FR2471649A1 - Video recording disc - Google Patents

Abstract

Ablative optical recording medium comprises a light reflecting substrate coated with a layer of light absorbing dye offormula (I) in which X is hydrogen or chlorine and M is lead, aluminium, vanadyl or tin (+4). The thickness of the dye layer is pref. chosen to minimise the reflectivity to a light source emitting light of about 750-850 nm wavelength. The (I) form smooth, optical quality light absorption layers which ablate on the action of recording beams from low power aluminium gallium arsenide layers operating at 750-850 nm. The (I) absorb strongly at this wavelength and give recorded information having a very high signal to noise ratio. The prods. are esp. useful as video discs

Description

The present invention relates to a new recording medium

  optical. More particularly, it relates to an optical recording medium with

  use with a solid state injection laser.

  In US Pat. No. 4,097,895 of 27f: tsJune 1978, Spong described an ablation recording medium which consists of a light reflecting material, such as aluminum or gold, coated with a light absorbing layer, such as fluorescein. A focused laser beam, the intensity of which is modulated, for example by a Margon or helium-cadmium laser, when it is directed onto the recording medium, vaporizes or ablates the light absorbing material, leaving a hole and exposing the light reflecting layer. The thickness of the light absorbing layer is chosen so as to structure it a minimum reflectivity. After recording, there will be a maximum contrast between the minimum reflection factor of the light absorbing layer and the reflection factor of the light reflecting layer. On the other hand, when the light-reflecting material is itself composed of a thin layer on a non-conductive substrate, as there is little energy lost by reflection from the thin and absorbent layer, and little energy lost by transmission through the reflective layer, the energy absorbed from the light beam is concentrated

  into a very thin film, and the sensitivity to recording

very considerably.

This system works very well, but has the disadvantage that argon and helium-cadmium lesers are bulky devices requiring a comparatively large amount of electric current to operate them. In addition, an external light modulator is required. It would be desirable to work at lower levels of electrical current received, such as that required by state injection lasers

  solid, including gallium-alumi- arsenide lasers

  nium. These lasers operate between 750 and 850 manometers and 247t649 so absorbent materials at these wavelengths are required for the useful recording medium.

  in the registration system above.

  In order to be Lutile as a light absorbing layer, the materials must be able to be applied to form a thin and regular layer of optical quality and of a predetermined thickness; they must be absorbent at the frequency of the optical source used; and they must be ablated or melt to form regular holes in order to give a signal pattern having a signal-to-noise ratio of at least about 40 decibels. We have found an ablation recording medium, which consists of a a light reflecting layer and a light absorbing layer which absorbs at about 750-850 nm, comprising a dye having the formula

N M $ NI) IX

l

N C _

o X is hydrogen and chlorine and M is selected from the group consisting of lead, aluminum, vanadyle

or tin (+4).

  The invention will be better understood and other aims, characteristics, details and advantages thereof

  will appear more clearly during the description

  Explanatory which will follow made with reference to the accompanying schematic drawings given solely by way of example illustrating an embodiment of the invention and in which: - Figure 1 is a cross-sectional view of a recording medium according to the invention, before registration; - Figure 2 is a cross-sectional view of a recording medium according to the invention, after recording; and FIG. 3 is a schematic view of the recording and restitution system in which the recording medium can be used according to the invention. The dyes which are particularly suitable for use in the recording medium according to the invention include phthalocyanine. lead, chloroaluminum phthalocyanine, vanadyl phthalocyanine, stannic phthalocyanine, or

  chloro-aluminum chlorophthalocyanine.

  The above compounds all absorb at wavelengths from the solid state injection laser, and they can all be evaporated on a light reflecting layer to give regular, optical quality light absorbing layers which form information recorded with high signal-to-noise ratios. Vanadyl phthalocyanine has a refractive index

  2.4 and an absorption coefficient, K, 1.0 to 800 nm.

Chloro-aluminum chlorophthalocyanine has a refractive index of 3.2 and an absorption coefficient

from 0.5 to 800 nm.

  Lead phthalocyanine has a refractive index

  of 2.4 and an absorption coefficient of 0.4 at 800 nm.

