SE419383B - Method for processing frequency-modulated information on an information storage element and apparatus for processing the information - Google Patents

Abstract

The invention concerns the method and apparatus for recording video information in the form of a frequency- modulated signal on a video disk element 10 and for recovery of the video information from the video disk element. The recording apparatus has a laser as a source 30 for a laser writing beam 29, 29' and an optical writing unit 40, 41 for directing the stationary laser writing beam against a moveable video disk element 10. The video disk element comprises a substrate 22, which has a coating 26 that can be influenced by light on at least one surface 24. The optical writing unit 40, 41 focuses the beam to a small light spot 42 with a diameter of approximately 1 micrometer on the coating layer 26 which can be influenced by light. The intensity of the focused spot can be altered by control of a light intensity modulation unit 44. The light intensity modulator 44 changes the intensity of the laser writing beam 29, 29' with regard to a predetermined threshold intensity, which is high enough to form a first type of markings 37 in the coating layer. The length of the first type of marking depends on the speed of movement of the video disk element 10 and the time during which the intensity of the writing laser exceeds the predetermined or material-dependent threshold intensity. When the intensity of the laser writing beam falls beneath the predetermined threshold intensity, the formation of the first type of marking 37 ceases. The intervening portions of the coating layer that can be influenced by light, which portions are situated between consecutive markings of the first type, serve as a second type of marking 38. A motion control unit 28 rotates and translates the video disk element relative to the intensity-modulating writing beam. In this way, a linear succession of first and second markings is formed on the substrate. The first and the second markings 37, 38 have variable length and represent the frequency-modulated signal intended for the recording. By making use of the recording method and an apparatus for implementation thereof, video information is stored on the information storage element 10 in the form of a frequency-modulated signal 92, which has its information content in the form of a carrier signal with frequency variations over time, which vary from a central frequency. The frequency-modulated signal 92 occurs as a linear sequence of first and second markings 38 situated in the manner of grooves on the surface 24 of the storage element. In a preferred embodiment of the invention, the linear succession of first and second markings 37, 38 is situated in alternating relationship. The first type of markings reflects light in non-specular fashion. The second type of markings reflects light in specular fashion. The length of the specular light-reflecting regions and the non-specular light-reflecting regions represents consecutive half-periods for each whole period of a frequency-modulated signal. The length of these regions varies in inverse proportion to the momentary frequency of the frequency-modulated signal. In this way, the length of the specular light-reflecting and the non- specular light-reflecting regions is a representation in space of the frequency-modulated signal. A reading system is used to recover the video signal stored on the video disk element 10. This reading system comprises a reading laser 152 for generating a reading beam 150, and a motion control unit 28 for rotation and translation of the video disk element relative to the reading beam. An optical reading system 154, 156 directs the reading beam so that it impinges on regions 37, 38 with specular light reflecting ability and non-specular light reflecting ability situated consecutively one after the other on the video disk element 10. The optical reading system 154, 156 also collects the light reflected from these regions. The reflected light beam is intensity- modulated by the regions with specular light reflectivity and non-specular light reflectivity. The optical reading system also directs the reflected light beam onto a light detecting circuit 158, 164, 162 for changing of the intensity-modulated, reflected light beam into a corresponding frequency-modulated, electric signal, which is representative of the video signal stored on the video disk element. <IMAGE>

Description

7a1o1zo-oj¿ i 2 10 is 20 25 30 35 40 moved at a constant speed; and that the intensity of it to the light-I sensitive surface of the information storage element transmitted first light beam is lowered under the control of a second part of the varying frequency signal when the storage element is moved at a constant speed. Steering method generates a linear sequence of areas located in a track-like manner on said surface, which areas have alternating reflective light reflectivity and non-reflective light reflectance and represents the frequency modulated signal. The the second beam of light consists of polarized, collimated light and is thrown at the sequence of areas, while said movement produces relative movement between it other, in said areas cast the beam of light and the alternating areas of generating reflections from the reflectivity display areas, which represents the stored frequency modulated signal. The reflections are sensed and a frequency modulated electrical signal corresponding to the reflection is generated, it the frequency modulated electrical signal has its information content in the form of a carrier signal with frequency changes over time from a center frequency.

The apparatus for writing a frequency modulated signal on a video disc element comprises a movable writing beam and a video disc element mounted on a turntable.

The disc plate is driven by means of a motion control unit, which rotates the disc exactly circularly with a constant rotational speed, and a translational drive for movement of the writing beam at a very constant and very low speed along a radius thereof rotating disc. The rotary drive of the disc is synchronized with that of the writing beam. translational drive to generate a spiral track with a predetermined pitch. In a predetermined embodiment is the space between adjacent grooves in the spiral Zlftm from center to center. The markings are formed with a width of l / cm. Hereby a space or safety area of l fam is provided between markings in boundary tracks. If desired, the markings can be made as concentric circles by translating the writing beam in incremental steps.

According to a preferred embodiment, a microscope lens is mounted on one constant height above the video disc element on an air storage. This lens is used for focusing the writing beam on the photosensitive surface of the video disc element. The constant the height is necessary due to the short focal length of the lens. A dry microscope-E objective lens with a numerical aperture of 0.65 is used to focus a laser writing beam to a spot means diameter of l / Am on the photosensitive coating. After- as the coating rotates at a relatively high speed, it is in the photosensitive the coating formed the length of the mark depending on the duration of the staining even intensity exceeds the intensity required to form one marking.

A linearly polarized argon ion laser is used as the source of the writing beam.

A Pockel cell is used to rotate the plane of polarization of the writing beam with the looking at its fixed plane of linear polarization. A linear polarizer attenuates it 10 15 20 25 30 35 40 7810130-0 rotating the writing beam to an extent proportional to the difference in polarization between the light in the writing beam and the axis of the linear polarizer. Kom- the combination of the Pockel cell and the linear polarizer modulates the writing beam with the video information intended for storage. This modulation follows the pattern, which are provided by means of control signals which are obtained from a drive unit for Pockel cells.

The video signal to be recorded is applied to a frequency modulator circuit.

The output signal from the modulator circuit is a square wave, the frequency of which is proportional against the video signal. The duration of each cycle of the square waveform is variable, which is characteristic of a frequency modulated signal. A square wave is characterized because it has an upper voltage level and a lower voltage level. Eyrkantsvågens övre and lower voltage levels are amplified by the Pockel cell drive and utilized to control the Pockel cell. The Pockel cell changes the polarization angle of it thereby passing the light depending on the instantaneous voltage level of the control the signal. This changes the intensity of the writing beam to achieve the said markings.

Different types of video disc elements can be used according to the invention. According to a first embodiment comprises the video disc element a glass substrate with an upper surface, bearing a thin metal coating as a light-sensitive coating. At this design, the writing beam forms openings of variable length in a groove-like manner in the metal coating. With the first embodiment, a portion of the glass substrate is placed in each opening. The exposed portion of the glass substrate appears as a with non-reflective light reflectivity in relation to an incident reading beam. The intermediate portion of the metal coating has a reflective reflection ability, which means that a significant part of the reflected light returns along the path of the incident light beam. In a second embodiment, the video disc comprises the element a glass substrate with an upper surface, which carries a thin layer of a photoresist as a light-sensitive coating. With this design, the writing beam forms variable length exhibiting areas of exposed and unexposed photoresist material on barrier in the photoresist coating. The intensity of the writing beam is set to one area with exposed photoresist material is formed, e.g. during positive half cycles at the frequency modulated signal for storage and a range of unexposed photoresist material is left behind during the negative half cycles. Consequently, they are the first and second selections, which represent the stored information. one set of lines with exposed and unexposed portions of the coating.

A preferred embodiment of a reading apparatus utilizes a reading device. laser for generating a polarized, collimated light beam with a preferred polarization risation angle. An optical reading system directs and images the laser beam to hit the markings supported on the surface of the video disc element. The video disc element is used for storing a frequency modulated signal on its surface in the form of a set n '7810130-0 4 l0 l5 20 25 30 35 40 linear areas. The areas have varying reflective light reflection ability and non-reflective light reflectance. The optical reading system focuses the reading beam to a light spot with a diameter of about 1 micrometer and directs the focused spot to fall on the set of linear areas. Reading the intensity of the beam is adjusted so that a sufficiently strong reflected reading beam signal is picked up by the optical reading system.

The motion control unit of the turntable is arranged to rotate the video disc element with a sufficiently uniform rotational speed for reconstruction of the original frequency stored modulated frequency. A thus stored, typically frequency modulated signal varies in frequency between 2 MHz and 10 MHz. The video disc element rotational speed is preferably set to about 1800 rpn to change the spatially modulated frequency modulated signal to an electrical signal in real time. The motion control unit comprises a translation drive unit for moving the reading beam at a very constant and very low speed along the radius of the rotating disk so that the light beam falls on the one present on the disk the set of lines with light-reflecting and light-scattering areas.

The reflected reading captured by the optical reading system the beam is directed to a light sensing circuit for changing the intensity modulus. reflected light beam to a frequency modulated electrical signal, which responds against the intensity modulated reflected light beam. 7 A polarization-selective beam splitting element is located in the reading the path of the beam between the reading laser source and the video disc element. After the reading beam passed through the polarization-selective beam-splitting element the reading light beam is linearly polarized in the preferred plane. A quartz wave longitudinal plate is arranged between the polarization-selective beam-splitting element output and the video disc element. The quartz wavelength plate changes the light in the reading the beam from linear polarization to circular polarization. The reflected light maintains its circular polarization until it passes through the quartz wavelength plate a second gang. During this second passage through the quartz wavelength plate changes the reflected light by circular polarization back to linearly polarized light rotated 900 from the preferred plane, which is determined by the above-mentioned polarization. sation-selective beam splitting element.

