JPH08171741A - Production of photochromic glass thin film and optical information medium and its reproducing method - Google Patents

Abstract

PURPOSE: To inexpensively obtain a photochromic glass thin film having stable characteristics and to obtain an optical information medium having a high information carrying density formed by utilizing this photochromic glass thin film as well as to enable the reproduction of high-density information by using this optical information medium and by a method exclusive of methods of shortening the wavelength of reproducing light and increasing the numerical aperture of the optical system of a reproducing device. CONSTITUTION: The photochromic glass thin film is formed by the method having a stage for forming a glass film by a high frequency sputtering method using a glass plate placed with a silver halide chip or copper halide chip as a target and a stage for subjecting this glass thin film to a heat treatment. A glass plate contg. La, B and Al is used as the glass plate. The high-resolution reproduction is possible with the optical information medium provided with such photochromic glass thin film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a photochromic glass thin film, an optical information medium having a high information carrying density using the photochromic glass thin film, and a method for reproducing the optical information medium.

[0002]

2. Description of the Related Art Optical information media include read-only optical discs such as compact discs, rewritable optical recording discs such as magneto-optical recording discs and phase-change optical recording discs, and write-once optical discs using organic dyes as recording materials. There is a recording disc.

An optical information medium can generally have a higher information density than a magnetic recording medium, but in recent years, it has been required to further increase the information density in order to process enormous information such as images. In order to increase the information density per unit area, there are a method of narrowing the track pitch and a method of reducing the recording marks or phase pits to increase the linear density. However, if the track density or the linear density is too high for the beam spot of the reproduction light, the C / N becomes low, and finally signal reproduction becomes impossible. The resolution during signal reproduction is determined by the beam spot diameter. Specifically, when the wavelength of the reproduction light is λ and the numerical aperture of the optical system of the reproduction device is NA, the spatial frequency 2NA / λ is the reproduction limit. . Therefore, it is effective to shorten the wavelength of the reproduction light and increase the NA in order to improve the C / N ratio and the resolution during reproduction, and many technical studies have been made. Needs to be solved.

Under these circumstances, Japanese Patent Laid-Open No. 2-9692
No. 6 publication proposes a record carrier having a layer of a nonlinear optical material that realizes super-resolution. This non-linear optical material is a material whose optical properties change due to incident radiation, and its changes include changes in transmittance, reflectance, refractive index, or changes in the shape of its layer. .
By irradiating the information surface with the reproduction light beam through such a nonlinear optical material layer, it becomes possible to read out a smaller object portion.

The publication discloses a bleaching layer as a nonlinear optical material layer. The bleaching layer is one whose transmission increases as the intensity of the incident radiation increases, and gallium arsenide, indium arsenide and indium antimony are specifically mentioned as the material used for the bleaching layer. However, since the nonlinear optical material layer made of these materials needs to excite all absorption centers, reproduction light with high energy density is required, and material design and medium design are not easy.

Japanese Unexamined Patent Publication (Kokai) No. 6-75315 discloses, "Optical disc in which a thin film made of a photochromic substance having an absorption maximum in the vicinity of a light wavelength of at least 620 nm and not more than 690 nm and a reflective film are provided in this order on a transparent substrate. Reproducing method, wherein by irradiating light and / or heating, reproducing light is irradiated while keeping the transmittance of the thin film at a reproducing light wavelength low, and only during this irradiation period, a portion where the reproducing light beam spot is irradiated. The reproducing method of the optical disc is described in which the transmittance of the thin film at the reproduction light wavelength is set to be high in a smaller region to reproduce the light. Also, such reproduction is performed. As a device for
"The optical head for optically reproducing information recorded on the optical disk, and means for keeping the transmittance of the thin film at a reproduction light wavelength low by light irradiation and / or heating are provided. Optical disc reproducing apparatus "is described.

The photochromic substance mentioned in the above publication is usually a colorless and transparent positive photochromic compound, which develops color when irradiated with ultraviolet light and disappears by irradiation with visible light or heating, usually colored. It is a reverse photochromic compound that is decolored by irradiation with visible light and returns to its original state by irradiation with ultraviolet light or heating. The publication describes that recording is performed by the following mechanism.

