JP2010122373A - Optical information recording medium and two-photon absorbing material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the light intensity of a laser beam required to form a recording mark. <P>SOLUTION: A recording layer 101 of an optical information recording medium 100 contains a two-photon absorbing material. This two-photon absorbing material is a metal complex in which one or more molecules coordinate with a metal atom, and the material performs one-photon absorption of a recording light beam L1 by a change of state due to two-photon absorption upon irradiation with the recording light beam L1 which is recording light for information recording, and forms a recording mark by heat generation in response to the one-photon absorption. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical information recording medium and a two-photon absorption material, and is suitable for application to an optical information recording medium in which information is recorded using, for example, laser light and the information is reproduced using the laser light. is there.

  Conventionally, as an optical information recording medium, a disk-shaped optical information recording medium has been widely used, and generally a CD (Compact Disc), a DVD (Digital Versatile Disc), and a Blu-ray Disc (registered trademark, hereinafter referred to as BD). Etc. are used.

  On the other hand, in a recording / reproducing apparatus corresponding to such an optical information recording medium, various kinds of information such as various contents such as music contents and video contents or various data for computers are recorded on the optical information recording medium. ing. Particularly in recent years, the amount of information has increased due to high definition of video, high quality of music, and the like, and an increase in the number of contents to be recorded on one optical information recording medium has been demanded. There is a demand for further increase in capacity.

  Here, it is generally known that the spot size when the laser beam is condensed by the objective lens is determined by the wavelength of the laser beam and the numerical aperture NA of the objective lens. For this reason, in order to reduce the size of the recording mark and increase the capacity of the optical information recording medium, it is desirable to reduce the spot size by using laser light having a short wavelength.

  The miniaturization of the spot size has been achieved mainly by increasing the numerical aperture NA of the objective lens and shortening the wavelength of the laser beam. Currently, in the BD, the numerical aperture NA of the objective lens is 0.85, and the wavelength of the laser beam is 405 [nm]. However, it is difficult to further increase the numerical aperture NA or shorten the wavelength of the laser beam.

  For example, in order to increase the numerical aperture NA to 0.85 or more, a method different from the conventional method such as using near-field light is required. In order to shorten the wavelength of the laser light, it is necessary to ensure the transparency of the substrate and the protective layer of the optical information recording medium with respect to the wavelength of the laser light. That is, in any case, the cost of the recording / reproducing apparatus and the optical information recording medium cannot be avoided.

Therefore, as one of the methods for increasing the capacity of the optical information recording medium, an optical information recording medium has been proposed that records information three-dimensionally in the thickness direction of the optical information recording medium. In this optical information recording medium, a two-photon absorption material that foams by two-photon absorption is contained in the recording layer, and a recording mark made of bubbles is formed by irradiating laser light. (For example, refer to Patent Document 1).
JP-A-2005-37658

  By the way, in the optical information recording medium having such a configuration, a recording mark is formed by two-photon absorption of red (for example, 600 to 750 [nm]) laser light used in CDs and DVDs. Two-photon absorption is a kind of third-order nonlinear optical effect, and is a phenomenon in which one molecule simultaneously absorbs two photons via a virtual level and enters an excited state. ) Squared.

  For this reason, in an optical information recording medium containing a two-photon absorption material as a recording layer (hereinafter referred to as a two-photon absorption recording medium), two-photon absorption occurs only in the vicinity of the focal point where the electric field strength is the highest. Two-photon absorption does not occur in portions other than a small focal point. That is, the laser light travels in the recording layer with almost no absorption before reaching the focal point, and when it reaches the focal point, two-photon absorption occurs and is absorbed.

  Here, in the case of a general recording layer that absorbs one photon, since the laser light is absorbed in the entire area of the recording layer, the light intensity of the laser light is lowered before reaching the deep part of the recording layer. For this reason, it is difficult for the recording layer that absorbs one general photon to have, for example, 10 or more recording layers.

  On the other hand, in the two-photon absorption recording medium, since the laser light is hardly absorbed before reaching the focal point, it is possible to make the recording layer 10 layers or more.

As described above, in the two-photon absorption recording medium, the number of recording layers in the optical information recording medium can be increased, which is very advantageous for increasing the storage capacity in the optical information recording medium. However, in a two-photon absorption recording medium, it is necessary to use a laser beam having a very large light intensity in order to cause two-photon absorption. For this reason, high sensitivity of a two-photon absorption material has been studied (see, for example, Patent Documents 2 and 3).
JP 2007-332043 A JP 2004-279647 A

  By the way, as shown in Patent Documents 2 and 3, in a general two-photon absorption recording medium, a laser beam having a wavelength from red to infrared light (600 to 800 [nm]) (hereinafter referred to as a long wavelength laser beam). (Refer to Patent Document 2, for example).

This is considered to be due to the following reason. As shown in Non-Patent Document 1, the absorption cross section of a molecule that causes two-photon absorption is theoretically proportional to the number of conjugated π electrons. A molecule having a large π-electron system, that is, a molecule that absorbs a long wavelength has a larger two-photon absorption cross section.
Journalof Chemical Physics Vol.119, p.8327 (2003): Mark G. Kuzyk “Fundamental limits on two-photon absorptioncross sections”

  However, recording using a long wavelength laser has the following disadvantages.

  The diameter of the light beam (that is, the spot diameter) at the focal point when the laser light is collected by the lens is proportional to the wavelength of the laser light. That is, in the laser light, when the wavelength is doubled, the spot diameter is doubled, and the area of the spot is quadrupled.

  Here, in the case of laser light having the same light intensity, the light intensity at the focal point is 1/4 times and the photon density is 1/2 times. Further, since the two-photon absorption amount is proportional to the square of the photon density, assuming that the two-photon absorption cross section does not depend on the wavelength, the two-photon absorption amount becomes ¼ when the wavelength of the laser beam is halved. Will be reduced. In practice, the two-photon absorption cross-section varies with wavelength.

  In other words, in order to obtain a two-photon absorption amount similar to 400 [nm] using a laser beam of 800 [nm], the two-photon absorption cross section at 800 [nm] has a two-photon absorption cross-section of 400 [nm]. It needs to be 4 times the area.

In practice, in order to perform optical recording by two-photon absorption using a long wavelength laser, an emitted light intensity of about 10 [GW / cm ² ] is required, so a femtosecond laser such as a titanium sapphire laser is used. It is necessary to use it. In addition to being very expensive, this femtosecond laser has a low repetition frequency and insufficient performance for optical recording.

  In the case of recording using a long wavelength laser, the two-photon absorption medium has a large spot diameter and an overall small photon density at the spot. Therefore, the two-photon absorption medium has only a narrow range near the focal point where the photon density is relatively high. Absorption cannot occur, and a recording mark RM that is considerably smaller than the spot diameter is formed.

  That is, when recording is performed using a long wavelength laser, the two-photon absorption medium can form a recording mark RM smaller than the recording mark RM by one-photon absorption near the focal point, as shown in FIGS. . However, in the two-photon absorption medium, in order to detect the recording mark RM, it is necessary to make the spot diameter of the laser beam smaller than that at the time of recording, and it is necessary to irradiate laser light having a shorter wavelength than at the time of recording.

  For this reason, the two-photon absorption medium uses two types of lasers, a long wavelength laser and a short wavelength laser, for recording and reproduction. As a result, a recording / reproducing apparatus that records and reproduces a two-photon absorption medium requires two light sources that emit a long wavelength laser and a short wavelength laser, which increases costs.

  On the other hand, in the two-photon absorption medium, when recording is performed using a short wavelength laser such as 400 [nm], the photon density at the spot as a whole is increased due to the difference in the spot diameter described above. Two-photon absorption can occur with low light intensity.

  The two-photon absorption medium is capable of concentrating light energy in the vicinity of the focal point when recording using a short-wavelength laser, so that the recording has a size that is relatively close to the spot diameter but smaller than the spot diameter. A mark RM can be formed. That is, the two-photon absorption medium allows the recording / reproducing apparatus to use the same laser for recording and reproduction.

  However, two-photon absorption that causes two-photon absorption for short-wavelength laser light having a wavelength of less than 600 [nm], such as blue-violet laser light having a wavelength of 405 [nm] used in BD, for example. No material has been found that satisfies the conditions for causing two-photon absorption, and has not yet been proposed. Moreover, even if a material that causes two-photon absorption is discovered, it is considered that the light intensity of a general semiconductor laser is insufficient.

