surfaces, systems using electron beam sensitive surfaces, magnetic recording systems and, as in the present invention, systems in which a beam of radiant energy has an irreversible change 15 establishes on a surface, whereby information is written on that surface.

Photographic systems are described in U.S. Patent 3,234,326 which relates to recording on a continuous support such as a tape or film and U.S. Patent 3,361,873 relating to photographic recording of video information on a rotating disk according to a spiral path.

U.S. Patent 3,283,310 is an example of recording information on a thermoplastic film surface using an electron beam writing device 25 as disclosed in U.S. Patent 3,120,991.

In other systems, an electron beam is used to record information on a special recording medium. An example of this is U.S. Patent 3,350,503. Another example of the use of an electron beam on a photosensitive medium such as a photographic film is described in U.S. Patent 3,444,317.

In recent years, other high density recording methods have been described which rely on material removal or evaporation of material by laser beam bombardment.

These methods are briefly described in the journal "Electronics", March 3, 1969, page 110. Furthermore, a thermal microimage recording device with a laser has been described in greater detail by C.O. Carlson and H.D. Ives in a speech at the 1968 meeting of WESCON (Western Electronic 8 1 0 0 76 6 I% - 2 -

Show and Convention), which was published in part 12 of WESCON Technical Papers for 1968, page 1, section 16/1. The authors refer to articles in the December 23, 1966 issue of "Science," Vol. 54, no. 3756, pages 1550 and 1551, the "Proceedings of the Fall Joint 5 Computer Conference of 1966", pages 711-716 and an article in "Bell Systems Technical Journal" of March 1968, pages 385, 405.

These publications describe a recording technique using a thin metal coating on a support. The thin metal fleece melts quickly when exposed to heat, forming 10 small droplets within a recording dot. A highly concentrated spot of laser illumination can supply sufficient heat in a sufficiently short time so that a suitably modulated laser beam hitting a moving surface can cause a pattern of holes in the metal coating that can reproduce the recorded information upon reading.

As set forth in the Carlson and Ives nomination, the dimensions of the recorded dot or hole formed may be significantly smaller than the diameter of the laser beam. By suitable choice of the metal coating material, the coating thickness, the divergence of the laser and the dot power, a system for recording video frequencies with a reasonably high resolution can be developed. However, the quality of the video signal reproduced with such a recording is not good due to a low signal-to-noise ratio caused by the direct recording of the video signal on the recording medium. Furthermore, the use of a modulated laser beam 25 for selectively patterning holes in the metal coating of a video disc is not conducive to faithfully reproducing an amplitude-varying analog video signal. Likewise, reading the recorded information in the form of a trace of holes or dots on the surface of the disc is not suitable for recovering an analog video signal from the recorded track on the disc. The lack of fidelity of the reproduced video signal can be mainly attributed to the laser beam modulator's inability to write accurate analog signals on the coating on the disc.

The invention provides an improved apparatus and method for recording information on a video disc, wherein the recorded information is in the form of an elongated series of regions representing a frequency modulated information signal.

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The invention provides a video disc with a photosensitive coating that covers the disc carrier and serves to record characters representing the frequency-modulated information signal. A disc light source provides a light source of sufficient intensity to act on the sensitive coating of the video disc as it rotates evenly. An optical system defines an optical path between the light source and the sensitive coating on the disc in order to focus the light beam on the coating. A light intensity modulator is included in the optical path and responds to the frequency modulated information signal to modulate the light beam in intensity. The light intensity modulator transmits light over a predetermined intensity range, the intensity of the modulated light beam changing between a relatively high level and a relatively low level during each period of the frequency modulated signal. The light beam passes through the intensity-15 modulator and is optically focused on the sensitive coating to form the characters representing the frequency-modulated information signal. The resulting marks are in the form of an elongated series of regions with alternately high and low directional reflection coefficient perpendicular to the surface of the disc. In other words, viewed from the point above the surface of the disc, an incident light beam directed perpendicular to the surface is reflected alternately strongly and weakly in a direction opposite to that of the incident light beam.

According to a preferred embodiment, an initial input signal 25 having an information content in the form of a time-varying voltage is applied. Such a signal is suitable for display with a conventional television monitor. In such an embodiment, a frequency modulator responsive to the time-varying signal voltage converts the signal into a frequency modulated signal to control the light intensity modulator.

The strong and weakly transmissive states of the light intensity modulator cause a variation of the intensity of the resulting modulated light beam between a value above a predetermined intensity at which the focused light beam changes the sensitive cover layer and a value below the predetermined intensity at which the focused light beam changes sensitive coating does not change.