Chloro-aluminum chlorophthalocyanine has a refractive index of 3, 1 and an absorption coefficient of

0.3 to 800 nm.

  When the light reflecting layer is itself a layer on a substrate, the nature of the substrate is not critical. This substrate must have a flat and optically regular surface, to which a subsequently applied light reflecting layer adheres. A glass plate or disc or a plastic disc is suitable. If the light reflecting material can be formed to be an optically regular self-contained layer, the need for the substrate can be eliminated. The light reflecting material should reflect the light used for recording. Mention may be made, as suitable materials reflecting light, of aluminum, rhodium, gold or the like. The light reflecting material has a thickness that

  reflect the recording light.

  Current phthalocyanine dyes can be applied by traditional vacuum evaporation. The dye is introduced into a suitable container and placed in a vacuum chamber. The container is then connected to a current source. A substrate is placed above the dye. The vacuum chamber is evacuated to about 10o6 torr and current is applied to the container to raise the temperature of the dye to its evaporation temperature. Evaporation continues until a dye layer of the required thickness is deposited on the light reflecting layer, and at this time the current is interrupted and the

room is stale.

  We will now refer to the accompanying drawings.

  FIG. 1 shows a recording medium according to the invention, before exposure to a recording light beam, and it comprises a glass substrate 110, a light-reflecting layer 112 comprising a gold layer having approximately 6OX of thickness, and a layer 114 absorbing the light of one of the dyes of

  above mentioned phthalocyanine.

  Figure 2 shows a recording medium according to the invention, after exposure to a recording light beam, where the dye layer 114 has been removed to leave a hole 116, exposing the light-reflecting layer 112. It will be understood that a recording medium, after recording, comprises a certain

47 1649

  number of holes 116 rather than the only hole shown

in figure 2.

  The use of the recording medium according to the invention will be explained in more detail with reference to Figure 3. For recording, the light

  emitted by a gallium arsenide injection laser -

  aluminum 10, is modulated directly in response to an electrical signal received from a source 14o The modulated beam is enlarged by an optic system d2enregistrament 16 to increase the diameter of the laser beam modulated in intensity, so that it fills the desired opening d an objective 18 in the parallel parallel and perpendicular to the plane of the laser 100 The modulated and enlarged laser beam is totally reflected by a polarizing beam splitter 20 and it passes through a quarter-wave plate 22 causing the beam to rotate towards the objective 18. The modulated recording beam then impacts on a recording medium 24, as described in Figure 1, and it performs the ablation or evaporation of part of the light absorbing layer to expose part of the light reflecting layer o The recording medium 24 is rotated by the drive 26 of the turntable at around 1800 rpm A servo-focuser 28 maintains a constant distance

  between objective 18 and the surface of the recording medium

ment 24.

  For reading, an unmodulated and less intense laser beam, that is to say a beam which does not cause ablation in the recording medium, follows the same path as the recording beam towards the recording medium 24 The recorded reflection-deflection pattern modulates the light reflected through the objective 18 and the quarter-wave beam 220 The light, now rotated by 900eampolarization by the two passages through the quarter-wave plate 22, passes through the beam splitter polarizing 20 and is directed by an optical restitution system 30 to a photodetector 320 The photodetector 32 converts the beam of reflected light into an electrical output signal at terminal 34, which corresponds to the signal received from source 14. A track servo - 36 controls the light in the optical restitution system 30 to ensure that the track in the recording medium 24 is the same during the restitution as that used

during recording.

  The present invention will be better illustrated by the following examples which should in no case be

limit the frame.

Example 1

  A substrate was coated by evaporation of a layer of gold about 600A thick. The coated substrate was placed in a vacuum chamber above a cup

  evaporator containing lead phthalocyanine.

A power source was connected to the cup and the

vacuum chamber was evacuated to around 10-6 torr.

The cup was heated to about 300-400 C, the temperature at which the shutter was opened and the dye evaporated at - 4A per second. Evaporation continued until a layer of the order of 600A thick

be deposited on a layer of gold.

It deposited a regular film, amorphous

and carry on.