The polarization-selective beam-splitting element is susceptible to dependence of this 90 ° rotation in the reflected light beam to deflect it reflected the light beam to the light sensing circuit and prevents the light beam from re-entering the reading laser source. _ A scattering lens is used in the optical reading system for scattering the substantially parallel light beam from the reading laser source to at least fill the lens aperture opening.

In a second utldrinunlnrm by dr! The optical reading system is an optical one l0 20 25 30 35 40 L ~ 7810130-0 filter placed in the path of the reflected reading beam to filter out light with all wavelengths except for the wavelengths which the light from the the laser source has.

In a recording or recording apparatus, only the recording or the write function to write the frequency modulated information on one video disc element. In a video disc player, only the read function is used. for to retrieve the frequency modulated information stored on the surface of the video disc element.

* In a third operating mode, the read and write functions are combined in one even machine. In this combined device, the reading function is used for control of the accuracy of the information entered by the write function.

To realize the monitoring function, a reading beam is added from a helium-neon (He-Ne) reading laser to the path of the writing beam. The reading optics is set to direct the reading beam through the microscope lens during a small angle with respect to the writing beam. The angle is selected so that the reading beam illuminates an area on the same track that is written by the writing beam, but at a point that lies about 4-6 micrometers downstream relative to the writing spot. More specifically, readings are to fall on the information track just formed by the writing beam.

Sufficient time has been allowed to elapse for the formation of the information markings on the video disc element. In this way, the reading beam is thrown at alternating areas with different reflectivity. In an embodiment of the reading apparatus, the reading falls the beams of metal which are not heated by the writing beam and fall also on the glass substrate. which are exposed in the openings which are just formed by it slrwande stain. Areas with different reflectivity serve to change one falling reading beam of constant intensity to an intensity modulated, reflected reading beam.

In this monitoring operating mode, the laser reading beam is selected to operate with a wavelength different from the wavelength of the laser writing beam. A wavelength selection optical filter is placed in the path of the reflected light beam and has a tape, which includes the laser reading beam. Possible light of the laser writing beam, which follows the reflected path of the reading beam, is eliminated by the filter and can therefore do not interfere with the reading procedure.

The monitoring operating condition is used in connection with recording or writing the video information on the video disc element as an aid for checking the quality of the recorded signal. The output signals from the reading path are presented on an oscilloscope and / or a television monitor. Visual inspection of this presented signal indicates whether the markings are formed with the preferred operating frequency.

The preferred operating frequency is obtained when averaging the length of a mirror reflecting area, which represents a half cycle of a frequency modulated signal, is the same as the next subsequent area with non-reflective reflectivity, which represents the next subsequent half cycle of a frequency modulated signal.

Operating read mode after writing or the supervised operation Oh '7810130-0 10 15 20 _25 solar 35 40 the state is also used for error checking, especially on digital type information recorded. The entered video information is delayed for an interval equal to the accumulated values for the time delay, which begins with the frequency modulation of the input video information signal during the recording process and continues during the frequency demodulation of the recovered, reflected signal from the sensing circuit, and includes the delay in moving time of the point on the storage element, when it is moved from the point of storage of the input video the information signal to the point where the reading light beam hits. The recycled the information is then compared with the delayed input information due to role of accuracy. If there are too many differences, there is reason to either repeat the check and reset the unit or discard the disc element.

The reading device is suitable for use in connection with a household television tuner by adding a radio frequency modulator for adding the video signal to a suitable carrier frequency, which is adapted to one of the channels at a conventional household television receiver. The conventional television receiver the receiver then processes this signal in the same way as it is received from a conventional national transmitter station.

The invention is described in more detail below with reference to the accompanying drawing, in which Fig. 1 is a block diagram of the recording or writing apparatus, Fig. 2 is a cross-sectional view through a portion of a video disc element before being subjected to it recording by using the recording apparatus according to Fig. 1. Fig. 3 is a partial plan view from above of a video disc element after it has been subjected to it recording using the recording apparatus according to Fig. 1, Fig. 4 is a diagram showing the waveform of a video signature used in the recording the apparatus of Fig. 1, Fig. 5 is a diagram showing a waveform of a frequency modulated signal, which is used in the recording apparatus according to Fig. 1, Fig. 6 is a graphical representation of the intensity of the writing laser used in the recording apparatus according to Fig. 1, Fig. 7 is a graphical representation showing the modulated recording or writing beam and how it changes by means of the drawing apparatus according to Fig. 1, Fig. 8 is a circular cross-sectional view through the the element in Fig. 3, which view is taken along the line 8-8 in Fig. 3, Fig. 9 is a detailed block diagram of a suitable motion control unit, Fig. 10 is a block diagram of a reading apparatus, Fig. 11 is a block diagram of a combined reading device; and recording apparatus, Fig. 12 is a schematic visual representation showing the reading beam and the recording beam passing through a single objective lens, which is used in the block diagram according to Fig. 1 and Fig. 13 is a wiring diagram above a suitable stabilizing circuit intended to be used in the recording apparatus according to Fig. 1.

The same reference numerals have been used to indicate the same elements in the different drawing figures. The terms recording, recording and storage are used 10 15 20 25 30 35 40 7810130-0 interchangeable with the term writing. The term recovery is used interchangeably with the term reading.

The device for storing video information signal on an information storage element 10 is shown in Fig. 1. One as a source for one information signal serving circuit 12 is used to provide an information signal, which is to be recorded. This information signal, which is transmitted via a line 14, is a frequency modulated signal having its information content in in the form of a carrier frequency with frequency changes over time, which represent it for record intended information. Fig. 5 shows a typical example of a frequency modulated signal. The information signal source circuit l2 utilizes a video signal circuit 16 for providing an information signal on a line 16, which signal has its information content in the form of a voltage, which varies with the time format. Fig. 4 shows a typical example of a voltage signal which varies with time.

A frequency modulator circuit 20 is operable depending on the video signal circuit 16 for conversion of the time-varying signal to the frequency shown in Fig. 5. vein modulated signal on line l4.

The information storage element 10 is suspended on a turntable or a turntable. plate 2l. The element 10 is shown in Fig. 2 without any markings found thereon and comprises a substrate 22 with a first surface 24 and one which can be actuated depending on light skkt 26, which covers the first surface 24. A motion control unit 28 is arranged to apply uniform movement of the storage element 10 relative to a writing beam 29 ', which is generated of a light source 30. The motion control unit 28 is shown and described in more detail below with reference to Fig. 9. The motion control unit 28 comprises a rotary drive circuit 32 for apply uniform rotational movement to the information storage element 10 and a translated drive circuit 34, which is synchronized with the rotary drive circuit 32 for moving of the focused light beam 29 'radially across the coating layer 26. in the form of a frequency modulated the control threat 28 further comprises an electrical holding unit 36 synchronizing unit 36 of a constant ratio between the rotational movement applied to the element 10 by means of the rotary drive circuit 32, and the translational motion applied to the light beam 29 'by means of the translation drive circuit 34.

The light source 30 produces a light beam 29, which has a sufficiently high intensity. to cooperate with or change the co-laying layer 26 while it is present is in motion and is attached to the movable information storage element 10.

In addition, the intensity of the light beam 29 'is high enough to produce the pen markings or marks in the coating 26, which represent it for recording intended information. A suitable light source 30 includes a writing laser for generation of a collimated writing beam consisting of polarized, monochromatic light.

Fig. 2 shows a cross-sectional view through a first embodiment of a suitable one video disc element 10. A suitable substrate 22 consists of glass and has a smooth, flat, flat first surface 24. threat of light päverrhara coating layer 26 is formed on the surface l0 l5 20 25 m 35 40 7810130-0 B 24.

In one of the described embodiments, the coating layer 26 is a thin, opaque, metallized layer with suitable physical properties to enable localized heating in dependence on the layer being hit by the writing light beam 29 from the writing laser 30. During operation, the heating causes local melting of the coating. followed by retraction or retraction of the molten material towards the perimeter of the molten area. In the case of solidification, a permanent opening is left as shown at 37 in Figs. 3 and 8, in the thin metal coating layer 26. the opening 37 is a type of marking, which is used to represent the information.

In this embodiment, successively located openings 37 are separated by means of a portion 38 of the unaffected coating layer 26. The portion 38 is the second type of marking, which is used to represent the information. A more detailed description as to the method by which the markings 37 and 38 represents the fi sequence modulated signal, is given with reference to Figs. 5 - 8.

A moving optical unit 40 and a beam controlling optical unit 41 determine or together determine an optical path of the light beam 29 exiting the light source 30. The optical units project the reading beam 29 to a spot 42 the coating layer 26 supported by the storage element 10. is also centered by the lines denoted by the reference numerals 29 and 29 '.

A light intensity modulation unit 44 is located in the optical path 29 between the light source 30 and the coating layer 26. In its widest operating state In intensity, the light intensity modulating unit modulates the light beam 29 with the call the intended information. The modulation unit 44 operates under the control of a amplified by the frequency modulated signal shown in Fig. 5. This frequency modulated signal causes the unit 44 to change between its higher light transmission and its lower light emitting state during each cycle for the frequency modulated signal. This rapid change between transmission states modulates the light beam 29 with the frequency modulated signal for storage.

The light beam 29 is modulated as it passes through the light intensity modulation unit 44; Then the modulated light beam, which is now denoted by reference numeral 29 ', on the coating layer 26 of the optical units 40 and dl. When the modulated light beam 29 'falls on the coating layer 26, the mark is formed. rings on the layer 26, which markings represent the frequency intended for storage modulated the signal.