In order to establish an optimum average intensity level for the modulated light beam, the light intensity modulator may further include a negative feedback circuit for stabilizing the operating level 40 of the electrical control of the light modulator to provide optimum first q λ η n 7 «a • '* -4 -.

and obtain second predetermined intensities. The negative feedback circuit may include a level adjustment to selectively set the average power of the light beam to a predetermined value. To this end, a light sensor senses at least a portion of the light beam from the optical modulator in order to generate an electrical negative feedback signal representative of the average intensity of the light beam so that as the average level of the modulated light beam increases, the negative feedback signal increases the operating level of the optical modulator in order to stabilize the average intensity of the modulated light beam at a constant intensity level.

The heart of the optical modulator contains a Pockels cell controlled by a control circuit. The control circuit for the Pockels cell receives the frequency-modulated information signal at its input and the control circuit supplies corresponding control signals to the Pockels cell in response thereto.

The control circuit for the Pockels cell is coupled for AC voltage to the Pockels cell and the aforementioned negative feedback circuit is coupled for DC voltage to the Pockels cell.

The light source for generating the write light beam is a write laser, preferably an argon ion laser, which generates a collimated write beam of polarized manochromatic light.

The writing laser causes local heating when the light falls on the photosensitive coating of the video disc.

The video disc has a rigid disc-shaped support with a surface of an opaque metallized coating. The coating has suitable physical properties to cause local heating by the writing laser, causing it to locally melt, with the molten material retreating to the edge of the molten region. When solidifying, a permanent opening remains in the metallized coating. Under the correct operating conditions, the optical modulator 30 varies the intensity of the write laser beam between an intensity above the predetermined value at which the focused beam melts the metallized coating without evaporating it and an intensity below the predetermined value, where the focused beam metalized coating does not melt.

The disc-shaped video disc is rotated uniformly and has a radial translation movement relative to the writing beam in order to write the information on the disc according to a spiral cock. Both the rotational movement and the translation movement are controlled by an electrical synchronizing circuit which maintains a constant relationship between the rotational movement of the disc and the translational movement between the write laser beam and the disc.

A microscope objective lens for focusing the writing beam on the surface of the video disc can be held at a distance from the video disc 5 by means of a hydrodynamic air bearing created as the disc rotates relative to the objective lens carrier.

The objective lens has a greater aperture than the diameter of the reading light beam, and the optical system uses mirrors and lenses to diverge the writing light beam from the laser source 10 to fill at least the entrance pupil of the objective lens.

The rotary drive device comprises a spindle which rotates the disc precisely in a circle and the radial translation control circuit comprises a lead spindle mechanism for effecting a translation between the disc and the writing beam at a very constant speed according to a radius of the rotating disk.

Synchronization of the disc drive with the translation drive produces a spiral track with a predetermined pitch. If desired, concentric circles can be obtained by alternating translation and writing. According to a preferred embodiment using a spiral track, the distance between adjacent turns of the spiral is 2 µm from center to center. Assuming a dot diameter of the order of 1 µm, this provides a protection area of 1 µm between dots in adjacent turns of the track.

The microscope objective flange floats at a constant height above the disk on an air army. The constant height is desirable because of the shallow depth of field of the objective lens. A dry microscope objective lens with a magnification of 40 times has proved suitable for concentrating the energy of the laser beam on the disc surface to write dots of 1 µm diameter.

The reading part of the device according to the invention comprises a polarized and collimated reading light beam and an optical system between the light source and the video disc in order to focus the reading beam on the video disc. As the disc rotates, the relative movement between the reading light beam and the alternating regions of characters provides corresponding alternating reflections to the highly reflecting regions on the video disc. A light sensor responds to the reflections and provides a frequency-modulated electrical signal. The frequency-modulated electrical signal thus obtained has an information content in the form of a carrier frequency that varies with time.

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As mentioned previously, the video disc carries on its top surface an elongated series of regions arranged along a track. The sequence of alternating regions of high and low reflectance perpendicular to the surface of the disc represents a frequency modulated signal. The reading system preferably includes a low power laser for generating a reading light beam, a polarizing beam splitting cube and a quarter wavelength wafer. Light flows from the laser source through the polarizing beam splitter and the quarter wavelength plate. The quarter-wavelength wafer is used to rotate the incident reading-10 light beam 45 ° as it passes to the video disc.

The read beam is focused on the disc surface by the same objective lens used for the write beam. The objective lens has a larger aperture than the diameter of the reading beam. The reading optical system uses mirrors and lenses to diverge the reading beam from the laser source to cause it to fill at least the entrance pupil of the objective lens.

The reflected light from the video disc is mirrored and read again through the quarter wavelength wafer, in which it is rotated again at 45 ° to obtain a total rotation of 90 ° relative to the beam from the source.

The exiting reading beam reaches the polarizing beam splitting cube, which is configured so that it does not feed the reflected reading beam to the reading laser source, but to a sensor.

The reflected light from the video disc directed at the sensor represents a frequency-modulated signal whose information content is in the form of a carrier frequency which varies with time. The sensor's frequency-modulated output signal can be converted into a time-dependent signal voltage for display with a conventional television monitor.