The resulting recording medium was exposed to a series of pulses of light of 50 nanoseconds having a wavelength of the order of 800 nm coming from a laser with injection with continuous wave with the arsenjtue of gallium- aluminum in an apparatus like - in figure 3. Small holes of regular and smooth shape, were formed by ablation in the dye film for an output power of the laser of

around 31 milliwatts.

Example 2

  Following the general process of Example 1, a gold-coated substrate as in Example 1 was coated with a layer of chloroaluminum phthalocyanine about 51A thick. Small holes of formO about 5qX0A thick. Small regular X; 1 holes were formed by ablation in the dye film, at an output power of the laser of the order

of 42 milliwatts.

Example 3 Following the general process of Example 1, a gold coated substrate was coated with a layer of vanadyl phthalocyanine about 650A thick. The reflectivity O was of the order of 9% at 8000A. After resting for about six weeks, the reflectance was

unchanged.

  The incident threshold recording power, on the recording / required surface to perform ablation and form small smooth and regular holes with the laser was of the order of 3 to 3.5 milliwattso

Example 4

  Following the general process of Example 1, a gold coated substrate was coated with a layer of aluminum chlorophthalocyanine about 400A thick. The reflectance was around

13% at 800 nm.

  The incident threshold recording power on the recording surface, required to perform, by ablation, small smooth and regular holes, was of the order of 3 to 3.5 miIiwatts.o Comparison example Following In the general process of Example 1, gold coated substrates were coated with other phthalocyanine dyes. However, they did not prove to be suitable for the present application. The data is summarized at

following table.

BOARD

  Sample dye Phthalocyanine Phthalocyanine Phthalocyanine Phthalocyanine Phthalocyanine Phthalocyanine Phthalocyanine Phthalocyanine Phthalocyanine Phthalocyanine Phthalocyanine Comments low absorption at 800 nm of cadmium copper zinc nickel magnesium cobalt chromium of molybdenum chromium of phthalocyanine Polychlorophthalocyanine Polychlorophthalocyanine Manganese phthalocyanine Fluorochrome phthalocyanine It It!

  poor evaporation, poor absorption

tion at 800 nm no evaporation no absorption at 800 nm forms a granular film, low absorption at 800 nm low absorption at 800 nm no evaporation at 400 C, decomposition on heating decomposition on heating, weakly absorbent film on 800 nm low absorption at 800 nm no absorption at 800 nm this

24T1649

  Of course, the invention is in no way limited to the embodiment described and shown which has been given only by way of example. In particular, it includes all the means constituting technical equivalents of the means described as well as their combinations if these are carried out according to the spirit and implemented in

the scope of the claims which follow.

247 1649

Claims (9)

R E V E N D I C A T I O N S 1. Optical recording medium by ablation,   characterized in that it consists of a reflective material   health light coated with a layer of light absorbing dye having the formula N Q \ = C C -N \ Ne -x fi :, \ N M -> xD N C ^ N 20. o X is hydrogen QU chlorine and M is selected from the group consisting of lead, aluminum, vanadyle or tin (+4). 2. Recording medium according to claim 1, characterized in that the thickness of the abovementioned dye layer is chosen in order to reduce the reflectivity with respect to a light emitting source of the order of 750-850 nanometers wavelength. - 3. Recording medium according to claim 1, characterized in that a dye chosen from the group consisting of is used as the light-absorbing material. lead phthalocyanine, chloroaluminum phthalocyanine, vanadyl phthalocyanine,   stannic phthalocyanine and chlorophthalocyanine chloro- aluminum.   4. Recording medium according to claim 3, characterized in that the above-mentioned dye is lead phthalocyanine. 5. Recording medium according to claim 3, characterized in that the above-mentioned dye is chloroaluminum phthalocyanine 6. Recording medium according to claim 3, characterized in that the above-mentioned dye is vanadyl phthalocyanine.   7. Recording medium according to claim 3, characterized in that the above-mentioned dye is   chloro-aluminum chlorophthalocyanine.   8. Recording medium according to claim 3, characterized in that the thickness of the aforementioned coloring material is chosen in order to reduce the reflectivity to a light source emitting at about 750-850 wavelength nanometers.   9. Recording medium according to claim 1, characterized in that parts of the aforementioned light-reflecting material are exposed to form a pattern   absorbing light-reflecting the corresponding light video information.