JP3151464B2 - Optical recording medium and recording method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium for recording optical information, for example, an ordinary write-once optical disk, a hologram, an optical recording medium capable of calculating the sum / difference of images, and the like. And a recording method using the same.

[0002]

2. Description of the Related Art The photorefractive effect means that, for example, charge distribution or the like is generated inside a substance by laser irradiation.
This is a phenomenon in which the refractive index changes. Materials with photorefractive effect can be used with degenerate four-wave mixing (DFW
According to M), when the opposing pump lights P1 and P2 and the probe light Pr carrying optical information from different directions are made incident, one of the two pump lights interferes with the probe light, and Then, interference fringes corresponding to the optical information of the probe light are generated. Due to this interference fringe, the remaining one pump light is diffracted to generate a phase conjugate wave that goes against the probe light.

Materials having a photorefractive effect include BaTiO ₃ , LiNbO ₃ , KNbO ₃ , B
_{i 12 SiO 20, SBN (Sr} x Ba 1-x Nb 2 O 6),
Single crystals such as GaAs, InP and CdTe are well known. Among these single crystals of a dielectric material, for example, a single crystal of BaTiO ₃ , which has a large light amplifying effect and can easily generate a phase conjugate wave, has attracted particular attention.

[0004] However, it is difficult to obtain large single crystals of these dielectric materials for optical use. For example, a large BaTiO ₃ single crystal that can be used for optics is formed by TSSG (To SG) crystallizing on a seed crystal while gradually cooling a melt having a TiO ₂ excess composition.
p Seeded Solution Growth) method. However, in this TSSG method, the crystallization temperature and the crystallization amount of the crystal change with the change of the melt composition.
Strict control is required for the seeding temperature, the cooling rate of the melt, and the pulling rate of the seed rod. Therefore, it is generally very difficult to obtain a large single crystal of a high melting point material such as barium titanate by the TSSG method, and the obtained crystal is very expensive. This is the same for the single crystal of the other dielectric material.

More importantly, the optically recorded information generated by the photorefractive effect of these substances contains the probe light Pr and one of the pump lights P1.
, P2, the light rapidly disappears, and the phase conjugate wave as the recording information signal light obtained by irradiating the readout light almost simultaneously disappears. That is, even if these substances are used, it is impossible to stably store optically recorded information generated by the photorefractive effect for a long time.

[0006]

SUMMARY OF THE INVENTION The main object of the present invention is to provide an inexpensive, easy-to-manufacture device, and to simultaneously perform recording for short-term storage (instantaneous) and recording for long-term storage (persistence) by the photorefractive effect. Alternatively, the long-term storage record can be written alone, and further, the short-time storage record can be additionally recorded in a recording area having the long-term storage record,
An object of the present invention is to provide an optical recording medium that can be used as an optical disk for performing write-once recording, or can be further used as a hologram material, and a recording method using the same.

[0007]

This and other objects are achieved by the present invention which is defined below as (1) to (8). (1) On a substrate, a thin film that contains at least one kind of metal fine particles in a matrix, is heat-treated after being formed by a sputtering method, has an average particle size of 3 to 15 nm, The matrix is a ferroelectric material
Material or an amorphous material containing silicon oxide as a main component
Scan a is an optical recording medium. (2) Composite oxidation wherein the matrix contains titanium oxide
The optical recording medium according to the above (1), which is an object . (3) The optical recording medium according to (1) or (2), wherein the metal fine particles are Au, Ag, Cu, or an alloy thereof. (4) The optical recording medium according to any one of the above (1) to (3), which is used as an optical disc for write-once recording. (5) The above (1) to (1) to which are used as hologram materials
The optical recording medium according to any one of (4). (6) A recording method in which laser recording is performed by a degenerate four-wave mixing method using the optical recording medium according to any one of (1) to (7). (7) The recording method according to (6), wherein the optical information is recorded as a difference in light transmittance or reflectance. (8) The recording method according to (7), wherein optical information is recorded as interference fringes.