The optical system further comprises a beam straightener for directing the writing beam on the objective lens at an angle to the reading beam, whereby the beams strike the video disc at a distance after exiting the objective lens, the reading beam being the surface of the the disc strikes downstream of the write beam.

The writing beam is preferably a beam from a laser that works with argon ions, while the reading beam is preferably a beam from a laser working with helium and neon. The reflected reading beam passes through a filter impermeable to a beam generated by argon ions before it is supplied to the sensor, so that the energy of the 8 1 0 0 76 6 * 7 writing beam hardly reaches the sensor.

A frequency demodulator that responds to the pickup output signal provides a video output signal in the form of a time-varying voltage. A comparator may be provided for comparing the video output signal obtained when reading the video disc to a video input signal used for writing information on the video disc. The comparator output signal can be used to verify the quality of the information recorded on the video disc and may produce a signal indicating that no proper comparison or recording has been made.

A delay circuit receives a portion of the video input signal before it is applied to the comparator. The delay circuit causes a delay in the video input signal equal to the total delays from the frequency modulation of the video input signal to 15 and with the frequency demodulation of the signal from the sensor.

The delay time includes the time required for the video disc to move from the recording point of the information through the writing beam to the incident point of the reading light beam.

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The invention is explained in more detail below with reference to the drawing, which relates to an exemplary embodiment of a device according to the invention.

Fig. 1 is a block diagram of an apparatus according to the invention.

FIG. 2 is a sketch of the optical path through the objective lens of FIG. 1.

Fig. 3 is a representation of the distance between the point of impact of the writing beam and reading beam.

Fig. 4 is a block diagram of a stabilization circuit for the Pockels cell.

In Fig. 1, the writing device 10 comprises a writing head 12 which, according to a preferred embodiment, consists of a dry microscope objective 14 mounted on an air cushion support 16. A wish with a magnification of 40 times has been found to be suitable. A disc 18 is prepared in a special way and can be carried out according to known techniques, in which a very thin fleece of a metal with a reasonably low melting point and a high surface tension is applied to a support.

A crystal oscillator 20 controls the driving elements. The disc 18 is rotated by a first rotary drive device 22 coupled with a spindle 24. A second translation drive device 26 determines the position of the write head 12.

A translation carrier 28 which is driven by the translation drive device 26 via a lead spindle and an associated nut moves the writing head 12 in a radial direction relative to the rotating disc 18.

The carrier 28 is provided with suitable mirrors and lenses, so that the remaining part of the optics and electronics necessary for the writing device can be arranged in a stationary manner.

According to the preferred embodiment, the beam of a polarized cutting laser 30 consisting of an argon ion laser 30 passes through a Pockels cell 32 which is driven by the control circuit 34 for the Pockels cell. A frequency modulator 36 receives the video signal to be recorded and supplies suitable control signals to the control circuit 34 for the Pockels cell.

As described below, the video input signal consists of a signal 35 suitable for display on a television monitor. It is therefore a voltage that varies with time. The frequency modulator 36 is of the conventional embodiment and converts the time-varying voltage into a frequency-modulated signal whose information content is in the form of a carrier frequency with frequency changes over time corresponding to voltage variations over time.

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As is known, the Pockels cell 32 responds to the applied signal voltages by rotating the polarization plane of the light beam. Since a linear polarizer transmits light only with a predetermined polarization plane, a polarizer such as a Glan prism 38 of the preferred embodiment is included in the path of the write beam to obtain a modulated write beam 40. The modulated write beam actually follows the output of the frequency modulator 36.

The modulated write beam 40 exiting from the combination 32, 38 of the Pockels cell and the Glan prism is supplied to a first mirror 42 which directs the write beam 40 to the translation carrier 28. The first mirror 22 carries part of the allocate beam 40 to a stabilization circuit 44 for the Pockels cell that responds to the average intensity of the write beam in order to keep the energy level of the beam constant.

A lens 46 is included in the path of the writing beam 40 so as to diverge the substantially parallel beam so as to fill the input pupil of the objective lens 14 to obtain an optimal resolution. A dichroic mirror 48 is included in the path and arranged so that substantially all of the writing beam 40 is supplied to a second tiltable mirror 50. A mirror as described in Elliottijkan's patent applications are used in the present invention, The tiltable mirror 50 direct the beam through the lens 14 and can displace the point of impact of the beam 40 on the surface of the disc 18.

A series of holes 25 is formed in the metal cover layer by the writing beam. A hole is formed for each period of the frequency modulated signal represented by the modulated write beam 40. Since the modulated writing beam follows the output of the frequency modulator 36, the holes formed in the coating also follow the output of the frequency modulator. Since the information content of the output of the frequency modulator 36 is in the form of frequency changes with time about a carrier frequency, and since the sequence of holes and no holes represents the recorded information, and since the disk 18 rotates at a uniform speed, the sequence of holes and no holes to represent the recorded video information for 35, the holes being denser or more spaced and the sizes of the holes increasing or decreasing as the write beam 40 is controlled by the frequency-modulated output of the frequency modulator 36 changes.

