JP2010211844A - Recording and reproducing device for two-photon absorption recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a practical recording and reproducing device with which information is stably recorded on a two-photon absorption recording medium at a high speed. <P>SOLUTION: The recording and reproducing device includes: an ultra-short pulse laser light source 103 to output an ultra-short pulse laser beam of a repetition frequency of ≥1 GHz, a wavelength of 380-550 nm, peak power of ≥100 W, and a pulse width of ≤1 psec as recording light Lw to induce simultaneous two-photon absorption on a two-photon absorption recording medium 102 and record information on the two-photon absorption recording medium 102; a read laser light source 104 to output a continuous oscillating laser beam of a wavelength range of 440-660 nm as reading light Lr to read information from the two-photon absorption recording medium 102; and a detection means 105 to detect reflected light or fluorescence from the two-photon absorption recording medium 102 which has been irradiated with the reading light Lr. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a recording / reproducing apparatus for recording and reading information on a two-photon absorption material recording medium capable of recording information using non-resonant simultaneous two-photon absorption.

In recent years, among the nonlinear optical characteristics of organic compounds, the third-order nonlinear optical effect has attracted attention, and among them, non-resonant simultaneous two-photon absorption has attracted attention. Simultaneous two-photon absorption is a phenomenon in which a compound is excited by absorbing two photons at the same time. Of these, two-photon absorption occurs in an energy region where there is no (linear) absorption band of the compound. This is called two-photon absorption. In the present specification, “two-photon absorption” refers to “non-resonant simultaneous two-photon absorption” even if not specified in the following description.
Some types of polymers change their molecular structure or become fluorescent after being excited by two-photon absorption. At present, research is progressing to realize a multilayer optical disk in which the total number of recording layers is several tens to hundreds by using such a polymer as a recording material.

  The efficiency of two-photon absorption is proportional to the square of the applied photoelectric field (square characteristic of two-photon absorption). For this reason, when a laser is irradiated on a two-dimensional plane, two-photon absorption occurs only at a position where the electric field strength is high at the center of the laser spot, and no two-photon absorption occurs at a portion where the electric field strength is low in the peripheral portion. . Similarly, in the three-dimensional space, two-photon absorption occurs only in a region where the electric field strength at the focal point where the laser light is collected by the lens is large, and the two-photon absorption does not occur at all in a region outside the focal point because the electric field strength is weak. Absent. Compared with linear absorption where excitation occurs at all positions in proportion to the intensity of the applied photoelectric field, non-resonant two-photon absorption results in excitation at only one point inside the space due to this square characteristic. , The spatial resolution is significantly improved. That is, the two-photon absorption material can limit the range in which the two-photon absorption occurs to a narrow range of the focus of the laser beam.

  Therefore, in a recording medium using a two-photon absorption material, interference does not easily occur between the upper and lower recording layers, so that the interval between the layers can be easily reduced, and tens to hundreds of layers are expected.

  However, since many of the current two-photon absorption materials have extremely low two-photon absorption efficiency, in the conventional reports, a laser light source for writing information has a large peak power such as a Ti: Sapphire laser with extremely high peak power. Mode-locked ultrashort pulse solid-state lasers have been used, which has been a practical obstacle.

  On the other hand, Patent Documents 1 to 4 propose optical recording / reproducing apparatuses for performing information recording and information reproduction on a recording medium using the two-photon absorption material as described above.

  In Patent Document 1, as a recording / reproducing apparatus for a multilayer optical disk, a first light source that outputs a first laser beam used for reading information and obtaining a servo, and a second laser beam used for writing are disclosed. It has been proposed to use a laser beam having a different wavelength for reading and writing.

  As a tracking servo method for a multilayer optical disk, in Non-Patent Document 1, in two-photon absorption recording, a servo light source is provided separately from a recording light source, and a reflective surface is provided on the deepest layer of the multilayered recording layer. And a method of acquiring an error signal with a servo laser beam from a servo light source using the recording medium described above.

  On the other hand, Patent Document 2 discloses an optical recording / reproducing apparatus including a light source that oscillates a pulse laser having a pulse width of 1 ps or less and a frequency of 1 kHz or more as a light source for recording information in combination with a multiphoton absorption material. In particular, it is disclosed that the wavelength of the pulse laser is set to n times the center wavelength λa of the light absorption spectrum of the multiphoton absorption material.

  Further, Patent Document 3 uses a laser beam having a pulse width of 1 ps or less for a recording medium having a recording material (multiphoton absorption material) having a recording threshold energy of 10 nJ or less, and collects the laser beam on the recording medium. It has been proposed to use an objective lens that emits light having a numerical aperture NA of 0.6 or more.

  In Patent Documents 2 and 3, specifically, an example using MaiTai (registered trademark) manufactured by Spectra Physics, which is a Ti: Sapphire Laser having a center wavelength of 800 nm, a pulse width of about 100 fs, and a repetition frequency of 80 MHz is given.

  As described above, since many of the current two-photon absorption materials have extremely low two-photon absorption efficiency, it is necessary to use laser light with extremely high peak power. The peak power is a value obtained by dividing the pulse energy by the pulse width. Under the condition where the pulse energy is constant, the peak power can be increased by shortening the pulse width.

  On the other hand, the transfer rate (write speed) when recording information on a recording medium using a two-photon absorption material depends on the repetition frequency and peak power of the pulse laser. That is, by increasing the repetition frequency, the number of laser pulses necessary for writing one bit can be input to the material in a shorter time. Therefore, in order to improve the transfer rate, a higher repetition frequency and It is desirable to do. However, if the repetition frequency is increased while maintaining the same average output, the pulse energy and peak power decrease, so the number of laser pulses required to write 1 bit increases and the transfer rate is sufficiently improved. There is a fear that it can not be done. Therefore, it is necessary to set a higher repetition frequency while ensuring a peak power sufficient for two-photon absorption recording.

Many of the two-photon absorption materials currently being developed have a two-photon absorption cross section of 1 to 100 GM (Goepper Mayer: 1GM = 1 × 10 ⁻⁵⁰ cm ⁴ · s · molecule-1 · photon, which is an index of the absorption capacity. In order to perform data recording within a practical time range (practical transfer rate), an ultrashort pulse laser having a peak power of at least 100 W, preferably at least 1 kW, and a repetition frequency of at least 1 GHz. I need light.

  As described above, in the light source exemplified in Patent Documents 2 and 3, etc., the repetition frequency is about 80 MHz, the transfer rate is not sufficient, and it cannot be said that the size is sufficiently reduced. Furthermore, since it is very expensive, it is not suitable for mounting on a recording / reproducing apparatus.

  Here, the current state of the ultrashort pulse laser light source that outputs the ultrashort pulse laser light will be described. First, the operation of the ultrashort pulse laser will be described.

  The ultrashort pulse laser generates an ultrashort pulse by an operation called mode synchronization. In simple terms, mode synchronization means that the phases of many longitudinal modes are all synchronized in the frequency domain during laser oscillation (relative phase difference = 0). Therefore, due to multimode interference between longitudinal modes. This is a phenomenon that results in a very short pulse in the time domain.