  That is, when a long-wavelength laser beam is used as the recording beam, the emitted light intensity is insufficient, and it does not exist at all in the case of a two-photon absorption material that absorbs a short-wavelength laser beam that requires a relatively low emitted light intensity. It turns out that. As a result, in order to form a recording mark RM using two-photon absorption using a general semiconductor laser, the light intensity of the laser beam necessary to form the recording mark RM must be reduced. There was a problem.

  The present invention has been made in consideration of the above points, and intends to propose an optical information recording medium and a two-photon absorption material capable of reducing the light intensity of laser light necessary for forming a recording mark. is there.

  In order to solve such a problem, the optical information recording medium of the present invention is a metal complex in which one or more molecules are coordinated to a metal atom, and two photons according to irradiation of recording light for information recording A recording layer containing a two-photon absorption material that absorbs one-photon recording light by a change in state due to absorption is provided.

  Thereby, in the optical information recording medium, a recording mark can be formed by heat generation according to one-photon absorption.

  Further, the optical information recording medium of the present invention has a pulsed singular peak and a recording layer that is irradiated subsequent to the singular peak and forms a recording mark in accordance with a singular slope that has a smaller emitted light intensity than the singular peak. I did it.

  Thereby, in the optical information recording medium, a recording mark can be formed by heat generation according to a specific slope.

  Furthermore, in the optical information recording medium of the present invention, after the transition to the excited singlet state by two-photon absorption with respect to the recording light for information recording, the transition to the lowest triplet state is made, and recording is performed when the lowest triplet state is reached. A recording layer containing a two-photon absorption material that absorbs one photon is provided.

  Thereby, in the optical information recording medium, a recording mark can be formed by heat generation according to one-photon absorption.

In the optical information recording medium of the present invention, when Ph is a phenyl group, TCNE is tetracyanoethylene, and X is a general formula, a two-photon absorption material represented by the formula (1) is contained.
IrClX (Ph ₃ P) ₂ TCNE (1)

  As a result, the optical information recording medium can absorb two photons according to the recording light having a short wavelength.

Furthermore, the two-photon absorption material of the present invention is represented by the formula (1), where Ph is a phenyl group, TCNE is tetracyanoethylene, and X is a general formula.
IrClX (Ph ₃ P) ₂ TCNE (1)

  As a result, the optical information recording medium can absorb two photons according to the recording light having a short wavelength.

  According to the present invention, it is possible to realize an optical information recording medium capable of forming a recording mark by heat generation according to one-photon absorption, and thus reducing the light intensity of the laser beam necessary for forming the recording mark. .

  Further, according to the present invention, it is possible to realize an optical information recording medium that can form a recording mark by heat generation according to a specific slope, and thus can reduce the light intensity of the laser beam necessary for forming the recording mark. .

  Further, according to the present invention, an optical information recording medium capable of absorbing two photons in response to recording light having a short wavelength and thus reducing the light intensity of laser light necessary for forming a recording mark, and 2 A photon absorbing material can be realized.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. The description will be given in the following order.
1. Embodiment
2. Other embodiments

<1. Embodiment>
[1-1. Configuration of recording / reproducing apparatus]
As shown in FIG. 3, the recording / reproducing apparatus 10 is configured around a control unit 11. The control unit 11 includes a CPU (Central Processing Unit) (not shown), a ROM (Read Only Memory) in which various programs are stored, and a RAM (Random Access Memory) used as a work memory of the CPU. .

  When recording information on the optical information recording medium 100, the control unit 11 rotates the spindle motor 15 via the drive control unit 12 to rotate the optical information recording medium 100 placed on a turntable (not shown). Rotate at desired speed.

  The control unit 11 drives the sled motor 16 via the drive control unit 12 to move the optical pickup 17 in the radial direction along the movement axes G 1 and G 2, that is, on the inner or outer peripheral side of the optical information recording medium 100. It is made to move greatly in the direction toward.

  In addition, when recording information on the optical information recording medium 100, the control unit 11 supplies recording information supplied from the outside to the signal processing unit 13. The signal processing unit 13 generates recording data Sw by performing predetermined modulation processing and binarization processing on the recording information, and supplies the recording data Sw to the optical pickup 17.

  As a result, a recording light beam L1 modulated according to information is emitted from a short pulse light source 20 (detailed in detail) in the optical pickup 17.

  The control unit 11 controls the optical pickup 17 to irradiate the recording layer 101 with the light beam from the optical pickup 17 to the target position PG to which the recording light beam L1 of the optical information recording medium 100 is to be irradiated. It is designed to record information.

  Further, when reproducing information from the optical information recording medium 100, the control unit 11 supplies a read pulse signal that rises at an arbitrary interval to the optical pickup 17. As a result, the reading light beam L2 is emitted from the short pulse light source 20 in the optical pickup 17. The read pulse signal is generated at an interval corresponding to the recording interval of the recording mark RM.

  The optical pickup 17 receives the return light beam L3 returned from the optical information recording medium 100, and supplies a detection signal corresponding to the amount of received light of the return light beam L3 to the signal processing unit 13.

  The signal processing unit 13 generates a reproduction signal SRF indicating the amount of received light of the return light beam L3 based on the detection signal, and detects the recording interval of the recording mark RM. Further, the signal processing unit 13 generates reproduction data by performing predetermined binarization processing and demodulation processing on the reproduction signal SRF, and supplies the reproduction data to the control unit 11.

  As described above, the recording / reproducing apparatus 10 records information on the optical information recording medium 100 and reproduces information from the optical information recording medium 100.

  As shown in FIG. 4, the optical pickup 17 outputs a recording light beam L1 having a wavelength of, for example, 405 [nm] from the short pulse light source 20 based on the control of the control unit 11 during the information recording process. L1 is converted from divergent light into parallel light by the collimator lens 21 and then incident on the beam splitter 22.

  The beam splitter 22 has a reflection / transmission surface 22S that reflects or transmits the light beam at a predetermined ratio. When the recording light beam L1 is incident, the reflection / transmission surface 22S transmits the recording light beam L1 and makes the recording light beam L1 enter the objective lens. The objective lens 23 focuses the recording light beam L1 to focus on the target position PG in the optical information recording medium 100 to form a recording mark RM.

  Further, the optical pickup 17 causes the readout light beam L2 to be output in pulses from the short pulse light source 20 based on the control of the control unit 11 during the information reproduction process, and the target position in the optical information recording medium 100 is similar to the information recording process. It is designed to focus on PG.

  Here, when the recording mark RM is formed at the in-focus position of the reading light beam L2, the optical information recording medium 100 reflects the reading light beam L2 due to the difference in refractive index between the recording layer 101 and the recording mark RM. The return light beam L3 is generated. The optical information recording medium 100 allows the reading light beam L2 to pass through and hardly generates the return light beam L3 when the recording mark RM is not formed at the in-focus position of the reading light beam L2.

  The objective lens 23 converts the return light beam L3 from the optical information recording medium 100 into parallel light and makes it incident on the beam splitter 22. At this time, the beam splitter 22 reflects a part of the return light beam L3 by the reflection / transmission surface 22S and makes it incident on the condenser lens 24. The condensing lens 24 condenses the return light beam L3 and irradiates the light receiving element 25 with it.

  In response to this, the light receiving element 25 detects the light amount of the return light beam L3, generates a detection signal corresponding to the light amount, and sends it to the signal processing unit 13. As a result, the signal processing unit 13 can recognize the detection state of the return light beam L3 based on the detection signal.

  The optical pickup 17 moves the objective lens 23 in the thickness direction of the optical information recording medium 100 by an actuator (not shown), thereby focusing the recording light beam L1 and the reading light beam L2 at a desired depth (that is, in the thickness direction). Position).

  As described above, the recording / reproducing apparatus 10 performs information recording processing and information reproducing processing on the optical information recording medium 100.

  In the case where a reference layer (not shown) is formed in the optical information recording medium 100, the recording / reproducing apparatus 10 determines a position (that is, a target position PG) where a recording mark is to be recorded with reference to the reference layer. can do.

  In this case, the recording / reproducing apparatus 10 irradiates the reference layer with, for example, red laser light, and drives the objective lens 23 so that the red laser light is focused on the reference layer. The recording / reproducing apparatus 10 can focus the recording light beam L1 and the reading light beam L2 on the target position PG by separating the recording light beam L1 and the reading light beam L2 from the reference layer 104 by an arbitrary distance. it can.

[1-2. Configuration of short pulse light source]
[1-2-1. Configuration of short pulse light source]
As shown in FIG. 5, the short pulse light source 20 includes a laser control unit 31 and a semiconductor laser 34.