[0008]

The optical recording medium of the present invention has a ferroelectric matrix.
During the scan, or a thin film of metal fine particles are dispersed in a matrix of amorphous containing silicon oxide as a main component which was provided on the substrate, the thin film has a photorefractive effect. Such a thin film is obtained by using a matrix material and a metal fine particle material to form a film by, for example, a sputtering method. Thus, for example, BaTiO
Compared to the case of obtaining a large single crystal for optical use of a dielectric material having a photorefractive effect, such as ₃ single crystals,
Since it can be manufactured much more easily, it is inexpensive, and the film shape such as film thickness and area can be arbitrarily controlled.

Further, the optical recording medium of the present invention can
By irradiating the laser for an appropriate time under the WM condition, it is possible to record as a recording point for long-term storage. this is,
Although the reason is not clear, it is considered to be a result of some change in the dispersion state of the metal fine particles in the matrix thin film containing the metal fine particles by irradiating the laser light. Further, the recording points in the thin film thus generated can be erased by heat treatment.

Fujiwara [Fujiwara Hirofumi: Applied Physics, Vol. 59, No. 6]
No. 756-762 (1990)], when erythrosin B-containing polyvinyl alcohol, which is a material having a function similar to that of the present invention, is used as a phase conjugate mirror and irradiated with a laser under DFWM conditions, the readout light of the recording light information is obtained. Is generated. That is, a hologram is obtained. Further, this phase conjugate wave is composed of a saturated absorption component and a holographic component. The saturation absorption component disappears immediately when the pump light P1 and P2 are cut off, and the pump light is read out when the Pr light is cut off. Since it acts as light, it is attenuated by the time constant of the phosphorescent lifetime of the dye. The holographic component has an absorption or refractive index type grating recorded as a result of irreversible photochemical change in the organic dye-containing film. It is reported that when irradiated, a phase conjugate wave corresponding to the recorded hologram continues to be generated while attenuating with time. Therefore, it is described that the sum / difference of images can be calculated by using the difference between the time constants of attenuation of these components and the use of polarized laser light as the irradiation laser. However, when such an organic dye-containing film is used, the holographic component of the phase conjugate wave is attenuated over time due to a read operation by laser irradiation. That is, there is a problem that durability against laser irradiation and material stability are poor.

On the other hand, in the matrix thin film of the present invention in which metal fine particles are dispersed, long-term storage of signals and the like corresponding to the holograms recorded at recording points does not attenuate due to a read operation, and furthermore, laser irradiation is performed. By selecting the conditions, a very fast write response is exhibited. That is, since the material to be used has high durability against laser irradiation, it is possible to write a long-term storage record by short-time irradiation with high-intensity light. Further, once the optical information is written, the recording point is hardly attenuated or relaxed, and is stable and has high storage stability. In addition, the written information is a recording point for long-term storage, which is extremely stable and has no reproduction deterioration due to the reading operation. Furthermore, since the recording point does not lose the property of exhibiting the photorefractive effect of the matrix, multiplex recording is possible as a recording point for short-time storage.
Therefore, by utilizing the recordability for long-term storage and the recordability for short-term storage having excellent recording signal stability and preservability, recording points and interference due to optical information, that is, a change in reflectance and a change in transmittance are utilized. An optical recording medium such as a write-once optical disc capable of recording information carrying information such as a hologram by stripes is realized. Further, it is possible to calculate the sum / difference of images using the recorded hologram.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The optical recording medium of the present invention has, on a substrate, a thin film containing at least one kind of metal fine particles in a matrix. The matrix is a ferroelectric material or a material containing silicon oxide as a main component.

As the fine metal particles to be used, Au, A
g, Cu or an alloy thereof is preferable, but various single metals and alloys can be used, and there is no particular limitation. By using these metal fine particles, a film having high durability and stability of the optical recording medium against laser irradiation and having a photorefractive effect is realized. Such fine particles preferably have an average particle size on the order of nanometers, and each fine particle is preferably present in isolation in a thin film.

