JPH0436876B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel optical recording medium, particularly an optical recording medium used in a solid-state injection laser. US Pat. No. 4,097,895 describes an ablative recording medium comprising a light reflective material such as aluminum or gold coated with a light absorbing layer such as fluorescein. A focused, intensity-modulated laser beam, such as from an argon or helium-cadmium laser, evaporates or ablates the light-absorbing material on the recording medium, leaving an aperture and exposing the light-reflecting layer. The thickness of this light-absorbing layer is chosen to give the lowest reflectance of the structure, so that after recording there is a maximum contrast between the minimum reflectance of the light-absorbing layer and the reflectance of the light-reflecting layer. Moreover, if the light-reflecting layer itself is a thin layer on a non-conducting substrate, almost no energy is lost due to reflection from the thin light-absorbing layer, and almost no energy is lost due to transmission through the reflective layer. The energy absorbed from the light beam is concentrated within an extremely thin film,
Recording sensitivity is surprisingly high. Although this method works well, it has the drawback that argon lasers and helium-cadmium lasers are large devices that require relatively large input power to operate, and they also require an external optical modulator. It is desirable to operate at even lower input power levels, such as in solid state injection lasers, including aluminum gallium arsenide lasers. Since these lasers operate at wavelengths of approximately 750-850 nm, recording media useful in the above recording systems require materials that absorb at this wavelength. To be useful as a light-absorbing layer, a material must have optical quality and be compatible with the formation of a thin smooth layer of a given thickness, must be absorbing at the frequency of the light source used, and must be absorbent at the frequency of the light source used. or must be fused to form a smooth aperture that provides a signal pattern with a signal-to-noise ratio of at least 40 dB. Containing a light-reflecting layer and a dye with the formula below:
An ablative recording medium has been discovered that includes a light absorbing layer exhibiting absorption between 750 and 850 nm. However, X is hydrogen or chlorine, and M is selected from the group consisting of lead, aluminum, vanadyl, and tin (+4). Dyes particularly suitable for the recording medium of this discovery are those containing lead phthalocyanine, chloroaluminum phthalocyanine, vanadyl phthalocyanine, tin phthalocyanine or chloroaluminum, chlorophthalocyanine. All of the above compounds absorb at the wavelength of solid-state injection lasers and can be deposited on the light-reflecting layer to provide a smooth optical quality light-absorbing layer that forms recorded information with a high signal-to-noise ratio. Vanadyl phthalocyanine has a refractive index of 2.4 and a wavelength of 800 nm.
The absorption coefficient K of is 1.0. Chloroaluminum phthalocyanine has a refractive index
3.2, the absorption coefficient at 800nm is 0.5. Lead phthalocyanine has a refractive index of 2.4 and an absorption coefficient of 0.4 at 800 nm. Chloroaluminum chlorophthalocyanine has a refractive index of 3.1 and an absorption coefficient of 0.3 at 800 nm. When the light-reflecting layer itself is a layer on a substrate, the nature of the substrate is not important, but the substrate must have an optically smooth surface to which the light-reflecting layer to be applied adheres. Glass plates, glass discs or plastic discs are suitable. If the light-reflecting material can be formed as an optically smooth free-standing layer, a substrate is not required. The light-reflecting material must reflect the recording light. Suitable light-reflecting materials include aluminum;
Rhodium, gold, etc. This light-reflecting material has a thickness that reflects recording light. The phthalocyanine dyes of this invention can be deposited by conventional vacuum deposition. The dye is placed in a suitable container in a vacuum chamber, and the container is connected to a current source. A substrate is placed on top of the dye, the vacuum chamber is evacuated to about 10 ^-6 mmH _g , and an electric current is passed through the container to raise the temperature of the dye to its vaporization temperature. The deposition continues until a desired thickness of dye layer is deposited on the light-reflecting layer, at which point the current is cut off and air is admitted into the vacuum chamber. Next, the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a recording medium embodying the present invention before being exposed to recording light, with a glass substrate 110 and a thickness of approximately
It comprises a light-reflecting layer 112 made of a 600 Å gold layer and a light-absorbing layer 114 made of one of the above-mentioned phthalocyanine dyes. FIG. 2 shows a recording medium embodying the invention after exposure to recording light, with dye layer 114 ablated leaving apertures 116 and exposing light reflective layer 112.
Although only one hole is shown in FIG. 2, there are a plurality of holes, or pits 116, in the recording medium after recording.
It turns out that there is. The use of the recording medium of this invention can be explained in more detail with reference to FIG. For recording, aluminum gallium arsenide injection laser 10
The light emitted by the laser beam is directly modulated in accordance with the input electrical signal 14, and this modulated light is expanded by the recording optics 16 to increase the diameter of the intensity-modulated laser beam in a plane parallel to and perpendicular to the plane of the laser 10. The required aperture of the objective lens 18 is filled. This expanded modulated laser beam is totally reflected by the polarizing beam splitter 20, passes through the quarter-wave plate 22 for beam rotation, and enters the objective lens 18.
Furthermore, the modulated recording beam is transmitted to the recording medium 2 shown in FIG.
