JPH0414620A - Optical recording and reproducing method - Google Patents

Abstract

PURPOSE:To attain high speed recording with a light source of low power by using a laser beam for optical write and radiating a read out laser beam under the condition so as to generate surface plasmon onto a recording medium for the purpose of reading recorded information. CONSTITUTION:A metallic layer is formed by vapor-depositting silver in the thickness of 500Angstrom onto a quartz base by the vacuum vapor deposition method, a single molecule film of arachidonic acid cadminum salt is depositted thereon by the LB method to form a recording medium 5. Al is vapor-depositted onto the medium 5 in the thickness of 6500Angstrom , a spacer 9 is provided and a quartz made prism 3 is provided on the spacer 9. Air 4 is used for a medium between the prism 3 and the recording medium 5. Then the recording medium 5 is placed in an optical system and a He-he laser light source is employed for a laser light source 10, an ND filter 11 adjusts the power, the laser beam is subjected to p-polarization by a polarizer 12 via a half mirror 16 and the resulting light is made incident in the recording medium 5 placed on an XY stage 8 on a goniometer 13. The incident angle is set optionally by turning the goniometer 13. The reflecting light is detected by a photodiode 14 and recorded on a recording meter 16 via a lock-in amplifier 15.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical recording and reproducing method using an optical recording medium having a structure consisting of a dielectric thin film layer deposited on a metal layer, and in particular, to The present invention relates to a reproducing method in which recorded information is read out by irradiating the recording medium with a reading laser beam under conditions that can generate surface plasmons on the recording medium.

(Prior Art) Optical disks and optical cards have recently been attracting attention as central players in office automation. Various types of recording media are being considered for the optical disks and optical carts, but those using organic materials are attracting attention because of their cost and ease of manufacture.

On the other hand, various recording methods have been devised, but the method widely used for compact discs, etc.
Forming pit-like holes on the recording medium according to the information signal,
One example is a method in which recording is reproduced by utilizing the fact that the readout light is diffracted by such pits, and the reflectance or transmittance changes compared to a portion without pits.

In this case, when the depth h of the pit is such that the phase difference between the laser light passing through the pit portion and the non-pit portion is 18°, the interference effect becomes maximum. When detecting the presence or absence of pits using secondary reflected light, if the refractive index of the recording medium is nlt and the wavelength of the laser beam is λ, the signal reading efficiency is maximum when nI - h = λ/4 holds. Become.

Now, n, = 1.5 (-boat fishing plastic), λ = 63
Assuming that it is 2.8 nm (He-Ne laser),
The value of h is 0.11 μm.

In addition, when trying to detect the presence or absence of pits by the transmittance of readout light, the readout light is incident on the recording medium from the air phase and transmitted to the air phase layer, and the pit depth at which the signal readout efficiency is maximum is determined. h is given by n, · h; λ/2. As in the previous case, no = 1.5゜λ =
If it is 632.8 nm, the value of h will be 0.22 μm.

Therefore, even if the reflection method is used, the thickness of the recording layer of the recording medium is required to be at least about 0.11 μm, and if the transmission method is used, an even thicker layer is required. This means that optical recording is read-only recording (ROM).
), there is no particular problem, but when performing additional recording, it is necessary to form a pit with a certain depth or more.
Even if the organic recording medium mentioned above is used, it is extremely difficult to form pits at high speed or with low power.

In addition, writeable optical carts (for example, special public
16, etc.), the thickness of the recording layer is about 0.1 μm, and there is a similar problem.

Furthermore, during recording and reproduction, in order to reduce the influence of noise that causes reading errors, it is necessary to have a large difference in reflectance or transmittance between the recorded area and the non-recorded area, that is, C/
In addition to having a large N ratio, it is also required that the reflectance or transmittance of the non-recording area itself be as large as possible.

However, in ordinary optical discs and optical cards, these values are at most 50%, and generally only about 20 to 35%.

[Problem to be solved by the invention]

This invention was made in order to solve the problems of the prior art related to the present invention, and the purpose of the present invention is to enable high-speed recording with a low-power light source, and to make recorded information written in this way highly sensitive. The object of the present invention is to provide an optical recording and reproducing method that can reproduce data.