  The semiconductor laser 34 is a general semiconductor laser using semiconductor light emission (for example, SLD 3233 manufactured by Sony Corporation). The semiconductor laser 34 outputs a laser beam LL (that is, a recording light beam L1 or a reading light beam L2) in a pulsed manner under the control of the laser control unit 31.

  The laser control unit 31 includes a pulse generator 32 and an LD (Laser Diode) driver 33. As shown in FIG. 6A, the pulse generator 32 generates a pulse signal SL that discretely generates a pulsed generation signal pulse SLw and supplies the pulse signal SL to the LD driver 33. At this time, the pulse generator 32 controls the signal level of the generation signal pulse SLw in accordance with, for example, control of an external device.

  As shown in FIG. 6B, the LD driver 33 generates a laser drive voltage DJ that generates a drive voltage pulse DJw corresponding to the generation signal pulse SLw by amplifying the pulse signal SL at a predetermined amplification factor. And supplied to the semiconductor laser 34. At this time, the voltage value of the drive voltage pulse DJw is determined according to the signal level of the generation signal pulse SLw.

  The semiconductor laser 34 outputs a laser beam LL in a pulsed manner according to the laser driving voltage DJ.

  As described above, the short pulse light source 20 directly outputs the laser beam LL from the semiconductor laser 34 under the control of the laser control unit 31.

[1-2-2. Laser pulse output by relaxation oscillation mode]
The following equation shows a so-called rate equation representing the characteristics of the laser. Γ is the confinement factor, τ _ph is the photon lifetime, τ _s is the carrier lifetime, C _s is the spontaneous emission coupling coefficient, d is the active layer thickness, q is the elementary charge, g _max is the maximum gain, and N is the carrier density. , S is the photon density, J is the injected carrier density, c is the speed of light, N ₀ is the transparent carrier density, and _ng is the group refractive index.

7 and 8 show the relationship between the carrier density N, the injected carrier density J, and the photon density S derived from the equation (1). In FIGS. 3 and 4, Γ = 0.3, Ag = 3e- ¹⁶ [cm ² ], τ _ph = 1e ^-12 [s], τ _s = 1e ^-9 [s], C _s = 0.03 , D = 0.1 [μm], q = 1.6e ⁻¹⁹ [C].

  As shown in FIG. 8, a general semiconductor laser starts to emit light at a pre-saturation point Sl where the carrier density N is slightly before the saturation state as the injected carrier density J (that is, the laser driving voltage DJ) increases. To do. As shown in FIG. 7, the semiconductor laser increases the photon density S (that is, the emitted light intensity) as the injected carrier density J increases. Further, as shown in FIG. 9 corresponding to FIG. 7, it can be seen that the photon density S further increases as the injected carrier density J further increases.

  In FIGS. 10, 11 and 12, the photon density S is expressed with the time from the start of applying the laser drive voltage DJ (ie, injected carrier density J) at the points PT1, PT2 and PT3 shown in FIG. 9 as the horizontal axis. It is shown as a vertical axis.

  As shown in FIG. 10, at the point PT1, which represents the case where the largest laser drive voltage DJ is applied, the photon density S greatly oscillates due to relaxation oscillation, and its amplitude increases, and the amplitude period (that is, from the minimum value). It was confirmed that the vibration period ta that reaches the minimum value was as small as about 60 [ps]. As for the value of the photon density S, the amplitude of the first wave that appears immediately after the start of light emission is the largest, gradually attenuates to the second wave and the third wave, and eventually becomes stable.

The maximum value of the first wave in the photon density S at the point PT1 is about 3 × 10 ¹⁶ , which is about three times the stable value (about 1 × 10 ¹⁶ ) that is a value when the photon density S is stabilized.

  Here, from the rate equation shown in the equation (1), the light emission start time τd from the start of applying the laser drive voltage DJ to the start of light emission can be calculated. That is, if the photon density S = 0 before oscillation, the upper equation in equation (1) can be expressed as the following equation.

Here, if the carrier density N and threshold value N _th, may represent the emission start time τd as in the following equation.

  That is, it can be seen that the emission start time τd is inversely proportional to the injected carrier density J.

  At the point PT1 shown in FIG. 10, the light emission start time τd is calculated to be about 200 [ps] from the equation (3). At this point PT1, since the laser drive voltage DJ having a large voltage value is applied, the light emission start time τd is also shortened.

As shown in FIG. 11, at the point PT2 where the value of the laser drive voltage DJ applied is smaller than that at the point PT1, a clear relaxation vibration is generated, but the vibration amplitude is smaller than that at the point PT1, and the vibration The period ta has increased to about 100 [ps]. At the point PT2, the light emission start time τd is also about 400 [ps], which is longer than the point PT1. The maximum value of the first wave in the photon density S at the point PT2 was about 8 × 10 ¹⁵ , which was about twice the stable value (about 4 × 10 ¹⁵ ).

As shown in FIG. 12, at the point PT3 where the value of the laser drive voltage DJ supplied is smaller than the point PT2, there is almost no relaxation oscillation, and the light emission start time τd is relatively long as about 1 [ns]. Was confirmed. The maximum value of the photon density S at the point PT3 was almost the same as the stable value, and was about 1.2 × 10 ¹⁵ .

  In a general laser light source, by applying a relatively small laser drive voltage DJ that is a condition (voltage value) in which almost no relaxation oscillation is observed, such as point PT3, to the semiconductor laser, the output immediately after the start of the emission is intentionally made. The difference in incident light intensity is reduced, and the output of the laser beam LL is stabilized. Hereinafter, a mode in which the semiconductor laser 34 outputs the laser light LL with a low voltage that does not cause relaxation oscillation is referred to as a normal mode, and the laser light LL output in the normal mode is referred to as a normal output light LNp.

  However, in the short pulse light source 20 according to the present embodiment, the relaxation oscillation is generated like the points PT1 and PT2, thereby increasing the maximum value of the instantaneous emitted light intensity of the laser light beyond the stable value (for example, 1.5). More than twice). Further, since a large value can be selected as a voltage value for generating relaxation oscillation (hereinafter referred to as an oscillation voltage value α), a laser having a large emitted light intensity corresponding to the large oscillation voltage value α. The light can be emitted.

That is, by applying the laser drive voltage DJ having the oscillation voltage value α to the same semiconductor laser, it becomes possible to greatly increase the emitted light intensity of the laser light as compared with the conventional case. For example, at the point PT1, the photon density S due to the first wave of relaxation oscillation is about 3 × 10 ^16, which is compared with the point PT3 (about 1.2 × 10 ¹⁵ ) indicating the case where the conventional voltage value is applied, The emitted light intensity of the semiconductor laser 34 can be increased by 20 times or more.

  FIG. 13 shows the emitted light intensity measured when a relatively large laser driving voltage DJ is applied to a general semiconductor laser (SLD 3233VF, manufactured by Sony Corporation) in practice. From the figures, it was confirmed that the relaxation vibrations observed in the photon density S in FIGS. 10 and 11 appear as they are in the emitted light intensity, and that the same relaxation vibrations are actually generated as the emitted light intensity. FIG. 13 shows the waveform of the laser beam LL obtained when the laser drive voltage DJ is supplied to the semiconductor laser in a rectangular pulse shape. Hereinafter, the portion of the laser drive voltage DJ that is supplied in a pulse form is referred to as a drive voltage pulse DJw.

  FIG. 14A corresponds to FIG. For example, as shown in FIG. 14B, the laser control unit 31 of the short pulse light source 20 applies a laser drive voltage DJ having an oscillation voltage value α1 sufficient to cause relaxation oscillation to the semiconductor laser 34 as a drive voltage. Supply as pulse DJw. At this time, the laser control unit 31 uses the rectangular pulse over the time (hereinafter referred to as current wave supply time β) obtained by adding the light emission start time τd and the vibration period ta (τd + ta) as the drive voltage pulse DJw. A laser drive voltage DJ is applied.

  Thereby, as shown in FIG. 14C, the laser control unit 31 causes the semiconductor laser 34 to emit only the first wave due to relaxation oscillation, and causes the semiconductor laser 34 to emit a pulsed laser beam LL ( Hereinafter, this is referred to as vibration output light LMp).

  Further, the laser control unit 31 can reduce the time for applying the laser drive voltage DJ having a large voltage value by supplying the pulsed drive voltage pulse DJw, which is caused by overheating of the semiconductor laser 34 or the like. The trouble of the semiconductor laser 34 is suppressed.