The matrix used for the optical recording medium of the present invention is preferably a ferroelectric material . Ferroelectric materials are
The dielectric constant of a bulk polycrystal at room temperature is about 150 or more
Things . These are preferable in that the change in the refractive index and the change in the reflectance are large. The use of such a material having a high dielectric constant causes some interaction in a matrix film in which metal fine particles are dispersed, for unknown reasons, and results in a film having a high photorefractive effect.

As such a ferroelectric material, Perov
Skeite type compounds are preferred. Perovskite compound
The thing is A¹⁺B⁵⁺O_Three , A²⁺B⁴⁺O_Three , A³⁺B³⁺O
_Three , A_X BO_Three , A (B '_0.67B "_0.33) O_Three , A
(B '_0.33B "_0.67) O_Three , A (B_0.5 ⁺³ B_0.5 ⁺⁵ ) O
_Three , A (B_0.5 ²⁺ B_0.5 ⁶⁺ ) O_Three , A (B_0.5 ¹⁺ B_0.5
⁷⁺) O_Three , A³⁺(B_0.5 ²⁺ B_0.5 ⁴⁺ ) O_Three , A (B_0.25
¹⁺B_0.75 ⁵⁺) O_Three , A (B _0.5 ³⁺ B_0.5 ⁴⁺ ) O_2.75, A
(B_0.5 ²⁺ B_0.5 ⁵⁺ ) O_2.75And so on.
For example, BaTiO_Three , PbTiO_Three , KTaO_Three , N
aTaO_Three , SrTiO_Three , CdTiO_Three , KNbO
_Three , LiNbO_Three , LiTaO_Three , PZT (PbZrO
_Three -PbTiO_Three ), PLZT (PbZrO_Three -PbT
iO_Three : La_TwoO_Three ).

[0016]

The ferroelectric material includes titanium oxide
A composite oxide (titanate) is preferable, and in particular, a titanate perovskite compound having a dielectric constant of a bulk polycrystal at room temperature of about 100 to 300, for example, BaTiO ₃ ,
SrTiO ₃ , PbTiO _{3 and the} like are preferable.

The matrix used for the optical recording medium of the present invention may be an amorphous material containing silicon oxide as a main component and containing silicon oxide as a main component in an amount of 30 mol% or more in terms of SiO _2. Good. Examples of such a material include quartz glass, borosilicate glass, aluminosilicate glass, soda lime glass, and high silicate glass.

The thickness of a thin film in which metal fine particles are dispersed in such a matrix is generally about 0.01 to 5 μm. Further, two or more kinds of metal fine particle materials and, in some cases, matrix materials can be used.

[0020] While the deposition of a thin film of the optical recording medium of the present invention various methods are possible, sputtering of phosphorus in terms of productivity and the like
Using the budding method . As the sputtering method, alternate sputtering of a matrix material and metal fine particles, multi-source sputtering of a matrix material and metal fine particles, simultaneous sputtering of placing a metal chip on a matrix material target, or the like can be used. In addition, any method may be used for the sputtering method, and various conditions may be determined according to the method or apparatus to be used.

[0021]

The matrix thin film in which the metal fine particles thus formed are dispersed exhibits a broad absorption spectrum immediately after the formation. As the optical recording medium of the present invention,
It is preferable to perform a heat treatment on the composite matrix thin film in which the metal fine particles immediately after the film formation are dispersed. By performing the heat treatment, the fine metal particles dispersed in the matrix grow, the resonance absorption peak shifts to the longer wavelength side, and the spectrum waveform sharply rises. The heat treatment may be performed in the air or in an inert gas atmosphere, and an optimum heat treatment method, temperature, time, and the like may be selected depending on the metal fine particle material or matrix material to be used.

Regarding the change in the content of metal fine particles in the thickness direction of the obtained composite matrix thin film, whether the content is the same from the surface layer to the lower layer, or even if there is a portion that does not contain any metal fine particles, There may be a portion where the content changes stepwise or continuously.