[Means to solve the problem]

In the optical recording/reproducing method of the present invention, a recording medium having a structure in which a dielectric thin film layer is provided on a metal layer is irradiated with a writing laser beam according to recorded information, and pits are formed in the dielectric thin film layer. The optical recording process that forms the pits, and the reflection of pits and non-pit areas when the pits formed in the optical recording process are irradiated with the readout laser under conditions that can excite surface plasmons on the irradiated surface of the readout laser. It is characterized by having an optical reproduction process of reading recorded information written by detecting the difference in rate.

According to the present invention, reading laser irradiation under conditions that can generate surface plasmons on the recording medium is used to reproduce written recorded information. It is possible to obtain the difference in the reflectance of the area.

As a result, stable and accurate reproduction of recordings becomes possible.

Moreover, in optical recording, there is no need to form deep pits as in the conventional method, and the thickness of the recording layer for forming pits can be made thinner. Furthermore, if a thin recording layer is used,
In optical recording, pits can be easily formed even with low-power light, high-speed recording is possible, and productivity and cost reduction of recording media can be improved.

Hereinafter, the principle of the reproduction method of the present invention will be explained first.

Surface plasmon, also called surface plasma polariton, refers to a surface wave in which plasma vibrations localized on the surface of a solid (in this case, a metal layer) are coupled with external electromagnetic waves on the solid surface. (Sukekatsu Ushioda, Physical Properties Vol. 15, p. 587 (1989), Takao Kokufuda, Izumi Hirabayashi, Yoshinori Tokura, Applied Physics Vol. 45, p. 1069 (1976), and Hiroshi Kurosawa, Moekatsu Shioda, Laser Research Vol. 14 82 (1986), etc.].The dispersion conditions for surface plasmons existing at the air-metal interface are Ma.
It is determined from the boundary conditions of the equation xwe l l, and is expressed as. Here kx is the wave number of surface plasmon,
TM-wave. Further, ε1 is the dielectric constant of the metal, ω is the frequency of the surface plasmon, and C is the speed of light.

When exciting surface plasmons using external light, even if p-polarized electromagnetic waves are directly incident on the metal surface from the air side, it is impossible to excite surface plasmons because Re(ε1) is 0. . Therefore, the following method can be adopted to excite surface plasmons.

The first method is the 0tto arrangement (
A, 0tto, Zeitschrift der
Physik magazine, Vol. 216, pp. 398-410 (196
8th grade)). In this case, the space between the prism 3 and the metal layer 1 is filled with a medium 4 having a refractive index n1 smaller than the refractive index np of the prism, and its thickness is assumed to be dl. The medium 4 may be air (or vacuum) as long as it satisfies n,,〉nll, in which case 03~
It is 1. Critical angle θ for total reflection of P-polarized light wave of frequency ω.

When the light is incident on the prism at an incident angle θ larger than θ, the light is in the region of total reflection, but attenuated waves seep into the medium 4. Among the wave number vectors of this attenuated light, the components parallel to the interface are n, (ω/c) sin θ. Now medium 4
If the thickness dl of
/c) When the incident angle θ satisfies sin θ, this attenuated wave resonates with plasma vibrations that may exist at the interface between the medium 4 and the metal layer 1, and excites surface plasmons. At this time, the reflectance of the incident light 6 is reduced. Reflectance and θ at this time
Figure 2 schematically shows the relationship. At this time, the position of the reflectance dip (4) depends on ε1, so it differs depending on the metal used.On the other hand, the depth of the dip depends on the wavelength (ω) of the incident light used and the medium 4.
Although it is sensitive to the type and thickness d, the deepest point, ie, the conditions under which the reflectance can be minimized, can be easily determined using Fresnel's equation, and can also be obtained experimentally. When the medium 4 is air, the efficiency will be good when the magnitude of dl is about the wavelength of the incident light. Now, when a dielectric thin film 2 having a thickness d2 thinner than dl is deposited on this metal layer 1, the dispersion condition of surface plasmons deviates from equation (1). That is, it changes depending on the thickness d2 of the dielectric layer 2 and the dielectric constant εd of the dielectric layer 2. Now, assuming that the dielectric constant εd of the dielectric layer 2 used is constant, d2
As the value increases, the position of the dip becomes 0 as shown in Figure 2.
It changes continuously from 1 to θ2 (θ2>θI). Therefore, when an electromagnetic wave is incident at a constant angle of incidence, the reflectance changes depending on the thin film of the dielectric layer 2 on the metal layer 1. θ1 or θ2 whose incident angle gives the maximum value of each dip
, the change in reflectance becomes maximum depending on the presence or absence of the dielectric layer 2. That is, at this time, it is possible to obtain the largest C/N ratio. However, in order to obtain a large difference in reflectance at the 01 point or 02 point, the difference between θ1 and 02 must be sufficiently large, or the dip must be steep and its width must be small. The former can be easily achieved by increasing the thickness of the dielectric layer, but from the viewpoint of writing by optical recording, which will be described later, it is preferable that the dielectric layer be as thin as possible. on the other hand,
The width of the dip is sensitive not only to the wavelength (ω) of the incident light and the thickness of the medium 4, but also to the size of the imaginary part of the dielectric constant of the metal layer. For example, the dip width can be made significantly smaller than that of a metal with a large imaginary part such as gold. However, it must be noted that the smaller and steeper the width of the dip, the greater the change in reflectance caused by a slight change in the thickness d2 of the dielectric layer. That is, although an extremely thin dielectric layer can be used under the condition of a small dip width, the thickness of the dielectric layer must be uniform except for the recorded pit portions. However, even if the thickness of d2 is 25 and the metal layer is gold, the difference in reflectance can be maintained at 0.8 or more, and similarly when silver is used, the difference can be maintained at 0.9 or more. be.