The light intensity control unit 44 comprises an electrically controllable sub- unit 46, which is päverkbnr in dependence on the frequency modulator 20 for varying the intensity of the light beam 29 'over a predetermined intensity at which it focused the beam 29 'changes the coating layer 26, which is supported by the information storage element. In addition, the electrically controllable subassembly 26 can be actuated of the frequency modulator 20 for varying the intensity of the light beam during a predetermined 10 15 20 25 30 35 40 7810130-0 tuned intensity, at which the focused beam 29 'is not able to change the coating layer 26. The changes effected in the coating layer 26 represent the frequency modulated signal for storage. When the coating layer 26 consists of a photoresist layer, which is supported on the information storage element 10, the changes are in the form of exposed and non-exposed photoresist sections with a dimension analogous to that previously mentioned with respect to the markings 37 resp. 38.

When the coating layer 26 supported by the information storage element 10 is a metal coating, the electrically controllable subassembly 46 varies with the writing beam 29 'intensity over a first predetermined intensity at which it focused the jet 29 'melts the metal coating without evaporating it, and also varies the intensity of the writing beam below the predetermined intensity at which the The radius 29 'is not capable of melting the surface of the metal.

The light intensity modulation unit 44 comprises a stabilizing circuit 48 for generating a feedback signal, which is used for temperature stabilization of the working level of the electrically controllable subunit 46 for it to operate between a predetermined higher light intensity and a predetermined lower light intensity level. The light intensity modulation unit 44 has a light sensing circuit for sensing of at least a portion, shown at 29 ", of the light beam emitted from it electrically controlled subunit 46 to generate an electrical feedback signal, which represents the average intensity of the beam 29 '. The feedback signal is connected to the electrically controllable subassembly 46 via lines 50a and 50b to stabilize lisera work level.

The light sensing device generates an electrical feedback signal, which is representative of the average or mean of the modulated light beam 29 ' intensity. In this way, the light intensity modulation unit 44 is stabilized to emit the light beams with a substantially constant average power level. Stabilization circuit 48 also has a level setting device for selectively setting it average power level of the light beam 29 'to a predetermined value for forming an alternating arethane cycle in either a metal overlay layer 26 or a photoresist or other material.

The movable optical unit 40 comprises an objective lens 52 and a hydrodynamic lens. air storage 54 for curing the lens 52 over the coating layer 26. The of The laser beam 24 'generated by the laser source 30 consists of substantially parallel light beams.

In the absence of the lens 66, these have substantially parallel light rays substantially none tendency to diverge. Thus, the objective lens 52 has an entrance aperture or apparatus. turn 66, which has a larger diameter than the diameter of the light beam 29 '. The flat convex the scattering lens 66, which is located in the path of the light beam 29 ', is used to scatter the substantially parallel light beam 29 'so that it at least fills the objective the entrance opening 56 of the lens 52.

The beam controlling optical unit 41 comprises a number of mirror elements 58, 60, ivs1o13o-o W 10 l5 20 'so 40 62 and 64 to deflect the light beams 29 'and 29 "as desired. The mirror 60 is shown as a flat mirror and is used to create strictly circular tracks instead for the drawn spiral rafters. When generating spiral grooves, only one fixed is required Mirror.

As previously mentioned, the light source 30 generates a polarized laser beam 29.

The electrically controllable subassembly 46 rotates the polarization of this laser beam 29. plane under the control of the frequency modulated signal. A suitable electrically controllable subassembly comprises a Pockel cell 68, a linear polarizer 70 and a drive unit 72 for the Pockel cell. The drive unit 72 is essentially a linear amplifier and is actuated. bar depending on the frequency modulated signal on line l4. The output signal from the Pockel cell drive 72 provides drive signals to the Pockel cell 68 for rotation of the polarization plane of the laser beam 29. The linear polarizer 70 is oriented in a predetermined relationship with respect to the original polarization plane of the laser beam 29 emitted from the laser source 30. As shown in Fig. 7, the axis of the linear polarizer 70 is for maximum brightness. transmission located at right angles to the polarization angle of the light emitted from the source 30. As a result of this arrangement, the minimum amount of light emits from the risator 70 when the writing beam 29 is applied by means of the Pockel cell 28 a rotation of 00. Maximum amount of light exits from the polarizer 70 when the writing beam 29 by means of Pockel cell 28 is subjected to a rotation of 900. This described arrangement of the linear polarity risator is only a preferred choice. By aligning the axis of the polarizer 70 for transmission of the maximum amount of light with the polarization angle of that from the laser the light emitted by the source 30, the maximum and minimum states will be opposite from what has been described; when the light beam is subjected to a rotation of 0 ° and 900. However, the typewriter will work essentially the same way. The linear the polarizer 70 serves to attenuate the intensity of the beam 29, which is rotated away from its natural polarization angle, It is this attenuation function by the linear polarizer 70, which forms a modulated laser beam 29 ', which corresponds to the frequency modulated signal. A so-called "Glan prism" is suitable for use as a linear polarizer 70. 2 The Pockel cell drive 72 is AC connected to the Pockel cell 68.

The stabilizing feedback circuit 48 is DC connected to the Pockel cell 68.

Figs. 4-7 show selective waveforms for electrical and optical signals, which appear in the embodiment shown in Fig. 1 One of it as a video signal serving circuit lo alulrad vidvosignal is shown in lig. 4. In a typical device for generating such a video signal is a television camera or a video recording device ning. which replays a previously recorded signal generated by a television vision camera. A light spot scanner is another source of such a video signal; The The information signal shown in Fig. 4 is typically a signal with the voltage 1V peak -Race, which signal has its information content in the form of a by means of a line 73 10 15 20 25 30 35 40 7810130-0 represented voltage, which varies with the time format. The maximum instantaneous change the speed of a typical video signal is limited by the bandwidth of 4.5 MHz. This video signal is of that kind, which can be directly presented on a television monitor.

The video signal shown in Fig. 4 is applied to the frequency modulator 20 in Fig. 1.

The modulator 20 generates the frequency modulated waveform 74 of Fig. 5. the content of the waveform in Fig. 5 is the same as the information content in the waveform in Fig. 4, but the shape is different. The information signal in Fig. 5 is a frequency modulated signal, which has its information content in the form of a carrier signal, which has frequency variations with respect to the time around a center frequency. By comparison from the signals in Figs. 4 and 5 it can be seen that the lower amplitude range, which is generally denoted by 75, of the video path shape 73 in Fig. 4 corresponds to the lower frequency portion of the frequency modulated signal 74 of Fig. 5. Such a period of the frequency the lower frequency portion of the vein modulated signal 74 is generally indicated by a parenthesis 76.

An area of higher amplitude, generally designated by the reference numeral 77 of the video path shape 73, corresponds to the higher frequency portions of the frequency modulating a complete period of the frequency modulated signal 74 higher frequency portion is indicated by a parenthesis 78. An intermediate amplitude range generally denoted by a reference numeral 79, of the video waveform 73, corresponds to the intermediate frequency portions of the frequency modulated signal 74.

A single period of the higher frequency portion of the frequency modulated signal, which represents ~ the intermediate amplitude range 79, is indicated by a parenthesis 79a.

A comparison of Figs. 4 and 5 shows that the frequency shown in Fig. 1 the modulator 20 converts the time-varying voltage signal in Fig. 4 to a frequency modulated signal shown in Fig. 5.

Fig. 6 illustrates the intensity of the writing generated by the writing laser 30. the intensity of the writing beam 29 is shown to have a constant level, which is represented by line 80. After an initial start-up process, this intensity remains unchanged.

Fig. 7 illustrates the intensity of the writing beam 29 'after its passage through the light intensity modulation unit 44. The intensity modulated writing beam is displayed with a plurality of upper peaks 92, which represent the light intensity modulation unit f 44 higher light transmission conditions, and with a plurality of valleys 94, which represent the lower light transmission state of the light intensity modulation unit 44. Line 80, which represents the maximum intensity of the laser 30 is superimposed on the waveform 29 'for to show that any loss of light intensity is obtained in the unit 44. This loss indicate < by means of a line 96, which shows the difference in the intensity of that generated by the laser 30 the intensity of the light beam 29 'and the maximum intensity 92 of that of the unit 44 modulated light beams 29 '.

This intensity modulation of the writing beam 29 to form an intensity modulated writing beam 29 'is best damaged in Figs. 6 and 7. Fig. 6 shows l0 15 20 25 30 35 40 iaioiso-o ” the unmodulated beam 79 with a constant intensity. represented by the line 80. Fig. 7 shows the modulated beam 29 'with maximum intensity levels indicated at 92 and minimum intensity levels indicated at 94.

The intensity modulation of the writing beam 29 is related to that of the Pockel cell 68 rotational power, which is shown in lines 98, 10 and 10. The intersection of the line 98 and line 29 'shows the intensity of that emitted from the linear polarizer 70 beam 29 ', when the Pockel cell 68 does not add any rotation to the polarization angle for the light which passes through it. The intersection of line l00 and line 29 ' indicates the intensity of the beam 29 'emitted from the linear polarizer 70, when the Pockel cell 68 adds a rotational w 450 to the polarization angle thereof light, which passes therethrough. The section between line 102 and line 29 'shows the the density of the beam 29 'emanating from the linear polarizer 70, when the Pockel cell 68 adds a rotation of 900 to the polarization angle of the light which passes thereby. 7 The formation of an opening, e.g. the opening 37 shown in Figs. 3 and 8, by means of the intensity modulated beam 29 'shown in Fig. 7 is best understood by a comparative see between the two figures 7 and 8.