4 to ablate or evaporate a portion of the light-absorbing layer and expose a portion of the light-reflecting layer. Recording medium 24
is rotated by the turntable 26 at approximately 1800 revolutions/minute. The distance between the objective lens 18 and the surface of the recording medium 24 is kept constant by a focusing servo mechanism 28. In the case of reproduction, when an unmodulated weak laser that does not cause ablation on the recording medium is guided to the recording medium 24 along the same path as the recording beam, the reflected light is modulated by the reflective/non-reflective recording pattern, and the reflected light is reflected by the objective lens 18. and returns through the quarter-wave plate 22.
At this time, the light passes through the 1/4 wavelength plate 22 twice and is rotated by 90 degrees, and further passes through the polarization beam splitter 20 and is introduced into the photodetector 32 by the reproducing optical system. This photodetector 32 converts the reflected light beam into a signal source 1.
The input signal from 4 is converted into a corresponding electrical output signal and generated at the terminal 34. The tracking servo mechanism 36 monitors the light passing through the reproducing optical system 30 and tracks the recording medium 2.
This ensures that the track number 4 is the same as the one used for recording during playback. The invention will now be described by way of example, but this does not mean that the invention is limited to the details of this description. Example 1 A gold layer with a thickness of approximately 600 Å is deposited on a substrate by vapor deposition, the coated substrate is placed in a vacuum chamber, placed on a vapor deposition boat containing lead phthalocyanine, and a current source is connected to this boat to open the vacuum chamber. It was evacuated to approximately 10 ^-6 mmH _g . The boat was heated to about 300-400°, the shutter was opened, and the dye was deposited at a rate of about 4 Å/sec until a layer about 600 Å thick was deposited on the gold layer. This resulted in the formation of a smooth, amorphous, colorless, continuous coating. The recording medium thus obtained was exposed to a 50 nanosecond light pulse train with a wavelength of about 800 nm from an aluminum gallium arsenide continuous wave injection laser using the apparatus shown in FIG. The laser incident recording threshold required to ablate the hole was approximately 31 mW. Example 2 Following the procedure of Example 1, a gold-coated substrate as in Example 1 is coated with a layer of chloroaluminum phthalocyanine approximately 510 Å thick. The incident recording threshold of the laser required to form regularly shaped smooth holes in the dye thin film by ablation was about 42 mW. Example 3 Follow the procedure in Example 1 to create a gold-coated substrate with a thickness of approximately 650 Å.
When coated with vanadyl phthalocyanine, the reflectance was approximately 9% at 8000 Å. This reflectance remained unchanged even after being left for about 6 weeks. The laser incidence recording threshold of the recording surface required to form smooth, regularly shaped holes by laser ablation was about 3 to 3.5 mW. Example 4 Follow the procedure in Example 1 to coat a gold-coated substrate with a thickness of approximately 400 Å.
When coated with chloroaluminum/chlorophthalocyanine, the reflectance at 800 nm was approximately 13%. The laser incidence recording threshold of the recording surface required to form smooth and regularly shaped apertures by ablation was about 3 to 3.5 mW. Comparative Examples Other phthalocyanine dyes were deposited on gold-coated substrates following the procedure of Example 1, but their suitability for this application could not be demonstrated. This data is summarized in the following table.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a recording medium embodying this invention before recording, FIG. 2 is a cross-sectional view of a recording medium embodying this invention after recording, and FIG. 3 is a recording medium that can use the recording medium of this invention. 1 is a schematic diagram of a reproduction method. 110...Glass substrate, 112...Light reflective layer,
114... Light absorbing layer, 116... Ablation opening.

Claims (1)

[Scope of Claims] 1 Coated with a layer of light-absorbing dye having the following formula, where X is hydrogen or chlorine and M is selected from the group consisting of lead, aluminum, vanadyl and tin (+4): and an ablative optical recording medium comprising a layer of a light-reflecting material selected from the group comprising rhodium and gold. 2. The ablative optical recording medium according to claim 1, wherein the thickness of the light-absorbing dye layer is selected so as to minimize the reflectance to light having a wavelength of about 750 to 850 nm emitted from the light source. 3. When a portion of the light reflective material layer is exposed, a light reflection-absorption pattern corresponding to information is formed;
The ablative optical recording medium according to claim 2. 4. An ablative optical recording medium comprising a layer of light-reflecting material coated with a layer of light-absorbing dye having the following formula, where X is hydrogen and M is lead. 5. The ablative optical recording medium according to claim 4, wherein the thickness of the light-absorbing dye layer is selected so as to minimize the reflectance to light having a wavelength of about 750 to 850 nm emitted from the light source. 6. When a portion of the light reflective material layer is exposed, a light reflection-absorption pattern corresponding to information is formed;
The ablative optical recording medium according to claim 5. 7 X is chlorine, M is lead, vanadyl and tin (+4)
an ablative optical recording medium comprising a layer of light-reflective material coated with a layer of light-absorbing dye having the formula: 8. The ablative optical recording medium according to claim 7, wherein the thickness of the light-absorbing dye layer is selected to minimize the reflectance to light with a wavelength of about 750 to 850 nm emitted from the light source. 9. When a portion of the light reflective material layer is exposed, a light reflection-absorption pattern corresponding to information is formed;
The ablative optical recording medium according to claim 8.