The above was about the presence or absence of a dielectric layer on the metal layer, but
It is not necessary for the metal surface to come out in the pit part, but to have an appropriate depth (for example, 25 people) in the dielectric layer.
A recess may be formed.

As described above, it is possible to detect the presence or absence of a dielectric layer on a metal layer or a change in a thin film with high sensitivity.

The dielectric layer of the recording medium used here is an organic monomolecular film formed by the Langmuir-Prodgett method (LB method) or a cumulative film thereof (collectively referred to as a Langmuir-Prodgett film, or LB film for short); An organic monomolecular film formed by gas phase or liquid phase adsorption, an organic layer formed by a method such as a spin code, an organic layer formed by a vapor phase film forming method such as vapor deposition or CVD method, etc. can be used. In addition,
The thickness of the dielectric layer can range from 3 to 1000, for example.

Among these, the LB film is particularly preferable since it can satisfy various requirements during optical writing described below.

That is, as described above, recording is accomplished by irradiating the dielectric layer with a laser beam, melting or sublimating the dielectric in the irradiated area, and forming pits consisting of recesses. Therefore, since it is necessary for the dielectric layer to easily form pits by laser beam irradiation, it is preferable that the dielectric layer is made of an organic substance, and that its thickness is also preferably as thin as possible. Furthermore, as mentioned earlier, from the viewpoint of stability during readout, the thickness of the dielectric layer is required to be as uniform as possible. It is particularly preferable to use an LB film as the dielectric layer that can satisfy such requirements. This LB
By using a film, it is possible to stably and easily form an organic dielectric layer having a uniform thickness controlled on the order of molecular length over any area on the metal layer 2.

The laser beam during writing may be applied directly to the dielectric layer 2 without passing through the prism 3, or the dielectric layer 2 may be irradiated as transmitted light through the prism 3. The recording density is determined by the pit diameter, and when visible light is used as the laser light, it is a little less than about 1 μm. The light sources for the writing light and the reading light may be separate (including cases where the wavelengths are different) or the same, but the latter has the advantage that the optical system can be smaller.

A second method to excite surface plasmons is the retschmann configuration (E) as shown in FIG.

Kretschmann, Zeitschrift
der Physik, Vol. 241, pp. 313-324 (1971)). In this case, the read light is made to enter from the back surface of the recording medium 5, that is, from the side opposite to the dielectric layer 2. It is also possible to use a recording medium 5 that has the metal layer 1 directly on the prism 3, but in that case, the recording layer and the prism cannot be separated, and one prism is used for one recording medium. Become. When the metal layer 1 and the dielectric layer 2 are provided on the substrate 8, since the prism 3 and the recording medium 5 are each independent, it is possible to replace various recording media with respect to one prism.