  On the other hand, as shown in FIG. 14D, the laser control unit 31 supplies the semiconductor laser 34 with a drive voltage pulse DJw having an oscillation voltage value α2 that is sufficient to cause relaxation oscillation and is smaller than the oscillation voltage value α1. By doing so, it is possible to cause the semiconductor laser 34 to emit the vibration output light LMp having a relatively low emission light intensity. Hereinafter, the mode in which the semiconductor laser 34 generates relaxation oscillation and pulses the laser beam LL is referred to as relaxation oscillation mode, and is distinguished from the normal mode in which relaxation oscillation does not occur.

  As described above, the short pulse light source 20 can output the laser beam LL in the vibration relaxation mode by controlling the voltage value of the drive voltage pulse DJw so as to cause relaxation oscillation in the laser beam LL.

[1-2-3. Pulse output of laser light by singular mode]
The inventors of the present application supply the semiconductor laser 34 with a drive voltage pulse DJw having a singular voltage value β larger than the vibration voltage value α that causes relaxation oscillation in the laser light LL, thereby generating vibration output light from the semiconductor laser 34. It has been found that the laser beam LL having a greater intensity of emitted light than LMp can be output in pulses.

  Next, the result of an experiment in which the change in the laser beam LL is measured when the voltage value of the drive voltage pulse DJw is changed will be described.

  FIG. 15 shows the configuration of a light measurement device 41 that analyzes the laser light LL emitted from the short pulse light source 20.

  In the short pulse light source 20 in the light measuring device 41, the laser light LL emitted from the semiconductor laser 34 was supplied to the collimator lens 42.

  The laser light LL was converted from divergent light into parallel light by the collimator lens 42 and entered the condenser lens 45. After the laser beam LL is collected by the condenser lens 45, it is measured and analyzed by an optical sample oscilloscope 46 (C8188-01, manufactured by Hamamatsu Photonics Co., Ltd.) and an optical spectrum analyzer 47 (manufactured by ADC Co., Ltd., Q8341). It was done.

  A power meter 44 (manufactured by ADC Co., Ltd., Q8230) was installed between the collimator lens 42 and the condenser lens 45, and the emitted light intensity of the laser light LL was measured.

  As shown in FIG. 17, when a rectangular set pulse SLs having a pulse width Ws of 1.5 [ns] is set for the pulse generator 32, the pulse signal actually output from the pulse generator 32. The waveform of SL is shown in FIG. In this pulse signal SL, a signal pulse half-value width SLhalf which is a half-value width of a pulse that appears corresponding to the set pulse SLs (hereinafter referred to as a generation signal pulse SLw) was about 1.5 [ns]. .

  FIG. 17C shows the waveform of the laser drive voltage DJ actually output from the LD driver 33 when the pulse signal SL shown in FIG. In this laser drive voltage DJ, a voltage pulse half-value width Half, which is a half-value width of a pulse that appears in correspondence with the generation signal pulse SLw (that is, the drive voltage pulse DJw), is about 1.V according to the signal level of the generation signal pulse SLw. It changed in the range of 5 [ns] to about 1.7 [ns].

  At this time, the relationship between the signal level (maximum voltage value) of the generated signal pulse signal SLw and the voltage pulse half-value width Half in the drive voltage pulse DJw, and the signal level of the generated signal pulse signal SLw and the maximum voltage value Vmax in the drive voltage pulse DJw. FIG. 16 shows the relationship.

  As can be seen from FIG. 16, as the voltage value of the generation signal pulse SLw input to the LD driver 33 increases, the maximum voltage value Vmax of the drive voltage pulse DJw output from the LD driver 33 also increases. It can also be seen that the voltage pulse half-value width Half of the drive voltage pulse DJw gradually increases as the voltage value of the pulse signal SL increases.

  In other words, even when the setting pulse SLs having the same pulse width is set in the pulse generator 32, the maximum voltage value of the generation signal pulse SLw supplied to the LD driver 33 changes, so that the LD driver It can be seen that the pulse width and the voltage value of the drive voltage pulse DJw output from 33 change.

  FIGS. 18A and 18B show the results of measuring the laser beam LL output according to such a drive voltage pulse DJw with the optical sample oscilloscope 46. In FIG. 18, the horizontal axis indicating time is a relative value, and each waveform is shifted to make it easy to see the shape of the waveform.

  As shown in FIG. 18A, when the maximum voltage value Vmax of the drive voltage pulse DJw is 8.8 [V], the waveform LT1 of the laser beam LL has a relatively wide small output peak (time 1550 [ps]). Only one neighborhood) was confirmed, and no vibration due to relaxation vibration was observed. That is, this waveform LT1 indicates that the short pulse light source 20 outputs the normal output light LNp in the normal mode.

  As shown in FIG. 18A, when the maximum voltage value Vmax of the drive voltage pulse DJw is 13.2 [V], a plurality of peaks due to relaxation oscillation were confirmed in the waveform LT2 of the laser beam LL. That is, this waveform LT2 indicates that the short pulse light source 20 outputs the vibration output light LMp in the relaxation vibration mode.

  As shown in FIG. 18B, when the maximum voltage value Vmax of the drive voltage pulse DJw is 17.8 [V], 22.0 [V], 26.0 [V], and 29.2 [V], In the waveforms LT3, LT4, LT5, and LT6 of the laser beam LL, a peak that is the leading portion in the time axis direction and a slope portion that gently attenuates with fine vibration were confirmed.

  The waveforms LT3, LT4, LT5, and LT6 of the laser beam LL have no large peak after the first peak, and the waveform LT2 in the relaxation oscillation mode has the second wave and the third wave after the first wave (FIG. 18). (A)) is clearly different in shape.

  Since the resolution of the optical sample oscilloscope 46 used for the measurement is about 30 [ps] or more, it is not shown in each figure, but the peak width (half-value width) of the first peak is shown by an experiment using a streak camera. ) Was confirmed to be about 10 [ps]. Along with this, the maximum emitted light intensity of the leading peak also appears lower than actual.

  Here, the laser light LL when the maximum voltage value Vmax of the drive voltage pulse DJw is changed will be further analyzed.

  Similarly, the results of measurement by the optical spectrum analyzer 17 of the emitted light intensity of the laser light LL obtained when the maximum voltage value Vmax of the drive voltage pulse DJw is changed are shown in FIGS. Note that FIGS. 19A to 23A show results obtained by decomposing the laser beam LL for each wavelength, and FIGS. 19B to 23B show the laser beam LL as in FIG. The result of decomposition in the time axis direction is shown.

  As shown in FIG. 19B, when the maximum voltage value Vmax of the drive voltage pulse DJw is 8.8 [V], only one peak is seen in the waveform LT11 of the laser beam LL. It can be said that the laser beam LL is the normal output light LNp in the normal mode. Further, as shown in FIG. 19A, in the spectrum ST11, only one peak was confirmed at about 404 [nm]. From this, it can be seen that the waveform LT11 shown in FIG. 19B is based on the laser light LL having a wavelength of about 404 [nm].

  As shown in FIG. 20B, when the maximum voltage value Vmax of the drive voltage pulse DJw is 13.2 [V], a plurality of large peaks are seen in the waveform LT12 of the laser beam LL. It can be said that the vibration output light LMp is in the relaxation vibration mode. As shown in FIG. 20A, in the spectrum ST12, two peaks were confirmed at about 404 [nm] and about 407 [nm]. From this, it can be seen that the waveform LT2 shown in FIG. 20B is based on the laser light LL having wavelengths of about 404 [nm] and about 407 [nm].

  As shown in FIG. 21B, when the maximum voltage value Vmax of the drive voltage pulse DJw is 15.6 [V], the peak LT and the gently decaying slope portion are seen in the waveform LT13 of the laser beam LL. It was. At this time, as shown in FIG. 21A, in the spectrum ST13, two peaks were confirmed at about 404 [nm] and about 408 [nm]. In the spectrum ST13, the peak of about 406 [nm] confirmed in the relaxation oscillation mode moves 2 [nm] to the long wavelength side. Further, it was confirmed that the vicinity of 398 [nm] was slightly raised.

  As shown in FIG. 22B, when the maximum voltage value Vmax of the drive voltage pulse DJw is 17.8 [V], the waveform LT14 of the laser beam LL has a peak at the head and a slope portion that gently attenuates. It was. As shown in FIG. 22A, in the spectrum ST14, two large peaks were confirmed at about 398 [nm] and about 403 [nm]. In the spectrum ST14, the peak at about 408 [nm] was very small compared to the spectrum ST13 (FIG. 21B), and instead a large peak at about 398 [nm] was confirmed.