  In general, a semiconductor saturable absorbing mirror (SESAM) is used as one of mirrors constituting a laser resonator, and a mode-synchronized operation is performed by the effect of pulse sharpening in the SESAM. Furthermore, in the femtosecond region, the pulse has a wide spectral band, so it is necessary to compensate for the positive group velocity dispersion experienced when passing through optical components (solid laser medium, resonator mirror, etc.) in the resonator. is there.

  A method of obtaining a pulse in the femtosecond region by arranging SESAM as a resonator mirror, starting mode synchronization, and performing compensation of self-phase modulation effect and group velocity dispersion by a light pulse circulating in the resonator in the resonator. This is especially called soliton mode synchronization. This method has been widely adopted as an excellent practical method that can be self-started and is more resistant to misalignment than other methods (such as Kerr lens mode synchronization).

  As a mode-locked solid-state laser not limited to soliton mode-locking, a large laser having a resonator length of 2 m class corresponding to a repetition frequency of 80 MHz has been reported (for example, see Non-Patent Document 2).

The repetition frequency PRF is represented by PRF = C / 2L _cav when the speed of light is C and the resonator length is L _cav . When L _cav is 2 m, the PRF corresponds to 75 MHz. A large ultrashort pulse laser can provide a moderate repetition frequency (50 MHz to 100 MHz) and a relatively high peak power (100 kW to 1 MW). On the other hand, a mirror or the like for folding the resonator is required, and the resonator structure is complicated, which tends to increase the number of parts and increase the manufacturing cost. In addition, large lasers generally have a problem of low output stability. This is because, as the size of the apparatus increases, a slight mechanical fluctuation (positional deviation) of the resonator mirror causes a large beam position fluctuation and hence an output fluctuation. Therefore, such a large ultrashort pulse laser is operated on the premise of periodic mirror alignment. For example, the mirror needs to be optimally adjusted every day. Therefore, a low-cost and highly stable mode-locked solid-state laser with a reduced number of parts and reduced size is desired.

  On the other hand, Patent Documents 4 to 6 propose linear and small ultrashort pulse lasers. Specifically, in Patent Document 4, one end surface of a solid-state laser medium is used as a curvature mirror, and the resonator is configured by using this curvature mirror and a SESAM disposed on the other end surface of the solid-state laser medium. A mode-locked solid-state laser has been proposed. In Patent Document 5, a saturable absorption mirror is formed on a solid-state laser medium, and a negative dispersion mirror is also used as an output mirror to reduce optical components and reduce the size. A mode-locked solid-state laser has been proposed. Patent Document 6 proposes a linear mode-locked solid-state laser composed of a negative dispersion mirror and a SESAM arranged close to the laser medium. Each is equipped with a semiconductor saturable absorption mirror (SESAM) necessary for mode locking as one end of the resonator mirror. In either case, SESAM and laser crystal are brought close to or in close contact with each other, and a resonator waist is provided on the SESAM. As compared with the conventional case in which resonator spots are separately formed on both the SESAM and the laser crystal, a configuration example that is linear and can be miniaturized is given.

JP 2006-92657 A JP 2006-164451 A JP 2006-196084 A US Pat. No. 7,106,764 (FIG. 15) Japanese Patent Laid-Open No. 11-168252 (FIG. 3) Japanese Patent Laying-Open No. 2008-28379 (FIG. 1)

Proceedings of Laser Microscope Society vol.21 p.12-16, 1998, "High-density optical memory using organic photochromic materials" Honninger et al., Journal of Optical Society of America vol.16, p.46, 1999; (Figure 3)

  In Patent Documents 4 to 6, a miniaturized mode-locked solid-state laser is proposed. However, Patent Documents 4 and 5 are only an idea level, and a high repetition frequency is obtained. There is no description about the output or peak power, and it cannot be said that the requirements desirable in the two-photon absorption recording / reproducing apparatus are sufficiently satisfied. Also, in any document, the specific configuration and structure of the resonator holder There is no disclosure about the above, and it is not fully disclosed how to implement a compact, low-cost and stable ultrashort pulse laser.

  There are GigaOptics and Gigajet series as small mode-locked solid-state lasers on the market that have a repetition frequency exceeding 1 GHz (resonator length 150 mm), but since they are based on Ti: Sapphire, green lasers are used. Since it is necessary to use excitation light and a solid-state laser light source is required as an excitation light source, the excitation light source is large, resulting in a complicated overall configuration, and it cannot be said that the overall structure is sufficiently small. Expensive. Therefore, it cannot be said that it is suitable for incorporation into a recording / reproducing apparatus for a two-photon absorption recording medium.

  That is, at present, it can be said that a light source that can be said to be practical for incorporation into a two-photon absorption recording apparatus in terms of size, cost, and stability in addition to light source performance (peak power, repetition frequency, wavelength, pulse width) has been developed. Absent.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a practical recording / reproducing apparatus capable of recording information on a two-photon absorption recording medium at high speed and stably. is there.

The two-photon absorption recording medium recording / reproducing apparatus of the present invention is a recording / reproducing apparatus for recording and reading information on a two-photon absorption recording medium,
As recording light for inducing simultaneous two-photon absorption in the two-photon absorption recording medium and recording information on the two-photon absorption recording medium, a repetition frequency of 1 GHz or more, a wavelength of 380 nm to 550 nm, a peak power of 100 W or more, a pulse width An ultrashort pulse laser light source that outputs an ultrashort pulse laser beam of 1 psec or less;
A reading laser light source that outputs continuous wave light in a wavelength region of 440 nm to 660 nm as reading light for reading information from the two-photon absorption recording medium;
And detecting means for detecting reflected light or fluorescence from the two-photon absorption recording medium irradiated with the reading light.

  In particular, an ultrashort pulse laser light source includes a resonator having one end formed of a semiconductor saturable absorption mirror, a solid-state laser medium provided with a rare earth or a transition metal provided in the resonator, and the resonance A soliton mode-locked solid-state laser that oscillates soliton pulsed laser light, comprising a negative group velocity dispersion compensating element for controlling group velocity dispersion in the chamber, and a pumping optical system that outputs pumping light for pumping the solid-state laser medium And a non-linear optical element that converts the soliton pulsed laser light oscillated from the soliton mode-locked solid-state laser into a second harmonic.

  In the ultrashort pulse laser light source, the resonator length of the resonator is desirably 150 mm or less, and more desirably 75 mm or less.

In the ultrashort pulse laser light source, as the nonlinear optical element, any one of a periodically poled LiNbO ₃ element, a periodically poled LiTaO ₃ element, and a periodically poled KTiOPO ₄ is particularly suitable.

In the ultrashort pulse laser light source, the negative group velocity dispersion compensating element is a negative dispersion mirror, the negative dispersion amount is −3000 fs ² or more and 0 fs ² or less, and the transmittance is 0.1% or more and 3%. The following is desirable.

  In the ultrashort pulse laser light source, the negative group velocity dispersion compensation element is a negative dispersion mirror, and the negative dispersion mirror constitutes the other end of the resonator, and the ultrashort pulse laser light source comprises: It is desirable to provide a linear resonator holder that holds the semiconductor saturable absorption mirror constituting one end of the resonator and the negative dispersion mirror constituting the other end of the resonator in a straight line.