In this case, the refractive index n2 of the prism 3 and the refractive index nl of the substrate 8
It is desirable that I be equal, but they may be different. In addition, the substrate 8 is selected to be transparent without optical anisotropy, or to not absorb at least the writing and reading laser beams, and to avoid creating an air film at the interface with the prism 3. , this surface is required to be sufficiently smooth. Roughly speaking, np and ng are required to be larger than the refractive index n of the medium 4 on the dielectric layer 2 side. Of course, there is no problem if the medium 4 is air or vacuum (ns~1). The incident light 6 is a p-polarized light wave as in the 0tto arrangement. Even in this arrangement, the change in reflectance due to the coupling between the incident light 6 and the surface plasmon of the metal layer 1 is similar to that shown in Fig. 2, but the depth and width of the dip vary depending on the wavelength of the incident light and the type of metal. , is sensitive to the metal layer thickness dl. d,
If the metal layer 1 is too thick, total reflection will only occur, and the component parallel to the reflective surface of the incident light 6 will not be attenuated. Layer 1 must be made thinner. The maximum thickness of the metal layer 1 defined from this point of view is, for example, 10 mm for silver.
00 people, 1500 people for gold, and 1000 people for aluminum. In the case of silver, the depth of the dip is maximum when the dl is about 500 people.

Other conditions required for the dielectric layer 2 are as described by Otto above.
This is similar to what was stated in the layout.

When using the reproducing arrangement shown in FIG. 3, writing may be performed using refracted light from the prism side, or, considering light loss, the writing light may be directly directed from the medium 4 side to the dielectric. It is desirable that the light be incident on the body layer 2. However, since a simple structure can be used as an optical system for irradiating writing light, a method using refracted light from the prism side is preferable. In this case as well, the number of light sources may be one or more.

A third method for exciting surface plasmons is to create irregularities on the surface of the recording medium to break the translational symmetry along the surface. The simplest example is to use a diffraction grating in which sinusoidal grooves are cut in parallel, as shown in FIG. The wave number corresponding to the period a of the diffraction grating is g=2
If we set π/a, the plane wave (kX=(Tomoe)Sin) incident on the recording medium from the medium 4 at the incident angle θ has a black reflection type wave number change (kfg).=kX±n-g( n=
1.2.3...) and compare them (the plane of incidence is perpendicular to the groove and the incident light is p-polarized). Now, assuming that the second-order diffraction intensity is small and only the first-order (n=1) diffraction wave is considered, if either k±g=kX±g matches the wave number of the surface plasmon, the surface plasmon will resonate. is excited, and the intensity of the normal reflected light is reduced. If the groove direction is not perpendicular to the incident plane, what is the wave number vector corresponding to the periodic sound of the diffraction grating? =2π/, and if we set the wave number vector of the incident plane wave to, -bg=violet. +100 size 1
Excitation occurs where 1i'gl matches the wave number of the surface plasmon. In this case, except for the case of ff1g/'fX, surface plasmons are excited even if the incident light is S-polarized light. Such a diffraction grating is produced by first forming a grating as shown in FIG. 4 on the surface of the substrate 80 using, for example, photolithography technology, and then depositing a metal layer 2 thereon by a method such as vacuum evaporation or sputtering. It can be easily formed by Naturally, in this case, the thickness of the metal layer 2 is required to be appropriately thin so that the lattice on the substrate 8 is reflected on the surface of the metal layer. Alternatively, the diffraction grating may be formed by depositing the metal layer 2 on a flat substrate and then etching the metal layer. The magnitude of the amplitude of the diffraction grating is related to the coupling strength with the surface plasmon, and therefore has a large effect on the change in reflectance. There is a maximum value of Although the light is made to enter from the medium 4 side in FIG. 4, a prism may be provided on the back surface of the substrate 8 (the surface opposite to the metal layer 2) and the light may be made to enter from the prism side. That is, the Kret mentioned earlier
The same optical system as the Schmann arrangement may be used.

Various methods have been described above for detecting the presence or absence of pits on the dielectric layer 2 by exciting surface plasmons.However, for measuring the intensity of reflected light, a lock-in photodiode (for example, Hamamatsu Photonics 51223) and a lock-in photodiode are used to measure the intensity of reflected light. You can do this by combining an amplifier.

The recording medium used in the method of the present invention has a structure in which a dielectric thin film layer is provided on a metal layer. be selected accordingly.