The composite matrix thin film of the present invention thus provided on a substrate has a long-term storage recordability and a short-term storage recordability. For example, by irradiating a laser beam under DFWM conditions. It is possible to perform writing of the long- and short-term recording, independent reading of the long-time recording, simultaneous reading of the long- and short-term recording and the like. Here, the generation of the information light from which the short-time storage record is read under the DFWM condition and the generation of the read information light from the long-time storage record will be described. FIG. 1 is a schematic diagram showing an example of an optical system under DFWM conditions.

An appropriate laser beam is used as the light source 1 and pump light (P 1,
When the probe light (Pr) 6 carrying the information of the original image 10 and the probe light (Pr) 6 carrying the information of the original image 10 are incident, interference fringes corresponding to the information of the original image 10 are generated in the sample thin film 4. This interference fringe is usually read out by one of the pump lights (P1, P2) 51 and 52, and the read information light 7 having both recording information for short-time recording and long-time recording. Occurs. By projecting the generated read information light 7 on the screen 11 by the beam splitter 23, a reproduced image of the original image 10 is obtained on the screen 11. At this time, the short-time storage record is a record that disappears almost simultaneously with the interruption when the irradiation light is cut off, and the long-time storage record is a record according to the condition of the irradiation light even if the irradiation light is cut off. This is a record that is continuously held on an optical recording medium.

The optical recording medium of the present invention can record both such short-term storage recording and long-term storage recording optical information. On the optical recording medium of the present invention, it can be confirmed by visual observation that the light transmittance has changed in the area where the long-time storage record has been written, as compared with the area where the long-time storage record has not been written. That is, when optical information is written as interference fringes or the like, light transmittance and reflectance change from the surroundings. At this time, by using an optical recording medium having a high light transmittance, there is a great feature that loss of light absorption at the time of reading is reduced. in this way,
The optical recording medium of the present invention can be used for recording optical information as a recording point at which light transmittance or reflectance has changed from the surroundings.

[0027] Next, an example of a method of calculating the sum-difference image is first recorded first image I ₁ as described above as long storing recorded on the optical recording medium. However, the probe light (Pr) 6 and the pump light (P1, P2) 5
1 and 52 use polarized light parallel to each other. Next, using the second image I ₂ as the original image 10, the probe light (Pr) is used.
The pump light 6 and the pump light (P1, P2) 51, 52 are orthogonally polarized. As a result, a long-term storage record based on I ₁ previously recorded and a short-time storage record based on I ₂ generated by laser irradiation simultaneously occur, and the obtained long-term storage record of I ₁ is obtained. It is orthogonally polarized with the short-time storage record of I ₂ . Therefore, it is possible to calculate the sum and difference of the images by placing the analyzer on the image plane and adjusting the rotation.

It is preferable to use a laser as a light source for writing data on the optical recording medium of the present invention. The laser to be used is not particularly limited as long as the wavelength region is in the vicinity of the resonance absorption wavelength region of the metal used, and may be further subjected to pulse irradiation or continuous light irradiation,
What is necessary is just to select the intensity, recording time, irradiation method, etc. according to the laser used.

As recording to be written on the optical recording medium of the present invention, recording for short-time storage (instantaneous) and recording for long-term storage (persistence) are possible. The writing of the short-time storage record is performed using the DFWM condition and stored as interference fringes.
As the light source, for example, a pulse irradiation laser in a nano region to a sub pico region can be used. In this case, reading can be performed simultaneously or almost simultaneously under the DFWM condition. Also, at this time, by selecting the conditions,
Interference fringes generated by simultaneous irradiation of two light beams using two light beams of the light used under the DFWM condition can be read out by irradiating one light beam or two light beams simultaneously for reading.