When a positive photochromic compound is used, it is heated by absorption of reproducing light to be erased and the transmittance is improved. Since the temperature becomes high in the central portion of the reproduction light spot, the transmittance greatly increases as compared with the outer edge portion of the reproduction light spot. The photochromic layer other than the region where the reproduction light spot is applied needs to be constantly colored, that is, the state where the transmittance is low, and for this purpose, the photochromic layer is constantly irradiated with ultraviolet light. Therefore, the photochromic layer instantly returns to a low transmittance state after the spot of the reproduction light passes through.

On the other hand, when the reverse photochromic compound is used, the color is erased by the incidence of reproducing light and the transmittance is improved. Since the light intensity is strong at the center of the reproduction light spot,
The transmittance greatly increases as compared with the outer edge of the reproduction light spot. The photochromic layer is constantly heated and constantly maintained in a colored state, that is, a state of low transmittance. Therefore, the photochromic layer immediately returns to the low transmittance state after the spot of the reproduction light passes through.

In the publication, silver halide photochromic glass and T are used as inorganic materials exhibiting photochromism.
1Cl photochromic glass, reductive melting photochromic glass, CdO-containing photochromic glass, and heat-darkened photochromic glass are described. However, this publication does not describe specific examples using these photochromic glasses. That is, the publication does not describe a specific method for producing a photochromic glass thinned so that it can be used for an optical disc.

Further, as described above, in either case of using the positive photochromic compound or the reverse photochromic compound, since the photochromic layer must be constantly irradiated with ultraviolet rays or heated, the reproducing apparatus becomes complicated.

Japanese Unexamined Patent Publication (Kokai) No. 6-282034 discloses a multilayer thin film composed of at least a photochromic material (A) and an oxide (B), and has a composition modulation periodic structure of (A) and (B) in the film thickness direction. A photochromic thin film having is described. In Examples 1 and 2 of the publication, a mixture of AgCl and CuCl and SiO are alternately deposited by two-source alternating deposition to produce a multilayer thin film having a composition modulation periodic structure. The thickness of the produced multilayer thin film is 0.6 μm
And the thickness per layer is 7 nm in Example 1 and 11 nm in Example 2. According to the publication, excellent durability and sufficient color change contrast can be obtained by using such a multilayer thin film. However, since the method described in the publication is complicated, it is difficult to reduce the cost, and it is difficult to obtain a photochromic thin film having stable characteristics by alternate vapor deposition.

As a conventional method for producing photochromic glass, the same publication discloses that chlorine at the stage of glass melting,
Compounds such as silver and copper are mixed with a glass-forming substance to prepare a glass containing chlorine, silver and copper, and the glass is subjected to appropriate treatment (photochromic treatment) such as heat, X-ray and γ-ray irradiation. The method of imparting photochromic properties and the method of mixing the compounds such as chlorine and copper with the glass-forming substance at the stage of melting the glass to make a glass containing chlorine and copper, and infiltrating silver into the glass by ion exchange treatment. Then, a glass containing chlorine, silver, and copper is formed, and then a photochromic treatment is performed. In contrast to these conventional methods, in the same publication, it is difficult to permeate chlorine into glass by ion exchange treatment such as silver and copper due to the relationship of the ionic radius, etc. Need to be specially melted,
The glass will be limited. Moreover,
Since it is difficult to stably put chlorine in the glass, it is considered that the stability of the composition is deteriorated and stable photochromic characteristics are difficult to obtain.

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide a photochromic glass thin film having stable characteristics at low cost, and to provide an optical information medium having a high information carrying density using this photochromic glass thin film. In addition, it is possible to reproduce high-density information using this optical information medium by a method other than shortening the wavelength of the reproduction light and increasing the numerical aperture of the optical system of the reproducing apparatus.