For example, as shown in FIG. 1, FIG. 3, FIG. 4, and FIG.
A structure in which a dielectric thin film layer 2 and a dielectric thin film layer 2 are laminated can be used.

Examples of the substrate 8 include quartz, glass, silicon substrates, various plastic plates, and metal plates.

When writing or reading is performed by transmitting light through the substrate 8, transparent plastic plates such as acrylic plates can be used in addition to quartz and glass.

There are no particular restrictions on the material and method of forming the metal layer 1, as long as it can effectively create a difference in reflectance between pits and non-pits using surface plasmons.
For example, those formed of gold, silver, aluminum, copper, etc. by various film forming methods such as ordinary vapor deposition, CVD, and sputtering can be used. Note that the layer thickness is appropriately selected depending on the excitation method of surface plasmons.

In other words, when using the 0tto arrangement and a diffraction grating, there is no regulation on the film thickness, or there is no regulation on the film thickness.
When using the n-configuration, the thickness is preferably 2000 mm or less, and more preferably about the wavelength of the laser beam used. In addition, the optimal metal layer thickness in this case can be more precisely given by solving Fresnel's equation (
For example, K., Kurosawa, R.M., Pierce.
, S. Ushioda,PhysicalReview
8, Vol. 33, pp. 789-798 (1986)).

The dielectric i-film layer 2 is made of a material and layer thickness that has the characteristics necessary for optical writing and that can effectively create a difference in reflectance between pit and non-pit areas using surface plasmons. things are used.

For example, an LB film of an organic compound that can form a dielectric, an organic monomolecular film formed by vapor phase or liquid phase adsorption, an organic layer formed by a method such as a spin code, or a vapor phase film formation method such as vapor deposition or CVD method. An organic thin film formed by can be used.

In either method, the film thickness may range from 3 to 1000 people, more preferably from 5 to 200 people.

Note that a recording medium having a configuration in which the substrate 8 used in the surface plasmon excitation method shown in FIG. Obtainable.

〔Example〕

Next, embodiments of the present invention will be described in detail.

Example 1 Silver was deposited on a clean quartz substrate (25 mm x 38 mm, 1 mm thick) to a thickness of 500 layers by vacuum evaporation (filming rate 1 person/sec, degree of vacuum 3 x 10-6 Torr or less). , a metal layer was formed. A monomolecular film of cadmium araxinate salt was deposited on this metal layer by the LB method as described below to produce a recording medium.

First, a benzene solution containing araxic acid (nC19H39COOH) dissolved at a concentration of 1 mM is spread on an aqueous phase containing 4 × 10-'M cadmium chloride and adjusted to pH 6, 7, and 20 °C, and a single layer is placed on the water surface. A molecular film was formed. After solvent evaporation, the surface pressure of the monolayer on the aqueous phase was adjusted to 30 m
N/m and kept it constant. Next, the above-mentioned quartz substrate with a silver film, which had been immersed in the water phase in advance, was gently pulled up at a speed of 5 mm/min in the direction across the water surface, and the cadmium araxinate salt monomolecular film (thickness: 25.4 mm) was removed. ) was formed on the previously formed silver film to prepare a recording medium.

Optical recording and reproduction were performed using this recording medium. The details are described below.

First, as shown in FIG. 5, aluminum was deposited on a predetermined position of the recording medium obtained by the above method to a thickness of 6,500 layers by vacuum evaporation (filming rate of 5 persons/sec, degree of vacuum 3 x 1).
0-6 Torr or less), a spacer 9 is provided, and a quartz prism 3 (refractive index (n,
, = 1.457) was set. Here, the medium 4 between the prism 3 and the surface of the recording medium 5 is air. The recording medium on which this prism 3 was installed was placed at a predetermined position in the optical system shown in FIG. Output of laser light source 10 is 15m
Using a W He-Ne laser light source, ND filter 1
I adjusted its power in 1. Next, the laser beam from the light source 10 is converted into P-polarized light by a polarizer 12 via a half mirror 16, and then the configuration shown in FIG. The light was incident on a prism and a recording medium. The angle of incidence is a goniometer.
It was made possible to set it arbitrarily by rotating the . The reflected light was detected by a photodiode 14, passed through a lock-in amplifier 15, and was recorded as reflectance by a recorder 16. In this system, we set the incident light intensity to about 1 mW and varied the incident angle θ to the recording medium to find the point where the incident light resonates with the surface plasmon. When θ = 45.6°, the reflectance is the minimum (O, OS). Next, the transmitted light from the prism 3 or a laser beam is incident perpendicularly to the surface of the recording medium 5 to form pits with a diameter of about 1 μm and a depth of about 25 μm on the cadmium araxinate monolayer. did. At that time, the power was adjusted using the ND filter 11 so that the laser light intensity at the incident surface was about 5 mW. The irradiation time for forming one bit was 300 nsec.