  In the two-photon absorption recording medium recording / reproducing apparatus of the present invention, when information is recorded on the two-photon absorption recording medium by the ultrashort pulse laser light, the ultrashort pulse laser light is recorded from the two-photon absorption recording medium. Servo signal acquisition means for recording to receive servo light by receiving reflected light from the two-photon absorption recording medium at the time of reading information from the two-photon absorption recording medium by the continuous wave light It is desirable to include a servo signal acquisition means at the time of reading that receives the reflected light or fluorescence of the light and acquires the servo signal.

  The two-photon absorption recording medium recording / reproducing apparatus of the present invention outputs an ultrashort pulse laser beam as a recording light source that outputs an ultrashort pulse laser beam having a repetition frequency of 1 GHz or more, a wavelength of 380 nm to 550 nm, a peak power of 100 W or more, and a pulse width of 1 psec or less. A laser light source is provided, and in this wavelength range, a surface recording density equivalent to a Blu-ray disc that records and reproduces at 405 nm can be realized. In addition, since the recording bit can be made smaller as the wavelength of the recording light is shorter, the data amount per surface can be increased in density. Therefore, there is a possibility that the density can be increased by shortening the wavelength further than this wavelength range. On the other hand, the optical system is forced to cope with ultraviolet rays, and generally has a configuration made of quartz glass, which makes it impossible to use inexpensive optical components.

  In addition, if a laser beam having a repetition frequency of 1 GHz or higher, a peak power of 100 W or higher, and a pulse width of 1 psec or shorter is used, information recording at a very practical high transfer rate can be realized.

  The ultrashort pulse laser light source has a soliton mode-locked solid-state laser that oscillates soliton pulse laser light, and a nonlinear optical element that converts the soliton-pulse laser light oscillated from the soliton mode-locked solid-state laser into a second harmonic. Therefore, the ultrashort pulse laser light source can be configured in a small size, and a practical recording / reproducing apparatus that is stable and cost-effective can be configured. If the resonator length of the soliton mode-locked solid-state laser is about 150 mm or less, preferably 75 mm or less, an integrated resonator structure can be adopted and the stability can be further improved.

Schematic plan view of a mode-locked solid-state laser provided in the recording / reproducing apparatus of this embodiment Schematic side sectional view of a mode-locked solid-state laser provided in the recording / reproducing apparatus of this embodiment 1 is a schematic configuration diagram of a recording / reproducing apparatus for a two-light absorption recording medium according to an embodiment of the present invention. Schematic diagram of recording pulses for servo during information recording

  Hereinafter, an embodiment of a recording / reproducing apparatus for a two-photon absorption recording medium of the present invention will be described with reference to the drawings.

  First, an embodiment of the soliton mode-locked solid-state laser 10 provided in the ultrashort pulse laser light source 103 of the recording / reproducing apparatus 1 of this embodiment will be described in detail.

FIG. 1A is a schematic plan view of a soliton mode-locked solid-state laser 10 in this embodiment, and FIG. 1B is a 1B-1B cross-sectional view of the mode-locked solid-state laser 10 of FIG. 1A. As shown in the figure, the soliton mode-locked solid-state laser 10 of this embodiment includes an excitation optical system 13 that inputs the excitation light L ₀ from an oblique direction with respect to the resonator optical axis, and a Brewster angle with respect to the resonator optical axis. The resonator is arranged in the resonator so as to reflect the excitation light L ₀ incident by the excitation optical system 13 toward the solid-state laser medium 16 and transmit the oscillation light L resonating in the resonator. A dichroic mirror 18 disposed inside, a SESAM (semiconductor saturable absorption mirror) 14 constituting one end of the resonator, a negative dispersion mirror 20 serving also as an output mirror constituting the other end of the resonator, and the SESAM 14 and The solid-state laser medium 16 is disposed inside a resonator composed of the negative dispersion mirror 20.

Here, the excitation optical system 13 includes a SELFOC lens 28 for the excitation light L ₀ from the semiconductor laser 26 that emits excitation light L ₀ is converged on the solid-state laser medium.

In the above configuration, the excitation light L ₀ incident obliquely with respect to the resonator optical axis by the excitation optical system 13 is reflected by the dichroic mirror 18 and input to the solid-state laser medium 16, whereby the solid-state laser medium 16 is The light generated by excitation oscillates by the action of the resonator. The laser oscillation light (pulse laser light) L is partially transmitted through the output mirror (negative dispersion mirror) 20 and output to the outside. In the apparatus of this configuration, the beam waist of the laser oscillation light L that resonates in the resonator is formed only on the SESAM 14. Note that the solid-state laser medium 16 and the SESAM 14 are arranged close enough to allow sufficient oscillation even if the solid-state laser medium 16 does not have the beam waist of the oscillation light L formed thereon.

As the solid-state laser medium 16, a solid-state laser crystal capable of realizing an oscillation wavelength according to the characteristics of the target recording medium is appropriately selected from solid laser crystals capable of realizing an oscillation wavelength in a range of about 760 nm to 1100 nm. That's fine. Specifically, Yb: KGW (KGd (WO ₄ ) ₂ ), Yb: KYW (KY (WO ₄ ) ₂ ), Yb: YAG (Y ₃ Al ₅ O ₁₂ ), Yb: Y ₂ O ₃ , Yb: Sc ₂ O ₃ , Yb: Lu ₂ O ₃ , Yb: GdCOB (Ca ₄ GdO (BO ₃ ) ₃ ), Yb: SYS (SrY ₄ (SiO ₄ ) ₃ ), Yb: BOYS (Sr ₃ Y (BO ₃ ) ₃ ), Yb: YVO ₄ , Yb: GdVO ₄ , Alexander (Cr: BeAl ₂ O ₄ ), Cr: LiSAF (LiSrAlF ₆ ), Cr: LiSGAF (LiSrGaF ₆ ), Cr: LiCAF (LiCaAlF ₆ ), Cr: for (Mg ₂ SiO ₄ ), Cr: YAG (Y ₃ Al ₅ O ₁₂ ), Cr: Ca ₂ GeO ₄ , Ti: Al ₂ O ₃ , Nd : Glass, and Er: Yb: Glass. For example, Yb: KYW 1045 nm, Yb: YAG 1030 nm to 1100 nm, Yb: KGW 1000 nm or 1045 nm, Yb: Y ₂ O ₃ 1075 nm, Yb: Sc ₂ O ₃ 1041 nm, Nd: Glass 1060 nm Each oscillation wavelength can be obtained. If Cr: LiSAF, Cr: LiCAF, alexandrite, or the like is used, an oscillation wavelength of 760 nm to 1000 nm can be obtained.

  The thickness of the solid-state laser medium 16 and the rare earth addition concentration are set so that the excitation light can be sufficiently absorbed, for example, with an efficiency of 90%.

The negative dispersion mirror 20 plays a role of compensating for the group velocity dispersion in the resonator and also compensating for a positive chirp due to self-phase modulation generated in the solid-state laser medium 16 due to the high peak power of the optical pulse in the resonator. Although the amount of dispersion depends on operating conditions, the amount of dispersion is preferably in the range of about 0 to -3000 fsec ² . The amount of dispersion is set so that the overall group velocity dispersion in the resonator is 0 or less. Further, the transmittance T of the negative dispersion mirror 20 can be optimally extracted by setting the output coupling rate within a range of about 0.5 to 3%, for example, by mirror design.