In fact, the objective lens 14 and its associated air empty 16 float on an air cushion at a predetermined fixed distance above the surface of the disc 18. This distance is determined by the shape of the air empty 16 / the linear velocity of the disc 18 and the force with which the head is moved towards the disc 18. The fixed distance is necessary since the focal tolerance of a lens capable of distinguishing a 1 µm diameter dot is also of the order of 1 µm.

A second laser 52 of relatively low power provides a reading beam 54. According to the preferred embodiment, the reading laser 52 is a helium neon device which makes it possible to distinguish the reading beam 54 from the writing beam 40 by its wavelength. A polarizing beam splitting cube 56 transmits the reading beam 54 to a mirror 58 which directs the beam 54 through a second diverging lens 60 which widens the reading beam 54 to fill the entrance pupil of the objective lens 14.

A quarter-wavelength wafer 62 is included in the optical path and, together with the plane polarizing beam splitter 56, prevents light reflected from the disk 18 from reaching laser 52 again and interfering with its mode of oscillation. The quarter-wavelength wafer 62 rotates the polarization plane of the beam through 45 ° at each pass so that the reflected beam 90 is rotated relative to the polarizing beam splitter 56 and is therefore not transmitted.

A second mirror 64 in the path of the read beam 54 directs the beam onto the dichroic mirror 48 and can be adjusted to a limited extent so that the paths of the read beam and the write beam are substantially identical, with the difference that the dot of the read beam the disk 18 strikes downstream of the write beam, which will be explained in more detail.

A filter 66 impervious to the argon ion-generated beam is included in the path of light reflected from the beam splitter 56. The reading beam 54 generated with helium and neon and reflected by the surface of the disc the filter 66 can pass and reach a light detector 70 through a lens 68.

The reflected light from the reading beam strikes the light detector 70.

The light detector 70 operates in the usual manner and provides an electric current representative of the light incident thereon, in this case the light detector provides a signal represented by the configuration of holes and no holes formed in the coating. The configus ?. holes, not holes, is representative of the output of frequency modulator 36. The output of. the frequency modulator 36 is a carrier frequency with frequency changes with the 81 0 0 76 6 -11 time representing the video signal to be recorded. The hole and no hole configuration is representative of a carrier frequency with frequency changes with time representing the recorded video signal. The output of the light detector 70 is an electrical signal representing the recorded carrier frequency, frequency changes with the time representing the recorded video signal.

The output from the light detector 70 is supplied to a preamplifier 72 which provides a signal of sufficient amplitude for later processing. A video discriminator 74 provides a video output 10 signal that can be used in various ways, only two of which are exemplified.

The discriminator 74 is of the usual embodiment and operation.

It receives the frequency-modulated signal from the light detector 70 and converts it into a time-dependent voltage whose information content consists of a voltage that varies with time and is suitable for display on the television monitor 76.

In a first application, the video output signal is applied to a television monitor 76 and an oscilloscope 78. As is known, the television monitor responds to a voltage which varies with time. The information to be displayed on the television monitor is represented by a voltage that varies with time.

The television monitor 76 shows the image fidelity of the recording and the oscilloscope 78 indicates the signal-to-noise ratio of the recording and the quality of the recording, namely whether it is light or heavy. Although not shown, a suitable feedback loop through the Pockels cell stabilization circuit 44 may be employed to ensure good discrimination on the disc between a hole or black area and an area without a hole or area.

Alternatively, the video output of the discriminator 30 74 may also be applied to a comparator 80. The other input to the comparator 80 is derived from the video input signal supplied through a delay line 81. A delay equal to the total delays of the writing system and the time elapsed between the time of writing the information and the time required for the particular area of the disc to reach the read point to be communicated to the input video signal.

Ideally, the video output of the discriminator 74 should be identical in all respects to the video input after the correct delay.

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As previously mentioned, the output of the discriminator 74 is a time-varying voltage. The video input signal is also a time-varying voltage. All the differences noted represent errors that may be caused by imperfections of the surface of the disc or improper operation of the write circuits.

While this application is essential when recording numerical information, it is less essential when other information is recorded.

The output of the comparator 80 can be quantized and counted so that an acceptable number of errors for each disk can be determined. If the counted errors exceeded by default, the writing operation can be terminated. If necessary, a new disc can be written. A disc with excessive errors can then be reprocessed to serve as a new disc for later recording.

Techniques are known for moving the writing head 12 in a radial direction relative to the rotating disc 18. Although in FIG.

1, the rotary drive 20 and the translation drive 22 are driven independently, the. drives are synchronized to allow the writing unit 12 to perform a predetermined transverse movement for each revolution of the disk 18, by means of the common crystal oscillator 20.