The incident angle conditions for exciting surface plasmons on the pit surface formed as described above were found to be θ=45.1°.
When , the resonance was at its maximum and the reflectance was at its minimum (O, OS). In other words, the relationship between the reflectance and the incident angle θ is the same as in Figure 2, where θ = 45.1° (pit bottom,
That is, the silver surface), θ, = 45.6° (the surface of the cadmium araxinate monolayer film). Next, while maintaining the incident angle at 45.1[deg.], the reflection part was moved from the pit part to the non-pit part using the X-Y stage 18, and the reflectance was 0.96. In this state, change the incident angle to 45,6 again.
The reflectance decreased to 0.05 when the angle of incidence was changed to 0.05°, and when the reflection section 10 was moved from the non-pit section to the pit section using the X-Y stage 18 while maintaining the incident angle at this time, the reflectance decreased to 0.05. It became 0.96.

From the above, high-speed writing (300nsec or less) is possible.
The incident angle of the readout light is set to the angle at which the coupling with the surface plasmon in the pit or non-pit region is maximum (45 and 1, respectively).
When the reading light is scanned over the surface of the recording medium with the angle fixed at 45° and 45° and 6°, the reflectance changes from 0 to 0 depending on the presence or absence of pits.
91 changes, confirming that high-speed and highly accurate reading is possible.

Example 2 A quartz substrate (25 mm x 38 mm) whose surface was optically polished
, 1 mm thick), a silver layer and a monomolecular film of cadmium araxinate salt were formed in the same manner as in Example 1 to obtain a recording medium.

The back surface of the quartz substrate of this recording medium (the surface on which the silver film is not deposited) and the prism are bonded together, and the Kret shown in FIG.
The configuration for a 5chmann arrangement was obtained.

Next, a recording medium to which this prism was bonded was placed in the optical system used in Example 1, and optical recording and reproduction was performed. At that time, the recording medium is set on the X-Y stage 18 on the goniometer 13, and when writing, the goniometer 13 is rotated so that the recording medium is directly transferred from the air phase onto the cadmium araxinate monolayer. Irradiate laser light (5m
W.

Pit formation was performed for 300 nsec) L/L.

Next, the goniometer 13 was rotated again to make the laser beam enter the prism surface, and the excitation conditions for surface plasmon in the pit and non-pit areas were determined, and the incident angle of each incident light was 45.1 The reflectance was minimum (O, OS) at 45.6° and 45.6°. Conversely, when the incident angles to the pit and non-pit areas are set to 45.6° and 45.1°, respectively, the reflectance is 0.96, and when the incident angle is fixed at 45.6° or 45.1°, If the readout light is scanned,
It was found that the presence or absence of pits could be detected based on the difference in reflectance of 0.91.

Example 3 60% was deposited on a quartz substrate similar to that used in Example 2 by vacuum evaporation.
Create a gold film with a thickness of 0 people (filming speed 3 people/sec, degree of vacuum 3)
A water surface monomolecular film (surface pressure = 30 mN/m) of cadmium araxinate salt formed in the same manner as in Example 1 was applied to a substrate having The gold film was immersed at the same speed and then pulled up at the same speed to form a two-layer monomolecular cumulative film (thickness: 55.2) of cadmium araxinate salt on the gold film.

After forming pits in the monomolecular cumulative film in the same manner as in Example 2 except for using this recording medium, the excitation conditions for surface plasmon in pit areas and non-pit areas were determined, and the incident angle of the incident light was The angles were 46.2° and 47.2°, and the reflectance was 0.2 in both cases. On the other hand, while maintaining these incident angles, the reflectances of the non-pit portion and the pit portion were determined to be 0.82 and 0.71, respectively.