As the long-term storage recording, a recording method based on a density difference or a recording method based on interference fringes is possible.
In the recording method based on the density difference, recording is performed by forming an area having a difference in light transmittance or reflectance on an optical recording medium by irradiation with one light beam, simultaneous irradiation with two light beams, irradiation under DFWM conditions, or the like. The recording method using interference fringes records interference fringes generated by simultaneous irradiation of two rays or irradiation under DFWM conditions on an optical recording medium. Note that, as described above, even in the recording method using interference fringes, a difference in shading occurs at the recording point of the optical recording medium. As a light source, continuous light irradiation or pulse irradiation is appropriately selected and used, but writing can be performed in a picosecond order time by selecting light intensity and other conditions. Reading of long-term storage record is performed by one beam irradiation, two beam irradiation, DFW
Any of the irradiations under the M condition can be used, and is usually performed, for example, by irradiating one of the pump lights P1 and P2 in FIG.

Further, not only the short-time storage record and the long-time storage record can be read out alone, but also these read-outs can be performed at the same time, for example, when calculating a sum or a difference. It is possible to perform recording for a short period of time in an area where the recording has been recorded, and simultaneously read both records. Further, by changing the incident angle of the probe light under the DFWM condition, a plurality of probe lights having different incident angles are incident on the same area to enable multiplex sequential or simultaneous writing, and it is also possible to perform simultaneous reading of these. is there.

The recording point of the long-term recording formed on the optical recording medium of the present invention is stable without any change over time due to the read operation. In addition, record preservability is high. Therefore, it can be generally used as an optical disk or the like that performs write-once recording in which a recording point having a changed transmittance or reflectance is formed on an unrecorded portion. Further, usually, the recording is erased by heating at about 500 ° C. or more, so that an erasable medium can be obtained.

[0033]

The present invention will be described below in more detail with reference to specific examples of the present invention.

Example 1 Using an RF magnetron sputtering apparatus, an Au chip was placed on a BaTiO ₃ target, and simultaneous sputtering was performed.
Synthetic quartz glass was used as the substrate. The conditions for forming the thin film were such that the gas pressure was 5 × 10 ⁻³ Torr, the substrate temperature was 150 ° C., and the RF power was 100 W in an argon atmosphere. The Au concentration was controlled by the amount of the chip, and the film thickness was controlled by the sputtering time to form a thin film on the substrate.

Next, the thin film on this substrate was heat-treated at 900 ° C. for 1 hour to obtain a sample 1 having a BaTiO ₃ —Au-based polycrystalline composite thin film having the thickness, gold concentration and gold average particle diameter shown in Table 1. An optical recording medium was obtained.

[0036]

[Table 1]

Next, writing and reading of a record were performed using the obtained sample 1.

For writing, the DFWM optical system shown in FIG. 1 is further provided with a streak camera, a sample light (read information light 7) optical path and a reference light (probe light (Pr) 6) optical path for the streak camera. Was used. As a light source, the second harmonic of a Nd; YAG laser, a measurement wavelength: 532 nm, a pulse width: 7 ns, and a power: 0.89 MW /
cm ² was used.

<Standard intensity> Pump light (P1,
P2) 51, 52 and probe light (Pr) 6 are simultaneously incident on the sample thin film 4, the signal intensity of the generated read information light 7 is measured using a streak camera, and the reflectance of the read information light is calculated. This was defined as a standard strength (R _{DF WM} ).

<Writing of Information> In writing of information, the sample thin film 4 was irradiated with a laser in the same manner as in the standard intensity measuring method.

<Reading Information> In reading information, the sample thin film 4 is irradiated with one pump light (P 2) 52, that is, a back pump light, and the intensity of the diffracted light due to the interference fringes on the optical recording medium to be detected is measured by a streak camera. And measured as signal light (R _back ).

First, the sample 1 was irradiated with a laser for each time shown in FIG. 2 according to the information writing method. Next, the intensity of signal light generated in accordance with the above information reading method was measured at each irradiation time. The result is the reflectance ratio (R
_back / R _DFWM ) and shown in FIG.

Next, using the sample 1 which was subjected to laser irradiation for 10 minutes as an information writing operation, information was read at each time shown in FIG. The result is the reflectivity ratio (R _back / R
_DFWM ) and are summarized in FIG. 3 (temporal change (ns): Δ).