  The radius of curvature of the negative dispersion mirror 20 is calculated and determined by the Gaussian beam propagation design of the resonator. In order to make the resonator spot diameter (the beam waist of the oscillation light) as small as possible, the curvature is approximately the same as the resonator length. A hemispherical type is preferable with a radius. As a result, the resonator spot can be suppressed to about 50 μm in diameter, and the Q-switch phenomenon accompanying the shortening of the resonator length can be avoided. At the same time, the spatial alignment with the spot diameter of the excitation light can be satisfactorily achieved, and high efficiency can be achieved.

  The dichroic mirror 18 is coated with high reflection with respect to the wavelength of the excitation light Lo and low reflection with respect to the wavelength of the oscillation light L, thereby realizing high-efficiency excitation and low internal loss.

  The mode-locked solid-state laser 10 of this embodiment is a beam splitter 40 that reflects a part of the oscillation light L output from the negative dispersion mirror 20 as a constant power control means, and one of the oscillation light L reflected by the beam splitter 40. And a control unit 44 for controlling the output of the semiconductor laser 26 so that the light intensity detected by the photodiode 42 is substantially constant.

  The photodiode 42 detects the intensity of the light reflected by the beam splitter 40, converts it into an electric signal, and outputs it to the control unit 44. The control unit 44 assumes that the light intensity detected by the photodiode 42 is substantially constant. Thus, constant power control for controlling the semiconductor laser 26 is performed. Thereby, the average output of the mode-locked solid-state laser 10 can be maintained substantially constant.

  The excitation optical system 13 composed of the semiconductor laser 26 and the Selfoc lens 28 is fixed on the excitation optical system holder 30 made of, for example, a member made of copper, for example, by adhesion. The dichroic mirror 18 is fixed to a dichroic mirror holder 32, and the dichroic mirror holder 32, SESAM 14, negative dispersion mirror 20, and solid-state laser medium 16 are fixed to a resonator holder 34. Further, the beam splitter 40 and the photodiode 42 are fixed to the control system holder 35. These holders 30, 34, and 35 are fixed on a copper plate 36, and the copper plate 36 is fixed on a Peltier element 22 disposed on a substrate 46.

  The substrate 46 forms a housing together with the lid member 48 that is sealed and fixed so as to contain the holders 30, 34, and 35 and the components fixed to the holders. The lid member 48 is provided with a transmission window 48A for outputting the pulsed laser light L to the outside. The inside of the housing is sealed and is shielded from the outside world. As a method for fixing the lid member 48 to the substrate 46, various known methods such as welding such as laser welding and electric welding, seam joining, soldering, and adhesion using an adhesive can be used.

  The Peltier element 22 constitutes a temperature adjusting means together with the Peltier driving unit 24, and the Peltier element 22 is driven by the Peltier driving unit 24 to adjust the temperature of the resonator holder 34 and the excitation optical system holder 30.

  As described above, since the temperature of the resonator holder 34 can be adjusted by the temperature adjusting means, even if the temperature of the external environment fluctuates, the resonator is kept at a constant temperature, the resonator length varies, and each member such as a mirror Position fluctuations can be minimized. Thereby, it is possible to output an ultra-short pulse laser beam having a very stable output.

  Similarly, since the temperature of the excitation optical system holder 30 can be adjusted by the temperature adjustment means, it is possible to suppress wavelength fluctuations due to temperature fluctuations of the semiconductor laser 26, fluctuations in the relative position between the excitation optical system 13 and the resonator, and the like. it can.

  Next, a structure for attaching a laser component to the resonator holder 34 will be described. As shown in FIG. 1B, the resonator holder 34 includes a base portion 34C, and fixed portions 34A and 34B that are spaced apart from each other in the axial direction of the resonator on the base portion 34C. , 34B and 34C are integrally formed and formed in a substantially U-shape as a whole. The resonator holder 34 is preferably made of a metal having high thermal conductivity and rigidity, and copper is preferable. Furthermore, considering machinability, copper added with Te is more preferable.

  The outer surfaces of the fixed portions 34A and 38B of the resonator holder 34 are mounting surfaces to which the SESAM 14 and the negative dispersion mirror 20 constituting the resonator end are fixed, respectively, and this surface is perpendicular to the resonator axis. The distance between the mounting surfaces is set according to the desired resonator length. The resonator length is preferably shorter as long as the holder can be processed with sufficient accuracy. Specifically, considering the mechanical variation of the member due to temperature variation, the resonator length is 150 mm or less, and further 75 mm or less. Preferably there is. Further, by setting the resonator length to 150 mm or less, the repetition frequency can be 1 GHz or more and 75 mm or less to realize a repetition frequency of 2 GHz or more.

  Further, holes 38A and 38B for allowing light resonating inside the resonator to pass through are formed in the fixing portions 34A and 34B of the holder 34.

  The SESAM 14 and the negative dispersion mirror 20 are fixed to the mounting surface by adhesion. As shown in FIG. 1A, the SESAM 14 and the negative dispersion mirror 20 are configured such that an adhesive is applied to a portion other than a light incident region of a light incident surface on which light is incident, and one end surface and the other of the resonator holder 34 are applied. It is glued to the end face. Thus, by adopting a configuration in which the light incident surface of the SESAM 14 is bonded to one end side of the resonator holder 34, heat generated in the SESAM 14 can be efficiently exhausted, and instability of the operation due to distortion caused by heat can be removed as much as possible. it can. As an adhesive for adhering the SESAM 14 and the negative dispersion mirror 20 to the resonator holder 34, it is preferable to use an adhesive having a layer thickness of 2 μm or less and a change in hardening rate and a change in layer thickness due to stress of 1% or less. .

  One surface of the solid-state laser medium 16 is fixed to the surface of the fixed portion 34A facing the SESAM mounting surface by adhesion. The solid laser medium 16 is fixed to a surface by applying an adhesive to a portion other than the light transmission region. Similar to the SESAM 14 and the negative dispersion mirror 20, an adhesive having a layer thickness of 2 μm or less and a change in the curing rate and a change in the layer thickness due to stress of 1% or less is used as the adhesive for bonding to the resonator holder 34. It is preferable. As a fixing method by bonding the laser component to the resonator holder, it is preferable to apply the method described in Japanese Patent No. 3378109.

  As described above, the laser component parts such as the SESAM 14, the solid-state laser medium 16, the negative dispersion mirror 20, and the dichroic mirror holder 32 are fixed to one resonator holder 34, so it is necessary to prepare holders for each part. Thus, a simple and small configuration can be obtained, and the device can be manufactured at low cost.

  In the present embodiment, the solid-state laser medium 16 is arranged such that the light incident surface and the light emitting surface are orthogonal to the resonator axis (see FIG. 1A), but the direction orthogonal to the resonator axis. It may be arranged to be inclined by several degrees (for example, 2 degrees to 5 degrees). As a result, it is possible to suppress a component (satellite component) of the optical pulse that circulates around the resonator from remaining and reflecting at the boundary between the optical components. If tilted further, the beam shape may be distorted by astigmatism, and at the same time, an internal loss may occur due to the angular dependence of the reflectance of the non-reflective coating applied to the crystal.