Therefore, when the angle of incidence is 46.2°, the difference in reflectance is 0.
．． 62, and the angle of incidence is 47, . It was found that when the angle is 2°, the presence or absence of pits can be detected with a difference in reflectance of 0.51.

Example 4 Glass substrate (Corning 7059 25mm x 38
A sine-wave type diffraction grating having the structure shown in FIG. 4 was formed using photoresist on a sine-wave type diffraction grating having a structure shown in FIG. 4 using interference fringes of laser light. The amplitude of the obtained diffraction grating was 180,
In addition, there were 4,500 people in period a.

5 silver was deposited on the substrate having this diffraction grating by vacuum evaporation method.
A metal layer was formed by vapor deposition to a thickness of 0.00 mm.

Furthermore, a monomolecular film of a cadmium araxinate salt was formed on this metal layer by the same method as in Example 1 to prepare a recording medium. This recording medium was set in the optical system shown in FIG. 6 used in Example 1, and optical recording and reproduction was performed as follows.

First, in the optical system shown in FIG. 5, a recording medium having the above configuration was placed on the XY stage 18 on the goniometer 13. At this time, the incident light plane was adjusted to be perpendicular to the grooves of the diffraction grating of the recording medium. When the incident light intensity was set to about 0.7 mW and the incident angle θ to the recording medium was varied, the point at which the incident light and the surface plasmon resonated was determined, and it was found that θ = 2.
At 1.9°, the reflectance is at its minimum (O, OS). Next, adjust the incident light so that it is perpendicular to the recording medium.
Pits were formed in the monomolecular film of the cadmium araxinate salt under the following conditions: 0°), laser beam intensity of 5 mW, spot diameter of 1 μm, and hot irradiation time of 300 nsec. When we found the excitation conditions for surface plasmons in this pit, we found that the incident angle was 2.
When the angle was 1.3°, the reflectance was the minimum (0,08). Conversely, when the incident angles to the pit and non-pit areas are 21.9° and 21.3°, respectively, the reflectance is 0.80 and 0.7.
It was 2. Therefore, when the angle of incidence is 21.9°, the presence or absence of pits is detected based on the difference in reflectance of 0.72, and when the angle of incidence is 21.3°, the difference in reflectance is 0.64. I found out that it can be done.

In the examples described above, the LB method was used to form the dielectric layer, but the LB method can be used as long as it can produce an extremely thin and uniform film. Specifically, the LB method can be used. Film forming methods such as vacuum evaporation, MBE, and CVD can be used. Furthermore, the material constituting the dielectric layer 2 is not limited to cadmium araxinate salt.

Further, regarding the method of forming the metal layer, any film forming method that can similarly form a uniform thin film can be used, and is not limited to the vacuum evaporation method.

Further, the present invention is not limited in any way to the materials and shapes of the substrate and prism, and the light source.

(Effects of the Invention) As described above, according to the recording and reproducing method of the present invention, a thin dielectric layer can be used as the recording layer, so there is no need to irradiate with particularly high output light, and it is possible to High-speed writing is possible using a light source.Also, by using surface plasmons, it is possible to draw out a very large difference in reflectance between recorded and non-recorded areas, allowing stable and accurate reproduction of records. It is.

Furthermore, since the dielectric layer serving as the recording layer of the recording medium can be thin, the recording medium is highly productive and inexpensive. A schematic diagram showing an arrangement called the 0tto arrangement. Figure 2 is a diagram plotting the change in reflectance due to the coupling of surface plasmons and incident electromagnetic waves against the angle of incidence. Figure 3 is the geometry of the prism and recording medium. Of the target placement, retschm
FIG. 4 is a schematic diagram showing the structure of a recording medium used when exciting surface plasmons using a diffraction grating, and FIG. 5 is a schematic diagram showing an arrangement called ann configuration.
FIG. 6 is a schematic diagram showing the optical system used during recording and reproduction.

1--metal layer, 3--prism, 5--recording medium, 7--reflected light, 10--laser light source, 2--dielectric layer, 4--medium, 6--incident light, 8...Substrate, 1l-ND filler, 12-...Polarizer, 13-...Coniometer 14...Photodiode, 15-...Lock-in amplifier, 16...Record of ten words,
17-zs-Humira-1B-X-Y stage.