[0015]

This and other objects are achieved by any of the following constitutions (1) to (10). (1) A method for producing a photochromic glass thin film, which comprises a step of forming a glass thin film by a high frequency sputtering method using a glass plate on which a silver halide chip is mounted as a target, and a step of subjecting the glass thin film to a heat treatment. (2) The method for producing a photochromic glass thin film according to (1) above, wherein a glass plate on which a silver halide chip and a copper halide chip are mounted is used as a target. (3) The method for producing a photochromic glass thin film according to (1) or (2) above, wherein a glass plate containing La, B and Al is used as the glass plate to produce a photochromic glass thin film having a refractive index of 1.6 or more. (4) An optical information medium having a photochromic glass thin film formed on the surface of a substrate by the method according to any one of (1) to (3) above. (5) The optical information medium according to (4) above, which has pits carrying information on the surface of the substrate. (6) The optical information medium according to (5) above, which has a reflective layer on the upper side or the lower side of the photochromic glass thin film. (7) The optical information medium according to (4) above, which has a recording layer above or below the photochromic glass thin film. (8) A reflective layer is provided and a recording layer exists between the photochromic glass thin film and the reflective layer, or a photochromic glass thin film exists between the recording layer and the reflective layer.
Optical information medium. (9) The optical information medium according to (7) or (8), which has a phase-change recording layer or a magneto-optical recording layer. (10) A method for reproducing information carried by the optical information medium according to any one of (4) to (9) above, which comprises irradiating a beam spot of reproducing light on a photochromic glass thin film, A reproducing method of an optical information medium which improves reproduction light transmittance in the vicinity of the center, and reduces reproduction light transmittance of a photochromic glass thin film after passing through the beam spot to perform high resolution reproduction.

[0016]

In the present invention, the target is a glass plate on which a chip of a compound (silver halide, copper halide, etc.) for expressing photochromism is mounted.
A glass thin film is formed by the high frequency sputtering method, and the glass thin film is heat-treated. The thus-produced glass thin film has photochromic properties because precipitated particles containing halogen, silver, copper, etc. are dispersed in the glass matrix.

In the present invention, since a glass containing halogen in advance is not used, a photochromic glass thin film having a stable composition can be manufactured and stable photochromic characteristics can be obtained.

The optical information medium of the present invention having such a photochromic glass thin film can reproduce high density information by the following mechanism.

When reproducing the optical information medium of the present invention, the beam spot of the reproduction light is irradiated onto the photochromic glass thin film to reduce the effective beam spot diameter contributing to the reproduction, thereby improving the resolution during reproduction. . If a photochromic glass thin film containing La, B and Al as a matrix component is used in the present invention, low-power reproduction light can be used. Therefore, the burden on each part of the medium is small, the degree of freedom in selecting the material for each part is high, and the repeating durability is also good. Further, such a photochromic glass thin film is immediately darkened without irradiation with ultraviolet light or heating after passing through the beam spot of the reproduction light to reduce the reproduction light transmittance again, so that it is similar to the conventional optical information medium reproducing apparatus. It is possible to use a reproducing apparatus equipped with only a normal optical head.

[0020]

Specific Structure The specific structure of the present invention will be described in detail below.

Photochromic produced by the present invention
The composition of the glass thin film is not particularly limited, and at least the halogen
Any glassy material in which precipitated particles containing silver halide are dispersed
However, when it is applied to an optical information medium as described below,
Is a lantern board in which precipitated particles containing silver halide are dispersed.
Rate-based photochromic glass is preferred
Yes. Such photochromic glass is available, for example, in the United States.
Patent No. 3,703,388 and J.Appl.Phys.,46
(2) In 689 (1975), the heat-darkened photochromic glass was used.
It has been described. In addition, in these documents,
There is no description about thinning the Romic glass.

The basic components of the lanthanum borate-based photochromic glass are B ₂ O ₃ , Al ₂ O ₃ and L.
a ₂ O ₃ is used.