  As shown in FIG. 19B, when the maximum voltage value Vmax of the drive voltage pulse DJw is 38.4 [V], the peak LT of the head portion and the slowly decaying slope portion are clear in the waveform LT15 of the laser beam LL. It was seen in. Further, as shown in FIG. 19A, in the spectrum ST15, two peaks were confirmed at about 398 [nm] and about 404 [nm]. In the spectrum ST15, when compared with the spectrum ST14 (FIG. 18B), the peak of about 408 [nm] disappeared completely, and a clear peak was confirmed at about 398 [nm].

  For these reasons, in the short pulse light source 20, the drive voltage pulse DJw having the singular voltage value β (that is, the maximum voltage value Vmax) larger than the vibration voltage value α is supplied to the semiconductor laser 34, and thus the vibration output light LMp and Was confirmed to output laser beams LL having different waveforms and wavelengths. Also, the light emission start time τd did not agree with the equation (3) derived from the rate equation described above.

  Here, attention is focused on the wavelength of the laser beam LL. As the maximum voltage value Vmax increases, the laser light LL changes to the normal output light LNp (FIG. 19) and the vibration output light LMp (FIG. 20), and further changes the wavelength from the vibration output light LMp.

  Specifically, as illustrated in FIG. 20, the vibration output light LMp has the normal output light in addition to the peak of substantially the same wavelength as the normal output light LNp (within the wavelength of the normal output light LNp ± 2 [nm]). It has a peak on the long wavelength side of about 3 [nm] (within 3 ± 2 [nm]) from LNp.

  On the other hand, the laser beam LL shown in FIG. 23 is more than the normal output light LNp in addition to the peak of the same wavelength as the normal output light LNp ((within the wavelength of the normal output light LNp ± 2 [nm])). About 6 [nm] (within 6 ± 2 [nm]) has a peak on the short wavelength side.Hereinafter, this laser light LL is referred to as a specific output light LAp, and the mode of the semiconductor laser 34 that outputs the specific output light LAp is This is called singular mode.

  Here, when comparing the laser beam LL with the maximum voltage value Vmax of 15.6 [V] (FIG. 21A) and the laser beam LL with 17.8 [V] (FIG. 22A), the longer wavelength side This peak disappears, and a short wavelength peak appears instead. That is, in the process in which the laser light LL changes from the vibration output light LMp to the singular output light LAp as the maximum voltage value Vmax increases, the peak on the long wavelength side gradually attenuates, and instead the peak on the short wavelength side increases. I can say.

  In addition, since the specific slope ASP is confirmed over a long time compared to the specific peak APK, the light energy of the specific slope ASP (near wavelength 404 [nm]) is the specific peak APK (near wavelength 398 [nm]). It was confirmed that it was much larger than the light energy of (FIG. 23A).

  Hereinafter, the laser light LL in which the peak area on the short wavelength side is equal to or larger than the peak area on the long wavelength side is referred to as the specific output light LAp, and the laser light LL in which the peak area on the short wavelength side is less than the peak area on the long wavelength side is oscillated. The output light is LMp. When two peaks overlap as shown in FIG. 22, the wavelength of the normal output light LNp and the wavelength on the short side of 6 [nm] from the normal output light LNp are set as the center wavelengths of the respective peaks, and the center wavelength. Let the area in the range of ± 3 [nm] be the area of the peak.

  Therefore, the laser light LL (FIG. 21) having the maximum voltage value Vmax of 15.6 [V] becomes the vibration output light LMp, and the laser light LL (FIG. 22) having the maximum voltage value Vmax of 17.8 [V] is a singular output. It becomes light LAp.

  Based on the above, the laser light LL in the singular mode will be summarized.

  The semiconductor laser 34 transitions to a singular mode when a laser drive voltage DJ of β having a singular voltage value larger than the voltage value causing relaxation oscillation is applied, and as shown in FIG. A singular output light LAp composed of a peak APK and a slope ASP that subsequently appears is emitted.

  The wavelength of the specific peak APK is shifted to the shorter wavelength side by about 6 [nm] than the wavelength of the laser light LL in the normal mode. In other experiments, similar results are obtained even when semiconductor lasers having different wavelengths of the laser light LL in the normal mode are used.

  As a result of measurement with the power meter 44 (SLD 3233 manufactured by Sony Corporation as the semiconductor laser 34), the emitted light intensity of this singular peak APK is about 12 [W], and the maximum emitted light of the laser light LL in the relaxation oscillation mode. It was confirmed that it was very large compared to the strength (about 1 to 2 [W]). Since the resolution of the optical sample oscilloscope 46 is low, the intensity of the emitted light is not shown in the drawing.

  As a result of analysis by a streak camera (not shown), the singular peak APK has a peak width of about 10 [ps], which is smaller than the peak width (about 30 [ps]) in the relaxation oscillation mode. Was confirmed. The peak width is not shown in the drawing because the resolution of the optical sample oscilloscope 46 is low.

  The wavelength of the specific slope ASP is the same as the wavelength of the laser beam LL in the normal mode, and the maximum emitted light intensity is about 1 to 2 [W]. Furthermore, the specific slope ASP was confirmed to have a total light energy larger than the specific peak APK.

  In practice, the laser control unit 31 of the short pulse light source 20 applies a laser drive voltage DJ having a singular voltage value β higher than the oscillation voltage value α to the semiconductor laser 34 as a drive voltage pulse DJw.

  Thereby, as shown in FIG. 22, the laser control unit 31 causes the semiconductor laser 34 to transition to the singular mode, and emits the singular output light LAp having a very large singular peak APK from the semiconductor laser 34 as the laser light LL. Can be made.

  As described above, the short pulse light source 20 controls the pulse generator 4 to apply the drive voltage pulse DJw having a voltage value sufficient to cause the semiconductor laser 34 to transition to the singular mode. The optical LAp can be output.

  That is, the recording / reproducing apparatus 10 can form the recording mark RM using two-photon absorption due to a large light intensity, for example, by emitting the specific output light LAp as the recording light beam L1 (details will be described later).

  Further, the recording / reproducing apparatus 10 can generate the return light beam L3 with an appropriate light amount by emitting the vibration output light LMp or the normal output light LMp as the read light beam L2, for example, and improve the quality of the reproduction signal SRF. It is made like that.

[1-3. Configuration of optical information recording medium]
As shown in FIGS. 25A and 25B, the optical information recording medium 100 functions as a medium for recording information as a whole by forming the recording layer 101 between the substrates 102 and 103. ing.

  Substrates 102 and 103 are made of glass, and transmit light at a high rate. The substrates 102 and 103 are configured in a disk shape having a circular hole at the center where the diameter dx is about 120 [mm] and the thicknesses t2 and t3 are, for example, 0.6 [mm]. The substrates 102 and 103 may be formed in various shapes such as a square plate shape or a rectangular plate shape. Moreover, there is no restriction | limiting in the size of the board | substrates 102 and 103, Furthermore, it does not necessarily need to have a hole in the center.

A multilayer inorganic layer (for example, Nb ₂ O ₂ ) that is not reflected by a light beam having a wavelength of 405 [nm], for example, on the outer surfaces of the substrates 102 and 103 (surface that does not contact the recording layer 101). (4 layers of / SiO ₂ / Nb ₂ O ₅ / SiO ₂ ) AR (AntiReflection coating) treatment is performed.

  Further, as the substrates 102 and 103, ultraviolet light having a wavelength of less than 400 [nm] may be blocked by selecting a material or performing a surface treatment. Thereby, the substrates 102 and 103 can prevent the ultraviolet light from being exposed to the recording layer 101, and can improve the durability of the recording layer 101.

  The substrates 102 and 103 are not limited to glass plates, and various optical materials such as acrylic resin and polycarbonate resin can be used. For example, by using a polycarbonate resin as the substrates 102 and 103, a function of blocking ultraviolet light can be added to the substrates 102 and 103. The thicknesses t2 and t3 of the substrates 102 and 103 are not limited to the above, and can be appropriately selected from a range of 0.01 [mm] to 1.2 [mm]. The thicknesses t2 and t3 may be the same or different. In addition, the AR treatment is not necessarily performed on the outer surfaces of the substrates 102 and 103.

  The recording layer 101 has a diameter φ equal to or slightly smaller than that of the substrates 102 and 103, and its thickness t1 (= 0.01 [mm] to 0.5 [mm]) is sufficiently larger than the height of the recording mark RM. Designed to be For this reason, the recording layer 101 forms a plurality of recording marks not only in the surface direction of the optical information recording medium 100 but also in the thickness direction, and the recording marks are arranged three-dimensionally.