  Next, a specific configuration example of the laser component of the mode-locked solid-state laser 10 according to the embodiment will be described.

  As the semiconductor laser 26 of the excitation optical system 13, for example, a semiconductor laser that outputs excitation light having a wavelength of 980 nm, an emitter width of 50 μm, and an output of 2 W is used. The selfoc lens 28 focuses the excitation light emitted from the semiconductor laser 26 onto a solid-state laser so that the diameter of the focused spot is about 50 μmφ.

  As the solid-state laser medium 16, Yb: KYW having a thickness of 1.5 mm and a Yb addition concentration of 5 at% is used. Both surfaces of the solid-state laser medium 16 are optically polished, and an antireflection coating having a reflectance of 0.5% or less is applied to the oscillation light wavelength of 1045 nm and the excitation light wavelength of 980 nm.

As the SESAM 14, one having a modulation depth (ΔR) of 0.6% and a saturation fluence of 70 μJ / cm ² is used.

The negative dispersion mirror 20 has a dispersion amount of −800 fsec ² and an oscillation light transmittance of 1.8%. The radius of curvature of the mirror surface (concave surface) is 50 mm.
The distance between the negative dispersion mirror 20 and SESAM, that is, the resonator length is 50 mm. That is, a resonator holder in which the distance between the mounting surfaces is set so that the resonator length is 50 mm is used.

  The dichroic mirror 18 is coated with a reflectance of 95% or more with respect to the wavelength of the excitation light and a reflectance of 0.2% or less with respect to the wavelength of the oscillation light. Low internal loss is realized.

  The inventor has confirmed that the mode-locked solid-state laser 10 having the above configuration example can output ultrashort pulse laser light having an average output of 600 mW, a pulse width of 200 fsec, a repetition frequency of 2.9 GHz, and a peak power of 1 kW.

  In addition, the following test was performed on the mode-locked solid-state laser 10.

  A temperature cycle test was performed in which the outside air temperature was changed in the range of 10 ° C. to 45 ° C. without constant power control. The temperature of the resonator is adjusted by the temperature control means. The output fluctuation in this temperature cycle test was 10% or less.

As a long-term running test, a aging test of 3000 h or more was performed without constant power control. The output fluctuation in this aging test was 10% or less. In the long-term running test, the temperature of the resonator was adjusted by the temperature control means, but the outside air temperature was not adjusted. The range of temperature fluctuation was about 15 ° C.
Similarly, as a long-term running test, power constant control was performed and a time-lapse test for 1000 hours was performed. The output fluctuation in this aging test was ± 0.5%. Compared to the long-term running test without constant power control, it was confirmed that the output stability was greatly improved.

  From this test result, the output fluctuation of 10% or less in the temperature cycle test without the constant power control and the aging test is compared with the conventional large mode-locked solid-state laser that requires alignment adjustment every time it is used. It can be said that it is sufficiently stable. Furthermore, it became clear that a much higher stability can be achieved by performing constant power control.

  An ultrashort pulse laser light source, which is a recording light source of the recording / reproducing apparatus of the present embodiment described later, is configured by combining the mode-locked solid-state laser 10, a nonlinear optical element, and a condenser lens, and is output from the solid-state laser 10. The second harmonic of the pulse laser L is output.

As the nonlinear optical element combined with the mode-locked solid-state laser of the above configuration example, a periodic polarization inversion element having a polarization inversion period set to an optimum value for the fundamental wave of 1045 nm is used. Specifically, PPKTP (periodic polarization inversion KTiOPO ₄ ), PPLN (periodic polarization inversion LiNbO ₃ ), and PPLT (periodic polarization inversion LiTaO ₃ ) are preferable. When these are used, the output of the ultrashort pulse laser light source is In addition, a second harmonic (522 nm) having an average output of 120 mW (conversion efficiency of 20%) and a peak power of 100 W or more could be realized. At this time, the pulse width was about 300 to 500 fsec. The polarization inversion period of the element was set to an optimum value for the fundamental wave of 1045 nm. Specifically, the thickness was about 8 μm for PPKTP, 6 μm for PPLN, and 7 μm for PPLT. The element length was 3 mm to 5 mm, and the fundamental wave output from the mode-locked solid-state laser 10 was narrowed down to the diameter of a focused spot of about 20 μm on the element end face by a condenser lens.

  By using such an ultrashort pulse laser light source, extremely practical two-photon absorption recording can be realized.

  In the above configuration example, Yb: KYW was used as the solid-state laser medium, but an oscillation wavelength of 760 nm to 1100 nm was achieved by appropriately selecting a combination of the laser crystal of the solid-state laser medium and an additive (rare earth or transition metal). It is possible to output laser light having a wavelength of 380 nm to 550 nm as the second harmonic by combining with the SHG element.

  Next, an embodiment of a recording / reproducing apparatus for a two-photon absorption recording medium of the present invention provided with the above ultrashort pulse laser light source will be described.

  FIG. 2 shows a schematic configuration diagram of the recording / reproducing apparatus 100 of the two-photon absorption recording medium of the present embodiment. The recording layer of the recording medium 102 used for recording and reproduction in the recording / reproducing apparatus 100 of the present embodiment is provided with a two-photon absorption material, and two-photon absorption is caused by irradiation with recording light having a wavelength of 380 to 550 nm. Information recording is possible, and signal light is generated by irradiation with readout light having a wavelength of 400 to 660 nm. The recording layer may generate reflected light (having the same wavelength as the readout light) with the refractive index of the readout light changed as signal light, or fluorescence with a wavelength of 420 to 700 nm as signal light by irradiation of the readout light. However, in the present embodiment, a case where a signal light that generates fluorescence is used will be described. JP-A-2006-164451 discloses an example of a compound having a linear absorption wavelength of 200 nm, a two-photon absorption wavelength of 400 to 500 nm, and a fluorescence wavelength of 600 nm.

  The two-photon absorption recording medium recording / reproducing apparatus 100 of the present embodiment has a repetition frequency of 1 GHz or more and a wavelength of 380 nm as recording light Lw for inducing two-photon absorption to record information on the two-photon absorption recording medium 102. 550 nm, peak power 100 W or more, ultrashort pulse laser light source 103 that outputs an ultrashort pulse laser beam with a pulse width of 1 psec or less, and readout light Lr for reading information from the two-photon absorption recording medium 102 440 nm to 660 nm A reading laser light source 104 that outputs continuous wave light in a wavelength band and a detector 105 that detects signal light (here, fluorescence) Ls from the two-photon absorption recording medium 102 irradiated with the reading light Lr. Yes.