B ₂ O ₃ and Al ₂ O ₃ mainly form a glass network. The content of B ₂ O ₃ is preferably 15 to 50% by weight, more preferably 20 to 45%.
%, And the content of Al ₂ O ₃ is preferably 0.
1 to 25% by weight, more preferably 0.3 to 15% by weight, and the content of B ₂ O ₃ + Al ₂ O ₃ is preferably 1
It is 5 to 60% by weight, and more preferably 20 to 50% by weight.

It is considered that La has the action of facilitating the migration of Ag in the glass network by coordinatively bonding to the ions constituting the glass network, thereby facilitating darkening and fading. The content of La ₂ O ₃ is preferably 20 to 70% by weight, more preferably 35 to 55%.
% By weight.

Halogen and Ag are present in the precipitated particles in the glass. The precipitated grains are usually a composite structure containing a crystalline phase and contain silver halide. The darkening of the glass is caused by the dissociation of halogen and Ag, and the darkened glass is discolored by the recombination of halogen and Ag. As the halogen, at least one selected from chlorine, bromine and iodine is used. The halogen and Ag contents in the glass may be appropriately determined so that a desired concentration can be obtained during darkening and a desired transparency can be obtained during fading. The total content of halogen is preferably 0.1 to 15% by weight, more preferably 0.3.
10 to 10% by weight. The content of Ag is preferably 0.
It is 2 to 10% by weight, and more preferably 0.4 to 5% by weight. If the amount of at least one of halogen and Ag is small, it is difficult to achieve sufficient darkening. If the amount of halogen and / or Ag is large, the diameter of the deposited particles becomes too large, light scattering increases, and the darkening ability decreases. The average diameter of the deposited particles is preferably about 5 to 30 nm.
Since silver halide forms a solid solution with other halides, the atomic ratio Ag / halogen is usually smaller than 1.

It is preferable that Cu is contained in the deposited particles as a sensitizer for increasing photosensitivity. The Cu content is preferably 0.01 to 0.5% by weight, more preferably 0.02 to 0.4% by weight. If the amount of Cu is small, the sensitizing effect is insufficient, and if it is large, the sensitivity is decreased.

In the glass, Ta ₂ O ₅ , Nb ₂ O ₅ and Th are formed by substituting at least part of Al ₂ O _3.
It is preferable that at least one selected from the group consisting of O ₂ , TiO ₂ and ZrO ₂ is included. These oxides have a function similar to that of Al ₂ O _3, and also have a function of controlling the optical characteristics (refractive index and dispersion) of the glass matrix.

In addition to these, in the glass, if necessary, 2
A valent metal oxide may be contained. Examples of the divalent metal oxide include MgO, CaO, SrO, BaO, CdO,
At least one selected from the group consisting of ZnO and PbO is preferable. These oxides have the function of improving the photosensitivity and controlling the optical characteristics of the glass matrix. Among these, CdO has a high photosensitivity improving effect like Cu. The total content of divalent metal oxides is preferably 0.1 to 30% by weight, more preferably 0.3 to 2
It is 5% by weight.

The preferred thickness of the photochromic glass thin film may be determined according to the object of application and its composition, but when applied to the optical information medium described later, it is preferably 5-100 nm, more preferably 10-nm. It is 50 nm.
If the photochromic glass thin film used as the mask layer in the optical information medium is too thin, the masking effect will be insufficient, and if it is too thick, the light transmittance upon irradiation with reproducing light will be insufficient, and the amount of return light of the reproduced signal will be small. / N is reduced.

The refractive index of the photochromic glass thin film is not particularly limited, but it is usually 1.6 or more, particularly 1.7 or more as long as it exhibits good photochromic characteristics.

In the present invention, first, a glass thin film is formed by a high frequency sputtering method, and the glass thin film is heat-treated to manufacture a photochromic glass thin film.
In the high frequency sputtering method, a glass plate on which a silver halide chip is placed is used as a target. When Cu is contained in the precipitated particles, silver halide and copper halide are placed as a target. The use ratio of each chip to the glass plate may be determined according to the composition of the desired photochromic glass thin film. The above elements and compounds other than halogen, Ag, and Cu are contained in the glass plate.