Line l00 is drawn midway between intensity level 92, which represents a 44 higher light transmission state, and the intensity level 94, which represents the unit's lower light transmission state. Line l00 represents the intensity, generated by the unit 44, when the Pockel cell 68 rotates the polarization angle thereof writing beam 29, which passes therethrough, over an angle of 450. In addition, represents line 100 the threshold intensity of the modulated beam 29 'required to form a mark in the light-sensitive coating layer 26. This threshold is reached by rotating the angle of polarization of the writing beam 29 through an angle of 45 °.

A comparison between Figs. 7 and 8 shows that an opening 37 is formed below that the Pockel cell 68 rotates the polarization angle of the writing beam 29, which passes thereby, between the angle 45 ° and 900 ° and back to 45 °. Some opening is formed while the Pockel cell rotates the polarization of the passing beam 29 passing through it. angle between 450 and 00 and back to 45 °.

To return to Fig. 3, there is shown a top view of the video disc element, as shown in Fig. 8 in radial cross-sectional view. An examination of this figure 3 facilitates the first of that way. on which the set of lines of light reflecting and light scattering areas 38 and 37 are formed on the video disc element 10. The disc element l0 rotated at a predetermined rotational speed of 1800 rpm and the markings 37 and 38 is formed in the light-coated coating layer 26 as shown by reference I to Fig. 8. The motion control unit 28, which is shown in Fig. 1, forms the openings 37 circular barrier-like manner. Reference numeral 104 denotes a section of a inner bar and the reference numeral 105 denotes a section of an outer groove.

A dashed line l06 represents the center line of the rafter l05 and a dashed line l07 represents the center line of the track l04. The length of a line l08 represents the distance l0 15 20 25 30 35 40 13 7810130-0 between the center lines 106 and 107 of adjacent grooves 105 and 104. 2 micrometers are a typical distance between the center lines of adjacent tracks. The width of an opening 37 is indicated by the length of a line 109. A typical width of an opening is 1 micro- meter. The distance between adjacent openings is represented by the length of a line 110. This distance between adjacent barriers is called the intertrack. region) and typically has an extent of 1 micrometer. The length of an opening is represented by a line 112 and typically varies between 1.0 and 1.5 micrometers.

All of these dimensions depend on many variables in the recorder.

For example, these dimensions vary depending on the frequency range generated of the frequency modulator 20, the size of the spot 42 formed by the optical scripts units 41 and 42 and the rotational speed selected for the disc element 10.

Fig. 9 shows a more detailed block diagram of the motion control unit 28 according to Fig. 1. The rotary drive circuit 32 comprises a spindle servo circuit 130 and a spindle shaft 132. The spindle shaft 132 is integrally connected to the turntable or the disc plate 21. The spindle shaft 132 is driven by a motor 134 of the printed circuit type.

The rotational motion provided by the motor 134 is controlled by the spindle servo circuit 130, which phase locks the rotational speed of the turntable 21 at a signal which is generated of a color subcarrier crystal oscillator 136 tor), which forms part of the synchronization unit 36. The synchronization unit 36 further has a first division circuit 138 and a second division circuit 140. The first division circuit 138 reduces the color carrier frequency generated in oscillator circuit 136. down to a rotational reference frequency. The spindle shaft 132 contains a tacho meter 143 for generating a frequency signal indicating the axis 132 and the turntable 21 exact rotational speed. The tachometer signal is obtained via a line 142 and the rotation reference signal from the first division circuit 138 is obtained on a line 144. The tachometer signal on line 142 is applied to the spindle servo circuit 130 and rotated. The reference signal on line 144 is also applied to the spindle servo circuit 130.

Circuit 130 compares the phases of these two input signals. When the phase of the tachometer signal is before the phase of the rotation reference signal. is the rotation speed too high and a signal is generated in the spindle servo circuit 130 to be supplied via a line 146 to the motor 134 i and to reduce the rotational speed and bring the tachometer signal into phase with the rotation reference signal. When the phase of the tachometer signal comes after the rotation reference the phase of the purge signal when compared in the spindle servo circuit 130, is the rotational speed too small and a signal is generated in the spindle servo circuit 130 to via a line 148 is applied to the motor 134 in order to increase the rotational speed and bring the tachometer the signal in phase with the rotation reference signal.

The second division circuit 140 reduces the color generated by the oscillator 136 the frequency of the subcarrier down to a translational reference frequency for moving the translation drive circuit 34 at a fixed distance for each completed revolution of the element 10. In the preferred embodiment, for each rotational revolution of the element 10 15 20 25 30 35 40 14 7a1o1zo-o The travel distance by means of the translation drive circuit a distance of 2 micrometers.

The crystal oscillator 136 with its two division circuits 138 and 140 operates as an electrical synchronizing circuit for maintaining a constant relationship between the rotational movement of the disc element, which is obtained by means of the rotary drive unit 32, and the translational movement between the writing jet 29 and the coating layer 26 is obtained by means of the translation drive 34.

The movable optical units illustrated in Figs. 1, 10 and 11 are mounted on a support plate, which is shown at 142. This movable plate is driven in the radial direction by means of the translation drive unit 34, which moves the plate 142 2.0 micrometers per second rotational rotation of the spindle shaft 132. This translational movement is radial with respect to on the rotating disk member 10. The radial displacement at the spindle shaft 132 each rotation revolution is referred to as the ascent or division record. Since the a uniformity in the division of the final record depends on smooth movement of the optical units mounted on the plate 142, a lead screw 143 is carefully arranged in the translation drive unit 34, when a translation drive nut 144, which forms engages the lead screw 143 and makes the coupling between the nut 144 and the plate 142 as rigid as possible, which is illustrated by means of a rod 146. In Fig. 10 a reader, which is used to recover the frequency modulated signal, which is stored on the information storage element 10 as a previously described set lines of markings 37 and 38 or a linear sequence of markings 37 and 38.

A reading beam 150 is generated by a reading laser 152, which produces a polarized, collimated light beam 150. A support member, such as the turntable or turntable 21, used to support the information storage element 10 in a substantially predetermined tuned position. ' A stationary optical reading unit 154 and a moving optical unit 156 provides an optical reading path over which the reading light beam 150 is cast between the laser source 152 and the information storage element 10. In addition, either of the optical units are used to focus the light beam 150 on the alternating ones located light-reflecting areas 38 and light-scattering areas 37, which are supported in successive positions on the information storage element 10. The variable the optical unit 156 is used to collect the reflections from the light reflectors and the light scattering areas 37. The motion control unit 28 to 1 ~ maintains relative movement between the reading beam 150 and the successive alternately located areas 38 and 37 for reflection of light resp. scattering of light.

The optical units 154 and 156 also determine the optical path, above which the beam reflected from the whole-laying layer is thrown. It reflected the path of the beam is denoted by the reference numeral 150 '. This reflected light beam path 150 'includes a portion of the path of the original reading beam 150.

At the parts where the reflected beam 150 'coincides with the reading beam 150, both reference numerals 150 and 150 'are used. A light sensing element 158 is located in the path 150 'of the reflected light beam and is used to generate one 10 15 20 Pb 30 35 '10 S 7810130-o frequency-modulated electrical signal, which corresponds to the incoming refixes tion. The frequency-modulated electrical signal aistras by the light sensing element 158, appears on a line 160 and has its information content in form of a carrier frequency with frequency changes in time corresponding to the 1st degree information tion. The signal from the light sensing circuit 158 is applied to a discriminating circuit. circuit 162 via an amplifier 164. The discriminator circuit 162 is controllable in behavior of the output signal from the light sensing circuit 158 and is used to change the frequency-modulated electrical signal to a time-dependent voltage signal, which represents the 1st degree information. The time-dependent voltage signal is is also drawn as a video signal and appears on a line 165. This time dependent voltage signal has its information content in the form of a voltage, which varies with the time format and is suitable for presentation via a conventional television vision monitor 166 and / or an oscilloscope 168.

The optical reading units 154 and 156 further have a polarization selective radiation generating element 170, which acts as a radiation polarizing element. opposite the defrost straw 150 and which acts as a selective straw divider against the refracted straw 150 '. The optical reading units include further, a quarter-wave longitudinal plate 172. The strip polarizer 170 filters from the reading the straw 150 removes any light waves which are not aligned with the straw polarizer. 170 polarization axis1. With the polarization axis of the reading beam 150 fixed with a special orientation by means of the element 170 changes the quartz wavelength plate 172 the polarization pianist from 1inar to11 circular polarization. Element 170 and quartz the path length plate 172 is located in the path 150 of the reading light beam. The element 170 is owned between the core 152 of the reading beam 150 and the quartz wave longitudinal plate 172.

Quartz path length ~ the plot 1/2 is also located in the reflected beam of the reading beam. lane 150 '. The quartz wave length plate 172 thus not only changes the reading beam polarization from linear to circular under its path from the de-icing 152 to the information storage element 10, without the quartz path length plate 172 changing also the circularly poiarized, reflected the light to 11 back to 11 inwardly poiarize light, the rotator is rotated 900 with respect to the preferred direction, which is fixed with the core 152 and the element 170. This rotating beam 150 'is selectively directed on the light sensing element 158, which changes the reflected light beam 150 ' ti11 a corresponding electric sign. It should be noted that the element 170 is reduced. the intensity of the reading beam 150 as it passes therethrough. This reduction The intensity of the intensity is compensated by the original intensity of reading the strains 150 are set to a sufficiently high level to balance this reaction. tion.