In Fig. 2, in somewhat exaggerated form, the slightly different optical paths of the beam 40 of the writing laser 30 and the beam 54 of the reading laser 52 are shown. The writing beam 40 coincides with the optical axis of the microscope objective 14. The reading beam 54, on the other hand, makes an angle cx. with the optical axis, so that at some distance X equals o <. times the focal length of the objective downstream of the location where the writing beam 40 records hits the surface of the disc. The resulting delay between reading and writing 30 allows the molten metal to solidify, so that the record is read in its final state. If it were read too early with the metal still molten, there would be no clear information for setting the recording parameters.

This is best seen in Figure 3, where two points in the same information channel are spaced apart. Point A, where the writing beam 40 strikes the disc, lies on the optical axis of the objective lens 14. On a The distance from point A in the direction of movement of the carrier as indicated by the arrow is the reading point B, which is at an angle to the optical axis of the microscope objective 81 0 0 76 6 - .13 - 14. A distance between points A and B of 2 pn appears to provide suitable monitoring of the writing operation.

Finally, FIG. 4 shows an idealized schematic for a stabilization circuit 44 for a Pockels cell suitable for use in the device of FIG. 1. As is known, a Pockels cell rotates the polarization plane of the supplied light as a function of an applied voltage. Therefore, the Pockels cell is used to rotate planar polarized light and the rotated light is passed through a planar polarizer such as a gloss prism. The light exiting the polarizer is amplitude modulated according to the applied voltage.

In other words, the usual mode of operation for a Pockels cell 32 and a Glan prism 38 is as a modulator of light intensity. Each period of the frequency modulator drives the Pockels cell through its full 90 ° operating range. Within this 90 ° operating range, there is an operating point 15 in which all of the supplied light is transmitted, which is referred to as full light transmission. A second operating point does not transmit light and is referred to as the full light block. The Pockels cell itself only rotates the polarization plane. The Glan prism transmits light in one plane of polarization and transmits no light at all in a plane perpendicular thereto.

Depending on the individual Pockels cell, a voltage change of about 100 V causes the cell to rotate the polarization plane through 360 °. However, the transmission characteristic of an individual cell may shift spontaneously, corresponding to a voltage change of ± 50 V, and therefore a negative feedback loop is desirable to keep the cell within a useful and fairly linear operating range.

The stabilization circuit 44 includes a photosensitive silicon diode 82 which reflects a portion of the write beam 40 through the mirror 42 of FIG.

1 receive- The silicon diode 82 functions similarly to a solar cell 30 and is a source of electrical energy when exposed to incident radiation. One terminal of the silicon diode 82 is connected to a common reference voltage 84 indicated by the usual ground symbol and the other terminal is connected to one input of a differential amplifier 86. The silicon cell 82 is bridged by a load 88 which has a linear response makes possible.

The other input of the differential amplifier 86 is connected through a suitable voltage divider 90 to the common reference 84. A power source 92 is connected to the voltage divider 90 and allows the differential amplifier 86 to be set so that the average light level transmitted by the Pockels cell 32 is set.

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A pair of output terminals of the differential amplifier 86 are connected through resistors 94 and 96, respectively, to the input terminals of the Pockels cell 32 of FIG. 1. It may be noted that the Pockels cell AC control circuit 34 is coupled to the Pockels-5 cell 32, while the DC differential amplifier 86 is coupled to the Pockels cell 32.

The system is energized during operation. The light from the writing beam hitting the silicon diode 82 generates a differential voltage at the input of the differential amplifier 86. Initially, the voltage divider 90 is set to generate light at a predetermined average intensity level. Then, as the average intensity level of the light hitting the silicon cell 82 increases or decreases, a correction voltage is generated in the differential amplifier 86. The correction voltage applied to the Pockels cell 32 has a polarity and magnitude such that the average intensity level is returned to the predetermined level.

The invention therefore provides an improved video disc recording apparatus. A microscope objective mounted on an air army floats a predetermined distance from the surface of a metallized disc. The metallized coating is chosen such that a laser beam, when suitably modulated, can deliver enough energy to melt local areas on the surface. Under the influence of the surface tension, the molten metal retreats, creating a blank area with a diameter of about 1 pn.

A second low energy laser using substantially the same optical path is directed through the same microscope objective lens but strikes the surface of the disc a short distance downstream from the writing point. The reading beam is fed back through a suitable optical system, which excludes the reflected energy from the writing beam 30 and allows the information written on the disc to be analyzed.

The displayed information can be used inter alia to control the intensity of the write beam to ensure appropriate recording levels and to determine whether an unacceptable number of errors have been made in recording.