Further, the same operation as the above <Standard intensity> was performed for each time shown in FIG. 3 using the sample 1 in order to verify the reading light history. The same sample (sample 1) was used for this measurement, and the measurement point on the sample surface was changed for each measurement. The results are represented by the reflectance ratio (R _back / R _DFWM ), and are summarized in FIG. 3 (readout light history (ns): □). In addition, at the point where writing was performed on the optical recording medium, it was confirmed by visual observation that the light transmittance changed.

Example 2 Example 1 was repeated except that the BaTiO ₃ target of Example 1 was changed to a SiO ₂ target and the RF power was set to 200 W.
Form a thin film in the same manner as substrate as, film thickness shown in the sample 2-4 in Table 1, the gold concentration, the sample thin film 4 having SiO ₂ -Au based amorphous composite thin film having a gold average particle size obtained.

Next, using the samples 2 to 4 obtained,
Recording and reading were performed in the same manner as described above. The results are represented by the reflectance ratio (R _back / R _DFWM ) and are shown collectively in FIG. 2 (Sample 2: Δ, Sample 3: ○, Sample 4: Δ).

From the results shown in FIG. 2, it can be seen that Sample 1 (■) having a BaTiO ₃ —Au-based polycrystalline composite thin film, SiO ₂ —Au
Samples 2 to 4 (Δ, ○,
In both cases, the reflection ratio of the readout light increased until the laser irradiation time was 5 minutes, but did not increase after 5 minutes, and the recording intensity was saturated at the irradiation time of 5 minutes. Understand.

From FIG. 3 showing the change with time, the reading signal reflection ratio (△) and the reading light history (□) of the sample 1 were measured. As a result, the reading signal reflection ratio (△) of the sample 1 under the used conditions was measured. In addition, there was no change in the reading light history (□) with time, and no deterioration in signal and laser intensity was observed. With respect to Samples 2 to 4, the change with time of the read signal reflection ratio was measured, but no change with time was observed as in Sample 1.

Example 3 Using sample 1, a pulse width of 40 ps and a power of 46 MW / cm
^{In the same} manner as in Example 1, laser irradiation time dependency, change over time in signal recording intensity, and readout light history were measured in the same manner as in Example 1 except that the value was set to 2. As a result, as a result of measuring the laser irradiation time dependency, the intensity of signal recording was saturated by several times of pulse irradiation. In addition, no deterioration was recognized in any of the change with time and the reading light history as in Example 1. The result of the change with time is represented by a reflectance ratio (R _back / R _DFWM ), and is shown in FIG. 3 (change with time (ps): ●).

Example 4 A sample thin film 4 was prepared in the same manner as in Example 1 except that an SrTiO ₃ target was used instead of the BaTiO ₃ target, and laser irradiation was performed in the same manner as in Example 3 except that this sample was used. The time dependency, the change over time of the signal recording intensity, and the reading light history were measured. As a result, the same results as in Example 3 were obtained for all the measurement items.

Comparative Example 1 A sample thin film 4 was prepared in the same manner as in Example 4 except that an Au chip was not mounted on the target using a BaTiO ₃ target, and information writing and reading were performed in the same manner as in Example 1. Information light 7 based on interference fringes on recording points
Could not be detected. In addition, no difference in shading of the recording points could be confirmed.

Comparative Example 2 Each process was performed in the same manner as in Comparative Example 1 except that the SrTiO ₃ target was used instead of the BaTiO ₃ target. No detection and no confirmation of the shading difference was possible.

Example 5 A 3.5 inch φ, 2.0 mm thick synthetic quartz glass disk-shaped substrate was used, and BaTiO3 was formed in the same manner as in Example 1.
After forming a _3- Au thin film, it was heat-treated to obtain an optical disk medium. The thickness of the thin film was 5000 A and the gold concentration was 15.0.
vol%, the gold average particle diameter was 15.0 nm.