Quartz path1langds ~ p1atLan 1/2 gives a total rotation of 9D ° on the reflected beam 150 'with respect to the reading beam 150 during the change from linear pole risation tI11 circular polarization ooh tiiihaka ti11 iinjär poiarisation. As ; 7810130-o l0 IH 20- 25 iso 35 40 previously mentioned, the element 170 is also a beam splitting cube in the reflected one the reading beam path l50 '. Since the reflected reading beam l50 ' polarization plane is shifted 900 due to the double passage of the beam through quartz wavelength plate l72, the element 177 directs beam splitting cube section the reflected reading beam 150 'against the light sensing circuit 158.

A suitable element with the property of a light sensing element 158 is a photo- diode. Each such element 158 is capable of changing the reflected frequency modulated the light beams 150 'into an electrical signal with its information content in the form of a carrier frequency with frequency variations in time, which vary from carrier the frequency. The optical units l54 and l56 further comprise the objective lens 52, which is supported by a hydrodynamic air storage element 54, which supports lens 52 above the coating supported by the information storage element 10 layer 26. As previously mentioned, the reading beam 150 consists essentially of parallel light rays. The objective lens 52 has an entrance opening 56 which has larger diameter than the diameter of the reading beam 150, when generated by the laser beam. source l52. A plano-convex scattering lens 154 is arranged between the laser source 152 and the entry aperture 56 of the objective lens 52 to project the substantially parallel ones the light rays, which form the reading beam 150, to a light beam l50 with a sufficiently large diameter to at least fill the objective lens 52 entrance opening 56. The optical units l54 and l56 further have a number stationary, planar mirrors 176 and 178 to deflect the reading light beam l50 and the reflected light beam l50 'along a path which is calculated for that the reading light beam 150 should fall on the previously mentioned elements.

An optional optical filter 18D is located in the reflected beam lane l50 'and filters out all wavelengths except for reading light ~ the wavelengths of the beam. The use of this filter 180 improves the image quality of the image presented by the television monitor 166. This filter l80 is significantly, when the reading system is utilized with the writing system, which is approached below with reference to Fig. 11. In a device set up for both reading and writing, a portion of the writing beam 29 is thrown along the reflected reading beam. e lens bana l50 '. The filter stops this part of the writing beam and transmits it radiated rays l50 'full intensity.

An optional collection lens 182 is located in the path of the reflected beam l50 'to cast the reflected beam on the light sensing element l58 active area. This collection lens l82 'reduces the reflected beam l50' diameter and concentrates the light intensity of the reflected beam on the sensing element l58 active area.

Amplifier 164 amplifies the output signal from the light sensing element 158 and increases the amplitude of the frequency modulated electrical signal which is generated of the light sensing element 158, in order to adapt to input signal requirements of l0 l5 20 25 30 35 40 of 7810130-o demodulator l62. _ The electric and optical waveforms shown in Figs. 4 ~ 7 are also generated the reading apparatus shown in Fig. 10 during recovery of the frequency modulated one the signal, which is stored on the coating layer supported by the disc element 10 Fig. 6 shows a writing laser beam generated by means of a laser source, which has the constancy intensity, which is represented by line 80. The reading laser 152 generates a reading beam l50 with constant intensity but at a lower level. Fig. 7 shows a intensity modulated laser writing beam. The reflected reading beam l50 'is intense site modulated due to the fact that it hit the light reflectors and light scattering areas 38 and 37, which are supported on the disc member 10. The reflective The reading beam l50 'will not be a perfect square wave of the kind that shown in Fig. 7. Instead, the corners of the signal pulses are rounded due to the reading the final dimension of the stain.

Fig. 5 shows a frequency modulated electrical signal with its information content in the form of a carrier signal, which has frequency changes over time varying around the center frequency. The output of the light sensing element 158 is the same type of signal. Fig. 4 shows a video signal with its information content in the form of a voltage, which varies with the time format. The output signal from demodulator l62 is the same type of signal.

The motion control unit 28 shown in Fig. 10 operates in the same manner as the motion control unit 28 in Fig. 1. In the reading apparatus, the motion control unit 28 generates a rotary movement of the disc element under the control of a rotary drive unit 32. The unit 28 further generates a translational movement for moving the moving optical image. the reading unit 156 radially over the surface of the storage element.

The unit 28 further has a synchronizing circuit for maintaining one constant relationship between the rotational movement and the translational movement, so that the reading beam l50 hits the information tracks supported by the disc element l0. Sections of typical information tracks are shown at l04 and l05 in Fig. 3.

Fig. 11 shows a block diagram of the combination of the typewriter according to Fig. 1 and the reading apparatus according to Fig. 10. The elements shown in Fig. 11 work on in the same way as previously described, so this detailed function is not repeated here. Only a brief description is given in order to avoid repetition and ambiguity.

The path of the unmodulated writing beam is displayed at 29 and the modulated writing beam the path of the beam is displayed at 29 '. A first optical device determines the modulated beam path 29 'between the output of the linear polarizer 70 and the coating layer The stationary optical writing unit 41 includes the mirror 58. The movable, the optical writing unit 40 includes the scattering lens 66, a partially transmitted mirror 200, a flat mirror 60 and the objective lens 52. The modulated writing the beam 29 'is thrown as a writing spot 42 on it depending on light-sensitive the coating layer and cooperates with the coating to form those previously described the markings. 10 15 20 25 30 35 40 '7a1o1zo-o The path of the reading beam is displayed at 150. The optical reading units defines a second optical path for the reading beam 150 between the reading laser 152 and the information storage unit 10. The stationary optical reading unit 154 includes the mirror 176. The movable optical reading unit 156 includes the scattering lens 174, the polarization displacement device 172, a second fixed mirror 202, the selective transmitting mirror 200, the flat mirror 60 and Insert 52. The reading beam 150 is thrown as a reading spot 157 at a point located at a downstream distance from the writing area 42, which is more completely is written with reference to Fig. 12. The mirror 200 is a dichroic mirror, which is transmitting at the wavelength of the writing beam 29 'and which is reflective at the wavelength of the reading beam 150 '.

The intensity of the writing beam 29 'is greater than the intensity of the reading beam 150.

While the writing beam 29 'must change it depending on the light-sensitive coating layer 26 to provide markings representing that for storage viewed video signal, the intensity of the reading beam 150 need only be high enough to illuminate the markings formed in the coating layer 26 and give a reflected light beam 150 "with sufficiently high intensity to achieve a good signal after collection with the optical reading unit and conversion from an intensity modulated, reflected beam 150 'to a frequency modulated, electric signal by means of the light sensing circuit 158.

The fixed mirror 58 in the optical path of the writing beam and the two fixed mirrors 176 and 202 in the optical path of the read beam are used to direct the write beam 29 'toward the objective lens 56 at a controlled angle in relation to the reading beam 150.

This angle between the two beams incident on the storage element gives a mean space between the writing stains 42 and the reading stains 157, when these are each discarded on the coating layer 26.

A sufficiently large gap in the operation of the apparatus has been found to be 14-6 micrometers. This distance corresponds to an angle1, which is a11tfor 1iten to indicate This is shown in Fig. 12. Consequently, for the sake of clarity, this angle is excessive in Fig. 12. g The reading beam 150 'is demodulated in a discriminator circuit 162 and present. on a conventional television monitor 166 and an oscilloscope 168. television the monitor 166 displays the image quality of the recording and the oscilloscope 168 displays the video signal. 1en more in deta1j. This read function immediately after the write function makes it possible to momentarily monitor the quality of the video signal1 during the recording operation 1itet. In the event that the quality of the 1graded signal is poor, it is immediately obtained knowledge of this and the writing process can be corrected or the information Storage element 10, which stores the video information signal with such quality, cash race.

At the time of reading after recording, the writer 30 and 10 15 20 25 30 35 40 19 '7810130-0 the reading laser l52 at the same time. A dichroic mirror 200 is used to combine the reading beam l50 with the writing beam 29 '. At this working condition reading after recording, the wavelength of the writing beam 29 is selected to differ from that of the reading beam l50 wavelength. An optical filter 180 is used to block any part of the writing beam, which followed the path of the reflected reading beam. Consequently the optical filter 180 transmits the reflected reading beam 150 'and filters the removes any part of the laser writing beam 29 'which follows the reflected reading. path l50 '.

In the comparative working condition, the function of reading after writing is as described with reference to Fig. 11. When operating under this supervision operating state, a comparator circuit 204 compares the output of the demodulator 162 with it original video information signal, obtained from source 18.

More specifically, the video output signal from discriminator 162 is applied to one comparator 204 over a line 206. The second input signal to comparator 204 is taken from the video source 16 via line 18, an additional line 208 and via a delay The delay line 210 applies to the input video information signal a time delay equal to the accumulated delay values starting from the frequency modulation of the input video information signal and on to the frequency demodulation of the recovered electrical signal from the sensing circuit l58. This delay also includes the delay in terms of travel time from the point on the storage element 10 at which the input video information the signal is stored on the information storage element by means of the write spot 42 with the setting to the point at which the reading spot l57 hits.

The correct delay amount is best achieved by the delay circuit 210 is performed for variable delay, the delay being set to optimal feature.

Under ideal conditions, the video output signal from discriminator l62 is identical in all respects with the video input on lines 18 and 208. Each performance difference represents errors, which may have been caused by defects or defects in the disc the surface of the element or malfunctions of writing circuits. This application is although it is essential when recording digital information, less critical when other information is recorded.

The output of the comparator circuit 204 can be counted in a counter (not shown) for determining the actual number of errors that occur on a disc element.