  A reference layer (not shown) that reflects at least a part of the recording light beam L1 may be provided at the interface between the recording layer 101 and the substrate 102 or 103. In this case, servo guide grooves or pits may be formed in the reflective layer. For example, by forming a spiral track with lands and grooves similar to a general BD-R (Recordable) disc or the like, the target position PG where a recording mark should be recorded can be determined with reference to the track. It becomes possible.

  The recording layer 101 is formed by dispersing a two-photon absorption material that absorbs a two-photon light beam into a binder resin as a main component.

  As the binder resin, various resin materials having high transmittance with respect to the light beam can be used. For example, a thermoplastic resin that is softened by heat, a photocurable resin that is cured by a crosslinking or polymerization reaction by light, a thermosetting resin that is cured by a crosslinking or polymerization reaction by heat, and the like can be used.

  The resin material is not particularly limited, but PMMA (Polymethylmethacrylate) resin, acrylic resin, polycarbonate resin, norbornene resin, nitrocellulose and the like are preferably used from the viewpoints of weather resistance and light transmittance.

  Further, as a binder resin, a resin material that does not transmit an ultraviolet light beam having a wavelength of less than 400 [nm] or an ultraviolet absorbing material that absorbs ultraviolet rays may be added to the resin material because of weather resistance. Furthermore, various additives can be added to the binder resin from the viewpoints of recording characteristics, manufacturing characteristics, strength characteristics, and the like.

  As the two-photon absorption material, it is preferable to use a material having a property of generating heat by generating two-photon absorption with respect to a light beam having a wavelength of 400 nm or more and less than 600 nm. Further, as the two-photon absorption material, a material that causes two-photon absorption with respect to a blue-violet light beam of 400 nm or more and less than 500 nm is preferable. The foaming due to the two-photon absorption refers to a reaction caused by thermal decomposition, that is, one that occurs in the heat mode.

  Further, the two-photon absorbing material is preferably a material that generates heat by absorbing one photon due to a change in the state of the two-photon absorbing material generated as a result of the two-photon absorption. In particular, the two-photon absorbing material is preferably a material that generates two-photon absorption with respect to a specific peak APK having a high light intensity and can generate heat by absorbing a specific slope ASP having a large total light energy.

  The state change due to the two-photon absorption may be a chemical change or a structural change, and is particularly preferably a structural change caused by transition from the ground state to the excited state according to the two-photon absorption. This excited state is preferably at least a triplet state. This is because the lowest triplet state is a spin-forbidden state and thus has a long lifetime, and the two-photon absorption material in the lowest triplet state can sufficiently absorb the specific slope ASP irradiated for a relatively long time. .

  The form of change from the ground state to the lowest triplet state is not particularly limited, and the transition from the ground state to the lowest triplet state may be made directly. As shown in FIG. A transition to the lowest triplet state may be made via the singlet state.

  The two-photon absorption material is preferably a metal complex formed by coordination of one or more molecules to a metal. This is because, in such a metal complex, after changing from a ground state to a singlet excited state by two-photon absorption, a crossing between terms can be rapidly caused by a heavy atom effect of a metal atom to make a transition to a minimum triplet state.

  Although it does not restrict | limit especially as a metal, It is preferable that they are transition metals, such as iridium, osnium, ruthenium, gold | metal | money, platinum. This is because a complex can be easily formed.

  Although it does not restrict | limit especially as a molecule | numerator coordinated to this metal, It is preferable to contain tetracyanoethylene. Tetracyanoethylene has a relatively small energy difference between the π orbit and π * orbital (see Non-Patent Document 2), makes it easy to transition to the lowest triplet state, and keeps the lowest triplet state for a long time. It is because it can be kept over.

In addition to tetracyanoethylene, the molecule that coordinates to the metal contains various electron donating groups or electron withdrawing groups such as Cl, NCS, CO, Br, NCO, Ph ₃ P, and Ph ₃ As. Also good. These electron donating groups or electron withdrawing groups affect the π-electron cloud centered on tetracyanoethylene, can affect the probability of occurrence of two-photon absorption, and can improve the probability of two-photon absorption. . The point is that the two-photon absorption material (that is, the metal complex) as a whole may have a structure that sufficiently generates two-photon absorption.

The two-photon absorption material is particularly preferably an iridium complex shown below. This is because tetracyanoethylene and Ph ₃ P can form a π electron cloud in the iridium complex and exhibit two-photon absorption characteristics. Ph is a phenyl group, TCNE is tetracyanoethylene, and X is a general formula.
IrClX (Ph ₃ P) ₂ TCNE (1)

As shown in the chemical formula (2), chemical formula (3) and chemical formula (4), the general formula X is particularly preferably Cl, NCS, or NCO. This is because the overall π-electron cloud balance of the iridium complex can be adjusted to exhibit good two-photon absorption characteristics. Hereinafter, the compounds represented by the formula (2), the formula (3), and the formula (4) are referred to as a compound 1, a compound 2, and a compound 3, respectively.
IrCl (CO) (Ph ₃ P) ₂ TCNE (2)
IrNCS (CO) (Ph ₃ P) ₂ TCNE (3)
IrNCO (CO) (Ph ₃ P) ₂ TCNE (4)

  The content ratio of the two-photon absorbing material is not particularly limited, but in order to sufficiently absorb the recording light beam L1 and reliably form a recording mark, the weight ratio is 0.001 [%] with respect to the binder resin. It is preferable that it is 0.05 [%] or more. The content ratio of the two-photon absorption material is preferably less than 20.0 [%], more preferably less than 10.0 [%] in order to prevent adverse effects such as a decrease in transmittance.

  The recording layer 101 is preferably formed with a recording mark RM by foaming according to heat generation. This foaming may be caused by vaporization due to thermal decomposition or evaporation of the two-photon absorption material, and may be caused by thermal decomposition or evaporation of a mixed component such as a binder resin or various additives added to the binder resin. May be generated. The recording layer 101 may contain a vaporizing material that vaporizes in response to heat.

  Next, a method for manufacturing the optical information recording medium 100 will be described.

  For example, when a thermoplastic resin is used as the binder resin, the two-photon absorbing material is added to the heated thermoplastic resin, and the two-photon absorbing material is dispersed in the binder resin by kneading with a kneader.

  Then, after the binder resin in which the two-photon absorption material is dispersed is spread on the substrate 103 and cooled to produce the recording layer 101, for example, a UV adhesive or a PSA (Pressure Sensitive Adhesive) sheet is used. Thus, the optical information recording medium 100 can be manufactured by bonding the substrate 102 to the recording layer 101.

  When the thermoplastic resin is diluted with an organic solvent or the like (hereinafter, this thermoplastic resin is called a solvent-diluted resin and is distinguished from a thermoplastic resin that is molded by heating), the two-photon absorption material is preliminarily used as the organic solvent. After the dispersion, the solvent-diluted resin is dissolved in the organic solvent, or the two-photon absorbing material is added to the solvent-diluted resin diluted with the organic solvent and stirred to disperse the two-photon absorbing material in the binder resin.

  Then, after the binder resin in which the two-photon absorption material is dispersed is spread on the substrate 103 and heated and dried, the recording layer 101 is produced, and then the substrate 102 is adhered to the recording layer 101 using, for example, a UV adhesive. The optical information recording medium 100 can be manufactured.

  Further, when a thermosetting resin or a photocurable resin is used as the binder resin, the two-photon absorbing material is dispersed in the binder resin by adding the two-photon absorbing material to the uncured resin material and stirring.

  Then, the binder resin in which the two-photon absorption material is dispersed is spread on the substrate 103, and the optical information recording medium 100 is subjected to photocuring or thermosetting with the substrate 103 placed on the uncured recording layer 101. Can be produced.

  Further, the two-photon absorption material may be bonded to the binder resin. In this case, after the two-photon absorption material is dispersed in the binder resin, it is bonded to the binder resin by heating or the like. The functional group of the two-photon absorption material may be directly bonded to the binder resin, or may be indirectly bonded to the binder resin using a coupling agent or the like.

[1-4. Example]
In Examples, Compound 1 to Compound 3 were actually synthesized and the optical information recording medium 100 was produced using them.

First, compounds 1 to 3 were prepared according to the method described in Non-Patent Document 2.
Journal of the American Chemical society Vol. 90 No. 14 Page 3705Year 1986

A commercially available tetracyanoethylene was used. IrCl (CO) (Ph ₃ P) ₂ was prepared according to the methods described in Non-Patent Document 3 and Non-Patent Document 4.
PB Chock and J. Halpern, J. Am. Chem. Soc., 88, 3511 (1966) JP Collman, FD Vastine, and WRRoper, ibid., 88, 5053

IrNCS (CO) (Ph ₃ P) ₂ and IrNCO (CO) (Ph ₃ P) ₂ were prepared from IrCl (CO) (Ph ₃ P) ₂ by a metathetical process. That is, by reacting IrCl (CO) (Ph ₃ P) ₂ with 10-fold amount of NaSCN at a molar ratio in an acetone solution at 50 ° C. for 30 minutes, IrNCS (CO) (Ph ₃ P) ₂ , IrNCO ( CO) (Ph ₃ P) ₂ was obtained.