Claims (1)

[Claims] 1. A recording medium having a structure in which a dielectric thin film layer is provided on a metal layer is irradiated with a writing laser beam according to recorded information, and light that forms pits in the dielectric thin film layer. recording process and
The pits formed during the optical recording process are detected using the difference in reflectance between pits and non-pit areas when the readout laser is irradiated with the readout laser under conditions that can excite surface plasmons on the irradiation surface of the readout laser. 1. An optical recording and reproducing method comprising: an optical reproducing step of reading out recorded information written by the method. 2. The optical recording and reproducing method according to claim 1, wherein the writing laser beam and the reading laser beam are obtained from the same light source. 3. The optical recording and reproducing method according to claim 1 or 2, wherein the writing laser beam and the reading laser beam are obtained from different light sources. 4. The optical recording and reproducing method according to any one of claims 1 to 3, wherein the dielectric thin film layer has a thickness of 3 Å or more and 1000 Å or less. 5. The optical recording and reproducing method according to any one of claims 1 to 4, wherein the dielectric thin film layer comprises a monomolecular film or a monomolecular stacked film of an organic compound. 6. A prism constituting an optical system during readout is installed on a dielectric layer via an air barrier film, a readout laser beam is incident from the prism side, and the intensity of p-polarized light among the reflected waves is measured. 6. The optical recording and reproducing method according to any one of 1 to 5. 7. The optical recording and reproducing method according to claim 6, wherein the thickness of the air film is in the range of 500 to 10,000 Å. 8. The prism that constitutes the optical system during readout is placed on the metal layer on the side on which the dielectric layer is not deposited, either through a transparent substrate or directly, and the readout laser beam is incident from the prism side to detect the reflected waves. Claim 1: Measuring the intensity of p-polarized light
6. The optical recording and reproducing method according to any one of . 9. The optical recording and reproducing method according to claim 8, wherein the metal layer of the recording medium has a thickness of 50 to 2000 Å. 10. Using a recording medium in which a recording layer consisting of a metal layer and a dielectric thin film is provided on the diffraction grating surface of a substrate having a diffraction grating, a readout laser beam is incident from the dielectric thin film surface without going through a prism. 6. The optical recording and reproducing method according to claim 1, wherein the intensity of reflected light is measured. 11. Claim 1, wherein the metal layer has a thickness of 50 to 2000 Å.
0. The optical recording and reproducing method according to 0. 12. Reproduction in which recorded information is read by irradiating a reading laser onto a recording medium having pits formed in a dielectric thin film layer provided on a metal layer in accordance with recorded information and detecting the pits. In the method, the dielectric thin film is formed by utilizing the difference in reflectance between pits and non-pit areas when the readout laser is irradiated with the readout laser under conditions that can excite surface plasmons on the irradiation surface of the recording medium. A reproduction method characterized by reading recorded information written by detecting pits formed in a layer. 13. The reproduction method according to claim 12, wherein the dielectric thin film layer has a thickness of 3 Å or more and 1000 Å or less. 14. The regeneration method according to claim 12 or 13, wherein the dielectric conductor thin film layer comprises a monolayer or a monolayer cumulative film of an organic compound. 15. A prism constituting an optical system during readout is installed on a dielectric layer via an air barrier film, a readout laser beam is incident from the prism side, and the intensity of p-polarized light among the reflected waves is measured. 15. The regeneration method according to any one of 12 to 14. 16. The regeneration method according to claim 15, wherein the thickness of the air film is in the range of 500 to 10,000 Å. 17. A prism constituting the optical system for readout is placed on the metal layer on the side on which the dielectric layer is not deposited, either through a transparent substrate or directly, and the readout laser beam is incident from the prism side to detect reflected waves. 15. The reproducing method according to claim 12, wherein the intensity of p-polarized light is measured. 18. The reproducing method according to claim 17, wherein the metal layer of the recording medium has a thickness of 50 to 2000 Å. 19. Using a recording medium in which a recording layer consisting of a metal layer and a dielectric thin film is provided on the diffraction grating surface of a substrate having a diffraction grating, a readout laser beam is incident from the dielectric thin film surface without going through a prism. 15. The reproducing method according to claim 12, wherein the intensity of the reflected light is measured. 20. Claim 1, wherein the metal layer has a thickness of 50 to 2000 Å.
9. The regeneration method described in 9.