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Claims (39)

1. An information processing device, characterized by a first means providing a video information signal to be recorded, the information content of which is in the form of a carrier frequency which varies with time according to the information to be recorded; a recording carrier having a carrier with a first surface and a photosensitive coating on the first surface for recording characters representing the video signals? a first light source providing a light beam of sufficient intensity to act on the coating and to change the coating to leave marks thereon representing the video information; means for effecting relative movement of the record carrier relative to the light beam; a first optical means for defining a first optical path between the first light source and the recording carrier with the coating and for focusing the first light beam on the coating; a light intensity modulator included in the optical path between the light source and the cover on the record carrier, operating over an area between a strong light transmissive state and a weak light transmissive state to modulate the light beam in intensity with the information to be recorded; which light-intensity modulator in response to the frequency-modulated signal varies between its strong light-transmissive state and its weakly light-transmissive state during each period of the frequency-modulated signal in order to modulate the light beam in intensity with the frequency recording modulated electrical signal; wherein the light 25 passes the light intensity modulator and is focused on the coating by the optical member to change the coating by recording characters representative of the video information; a second light source that provides a second light beam? a second optical means for defining an optical path between the second light beam and the recording carrier comprising a portion of the first optical path, for focusing the second light beam on the cover layer; the second light beam having a sufficient intensity to illuminate selected parts of the coating on the support and having a sufficient intensity to illuminate selected parts of the coating on the support, the second light beam being strongly reflected by certain exposed areas; the second optical member also being used to receive the reflections from certain exposed areas; as well as a sensor which, in response to the reflected light, generates a frequency-modulated electrical signal corresponding to the reflections, the information content of which is 81 0 0 76 6 ψ * - 16 - in the form of a carrier frequency which varies with time in accordance with the recorded video information. 2. Device as claimed in claim 1, characterized in that the first element comprises a means which supplies an initial information signal, the information content of which consists of a time-varying voltage; and a frequency modulator which, in response to the means providing an initial information signal, converts the time-varying voltage into a frequency-modulated signal. 3. Device as claimed in claim 2, characterized by a demodulator which, in response to the output signal of the sensor, converts the frequency-modulated electrical signal into a time-dependent signal voltage representing the recorded video information, which time-dependent signal voltage has an information content in the form of a voltage that varies with time and is suitable for display with a conventional television monitor. Apparatus according to claim 3, characterized by a means for comparing the video information signal in the form of a time-varying voltage from the demodulator with the initial information signal. Device according to Claim 4, characterized in that the second light beam on the recording carrier is focused on a point on the carrier downstream of the incident point of the first light beam, the device further comprising a delay means in the signal path of the initial information signal which causes a time delay of the initial information signal equal to the total delays from the frequency modulation of the initial information signal through to the frequency demodulation of the signal from the sensor, including the delay time corresponding to the motion from the point on the support from the point of impact of the first beam to the point of impact of the second beam. 6. Apparatus according to claim 2, characterized in that the light intensity modulation means comprises an electrically controllable means which, in response to the frequency modulator, varies the intensity of the first light beam between a value above a predetermined intensity, the focused first beam being the coating changes and a value below the predetermined intensity at which the focused first beam does not change the coating, which changes are representative of the frequency modulated signal. Device as claimed in claim 6, characterized in that the initial 81 0 0 76 6 - 17 - φ · »information signal has an information content in the form of a time-varying voltage suitable for display with a conventional television monitor; the first light source including a writing laser for generating a collimated writing beam of polarized monochromatic light and the carrier forming a smooth and flat rigid disc with the first surface being a flat surface; wherein the coating is a thin and opaque metallized coating with suitable physical properties to allow for local heating due to light incident from the write-10 laser, which heating causes local melting, with retraction of the molten material to the edge of the molten area, leaving a permanent gap in the thin metalized coating upon solidification; while the electrically controllable member in response to the frequency modulator varies the intensity of the write beam between a value above the predetermined intensity at which the focused beam melts the metallized coating without evaporating it and a value below the predetermined intensity at which the focused beam metallized surface does not melt. 8. Device as claimed in claim 1, characterized in that the recording carrier 20 is disc-shaped; wherein the relative motion inducing means comprises a rotational driving device for generating a uniform rotational movement of the disc; while the device further includes a translation drive device synchronized with the rotation drive device to move the first and second focused light beams radially across the first surface of the disc-shaped record carrier; and an electrical synchronizer for maintaining a constant relationship between the rotational movement and the translational movement. 9. Device according to claim 6, characterized in that the light intensity modulator further comprises a negative feedback device for stabilizing the operating level of the electrically controllable member in order to obtain the intensity levels of the first light beam above and below the predetermined intensity. the light intensity modulator including a light sensor for recording at least a portion of the modulated first light beam emerging from the electrically controllable member, to obtain an electrical negative feedback signal representative of the intensity of the modulated first beam, which negative feedback signal is supplied to the electrically controllable member to stabilize its operating level. 