Under normal temperature, a monovalent iridium complex (IrX (CO) (Ph ₃ P) ₂ ; X = Cl, NCS, CO) was dissolved or suspended in a small amount of benzene. When the solubility was poor, the solution was heated to a temperature slightly higher than room temperature (50 to 70 [° C.]).

  Compound 1 to Compound 3 were obtained by adding an equivalent amount of solid tetracyanoethylene to the iridium complex and stirring and reacting with a magnetic stirrer.

  Next, Samples S1 to S3 as the optical information recording medium 100 were produced using the compounds 1 to 3. For convenience, the production of the sample S1 will be described, and the description of the sample S2 and the sample S3 produced in the same manner will be omitted.

  0.104 [g] Compound 1, 5.18 [g] polycarbonate (molecular weight of about 36000) was dissolved in chloroform 350 [ml] and stirred to obtain a uniform adjustment solution.

  Chloroform is put into a cylindrical container having a flat bottom having a diameter of 13 [cm], and the adjustment solution is added so that the solid content concentration of Compound 1 and polycarbonate is 0.02 [%] by weight, and 0.02 [% The solution was prepared. Further, a polycarbonate (molecular weight of about 36000) is added to and dissolved in a 0.02 [%] solution so that the solid content concentration of Compound 1 and the polycarbonate is 1 [%] by weight, and the 1 [%] solution is dissolved. Adjusted. That is, of the solid content weight of this 1 [%] solution, 0.394 [%] is compound 1, and the remaining 99.60 [%] is polycarbonate.

  This 1% solution was dried in a cylindrical container as it was, then taken out from the cylindrical container and further dried with hot air of about 160 [° C.]. As a result, a film having a diameter of 13 [cm] and a thickness of about 330 [μm] was obtained. From this film, a disc-like film having a diameter of about 11.8 [cm] having a hole having a diameter of about 4 [cm] at the center (that is, the recording layer 101) was cut out.

  This disk-like film was bonded to a polycarbonate plate (that is, the substrate 103) having a diameter of 12 [cm] and a thickness of 0.8 [mm] and a diameter of 15 [mm] at a central hole using a 15 [μm] PSA sheet. . Further, the same PSA sheet was used on the opposite side of the disk-shaped film and bonded to a polycarbonate sheet (that is, the substrate 102) having a thickness of 40 [μm], thereby producing a sample S1 as the optical information recording medium 100.

  A spiral guide groove for guiding the recording light beam L1 is formed on the polycarbonate sheet in advance, and a laser beam of 650 [nm] is reflected on the adhesive surface side (recording layer 101 side), so that 405 [nm]. A dielectric layer (that is, a reference layer) that transmits a laser beam of This dielectric layer is composed of silicon nitride (80 [nm]), silicon oxide (110 [nm]), silicon nitride (80 [nm]), silicon oxide (110 [nm]), silicon nitride (80 [nm]). 5 layer structure.

  Then, by applying a laser drive voltage DJ having a drive voltage pulse DJw of 20 [V] to the semiconductor laser 34 of the recording / reproducing apparatus 10, a recording light beam L1 having a wavelength of 405 [nm] is emitted from the semiconductor laser 34. . The recording / reproducing apparatus 10 condenses this with an objective lens 23 having NA (Numerical Aperture) = 0.85, and irradiates the recording layer 101 in the samples S1 to S3.

  The recording / reproducing apparatus 10 continuously applies the reading light beam L2 (normal output light LNp) having an optical power of 1.0 [mW] through the objective lens 23 having the same wavelength and the same numerical aperture NA as the recording light beam L1. Irradiated. At this time, the light receiving element 25 was able to detect the return light beam L3 having a sufficiently detectable light amount from the position irradiated with the recording light beam L1 from any of the samples S1 to S3.

  That is, in the samples S1 to S3, it was confirmed that the recording mark RM can be formed by the recording light beam L1 (that is, the specific output light LAp) emitted from the short pulse light source 20.

  In Samples S1 to S3, it was confirmed that the recording mark RM can be similarly formed by the recording light beam L1 even when the target position PG is changed in the thickness direction of the recording layer 101.

  As described above, the samples S1 to S3 containing the compounds 1 to 3 represented by the formula (1) as the two-photon absorption material are recorded at arbitrary positions on the recording layer 101 by the pulsed recording light beam L1. It was confirmed that the mark RM can be formed.

[1-5. Operation and effect]
In the above configuration, the recording layer 101 of the optical information recording medium 100 is a metal complex in which one or more molecules are coordinated with a metal atom, and two-photons corresponding to irradiation of recording light for information recording It contains a two-photon absorption material that absorbs one photon of recording light by a change in state due to absorption.

  As a result, the recording layer 101 transitions from the ground state to the excited singlet state by two-photon absorption due to the two-photon absorption, and then quickly transitions to the lowest triplet state due to the heavy atom effect of the metal atom to emit the recording light. Absorbs one photon. Since the lifetime of the minimum triplet state is long, the two-photon absorption material can absorb recording light for one photon over a long period of time and generate sufficient heat, and can form a recording mark RM.

  The two-photon absorption material contains tetracyanoethylene. Here, tetracyanoethylene has a structure in which the absorption cross-section of two-photon absorption is large and two-photon absorption is likely to occur. Therefore, a metal complex in which tetracyanoethylene is coordinated to a metal atom can generate two-photon absorption with a sufficient probability.

  Moreover, it was confirmed that the recording layer 101 can form the recording mark RM using the general semiconductor laser 34 by containing the compounds 1 to 3 represented by the chemical formula (1).

  Further, the recording layer 101 is irradiated with the pulse-like specific peak APK and the specific peak APK, and forms a recording mark RM according to the specific slope ASP having a smaller emission light intensity than the specific peak APK.

  Here, the conventional laser light source used for the two-photon absorption increases the light intensity by adjusting the laser light in pulses using various optical components, and is very expensive in terms of configuration. In the present invention, a picosecond level laser beam (single output beam LAp) can be directly pulsed from the semiconductor laser 34 in the singular mode. Here, the singular output light LAp has a feature that it consists of a singular peak APK having a high light intensity and a singular slope ASP.

  In the present invention, paying attention to this feature, a recording mark RM can be formed using a general semiconductor laser 34 by generating heat by supplementing the energy shortage at the specific peak APK with the energy of the specific slope ASP. .

  Further, the two-photon absorption material does not absorb the recording light beam L1 in a region other than the vicinity of the focal point of the recording light beam L1 because the one-photon absorption occurs only at the portion where the two-photon absorption occurs and the state change occurs. Therefore, the recording layer 101 can reach the focal point with almost no decrease in the intensity of the recording light beam L1, as in the case of using a normal two-photon absorption material.

  In addition, the recording layer 101 contains a two-photon absorption material that changes its state by absorbing the specific peak APK by two photons and generates heat by absorbing the specific slope ASP by one photon. As a result, the recording layer 101 can convert the energy of the singular slope ASP having a large total energy into heat, and can efficiently form the recording mark RM.

  Further, the recording layer 101 transitions to the excited singlet state by two-photon absorption with respect to the recording light beam L1 as the recording light for information recording, and then transitions to the lowest triplet state. 2 contains a two-photon absorption material that absorbs the recording light beam L1 by one photon.

  As a result, the recording layer 101 can absorb one photon of the recording light in a minimum triplet state with a long lifetime (on the order of microseconds), so that the recording mark RM can be formed with sufficient heat generation.

  Further, the two-photon absorption material is any one of the chemical formula (2), the chemical formula (3), and the chemical formula (4), so that a recording light beam of 405 [nm] having a short wavelength of less than 600 [nm]. L1 can be absorbed by two photons.

  According to the above configuration, the recording layer 101 of the optical information recording medium 100 generates two-photon absorption in response to the recording light beam L1 having a short wavelength. As a result, the recording layer 101 can concentrate the energy of the recording light beam L1 to a small focal point, and the recording light beam necessary for two-photon absorption compared to the two-photon absorption of the light beam having a long wavelength. The light intensity of L1 can be reduced.