In order to facilitate the precipitation of silver halide and copper halide, it is preferable to use a target in which chips of sodium halide are mounted on a glass plate in addition to chips of silver halide and copper halide. preferable. That is, the amount of halogen is set to be excessive with respect to Ag or Cu. In this case, it is preferable to use sodium halide containing the same halogen as that of silver halide or copper halide.

During the sputtering, the substrate may be heated if necessary.

The heat treatment applied to the glass thin film formed by the high frequency sputtering method is to grow the deposited particles and to develop the photochromic characteristics. The conditions of this heat treatment are not particularly limited, and may be appropriately determined depending on the composition and thickness of the glass thin film so that desired photochromic characteristics can be obtained. The heat treatment is preferably performed in an inert atmosphere.

FIG. 1 shows an example of the structure of an optical information medium using the photochromic glass thin film manufactured according to the present invention. The optical information medium 1 shown in FIG. 1 is a read-only optical information medium, and has a photochromic glass thin film 3 on a substrate 2 having pits 21 carrying information, and a protective layer 10 on the photochromic glass thin film 3. Have.

FIG. 2 shows another configuration example of the read-only optical information medium. The optical information medium 1 shown in FIG. 2 has the same configuration as the optical information medium 1 shown in FIG. 1 except that the reflective layer 4 is provided between the photochromic glass thin film 3 and the protective layer 10.

In the optical information medium having the structure shown in FIG.
The reproducing light may be irradiated through the protective layer 10 or the reproducing light may be irradiated from the protective layer 10 side. In the optical information medium having the structure shown in FIG. 2, reproduction light is emitted through the base. However, the reflective layer 4 may be provided between the photochromic glass thin film 3 and the substrate 2 to irradiate the reproducing light from the protective layer 10 side.

When reproducing light is irradiated through the substrate, the substrate is made of a material which is substantially transparent to the reproducing light, such as resin or glass. The pits on the surface of the substrate are convex portions or concave portions for reading information by using the phase difference. The shape and dimensions of the substrate are not particularly limited,
It is usually disk-shaped, and its thickness is usually 0.2-
The diameter is about 3 mm and the diameter is about 50 to 360 mm. Grooves for tracking, addresses, etc. may be provided on the surface of the substrate.

The photochromic glass thin film 3 is a photochromic glass thin film manufactured according to the present invention. This photochromic glass thin film has a dark color at room temperature and fades upon irradiation with visible light depending on its intensity.
The thin film of the above-mentioned lanthanum borate-based photochromic glass is particularly preferable because it exhibits such behavior and, in addition to fading due to the photonic effect, fading due to heating by light irradiation.

The laser beam of the reproducing light applied to the optical information medium 1 is focused near the photochromic glass thin film 3. Within the surface of the photochromic glass thin film, the reproduction light becomes a beam spot having an intensity distribution similar to a Gaussian distribution. That is, the beam spot of the reproduction light has an intensity distribution in which the intensity decreases from the vicinity of the center toward the periphery. Therefore, by using the reproduction light having an appropriate power, the energy distribution can be made such that only the vicinity of the center of the beam spot of the photochromic glass thin film becomes transparent, and the effective beam spot diameter of the reproduction light can be narrowed. In the illustrated example, the diameter of the beam spot of the reproduction light is φ _0, and the region in which the transparentization due to fading has occurred is shown as H. A region L in the beam spot, which is not transparent due to insufficient light energy is shown.

When a photochromic glass thin film having an appropriate composition is used, the light transmittance of the photochromic glass thin film is lowered without irradiation with ultraviolet light or heating when the beam spot of the reproducing light passes and returns to room temperature. It returns to the state before irradiation of the reproduction light. Therefore, it is possible to prevent the influence of crosstalk noise due to the pits adjacent to each other in the radial direction and the track direction.