  The recording / reproducing apparatus 100 includes a quadrant detector 106 and a beam splitter 107 that reflects a part of light from the recording medium 102 toward the quadrant detector 106 as tracking servo means. Further, an intensity modulator 108 that modulates the intensity of recording light (hereinafter referred to as ultrashort pulse laser light) Lw output from the ultrashort pulse laser light source 103 according to information to be recorded, and a predetermined amount of the ultrashort pulse laser light Lw. A polarizing beam splitter 109 that reflects polarized light toward the recording medium 102 is provided, and a broadband λ / 4 wavelength plate 110, a condensing optical system 111, and an objective lens 112 are provided between the polarizing beam splitter 109 and the recording medium 102. ing. In addition, a beam splitter 113 that reflects a part of the readout light Lr output from the readout laser light source 104 toward the recording medium 102 is provided, and the readout light Lr is adjusted coaxially with the optical axis of the recording light. The light is reflected by the beam splitter 113 and irradiated onto the recording medium 102 through the beam splitter 107, the polarization beam splitter 109, the broadband λ / 4 wavelength plate 110, the optical system 111, and the objective lens 112. The objective lens 112 has an aberration correction function. The signal light Ls generated from the recording medium 102 when irradiated with the readout light Lr is configured to be detected by the detector 105 via the objective lens 112, the optical system 111, and the like. Between the recording medium 102 and the detector 105, a reading light cut filter 115, a condensing lens 116, and a pinhole 117 arranged confocally to constitute a confocal optical system are provided. The pinhole 117 has a function of removing the signal light Ls from outside the focused spot and increasing the spatial resolution.

  Further, the objective lens 112 is provided with a drive mechanism 119 that receives an error signal (servo signal) from the quadrant detector 106 and maintains focusing and tracking.

  The ultrashort pulse laser light source 103 includes the soliton mode-locked solid-state laser 10 that oscillates the soliton pulse laser light L and the soliton-pulse laser light L oscillated from the soliton mode-locked solid-state laser 10 described above. A non-linear optical element (SHG element) 11 that converts the light into a laser beam, and a lens 12 that condenses the soliton pulsed laser light L oscillated from the solid-state laser 10 onto the end face of the non-linear optical element 11, and an ultrashort pulse laser light source. From 103, the second harmonic of the soliton pulse laser beam (fundamental wave) L output from the solid-state laser 10 is output as the recording beam (ultrashort pulse laser) Lw. As the nonlinear optical element 11, PPKTP, PPLN, and PPLT are suitable.

  As the intensity modulator 108, for example, an electro-optic modulation element can be used, and specifically, a high-speed electro-optic modulation element having a waveguide type Mach-Zender interferometer configuration can be used. In the present embodiment, the intensity is modulated with respect to the second harmonic, but the intensity modulator is inserted between the SHG element 11 and the solid-state laser 10 and output from the solid-state laser 10. After the fundamental wave is intensity-modulated, the fundamental wave may be converted to the second harmonic through the SHG element 11.

  The readout laser light source is not particularly limited as long as it outputs continuous wave light in the wavelength range of 440 nm to 660 nm. Examples of the light source that outputs laser light having a wavelength in the range of 440 nm to 660 nm include an argon ion laser having a wavelength of 488 nm and a He-Ne laser having a wavelength of 632.8 nm. In addition, when the two-photon absorption material generates fluorescence, the wavelength of the reading light may be appropriately selected within a wavelength range in which fluorescence can be excited, and the light source needs to be selected according to the two-photon absorption material. .

  The readout light cut filter 115 is an optical filter that cuts the readout light Lr and allows only fluorescence to pass therethrough, thereby preventing SN reduction during readout. However, when the readout light and the fluorescence are close to each other, this filter cuts off the fluorescence at the same time.

  From the viewpoint of improving SN and recording density, it is desirable that the readout light and the signal light are as far apart as possible and have a shorter wavelength. For example, when the fluorescence wavelength of the signal light is 670 nm and the readout light is 630 nm, the wavelengths of the readout light and the signal light are close (the wavelength difference between the two lights is small) to avoid crosstalk with the readout light. If the reading light is sufficiently cut, the fluorescence amount is cut by about half at the same time, and the SN is decreased. On the other hand, when the fluorescence wavelength is 600 nm and the readout light is 488 nm, the wavelength difference between the two is 100 nm. Therefore, the transmission loss of fluorescence by the filter can be made almost zero, and the SN can be improved.

  In the case of a two-photon absorption material in which the refractive index is modulated by two-photon absorption, the readout light is reflected and modulated, so it has the same wavelength as the signal light and is not separated by the wavelength difference, but by the refractive index difference. Because of the separation, there is no problem as described above. However, there are some aspects where it is difficult to design materials that take the difference in refractive index.

  In the recording / reproducing apparatus 100 for a two-photon absorption recording medium having the above-described configuration, when recording information, the ultrashort pulse laser beam Lw from the ultrashort pulse laser light source 103 is modulated by an intensity modulator in accordance with information to be recorded. By irradiating the recording medium 102, information is written to the recording layer of the recording medium 102. The pulsed laser light Lw output from the light source 103 is modulated by the intensity modulator, and only the predetermined polarized light is reflected toward the recording medium by the polarization beam splitter, and this polarized light is λ / The recording medium is irradiated through a four-wavelength plate, an optical system, and an objective lens. At this time, the objective lens is driven by the drive system, and the laser beam is condensed at a desired depth direction position. Two-photon absorption occurs only in the condensing region of the laser light, the material physical property of the condensing region changes, and a compound that generates fluorescence when irradiated with readout light is obtained.

  On the other hand, at the time of reading, the reading light Lr from the reading laser light source 104 is reflected by the beam splitter, travels on the same axis as the optical axis of the recording pulse laser light Lw, and is irradiated onto the recording layer of the recording medium. By this irradiation, fluorescence is generated as signal light Ls from the recording area. The signal light Ls travels in the opposite direction on the optical axis of the readout light Lr, passes through the beam splitter, and is detected by the detector through the lens and pinhole, thereby reading out the information.

  Generally, when recording and reading information on a recording medium, it is necessary to apply a servo to the recording medium (disk) that rotates at high speed in order to always maintain focus and tracking. A tracking servo method in this embodiment will be described.

  The recording / reproducing apparatus 1 of the present embodiment is configured to acquire a servo signal with a recording light when performing information recording, and to acquire a servo signal with a reading light for performing reading when performing information reading. That is, it includes a servo servo means for recording including an ultrashort pulse laser light source 103 that is a light source for recording light and a four-divided photodiode 106, and a reading laser light source 104 that is a light source for reading light and a four-segment photodiode 106. By providing the servo acquisition means at the time of reading, accurate tracking servo can always be performed. In addition, as a recording medium having a multi-layer structure, a recording medium having a slight refractive index difference between the recording layer and an intermediate layer provided between the recording layers is used.

Specifically, as shown in FIG. 3, the servo at the time of recording maintains a peak power P ₁ that causes two-photon absorption to the recording pit (1) when recording data. For the non-recording pit (0), the peak power is not lowered to zero completely, and two-photon absorption does not occur, but the intensity modulator is maintained so as to maintain the peak power P ₀ sufficient for servo signal acquisition. To control the power of the recording light. Peak power P _o at the time the servo may be controlled to be about 1/10 of the peak power P ₁ at the time of recording. As a result, servo acquisition is possible without interruption during recording.

  On the other hand, the servo at the time of reading is performed by using a part of the reading light in the same way as the reading of a conventional CD, DVD or the like. As described above, in this embodiment, it is possible to realize a highly accurate servo by switching and using light (light source) for servo signal acquisition between recording and reading.