10. Device according to claim 9, characterized in that the light sensor has an 81 0 0 76 6 -18-W 'κ. generates electrical feedback signal representative of the average intensity of the first light beam emerging from the electrically controllable member, thereby stabilizing the operating level of the light intensity modulator so as to output the modulated first light beam with substantially constant average power. 11. Device according to claim 7, characterized in that the first and second optical members comprise an objective lens and a hydrodynamic air bearing for supporting the lens above the first surface of the recording carrier. The device according to claim 11, characterized in that the collimated first light beam is substantially parallel and the objective lens has an input pupil larger than the diameter of the first light beam supplied by the first light source; the first optical member further comprising mirrors for folding the path of the first light beam 15 from the first light source and a diverging lens for spreading the substantially parallel light beam from the first light source so as to at least cover the entrance pupil of the objective lens fill. 13. Device as claimed in claim 6, characterized in that the first light source generates a polarized laser beam and the electrically controllable member comprises a member for rotating the polarization plane of the first laser beam emanating from the first source under the control of an initial frequency modulated signal; and a linear polarizer whose output signal consists of a modulated laser beam corresponding to the initial frequency modulated signal. The device of claim 10, including the. characterized in that the negative feedback device includes a level adjuster for selectively adjusting the average power of the modulated first light beam to a predetermined value. 15. Device according to claim 10, characterized in that the electrically controllable element comprises a control circuit for a Pockels cell and a Pockels cell, the control circuit in response to the initial frequency-modulated signal providing corresponding control signals to the Pockels cell and wherein the AC voltage Pockels cell driver circuit is coupled to the Pockels cell and the DC stabilizing stabilizer feedback 35 is coupled to the Pockels cell. Device according to claim 1, characterized by a beam polarizer and a polarization shifting member for shifting the plane of polarization of the second beam, the polarizer and the shifting member being included in the path of the second beam, the 81 0 0 76 6 - 19 - base polarizer is included. between the second light beam source and the slider and wherein the slider rotates the second light beam during the forward and reverse passage through the slider to and from the recording carrier and the polarizer transmits the intensity of the reflected second light beam transmitted through the slider to the second light beam source decreases significantly. Device according to claim 16, characterized in that the sliding member consists of a quarter-wavelength wafer for rotating the second light beam through 90 ° as it moves back and forth through the wafer. 18. Device as claimed in claim 16, characterized in that the beam polarizer consists of a polarizing beam splitting cube which directs the reflected second light beam via the sliding member to the light sensor. 19. Device as claimed in claim 12, characterized in that the second beam of light is collimated and substantially parallel; the input pupil of the objective lens having a larger diameter than the diameter of the second light beam supplied by the second light source and the second optical member comprising mirrors for folding the path of the second light beam supplied by the second light source, and a second diverging lens for spreading the substantially parallel light beam from the second light source so as to fill it at least the entrance pupil of the objective lens. 20. Device according to claim 19, characterized in that the first and the second optical member comprise a beam device for directing the first beam through the objective lens at an angle to the second beam, so that the beams exit from the the objective lens is spaced apart from the record carrier, the second beam striking the record carrier downstream of the first beam. 21. Device according to claim 1, characterized in that the first light source generates a laser beam caused by argon ions, while the second light beam generates a laser beam caused by helium and neon and wherein the second optical element contains a filter which is impermeable to a beam caused by argon ions included in the path of the second beam reflected from the record carrier to the sensor. Method for recording information on and recovering information from an information carrier by means of a pair of laser beams, characterized in that a frequency modulated electrical signal to be recorded is provided with a carrier frequency which varies with time in accordance with the information to be signed; that the intensity of the transmission of a first light beam to a photosensitive surface on the data carrier is controlled with the frequency-modulated signal as the control signal; moving the information carrier at a constant speed relative to the first light beam while it is focused on the photosensitive surface of the information carrier; the control comprising using the transmitted first light beam to irreversibly change the photosensitive surface of the information carrier under control of a part of the frequency-modulated signal while the member is moving at constant speed and decreasing the intensity of the transmitted first light beam to the photosensitive surface of the information carrier for leaving the photosensitive surface unaltered under the control of a second part of the frequency-varying modulated signal while the member moves at a constant speed, which control in the photosensitive surface of the record carrier elongated series of regions that track on the surface, which regions alternately exhibit a high and low directional reflection coefficient perpendicular to the surface, the sequence of alternating regions representing the frequency modulated signal; while casting a second light beam of polarized and collimated light on the array of regions and causing the movement and relative movement between the second beam of light and the alternating regions to generate reflections on the light reflecting regions representing the recorded frequency modulated signal; measuring the reflections and generating a frequency-modulated electrical signal corresponding to the reflections, the frequency-modulated electrical signal having an information content in the form of a carrier frequency that varies