When the number of errors counted exceeds a predetermined number, the write operation ends tion. If required, a new record can be made on a new disc element. Each disc elements with too many errors can be processed for reuse. In Fig. 11 comparator 204 compares the outputs available on lines 208 and 206. One alternative and more direct connection of the comparator 204 is to compare the output signals from the frequency modulator 20 and the amplifier 164 shown in Fig. 10. 10 15 20 25 30 35 40 20 7810130-0 Fig. 12 shows in slightly enlarged form the slightly different optical paths for the intensity modulated writing beam 29 'from the writing laser 30 and the unmodulated one the reading beam 150 from the reading laser 152. The information storage element 10 is moved in the direction indicated by an arrow 217. The figure shows an unexposed portion 26 ' of the coating layer 26 approaching the writing beam 29 'and a linear sequence of openings 37, which leave the intersecting area between the writing jet 29 'and the coating layer 26. The writing beam 29 'coincides with the optical of the microscope objective lens 52 shoulder. The center axis of the reading beam 150, denoted by 212, forms an angle with the center axis of the writing beam 29 ', which is designated 214. The angle is illustrated by means of a bidirectional arrow 216. Due to this small difference in the writing beam 29 'and the optical paths of the reading beam 150 through the lens 52, the writing spot falls 42 a distance in front of the reading spot 157. The writing spot 42 is in front of the reading the distance 157 a distance equal to the length of a line 218. The length of the line 218 is equal to the angle times the focal length of the objective lens 52. The resulting delay the writing between the writing and the reading allows the molten metal coating layer 26 to solidify so that the record is read in its final solidified state.

If it was read too early while the metal was still molten, it would reflect from the edges of the aperture can not produce a high quality signal presentation on the monitor 166.

Fig. 13 shows a preferred circuit diagram of a stabilization circuit 48 for a Pockel cell, which circuit is suitable for use in the apparatus of Fig. 1. It is known that a Pocke1 ~ cell 68 rotates the plane of polarization of a guided writing light beam 29 as a function of an applied voltage, which is detrimental with reference to Fig. 7.

Depending on the individual Pockel cell 68 causes a voltage change of the order of 100 V that the cell rotates the plane of polarization thereof thereby passing the light 00 ". The drive unit of the potcoal counter serves to amplify the output signal from the information signal source 12 to an output signal with a peak-to-peak value of 100 V.

This output signal is a properly input drive signal to the Pockel cell 68. the drive unit 72 of the cell generates a waveform which has the shape shown in Fig. 5 and has a voltage value from peak to peak of 100 V.

The Pockel cell should work at an average rotation of 450 in order to bring the intensity of the modulated light beam to reproduce as faithfully as possible the electric drive signal. A bias voltage must be applied to the Pockel cell to keep the Pockel cell at this average operating point. In practice, it varies the electrical bias voltage, which corresponds to a working point with a rotation of 45 °, tinuerligt. This continuously changing bias voltage is generated by utilization of a servo feedback loop. This sorvo feedback loop includes the comparison of the average value of the transmitted light with an adjustable reference value and supply of the difference signal to the Pockel cell by means of a direct voltage lO l5 20 25 30 35 40 Zl 7810130-0 amplifier. This arrangement stabilizes the working point. The reference value can be set to correspond to the average transmission, which corresponds to the the point of rotation above 450 and the servo feedback loop provides correction biases to maintain the Pockel cell at this average rotation of 450.

The stabilizing circuit 48 comprises a light sensing means 225. A silicon photodiode acts as a suitable light-sensing organ. Diode 225 senses one part 29 "of the writing beam 29 ', which is emitted from the optical modulator 44 and through the partially reflecting mirror 58, which is shown in Fig. 1. The photodiode 225 operates in essentially the same way as a solar cell and is an electrical energy source, when illuminated by incident radiation. An output terminal of the photodiode 225 is connected by a line 227 to a common reference potential 226. Photo- the second output connection of the diode 225 is connected via a line 230 to an input at a differential amplifier 228. The output terminals of the silicon cell 225 are shunted by means of a load resistor 232, which enables a state of linear response.

The second input of the differential amplifier 228 is connected via a line 238 to one adjustable arm 234 of a potentiometer 236. One end of the potentiometer 236 is connected to the reference potential 226 via a line 240. An electrical power source 242 is connected to the other end of the potentiometer 236, which enables input positioning the differential amplifier 228 to generate a feedback signal on lines 244 and 246 for setting the average power level for it modulated laser beam 29 'to a predetermined value.

The output poles of the differential amplifier 228 are resp. connected via resistive elements 248 and 250 and the output lines 244 and 246 to that of Fig. 1 showed the 68 input poles of the Pockel cell. The Pockel cell drive 72 is AC connected to the Pockel cell 68 by means of capacitive elements 252 and 254, while different The ration amplifier 228 is connected to the Pockel cell 68.

During operation, the system is activated. The part 29 'of the light from the writing beam 29 ', which falls on the silicon diode 225, generates a differential voltage at an input to differential amplifier 228. Initially, potentiometer 236 is set to the average transmission through the Pockel cell corresponds to a rotation of 450.

Then comes, if the average intensity level of the light, which falls on the silicon cell 225 either increases or decreases, a corrective voltage to be generated of the differential amplifier 228. The corrective voltage applied to the Pockel cell 68 has a polarity and a size adapted to return the average intensity level to the predetermined level, selected by setting the input the voltage to the second input of the differential amplifier across line 238 through see of the movable arm 234 along the potentiometer 236.

The adjustable arm 234 of the potentiometer 236 constitutes the means for selecting the average intensity level of the light generated by the writing laser 30. Optimal results 10 l5 20 25 30 35 40 22 7810130 ~ 0 when the length of one opening 37 is exactly equal to the length of the next on the following space 38, as previously described. The setting of the potentiometer 36 is the measure for achieving this similarity in length. When the length of an opening is equal to the length of the next adjacent space, a duty cycle of is obtained type half-half. Such a work cycle can be detected by checking the presence the information just written on the TV monitor and / or the oscilloscope l66 resp. l68, which have been previously described. Commercially acceptable results lies, when the length of an opening 37 varies between 40 and 60% of the total the length of an opening and its next subsequent space. In other words, measured the length of one opening and the next subsequent space. the opening can thus have one length, which falls in the range of 40-60% of the total length. IN Fig. 8 illustrates a circular cross-section of one with reference to Fig. 3 shows an information track, in which a reflective light-reflecting area 38 is located between a pair of non-reflective light-reflecting areas 37. In the circulating learning the cross-sectional view of Fig. 8, the incident reading or writing beam is moved relative to the element 10 in the direction represented by the arrow 277. This means carries that a reading beam first falls on the reflecting light reflecting area 38a and then falls on the non-reflective light reflecting area 37a. In this edition the positive half period of the record is represented the signal of a reflective light reflecting region 38a and the negative half period of the signal to be recorded is represented by the non-reflective light reflective area 37a. The operating cycle of the one shown with reference to Fig. 8 the signal is a 50% duty cycle insofar as the length of the reflecting light the reflecting area 38a, which is represented by a parenthesis 260, is equal to the length of the non-reflective light reflecting area 37a, which later length represented by parentheses 262. This preferred work cycle is accomplished by combined setting of the absolute intensity of the writing beam 29 by setting the power supply of the writing laser 30 and by setting the potentiometer 236 in to a level at which an aperture is formed at the beginning of a 45 ° rotation of the writing beam 29 polarization angle.

To refer to it with reference to Figs. 7 and 8 illustrated the process for forming openings, melting of a thin metal coating layer 26, when the power in the light spot exceeds a threshold value which is characteristic of the nature and thickness of the metal film and the properties of the substrate. Light- the power of the spot is modulated by means of the light intensity modulating unit 44. -off junctions are kept short to make the position of the ends of the holes or openings exactly independent of variations in the melting threshold. Such variations in melting the threshold value may be due to variations in the thickness of the metal the coating layer and / or the use of various materials as information storage layer. 10 15 20 25 30 35 40 23 7s1o1ao-o The average power in the light spot, which is required to form one opening in a thin metal coating layer 26 with a thickness between 200 and 300 Å, is of the order of 200 mw. Because the frequency modulated carrier frequency is approximately 8 MHz, 8 x 10 6 holes or apertures of variable length per second are formed , and the energy per hole is 2.5 x lÖ9 joules.

In this first embodiment, a video disc element 10 is a portion of the glass substrate exposed in each opening. The exposed portion of the glass substrate is acts as an area of non-reflective light reflectivity with respect to an incident the reading beam. The portion of the metal coating layer which remains between each other the following apertures appear as an area with high light reflectivity towards an incident reading beam.

When the formation of first and second markings takes place using a coating of a photoresist, the intensity of the writing beam 29 'is set to such level, that a 450-degree rotation of the plane of polarization produces a light beam 29 'with threshold intensity for exposure and / or interaction with photoresist coating layer 26, while the photoresist coating layer is in motion and applied to it movable information storage element l0. The combination of the Pockel cell 68 and The gloss prism 70 includes a light intensity modulating element which operates from the 450-degree setting state to a lower light transmitting state state, which relates to an operating state near the rotation 00, and to a more light transmitting state, which refers to an operating state close rotation 90 °. As the intensity of the writing beam 29 'increases over the initially set the level or the predetermined starting intensity, and increases towards it more light transmitting state, 'the incident writing light beam 29' exposes it illuminated by the photoresist. This exposure continues after the writing beam intensity when the maximum light-transmitting state and changes back down to the initial predetermined intensity, which relates to the rotation 45 ° of the plane of polarization of the light emitted from the writing laser 30. When the rotation falls below the value 450, the intensity of the writing beam 29 ', which exits, decreases from the Glass Prism 70 below the threshold intensity at which the focused writing the beam is not able to expose it to illuminate the photoresist. This shortcoming The ability to expose the illuminated photoresist continues after that of the writing beam intensity has reached the minimum light-transmitting state and begins to return against the initial, predetermined intensity, which refers to a rotation of 45 ° of the plane of polarization of the light emitted from the writing laser 30.