If necessary, a dielectric layer may be provided between the photochromic glass thin film 3 and the substrate 2 and / or between the photochromic glass thin film 3 and the protective layer 10. Since the photochromic glass thin film 3 has a high temperature to some extent during reproduction, when the substrate 2 and the protective layer 10 are made of a resin having low heat resistance, these may be thermally deformed. Prevents thermal deformation.
The constituent material of the dielectric layer is not particularly limited.
₂ , a mixture of SiO ₂ and ZnS, so-called LaSiON, Si, Al containing La, Si, O and N,
So-called SiAlON containing O and N, SiAlON containing Y, NdSiON or the like may be used.
The thickness of the dielectric layer is not particularly limited and may be appropriately determined so that the above-mentioned effects can be sufficiently exerted.
Approximately 250 nm. The dielectric layer is preferably formed by a vapor phase growth method such as a sputtering method or a vapor deposition method.

The reflective layer 4 is provided to increase the amount of light reflected from the medium. The material of the reflective layer is not particularly limited, and may be usually composed of a simple substance such as Al, Au, Ag, Pt, and Cu, or a high reflectance metal such as an alloy containing one or more of these. The thickness of the reflective layer is preferably 30 to 150 nm. If the reflective layer is too thin, it becomes difficult to obtain sufficient reflectance. Even if the reflective layer is thickened, the improvement in reflectance is small, which is disadvantageous in cost. The reflective layer is preferably formed by a vapor phase growth method such as a sputtering method or a vapor deposition method.

The protective layer 10 is provided for improving scratch resistance and corrosion resistance. This protective layer is preferably composed of various organic substances, but particularly preferably composed of a substance obtained by curing a radiation-curable compound or its composition with radiation such as electron beam or ultraviolet ray. . The thickness of the protective layer is usually about 0.1 to 100 μm, and may be formed by a usual method such as spin coating, gravure coating, spray coating, dipping or the like.

The photochromic glass thin film produced by the present invention can be applied to a recordable optical information medium, that is, an optical recording medium. When used as an optical recording medium, a recording layer is provided above or below the photochromic glass thin film of the above-mentioned read-only optical information medium. When the reflective layer is provided, the recording layer is provided between the photochromic glass thin film and the reflective layer, or the photochromic glass thin film is provided between the recording layer and the reflective layer. In the former case, a dielectric layer may be provided between the reflective layer and the recording layer, if necessary, in order to protect the recording layer and control heat dissipation. The substrate of the optical recording medium may be provided with pits carrying various reproduction-only information as needed.

In the optical recording medium, when reproducing light is incident from the photochromic glass thin film side, the beam spot is narrowed and irradiated onto the recording layer through the region H of the photochromic glass thin film, as in the above-mentioned reproduction-only optical information medium. As a result, the resolution during reproduction can be increased. On the other hand, when reproducing light enters from the recording layer side, the light beam that has passed through the recording layer selectively passes through the region H of the photochromic glass thin film, so that the reflected light with a narrowed beam diameter returns from the medium. , High resolution can be obtained.

Since high resolution is obtained as described above when reproducing the optical recording medium, the effect of the present invention does not depend on the structure of the recording layer. For example, a magneto-optical recording medium having a magneto-optical recording layer such as a rare earth element-transition element alloy system, Sb
Optical recording medium having a phase change type recording layer utilizing an amorphous-crystal phase change such as ₂ Se ₃ and optical recording medium having a write-once type recording layer using an organic dye such as a cyanine dye as a recording material The present invention can be applied to any of the above.

The specific value of the power of the reproducing light with which the optical information medium of the present invention is irradiated may be experimentally determined. Although it depends on the structure of the medium and the relative linear velocity of the beam spot of the reproduction light with respect to the medium, the reproduction light power P _R is usually 1 to
It is about 10 mW, and reproduction at 5 mW or less is also possible. The relative linear velocity of the medium with respect to the beam spot of the reproduction light is not particularly limited and may be appropriately set so as to enable reproduction by the above-mentioned action, but is usually about 1 to 10 m / s.

The wavelength of the reproducing light may be selected from a wavelength range that allows fading of the photochromic glass thin film.