with time. 23. A method according to claim 22, characterized in that providing a frequency-modulated electrical signal comprises providing an initial electrical signal with an information content in the form of a time-varying voltage and converting the the time-varying voltage in a frequency-modulated electrical signal whose information content is in the form of a carrier frequency that varies with time according to the variations of the voltage with time. A method according to claim 23, characterized in that the first and the second light beam are kept stationary and the recording means is moved at a constant speed relative to the stationary first and second beam. Method according to claim 23, characterized in that the control 81 0 0 76 6 c. 4 - 21 - consists of using the frequency-modulated signal to vary the intensity of the first light beam between a predetermined intensity at which the focused light beam changes the photosensitive surface and a predetermined intensity at which the focused beam does not change the photosensitive surface which changes are representative of the frequency modulated signal. 26. A method according to claim 25, characterized in that an initial information signal is applied, the information content of which is in the form of a voltage which varies with time and which is suitable for display with a conventional television monitor; the control comprising generating a modulated and collimated writing laser beam 1 of the polarized monochromatic light hitting the photosensitive surface of the recording member, which surface is provided with a thin and flat opaque metallized coating with suitable physical properties for it. allowing local heating due to light incident from the writing laser, which causes local melting, accompanied by retraction of the molten material to the edge of the molten region, so that a solid opening in the thin metallized material upon solidification coating remains; while control 20 includes using the frequency-modulated signal to vary the intensity of the writing beam above the predetermined intensity at which the focused beam melts the metallized coating without evaporating it and a value below the predetermined intensity at which the focused beam does not melt metalized surface. 27. Method according to claim 24, characterized in that a disc-shaped information carrier is used and the movement thereof comprises generating an even rotation of the disc and synchronizing the rotational movement with the movement of the recording member in order to obtain a relative movement of the first and second light beam radially across the surface of the disk-shaped recording member to maintain a constant relationship between the rotational movement and the translational movement. A method according to claim 26, characterized in that the control further comprises stabilizing the modulation level of the first light beam to obtain the intensity levels of the first light beam above 35 and below the predetermined intensity; measuring at least a portion of the laser write beam after modulation of the write beam to obtain an electrical negative feedback signal representative of the write beam intensity and use of the negative feedback signal in the control to stabilize the write modulation level -40 bundle. _ 8100 76 6 * v - 22 - 29. A method according to claim 28, characterized in that measuring at least a part of the writing beam produces an electrical negative feedback signal representative of the average intensity of the modulated writing beam, wherein the operating level of the light beam modulation is stabilized in order to produce the modulated writing bundle with a virtually constant average power. 30. A method according to claim 26, characterized in that the control comprises a rotation of the polarization plane of the write laser beam under control by the frequency-modulated signal and the linear polarization of the rotating beam to obtain a modulated laser beam. write beam corresponding to the frequency modulated signal. A method according to claim 28, characterized in that the control comprises a selective setting of the average power of the modulated write beam to a predetermined value. A method according to claim 28, characterized in that the control comprises amplifying the frequency modulated signal to obtain corresponding control signals for a Pockels cell, wherein the amplified AC voltage modulated signal is coupled to the Pockels cell and the DC feedback signal 20 is coupled to the Pockels cell. 33. A method according to claim 23, characterized in that the frequency-modulated electrical signal generated during measurement is demodulated to obtain a time-dependent signal voltage representing the recorded information, said time-dependent signal voltage having an information content in the a voltage that varies with time and is suitable for display with a conventional television monitor. 34. A method according to claim 22, characterized in that the polarization plane of the polarized second beam is shifted by rotating the second beam during the forward and reverse passage to and from the recording means, thereby increasing the intensity of the reflected second beam. supplied to the light beam source generating the second light beam is significantly reduced. A method according to claim 24, characterized in that the shift 35 comprises rotating the second light beam through 90 ° during the forward and reverse passage of the second light beam to and from the surface of the record carrier. 36. A method according to claim 33, characterized in that the time-dependent voltage obtained in the demodulation is compared with the initial information signal. 8 1 0 0 76 6 - 23 - A method according to claim 36, characterized in that the second light beam is focused on a point on the information carrier downstream of the incident point of the first light beam, while further delaying the initial information signal by a time equal to the 5 total delays from the frequency modulation from the initial information signal through to the frequency demodulation of the signal generated during measurement, including the time it takes for a point on the information carrier to move from the point of impact of the first beam to the point of impact of the second beam. A method according to claim 22, characterized in that an objective lens is used next to the recording means for receiving the first and second beams and for directing the beam on the data carrier, the first beam being passed through the objective lens at an angle with respect to the second bundle, so that the bundles exit from the objective lens at a distance from each other and meet the information carrier at a distance from each other. 39. A method according to claim 22, characterized in that the first light beam originates from an argon ion laser and the second light beam originates from a halium and neon laser, optically blocking the beam caused by argon ions in the reflection path from the record carrier before measuring the reflected second beam. 81 0 0 76 6