  Further, the recording layer 101 can generate heat in accordance with the recording light beam L1 having a relatively low light intensity by absorbing the recording light beam L1 by one photon according to the state change and generating heat. As a result, the recording layer 101 can reduce the two-photon absorption amount necessary for forming the recording mark RM as compared with the conventional method of forming the recording mark RM by simple two-photon absorption.

  As a result, the intensity of the emitted light of the recording light beam L1 necessary for forming the recording mark RM can be reduced, and the optical information recording medium capable of forming the recording mark RM using a general semiconductor laser 34 Can be realized.

<2. Other embodiments>
In the above-described embodiment, the case where the specific output light LNp is emitted from the semiconductor laser 34 as the recording light beam L1 has been described. The present invention is not limited to this, and various lasers such as a picosecond laser that outputs a pulse of laser light may be combined with a normal semiconductor laser, and two laser lights may be irradiated continuously or simultaneously.

  In the above-described embodiment, the case where the two-photon absorption material is made of a metal complex has been described. The present invention is not limited to this, and there is no limitation on the structure as long as it is a material that absorbs the recording light beam L1 by a state change caused by two-photon absorption.

  Furthermore, in the above-described embodiment, the case where the two-photon absorption material is dispersed or bonded to the binder resin has been described. However, the present invention is not limited to this, and for example, the two-photon absorption material is dispersed in an inorganic material such as glass. Anyway.

  Furthermore, in the above-described embodiment, the case where various resin materials are used as the binder resin has been described. However, the present invention is not limited to this, and for example, various additives and, for example, cyanine-based and coumarin-based materials may be used. Further, a sensitizer such as a quinoline dye or a benzophenone derivative may be added.

  Further, in the above-described embodiment, the case where two-photon absorption is generated with respect to the recording light beam L1 having the wavelength of 405 [nm] has been described, but the present invention is not limited to this, and is less than 600 [nm]. It is only necessary to generate two-photon absorption with respect to a short wavelength light beam.

  Further, in the above-described embodiment, the case where the recording light beam L1 and the reading light beam L2 are respectively irradiated from the surface on the substrate 102 side of the optical information recording medium 100 has been described, but the present invention is not limited to this. For example, the recording light beam L1 may be irradiated from the surface on the substrate 103 side, and each light or light beam may be irradiated from any surface or both surfaces.

  Further, in the second embodiment described above, the wavelength of the recording light beam L1 emitted from the short pulse light source 20 may be other than 405 [nm]. It is only necessary that the recording mark RM can be appropriately formed in the vicinity of the target position PG in the recording layer 101.

  Further, in the above-described embodiment, the case where the recording mark RM is formed three-dimensionally has been described. However, the present invention is not limited to this. For example, the recording mark RM includes only one virtual mark recording layer. The RM may be formed two-dimensionally.

  Further, in the above-described embodiment, for example, the case where the recording mark RM made of bubbles is formed by evaporating the two-photon absorption material by the two-photon absorption is described. However, the present invention is not limited to this. The recording mark RM may be formed by changing the refractive index. In this case, the recording mark RM made of a hologram can be formed by separating the recording light beam L1 emitted from one light source into two and irradiating the same target mark position from opposite directions.

  Further, in the above-described embodiment, the case where the return light beam L3 is received has been described. The present invention is not limited to this, and instead of the return light beam L3, a light receiving element that receives the transmitted light of the read light beam L2 is arranged to detect light modulation of the read light beam L2 according to the presence or absence of the recording mark RM. Thus, information may be reproduced based on the light modulation of the readout light beam L2. Furthermore, the substrates 102 and 103 may be omitted from the optical information recording medium 100 when a desired strength can be obtained with the recording layer 101 alone.

  Further, in the above-described embodiment, the case where the optical information recording medium 100 as the optical information recording medium is configured by the recording layer 101 as the recording layer has been described. However, the present invention is not limited to this, and has other various configurations. An optical information recording medium may be constituted by the recording layer.

  The present invention can also be used in a recording / reproducing apparatus that records or reproduces a large amount of information such as video content or audio content on a recording medium such as an optical information recording medium.

It is a basic diagram which shows formation of the recording mark by 1 photon absorption. It is a basic diagram with which it uses for description of formation of the recording mark by two photon absorption. It is a basic diagram which shows the structure of a recording / reproducing apparatus. It is a basic diagram which shows the structure of an optical pick-up. It is a basic diagram which shows the structure of a short pulse light source. It is a basic diagram which shows a pulse signal and a laser drive voltage. It is a basic diagram with which it uses for description of the relationship (1) of an injection | pouring carrier density and a photon density. It is a basic diagram with which it uses for description of the relationship between an injection | pouring carrier density and a carrier density. It is a basic diagram with which it uses for description of the relationship (1) of an injection | pouring carrier density and a photon density. It is a basic diagram with which it uses for description of the photon density in PT1. It is a basic diagram with which it uses for description of the photon density in PT2. It is a basic diagram with which it uses for description of the photon density in PT3. It is a basic diagram which shows an actual light emission waveform. It is a basic diagram with which it uses for description of a drive current and emitted light intensity | strength (1). It is a basic diagram which shows the structure of a light measuring device. It is a basic diagram which shows the relationship between a pulse signal and a drive voltage pulse. It is a basic diagram which shows the shape of each pulse. It is a basic diagram which shows the waveform of a voltage and a laser beam. It is a basic diagram which shows the laser beam in case of 8.8 [V]. It is a basic diagram which shows the laser beam at the time of 13.2 [V]. It is a basic diagram which shows the laser beam in case of 15.6 [V]. It is a basic diagram which shows the laser beam in case of 17.8 [V]. It is a basic diagram which shows the laser beam in case of 38.4 [V]. It is a basic diagram which shows the waveform of specific output light. It is a basic diagram with which it uses for description of the example of a state change. It is a basic diagram which shows the structure of an optical information recording medium.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Recording / reproducing apparatus, 11 ... Control part, 17 ... Optical pick-up, 20 ... Short pulse light source, 23 ... Objective lens, 100 ... Optical information recording medium, 101 ... Recording layer, 102, 103 ... ... recording layer, t1, t2, t3 ... thickness, L1 ... recording light beam, L2 ... reading light beam, L3 ... returning light beam, RM ... recording mark, APK ... single peak, ASP ... Singular slope.

Claims (12)

Two-photon absorption, which is a metal complex in which one or more molecules are coordinated to a metal atom, and absorbs the recording light by one-photon by a change in state due to two-photon absorption in response to irradiation of recording light for information recording An optical information recording medium having a recording layer containing a material. The two-photon absorption material is
The optical information recording medium according to claim 1, comprising tetracyanoethylene. The two-photon absorption material is
The optical information recording medium according to claim 2, comprising Ph ₃ P when Ph is a phenyl group. The two-photon absorption material is
When TCNE is tetracyanoethylene and X is a general formula, IrClX (Ph ₃ P) ₂ TCNE (1) represented by the formula (1)
The optical information recording medium according to claim 3. The two-photon absorption material is represented by any one of the following formulas (2), (3), and (4): IrCl (CO) (Ph ₃ P) ₂ TCNE (2)
IrNCS (CO) (Ph ₃ P) ₂ TCNE (3)
IrNCO (CO) (Ph ₃ P) ₂ TCNE (4)
The optical information recording medium according to claim 3. The above state change is
The optical information recording medium according to claim 1, wherein the optical information recording medium is a transition from a ground state to an excited state. The two-photon absorption material is
The optical information recording medium according to claim 6, after transitioning to an excited singlet state by a two-photon absorption reaction, transitioning to a minimum triplet state by the heavy atom effect of the metal atom. An optical information recording medium comprising: a pulse-like specific peak; and a recording layer that is irradiated subsequent to the specific peak and forms a recording mark in accordance with a specific slope that has a smaller outgoing light intensity than the specific peak. The recording layer is
The optical information recording medium according to claim 8, comprising a two-photon absorption material that changes its state by absorbing the two specific photons and generates heat by absorbing one specific photon of the specific slope. A two-photon absorption material that transitions to an excited singlet state by two-photon absorption with respect to recording light for information recording, then transitions to a minimum triplet state, and absorbs one-photon recording light in the lowest triplet state An optical information recording medium having a recording layer containing. When Ph is a phenyl group, TCNE is tetracyanoethylene, and X is a general formula, IrClX (Ph ₃ P) ₂ TCNE (1) containing a two-photon absorption material represented by the formula (1)
Optical information recording medium. When Ph is a phenyl group, TCNE is tetracyanoethylene, and X is a general formula, IrClX (Ph ₃ P) ₂ TCNE represented by the formula (1):
Two-photon absorbing material.

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