The Pocket cell drive circuit 72 is typically a high gain amplifier and high output voltage, which amplifier has an output signal which provides a swing or a variation from peak to peak of 100 V of the output voltage. This signal is intended to conform to the requirements required to operate the Pockel cell 68.

Typically, this means the mid-voltage value of the output signal from the Pockel cell drive unit 72 provides a sufficient control voltage to drive the Poçkel cell _ia1o1so-o ei 10 15 20 25 30 35 40 68 over 450, so that about half of the total available light from the laser 30 output from the linear polarizer 70. When the output signal from the drive circuit 72 becomes positive. more light is transmitted from the laser. When the output of the drive 72 becomes negative less light is transmitted from the laser.

In the first embodiment, in which a metal coating layer 26 is used, the output of the laser 30 is set to generate an intensity, which begins to melt the metal layer coating 26 on the disc element 10, when the output signal from the drive 72 is zero and the operating point of the Pockel cell is 45 °. When driving the output 72 of the unit 72 becomes positive, consequently the melting continues. When driven the output 72 of the unit becomes negative, however, the melting stops.

In a second embodiment, in which the photoresist coating layer 26 is used, the output signal from the laser 30 is set to generate an intensity which both illuminates and exposes the photoresist coating 26 as the output of the drive 72 generates its average voltage value. When the output of the drive 72 becomes positive, the actually the illumination and exposure of the photoresist by means of the writing beam to continue take. When the output of the drive 72 becomes negative, the illumination of the photoresist last, but the energy in the writing beam is sufficient to expose the illuminated area. the. The term "expose" is used herein with its technical meaning, indicating the physical calic phenomena, which are based on illumination of a photoresist material. The exposed the photoresist can be developed and the developed photoresist material is removed on conventionally. Photoresist material illuminated by light, which has insufficient intensity to expose the photoresist, can not be developed and removed. In both the first and second embodiments, as described above, are set the absolute power level 80, which is illustrated by the line 80 in Fig. 6, upwards and downward to achieve this effect by setting the power of the writing laser 30 supply. In combination with this setting of the absolute power level of the print laser 30 also uses, as previously mentioned, the potentiometer 26 to cause markings formed in the coating layer, when the beam 29 is rotated an angle greater than 45 °.

In a read-only apparatus of the type shown in Fig. 10 the optical filter l80 is optional and is generally not required. Its use in an apparatus which is used only for reading, causes a slight attenuation of it reflecting light beam, so a small increase in the intensity of the reading laser 152 is required. to ensure the same intensity at the detector 158 in comparison with a reader which does not use a filter 180.

The collection lens l82 is optional. In a properly arranged reading machine has the reflecting reading beam 150 'is substantially the same diameter as the photodetector 158 work area. If this is not the case, a collection lens l82 is used to concentrate the reflected reading beam l50 'on the smaller operating range of the selected photodetector 158. Although the above, presently preferred embodiments have been described in detail, it will be appreciated that the invention is limited only by the scope of the claims.

Claims (30)