  As described above, in a normal CD or DVD, the servo signal is acquired by the reading light itself. In the case of a write once type (CD-R, DVD-R, etc.), light of the same wavelength, that is, light from the same light source, is used as recording light and reading light, and servo signal acquisition is performed during recording and reading. Sometimes light of the same wavelength is used.

  However, in the two-photon recording material recording / reproducing apparatus of the present invention, since the recording light and the reading light have different wavelengths, there is a problem of how to obtain the servo signal. As with conventional optical recording media, it is conceivable to use light of the same wavelength for recording and reading. Specifically, as described in Patent Document 1 described above, it is conceivable to always use read light for servo signal acquisition. However, the wavelengths of the recording light and the reading light are different, and both cause a slight focal position shift and chromatic aberration of the optical system. Therefore, if servo is performed with the reading light at the time of recording, the position shift occurs and the recording light records. It becomes difficult to accurately follow the pit. Further, as described in Non-Patent Document 1 described above, it is conceivable to provide another light source different from the recording light and the reading light for servo signal acquisition. There is a problem that the positional deviation due to the wavelength difference occurs and the number of device parts increases.

  On the other hand, as in this embodiment, the servo acquisition light source is switched between recording and reading, recording light is used during recording, and servo signals are acquired using reading light during reading. Even during recording, the recorded position can be tracked accurately.

  In the two-photon absorption recording / reproducing apparatus of the present invention, examples of the two-photon absorption material provided in the recording layer of the recording medium 102 used for recording and reproducing information include, for example, JP-A-2005-195922, JP 2005-29726 A, JP 2005-25152 A, JP 2004-352770 A, JP 2004-341425 A, JP 2004-339435 A, JP 2004-279795 A, JP JP 2004-279794, JP 2004-279674, JP 2004-250545, JP 2004-224864, JP 2004-149517, JP 2004-126441, JP 2004- The two-photon absorption materials disclosed in 126440, 2004-123668, 2003-183213, 2002-172864, etc. can be used. The recording medium 102 is a two-photon absorption three-dimensional recording material such as, for example, Japanese Patent Laid-Open No. 2007-262155, Japanese Patent Laid-Open No. 2007-87532, Japanese Patent Laid-Open No. 2007-59025, Japanese Patent Laid-Open No. 2007-17887, JP 2007-17886, JP 2007-17885, JP 2006-289613, JP 2005-320502, JP 2005-164817, JP 2005-100606, JP JP 2005-100599, JP 2005-92074, JP 2005-85350, JP 2005-71570, JP 2005-55875, JP 2005-37658, JP 2003- A material provided with a two-photon absorption three-dimensional recording material disclosed in Japanese Patent No. 75961, Japanese Patent Laid-Open No. 2003-29376, or the like can be used.

In addition, as a specific recording medium, a method for manufacturing a recording medium including the compound D-231 as a two-photon absorption material will be described.
<Synthesis Method of Compound D-231>
Compound D-231 is synthesized according to the following chemical formula.

Synthesis of raw material compound 1 (Example)
2.7 g (12 mmol) of 4-benzoylphenylboronic acid and 2.8 g (10 mmol) of 1-bromo-4-iodobenzene are dissolved in 50 ml of dimethylformamide (DMF), and then 0.6 g (0.5 mmol) of tetrakis (triphenylphosphine) platinum. And 6.5 g (20 mmol) of cesium carbonate were added and heated for 8 hours under a nitrogen stream.
The reaction solution is allowed to cool, extracted with distilled water and about 600 ml of ethyl acetate, the aqueous layer is removed, the organic layer is separated, and dried over magnesium sulfate. The filtrate from which magnesium sulfate has been filtered off is evaporated to dryness on a rotary evaporator and purified by a silica gel column (ethyl acetate: hexane = 1: 10) to obtain 1.6 g (yield 48%) of colorless raw material compound 1. I was able to.

Synthesis of raw material compound 2 (Example)
0.68 g (2 mmol) of raw material compound 1, 0.63 g (2.5 mmol) of bis (pinacolato) diboron, 0.59 g (6 mmol) of potassium acetate and [1,1′-bis (diphenylphosphino) ferrocene] dichloropalladium 100 mg (0.12 mmol) was suspended in 50 ml of DMF and heated at 80 ° C. for 9 hours under a nitrogen stream. The reaction solution was allowed to cool, extracted by adding distilled water and ethyl acetate, the aqueous layer was removed, the organic layer was separated, and dried over magnesium sulfate. The filtrate from which magnesium sulfate has been filtered off is evaporated to dryness on a rotary evaporator and purified by a silica gel column (ethyl acetate: hexane = 1: 20) to obtain 0.65 g (yield 85%) of colorless raw material compound 2. I was able to.

Synthesis of raw material compound 3 (Example)
After dissolving 1.76 g (12 mmol) of 4-cyanobenzeneboronic acid and 2.8 g (10 mmol) of 1-bromo-4-iodobenzene in 60 ml of DMF, 0.6 g (0.5 mmol) of tetrakis (triphenylphosphine) platinum and 6.5 of cesium carbonate Add g (20 mmol) and heat at 120 ° C. for 8 hours under nitrogen flow. The reaction solution was allowed to cool, extracted by adding distilled water and about 600 ml of ethyl acetate, the aqueous layer was removed, the organic layer was separated, and dried over magnesium sulfate. The filtrate from which magnesium sulfate has been filtered off is evaporated to dryness on a rotary evaporator and purified by a silica gel column (ethyl acetate: hexane = 1: 10) to obtain 0.53 g (yield 21%) of colorless raw material compound 3. I was able to.

Example Synthesis of Compound D-231
0.5 g (1.3 mmol) of raw material compound 2 and 0.33 g (1.3 mmol) of raw material compound 3 are dissolved in a mixed solvent of 20 ml of distilled water and 14 ml of ethylene glycol dimethyl ether, and 14.6 mg (0.065 mmol) of palladium acetate, triphenylphosphine 34 mg (0.13 mmol) and 0.97 g (7 mmol) of potassium carbonate were added and heated under reflux for 2 hours. The reaction solution was allowed to cool, extracted by adding distilled water and dichloromethane, the aqueous layer was removed, the organic layer was separated, and dried over magnesium sulfate. The filtrate obtained by filtering off magnesium sulfate is evaporated to dryness on a rotary evaporator to obtain a crude product. The obtained crude product was purified by sublimation to obtain 0.11 g (yield 19%) of the target compound D-231.

A preparation example of a two-photon absorption recording material provided with D-231 is given.
(Preparation example 1 of two-photon absorption recording material)
Two-photon absorption compound: D-231 1.0 part by mass Dye precursor: DP-1 3.3 parts by mass Acid generator: PAG-1 5.0 parts by mass Binder: 100 parts by mass of polyvinyl acetate Coating solvent: Dichloromethane 2800 parts by mass Part

(Preparation example 2 of two-photon absorption recording material)
Two-photon absorption compound: D-231 1.0 part by mass Dye precursor: Lo-11 3.3 parts by mass Binder: poly (methyl methacrylate-co-ethyl acrylate)
(Aldrich, Mw = 101,000) 66.7 parts by mass Coating solvent: 1400 parts by mass of dichloromethane

(Preparation example 3 of two-photon absorption recording material)
Two-photon absorption compound: D-231 1.0 part by weight Monomer: M-1 92 parts by weight Polymerization initiator: I-1 2.0 parts by weight Binder: Cellulose acetate butyrate 100 parts by weight Coating solvent: Dichloromethane 2900 parts by weight

The dye precursor: DP-1, acid generator: PAG-1, monomer: M-1, and polymerization initiator: I-1 used are as follows.