As the optical system, the apparatus shown in FIG. 1 was used, and the second harmonic of a Nd; YAG laser as a light source, measuring wavelength: 5
Using 32 nm, pulse width: 40 ps, power: 40 MW / cm ² , the obtained optical disk medium was fixed to a rotating system equipped with a motor, and the film surface of the optical disk medium was a sample thin film 4 shown in FIG.
, And rotated at 3200 rpm to write a record. At this time, the optical disk medium
The pump was moved while keeping it perpendicular to the optical path of the pump light.

Next, when reading was performed by irradiating the back pump light (P2) 52, the recorded signal light was detected.

Example 6 Using the apparatus of FIG. 1, the second harmonic of a Nd; YAG laser as a light source, a measurement wavelength: 532 nm, a pulse width: 40 ps,
Power: 10 MW as original image 10 using 40 MW / cm ²
Information was written on Sample 1 using a φ ring. The number of pulse irradiation at the time of writing was set to five times.

When the back pump light (P 2) 52 was irradiated on the sample 1 24 hours after the writing of the information and the signal of the generated reading information light 7 was projected on the screen 11, the ring image could be confirmed visually. Was.

[0058]

The optical recording medium of the present invention is inexpensive because it is easy to manufacture, and can be used for short-time recording or long-time recording recorded as a difference in light transmittance or reflectance or interference fringes. Simultaneous or independent writing can be performed, and short-time recording can be additionally recorded in a recording area having long-time recording. In addition, by selecting the writing condition, it is possible to record the recording for a long time in a very short time. Furthermore, the written long-term storage record can be stored for a long time without deterioration, can be repeatedly reproduced many times, and can be used as an optical disc for write-once recording. Further, it can also be used as a hologram material capable of calculating the sum and difference of images.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an optical system under DFWM conditions used for writing, reading, and holography of an optical recording medium of the present invention.

FIG. 2 is a graph showing a relationship between a laser irradiation time in a write operation and a reflectance ratio in a read operation of the optical recording medium of the present invention.

FIG. 3 is a graph showing a temporal change of a reflectance ratio and a read light history used when reading a recorded signal recorded on the optical recording medium of the present invention.

[Explanation of symbols]

 Reference Signs List 1 light source 21, 22, 23 beam splitter 31, 32, 33 mirror 4 sample thin film 51, 52 pump light P1, P2 6 probe light Pr 7 read information light 81, 82, 83 lens 9 beam expander 10 original image 11 screen

Continued on the front page (72) Inventor Kohei Tsuno 3-3-8-216 Satsukioka, Ikeda-shi, Osaka (72) Inventor Masaru 1-7-8 Midorioka, Ikeda-shi, Osaka (72) Inventor Hajime Wakabayashi Hyogo (72) Inventor Masami Mori 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDC Corporation (72) Inventor Toru Kineri 1-1-13 Nihonbashi, Chuo-ku, Tokyo No. 1 TDK Corporation (56) References JP-A-63-300377 (JP, A) JP-A-49-96648 (JP, A) Oplus E, No. 1 118 (September 1989) p. 117-124

Claims (8)

(57) [Claims] 1. A substrate comprising a thin film comprising at least one kind of metal fine particles in a matrix, formed by a sputtering method, and then subjected to a heat treatment, wherein the fine particles have an average particle size of 3 to 15 nm. The matrix is a ferroelectric material or a main component
Optical recording medium containing silicon oxide . 2. A composite according to claim 1, wherein said matrix contains titanium oxide.
2. The optical recording medium according to claim 1, which is a composite oxide . 3. The method according to claim 1, wherein the fine particles of the metal are Au, Ag, and Cu.
3. The optical recording medium according to claim 1, wherein said optical recording medium is an alloy thereof. 4. The optical recording medium according to claim 1, wherein the optical recording medium is used as an optical disk for performing write-once recording. 5. The method according to claim 1, wherein the material is used as a hologram material.
5. The optical recording medium according to any one of items 1 to 4, 6. A recording method for performing laser recording by a degenerate four-wave mixing method using the optical recording medium according to claim 1. 7. The recording method according to claim 6, wherein the optical information is recorded as a difference in light transmittance or light reflectance. 8. The optical information is recorded as interference fringes.
Recording method.