In the above description, the single-sided medium in which the information carrying part or the recording part is provided on only one side of the substrate has been described. However, a pair of single-sided media are stuck together so as to seal the information carrying part or the recording part. The medium may be a double-sided medium or a double-sided medium in which the information carrying portion or the recording portion is provided on both sides of the base.

[0051]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Glass plate La ₂ O ₃ : 55% by weight, B ₂ O ₃ : 35% by weight, Z
nO: 8% by weight, CdO: 1.5% by weight, Al
₂ O ₃ : 0.5 wt% The above glass plate (diameter 3 inches, thickness 3 mm) was bonded to a backing plate, and CuCl chips (diameter 5 mm, thickness 1 mm) produced by the melting method were bonded on this glass plate. Three
5 pieces of individual and crystalline NaCl chips (5 mm square, 1 mm thick)
The individual pieces were attached and used as a sputtering target. Using this target, the high frequency sputtering method (input power 10
A glass thin film having a thickness of about 50 nm was formed by applying 0 watt for 30 minutes. When the absorption spectrum of this glass thin film was measured, an absorption peak was observed at 350 to 370 nm,
The presence of CuCl was confirmed.

Next, on the above glass plate, five AgCl chips (5 mm square, 1 mm thick) produced by the melting method and the above Cu were prepared.
One Cl chip and eight above-mentioned crystalline NaCl chips were attached, and the thickness was about 5 by the high frequency sputtering method under the above conditions.
A 0 nm glass thin film was formed. When this glass thin film was heat-treated at 500 ° C. for 30 minutes in an Ar atmosphere, it showed an inverse photochromic property. In this glass thin film, AgCl could not be identified by the absorption spectrum, but since the presence of CuCl was confirmed as described above, it is considered that precipitated particles containing Ag, Cu and Cl are formed in this glass thin film. To be The refractive index of this glass thin film was 1.85.

The effects of the present invention are clear from the results of the above examples.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view showing a configuration example of an optical information medium of the present invention.

FIG. 2 is a partial cross-sectional view showing a configuration example of an optical information medium of the present invention.

[Explanation of symbols]

 1 Optical Information Medium 2 Substrate 21 Pit 3 Photochromic Glass Thin Film 4 Reflective Layer 10 Protective Layer

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location // G11B 7/00 F 9464-5D

Claims (10)

[Claims] 1. A method for producing a photochromic glass thin film, which comprises a step of forming a glass thin film by a high frequency sputtering method using a glass plate on which a silver halide chip is mounted as a target, and a step of subjecting the glass thin film to a heat treatment. 2. The method for producing a photochromic glass thin film according to claim 1, wherein a glass plate on which a silver halide chip and a copper halide chip are mounted is used as a target. 3. La, B and Al as the glass plate
The method for producing a photochromic glass thin film according to claim 1 or 2, wherein a photochromic glass thin film having a refractive index of 1.6 or more is produced by using a material containing 4. An optical information medium having a photochromic glass thin film formed by the method according to claim 1 on the surface of a substrate. 5. The optical information medium according to claim 4, wherein the surface of the substrate has pits carrying information. 6. The optical information medium according to claim 5, further comprising a reflective layer above or below the photochromic glass thin film. 7. The optical information medium according to claim 4, which has a recording layer above or below the photochromic glass thin film. 8. The optical information medium according to claim 7, which has a reflective layer and has a recording layer between the photochromic glass thin film and the reflective layer or a photochromic glass thin film between the recording layer and the reflective layer. . 9. The optical information medium according to claim 7, which has a phase-change recording layer or a magneto-optical recording layer. 10. A method for reproducing information carried by the optical information medium according to claim 4, wherein the photochromic glass thin film is irradiated with a beam spot of reproducing light, and the center of the beam spot. A method for reproducing an optical information medium, which improves reproduction light transmittance in the vicinity, and reduces reproduction light transmittance of a photochromic glass thin film after passing through the beam spot to perform high resolution reproduction.