l0 l5 20 25 30 35 40 zs 7810130-0 PATENTKRAV. A method of processing frequency modulated information on an information storage element using a laser beam, the frequency modulated information having a carrier signal with frequency changes over time corresponding to the information, and the information storage element being moved at a constant speed relative to a laser beam , while focusing the light beam on a first surface of the information storage element, characterized in that the processing comprises recording the information on the information storage element (10) using the laser beam (29, 29 ') while reading stored information using a second laser beam (150, 150 '), the method comprising the method steps of generating a frequency modulated electrical signal for recording, which signal has a carrier signal with frequency changes over time corresponding to the information to be stored, that the first the light beam (29, 29 ') is applied to a light-sensitive surface of the information storage element (10), and the intensity of the light beam (29, 29') transmitted to the first surface is controlled by using the frequency modulated signal as a control signal, the control including the use of the light beam. transmitted first light beam (29, 29 ') for irreversible change of the light-sensitive surface of the information storage element (10) under the control of a part of the frequency modulated signal, when the storage element is moved at a constant speed, and lowering the intensity of it to the light-sensitive surface of the information storage element transmits the first light beam bundle under the control of a second part of the varying frequency having modulated signal, when the storage element is moved at a constant speed, whereby said control method in the light-sensitive surface of the storage element generates a linear sequence of areas (37, 38). in a groove-like manner on said surface, which areas have alternating reflective light reflectance and non-reflective light reflectance and which sequence of alternating areas represents the mod sequence modulated signal, that the second light beam (l50, l50 ') consists of polarized, collimated light and is cast on the sequence of areas (37, 38); , while said movement produces relative movement between the second beam of light beams (37, 38 ') cast on said areas (37, 38) and the alternating areas (37, 38) for generating reflections from the reflectivity areas, which represent the stored frequency modulated signal, that the reflections are sensed and that a frequency modulated electrical signal corresponding to the reflection is generated, the frequency modulated electrical signal having its information content in the form of a carrier signal with time frequency changes. Method according to claim 1, characterized in that the generation of the frequency modulated electrical signal comprises generating a first electrical signal, which has its information content in the form of a voltage signal varying with the time format. , and changing the time-varying voltage signal to a frequency-modulated electrical signal, which has its information content in the form of a carrier signal with frequency changes in time, which correspond to said variations with the time of the voltage signal. 3. A method according to claim 2, characterized in that the first and the second light beam (29, 29 ', 150, 150') are kept stationary and the information storage element is moved at a constant speed relative to the stationary first and the stationary second beam. Method according to claim 2, characterized in that the control comprises the use of the frequency modulated signal for varying the intensity of the first light beam (29, 29 ') over a predetermined intensity, where the beam changes the light-sensitive surface, and during a predetermined intensity, where the beam (29, 29 ') is not able to change the photosensitive surface, the change being representative of the frequency modulated signal. Method according to claim 4, characterized in that the first information signal has its information content in the form of a time-varying voltage signal, which is suitable for presentation on a conventional television monitor, that in the control: the first beam (29, 29) is generated. ') is a modulated, collimated laser writing beam of polarized monochromatic light, which is caused to fall on the photosensitive surface of the storage element (10), which surface is a thin, flat, opaque metal coating layer with suitable physical properties to enable local heating by influence in dependent that the writing beam falls thereon, the heating causing local melting followed by retraction of molten material towards the perimeter of the molten area while leaving a permanent opening in the thin metal layer during solidification of the metal, and that the control involves utilizing the frequency modulated signal for variation of the writing beam (29, 29) ') intensity above the predetermined intensity, where the beam melts the metal layer without evaporating it, and below the predetermined intensity, where the beam is not able to melt the metal layer. Method according to claim 3, characterized in that the storage element (10) has the shape of a disc and that the movement of the storage element (10) involves generating uniform rotational movement of the disc, and synchronizing the rotational movement with movement of the storage element (10). to provide relative motion of the first and second light beams (29, 29 '; 150, 150') radially across the surface of the disc-shaped bearing member to maintain a constant relationship between the rotational motion and the translational motion. Method according to claim 5, characterized in that the control comprises stabilizing the modulation level of the first light beam (29, 29 ') for operation between a predetermined higher light intensity and a predetermined lower light intensity, sensing at least a part (29 ") of the laser write beam (29 ', 29") after modulating this beam in order to generate an electrical feedback signal representing the intensity of the writing beam, and utilizing the feedback signal in the control for to achieve stabilization of the modulation level of the writing beam (29, 29 '). Method according to claim 7, characterized in that the sensing of at least a part (29 ") of the writing beam (29, 29 ') generates an electrical feedback signal, which is representative of the average intensity of the modulated writing beam, thereby stabilizing the working level of the light beam modulation. for emitting the modulated writing beam at a substantially constant average power level. Method according to claim 2, characterized in that the frequency-modulated electrical signal generated during the sensing is demodulated to generate a one-time-dependent voltage signal, which represents the stored information, the time-dependent voltage signal having its information content in the form of a time-varying voltage. and is suitable for presentation by means of a conventional television monitor. l0. Method according to claim 1, characterized in that the polarization plane of the polarized second beam (150, 150 ') is changed by rotation of the second beam during incident and reflected passage to and from the storage element, respectively, whereby the intensity of the reflected second beam (150'). which is returned to the light source (152) used to generate the second light beam when thrown onto the storage element (10) is substantially reduced. ll. Method according to Claim 9, characterized in that the time-dependent voltage signal generated during the demodulation is compared with the first information signal. l2. Method according to claim 11, characterized in that the second light beam (150, 150 ') is focused on the storage element (10) at a point thereon in the direction of movement behind the point at which the first light beam (29, 29% falls), and that the first information signal is applied a time delay equal to the accumulated delay values from the frequency modulation of the first information signal up to and including the frequency demodulation of the signal generated at the sensing, and comprising the delay in the movement time of the point on the storage element the point at which the first beam (29, 29 ') falls, to the point at which the second beam (l50, l50') falls. l3. Method according to claim 1, characterized in that an objective lens (52) is arranged adjacent to the storage element (10) for receiving both the first and the second beam (29, 29 '; 150, 150') and for directing the beams towards the method (10), the method comprising directing the first beam (29, 29 ') toward the objective lens (52) at an angle with respect to the second beam (10). 150, 150 '), whereby the beams are given a mutual distance when they emerge from the objective lens and faults on the storage element. A method according to claim 1, characterized in that the first light beam (29, 29 ') is an argon ion laser beam, the second beam (150, 150') is a helium-neon laser beam, and that the method comprises grips optical blocking of any part of the argon ion beam in the reflection path from the storage element (10), before the reflected second beam (150, 150 ') is sensed. 15. An apparatus for processing information in the form of a frequency modulated signal on an information storage element, the signal signal having its information content in the form of an office signal with frequency changes over time representing the information, the information storage element having a first surface with markings representing the information signal. Each apparatus comprises a device adapted to provide the storage element with a uniform tube, a light source for generating a light beam, and an optical device for attaching an optical path between the light source and the storage element first surface and for focusing the light beam on the first beam. characterized in that the apparatus is arranged for storing information in the form of a frequency modulated signal on the information diagram element (10) using a first laser beam (29, 29 ') and for reading stored information using a second laser beam ( 150, 150 '), that i The information storage element (10) has a substrate (22) with a light-sensitive coating (26) covering said first surface (24) and is arranged to preserve the markings (37, 38) representative of the information signal, that the first light beam (29, 38) 29 ') generated by said light source (30), has a sufficiently high intensity to grow with the coating (26) and to change the coating so that it retains the markings (37, 38) representative of the information signal, and that the apparatus further comprises a first device (16, 20) for generating a frequency-modulated video information signal for recording, a light intensity modulating unit (44) arranged in the optical path between the light core (30) and the coating (26) on the storage element, which is arranged to operate over an interval between a higher light transmitting state and a lower light transmitting state for intensity modulation of the first light beam (29, 29 ') with the the information intended for recording, the light intensity modulating unit (44) being actuatable in dependence on the frequency modulated signal and being arranged to change between its higher light transmitting state and its lower light transmitting state during each cycle of the frequency and frequency modulated signal. for intensity modulation of the first light beam (29, 29 ') with the frequency-modulated electrical signal intended for recording, and the first light beam (29, 29') is arranged to pass through the light intensity modulation unit (44) and is focused on the coating (26). means of said optical device (58, 142) for changing the coating so that it retains the markings (37, 38) representative of the video information, a second display (152) for generating the second light beam (150, 150 ') - a second optical device (70, 180, 176, 142) for fixing an optical path between the second light the core (152) and the storage element (10) including a portion of the first optical path, for focusing the second light beam bundle (150, 150 ') on the coating (26), the second light beam bundle (150, 150') having sufficiently high intensity for illuminating selected portions of the coating on the storage element (10) and thereby being reflected from certain illuminated portions and scattered from other illuminated portions, while other optical device (70, 180, 176, 142) is arranged to collect the said reflections from illuminated portions, and a sensing device (158, 164) which can be actuated depending on the reflected light, for generating a frequency-modulated electrical signal which corresponds to the reflections, the latter frequency-modulated signal having its information content in the form of a response with a response the 1st degree video information. Apparatus according to claim 15, characterized in that the first device comprises a device (16) for generating a first information signal, which has its information content 11 in the form of a voltage varying with the time format, and one depending on the device ( 16) for generating the first information signal actuator frequency modulator device (20) for converting the time-varying voltage signal to the frequency-modulated signal. Apparatus according to claim 16, characterized in that it comprises a demodulator device (162) which can be actuated depending on the output signal from the sensing device (158, 164) for changing the frequency-modulated electric signal to a time-dependent voltage signal representing the current. The video information, which has a time-dependent voltage signal, has its information content in the form of a voltage varying with the time format and is suitable for presentation with a conventional television monitor (166). Apparatus according to claim 17, characterized in that it comprises a device (204) for comparing the varying voltage with time having the video information signal from the demodulator device (162) with the first information signal. Apparatus according to claim 18, characterized in that the second light beam (150, 150 ') is arranged to focus on the storage element at a point (157) in the direction of movement behind the point (42) at which the first The light beam (29, 29 ') fails, and that the apparatus further comprises a delay device (210) in the signal path of the first information signal, which means a delay device for a time delay on the first information signal (29, 29') which is With the accumulated values of the delay from the frequency modulation of the first information signal to the frequency demodulation of the signal from the sensing device (158, 164, 162) and includes the delay with respect to the displacement zone. The operating time of the point on the storage element during movement from the point of impact (42) of the first beam (29, 29 ') to the point of impact (l57) of the second beam (l50, l50'). Apparatus according to claim 16, characterized in that the light intensity modulation unit (44) comprises an electrically controllable device (68, 72) which can be actuated in dependence on the frequency modulator device (20), for varying the first light beam (29, 29). ') intensity above a predetermined intensity, where the focused first beam changes the coating (26) and below the predetermined intensity, where the focused first beam is not able to change the coating, which change is representative of the frequency modulated signal. Zl. Apparatus according to claim 20, characterized in that the first information signal has its information content in the form of a time-varying voltage signal suitable for presentation on a conventional television monitor (166), that the first light source (30) comprises a writing laser for generating the first beam as a collimated writing beam (29, 29 ') of polarized monochromatic light, that the substrate of the storage element (10) forms a smooth, flat, rigid disk, on which the first surface is a flat surface, coating - the ring (26) is a thin, opaque metal coating layer having suitable physical properties to enable local heating depending on the writing beam bundle incident thereon, which heating causes local melting as a result of retraction of molten material towards the perimeter of the molten area while leaving a permanent opening in the thin metal layer after solidification, and that the electrically controllable device (68, 72) is kbar depending on the frequency modulator device (20) for varying the intensity of the writing beam over the first predetermined intensity, where the focused writing beam melts the metal layer without narrowing, and below the predetermined intensity, where the focused beam is not able to melt the metal layer. Apparatus according to claim 15, characterized in that the storage element (10) is disk-shaped, that the relative motion application device comprises a rotary drive device (32) for generating uniform rotational motion of the disk (10), and that the apparatus further comprises a translational drive device. (34) synchronized with the rotary drive device to relatively move the first and second focused light beams radially across the first surface of the disk-mounted storage element, and an electrical synchronizing device (36) for maintaining a constant relationship between the rotational motion and the translational motion. in Apparatus according to claim 20, characterized in that the light intensity modulation unit (44) comprises a feedback device (50a, 50b) for stabilizing the operating level of the electrically controllable device (68, 72) so that it operates between a predetermined higher light intensity and a predetermined lower light intensity, that the light intensity modulation unit comprises a light sensing device (48, 225) for sensing at least a part (29 ") of the modulated first light beam (29, 225). 29 '), emitted from the electrically controllable device, to generate an electrical feedback signal representative of the intensity of the modulated first beam, which feedback signal is arranged to be applied to the electrically controllable device (68, 72). to stabilize its level of work. Apparatus according to claim 23, characterized in that the light sensing device (48, 225) is arranged to generate an electrical feedback signal representative of the average intensity of the first light beam (29, 29 '), the operating level of the light intensity modulation unit (44) is designed to be stabilized to emit the modulated first light beam at a substantially constant average power level. Apparatus according to claim 21, characterized in that the first and second optical devices comprise an objective lens (52) and a hydrodynamic air storage device (54) for supporting the lens above the first surface of the storage element (10), and that the collimated first light beam (29, 29 ') have substantially parallel light beams, that the objective lens (52) has an entrance aperture with a diameter larger than the diameter of the first light beam, when emitted from the first light source (30), and that the first optical device further comprises a mirror device (58, 60) for deflecting the path of the first substantially parallel light beam (29) emitted from the first light source (30), and a scattering lens (66) for scattering the substantially parallel light beam from the the first light source to at least fill the entrance opening of the objective lens (52). Apparatus according to claim 20, characterized in that the first light source (30) is arranged to generate a polarized laser beam (29, 29 '), and that the electrically controllable device (68, 72) comprises a device (68) for rotation of the plane of polarization of the first laser beam from the first source under the control of the first frequency modulated signal, and a linear polarizer (70) used as an attenuation device for the rotated first laser beam (29, 29 ') for generating an output signal for an intensity modulated laser beam corresponding to the first frequency modulated signal. Apparatus according to claim 15, characterized by a beam polarizer (70) and a polarization change device (172) for rotating the polarization plane of the second beam (150, 150 '), that the polarizer and the polarization change device are arranged in the path of the second light beam with the beam polarizer located between the source of the second light beam (l52) and the polarization change device (l72), the polarization change device being arranged to rotate the second beam during accumulating, incident and reflected passage through the polarization change device to and from the storage electrons. And the polarizer (70) substantially reduces the intensity of the reflected second beam (150 ') transmitted through the polarization change device (172) to the core (152) of the second light beam. Apparatus according to claim 25, characterized in that the second light beam (150, 150 ') is collimated and has substantially parallel light beams, that the entrance aperture of the objective lens (52) has a larger diameter than the diameter of the second light beam (150, 150 '), which is obtained by means of the second light beam (152), and that the second optical device comprises a mirror device (176, 202) for deflecting the second light beam (150, 150') obtained by means of the second light beam (152). path, and a second scattering line (174) for scattering the substantially parallel light beam from the second light source (152) so that it at least fills the entry opening of the objective lens (152). Apparatus according to claim 28, characterized in that the first and second optical devices comprise a beam directing device (202) arranged to direct the first beam (29, 29 ') towards the objective lens (52) at an angle 1 with respect to the second the beam (150, 150 '), whereby the two beams are given a mutual distance when they emerge from the objective lens and fall on the storage element (10). Apparatus according to claim 15, characterized in that the first light source (30) is arranged to produce an argon ion laser beam, that the second light source (152) is arranged to produce a helium-neon laser beam, and that it the second optical device comprises an opaque filter (180) in relation to an argon ion beam in the path of the second beam (150, 150 ') after reflection from the storage element towards the sensing device (158, 164).