<Production of two-photon absorption recording medium>
The two-photon absorption recording medium can be produced as a thin film by spin-coating the two-photon absorption recording materials mentioned in Preparation Examples 1 to 3 on a slide glass.
Note that the two-photon absorption recording medium obtained by applying the two-photon absorption recording material described in Preparation Examples 1 to 3 to form a thin film is 522 nm obtained from the ultrashort pulse laser light source in the recording / reproducing apparatus of the above embodiment. It was possible to record information by non-resonant two-photon absorption at a wavelength of. In addition, for the reproduction of the information thus recorded, the recording medium obtained from Preparation Examples 1 and 2 obtained a fluorescence signal generated by the irradiation of 633 nm helium neon laser light from Preparation Example 3. In the recording medium, a reflected light signal obtained by irradiation with a semiconductor laser beam of 405 nm or 450 nm could be used.

  For a two-photon polymerization composition which generates a polymerization reaction by two-photon absorption, a recording reaction used in the two-photon absorption recording / reproducing apparatus of the present invention as a light source for generating a polymerization reaction and performing two-photon fine three-dimensional stereolithography A light source can be suitably used. That is, as a light source of a three-dimensional stereolithography apparatus, an ultrashort pulse laser light source that outputs an ultrashort pulse laser beam having a repetition frequency of 1 GHz or more, a wavelength of 380 nm to 550 nm, a peak power of 100 W or more, and a pulse width of 1 psec or less, A resonator formed of a semiconductor saturable absorption mirror 14, a solid-state laser medium 16 to which a rare earth element or a transition metal is added, and a group velocity dispersion in the resonator are controlled. And a soliton mode-locked solid-state laser 10 that oscillates soliton pulsed laser light, and a soliton mode-locked device. A nonlinear optical element 11 for converting soliton pulsed laser light oscillated from the solid-state laser 10 into a second harmonic; By applying an ultrashort pulse laser light source 103 formed by a, it is possible to obtain a compact and stable three-dimensional optical modeling apparatus.

  As the two-photon polymerization material used in the two-photon polymerization composition, JP-A-2006-78876, JP-A-2005-97538, JP-A-2005-29725, JP-A-2005-23126, Examples thereof include two-photon polymerization materials disclosed in JP-A-2005-15699, JP-A-2004-346238, JP-A-2004-292476, JP-A-2004-292475, and the like.

10 Soliton mode-locked solid-state laser 11 Non-linear optical element 12 Lens 13 Excitation optical system 14 SESAM
16 Solid-state laser medium 18 Dichroic mirror 20 Negative dispersion mirror 22 Peltier element 24 Peltier drive unit 26 Semiconductor laser 28 Selfoc lens 30 Excitation optical system holder 32 Dichroic mirror holder 34 Resonator holder 35 Control system holder 36 Copper plate 40 Beam splitter 42 Photodiode 44 control unit 46 substrate 48 lid member 48A transmission window 100 two-photon absorption recording medium recording / reproducing apparatus 102 two-photon absorption recording medium 103 ultrashort pulse laser light source 104 reading laser light source 105 detector 106 quadrant detector 107 beam splitter 108 intensity Modulator 109 Polarizing beam splitter 110 Wave plate 111 Condensing optical system 112 Objective lens 113 Beam splitter 115 Reading light cut filter 116 Condensing lens 117 Pinhole 119 Mechanism L soliton pulse laser light Lr reading light Ls signal light Lw recording light (ultrashort pulse laser beam)

Claims (8)

A recording / reproducing apparatus for recording and reading information on a two-photon absorption recording medium,
As recording light for inducing simultaneous two-photon absorption in the two-photon absorption recording medium and recording information on the two-photon absorption recording medium, a repetition frequency of 1 GHz or more, a wavelength of 380 nm to 550 nm, a peak power of 100 W or more, a pulse width An ultrashort pulse laser light source that outputs an ultrashort pulse laser beam of 1 psec or less;
A reading laser light source that outputs continuous wave light in a wavelength region of 440 nm to 660 nm as reading light for reading information from the two-photon absorption recording medium;
A two-photon absorption recording medium recording / reproducing apparatus comprising: a detecting unit that detects reflected light or fluorescence from the two-photon absorption recording medium irradiated with the reading light.   The ultrashort pulse laser light source includes a resonator having one end formed of a semiconductor saturable absorption mirror, a solid-state laser medium provided with a rare earth element or a transition metal provided in the resonator, and the resonator A soliton mode-locked solid-state laser that oscillates soliton pulsed laser light, comprising a negative group velocity dispersion compensating element for controlling group velocity dispersion in the light source and a pumping optical system that outputs pumping light for pumping the solid-state laser medium, 2. The two-photon absorption recording according to claim 1, further comprising: a nonlinear optical element that converts the soliton pulsed laser light oscillated from the soliton mode-locked solid-state laser into a second harmonic. Medium recording / reproducing apparatus.   3. The two-photon absorption recording medium recording / reproducing apparatus according to claim 2, wherein in the ultrashort pulse laser light source, a resonator length of the resonator is 150 mm or less.   3. The two-photon absorption recording medium recording / reproducing apparatus according to claim 2, wherein in the ultrashort pulse laser light source, a resonator length of the resonator is 75 mm or less. _{3. The} ultrashort pulse laser light source, wherein the nonlinear optical element is composed of any one of a periodically poled LiNbO ₃ element, a periodically poled LiTaO ₃ element, and a periodically poled KTiOPO _4. 4. The two-photon absorption recording medium recording / reproducing apparatus according to any one of claims 4 to 6. In the ultrashort pulse laser light source, the negative group velocity dispersion compensating element is a negative dispersion mirror, the negative dispersion amount is −3000 fs ² or more and 0 fs ² or less, and the transmittance is 0.1% or more and 3%. 6. The two-photon absorption recording medium recording / reproducing apparatus according to claim 2, wherein: In the ultrashort pulse laser light source, the negative group velocity dispersion compensating element is a negative dispersion mirror, and the negative dispersion mirror constitutes the other end of the resonator,
The ultrashort pulse laser light source includes a linear resonator holder that holds the semiconductor saturable absorption mirror constituting one end of the resonator and the negative dispersion mirror constituting the other end of the resonator on a straight line. The two-photon absorption recording medium recording / reproducing apparatus according to claim 2, wherein When recording information on the two-photon absorption recording medium with the ultrashort pulse laser beam, a servo signal at the time of recording is obtained by receiving the reflected light from the two-photon absorption recording medium of the ultrashort pulse laser beam. Acquisition means;
When reading information from the two-photon absorption recording medium by the continuous wave light, a servo signal acquisition means at the time of reading that receives a reflected light or fluorescence of the continuous wave light from the two-photon absorption recording medium and acquires a servo signal The two-photon absorption recording medium recording / reproducing apparatus according to claim 1, comprising:

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