JP2014216538A - Solid-state laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state laser device of flash lamp excitation enabling highly efficient stable laser oscillation.SOLUTION: The solid-state laser device is used that includes: a resonator that outputs laser light; a solid laser medium disposed in the resonator; a flash lamp that irradiates the laser medium with excitation light; and heating means, provided so as to cover at least a part of the laser medium, that heats up the laser medium.

Description

  The present invention relates to a solid-state laser device.

  Research on an optical imaging apparatus that irradiates a subject such as a living body with light from a light source such as a laser and images information in the subject obtained based on incident light has been actively promoted in the medical field. One of such optical imaging techniques is PAT (Photo Acoustic Tomography). In PAT, a subject is irradiated with pulsed light generated from a light source, and acoustic waves generated from tissue in the subject that absorbs the energy of pulsed light that has propagated and diffused in the subject are detected. This acoustic wave generation phenomenon is called a photoacoustic effect, and an acoustic wave generated by the photoacoustic effect is called a photoacoustic wave.

  A test site such as a tumor often absorbs more light than the surrounding tissue and expands instantaneously because the absorption rate of light energy is often higher than that of the surrounding tissue. A photoacoustic wave generated during the expansion is detected by an acoustic wave detector to obtain a received signal. By mathematically analyzing the received signal, the sound pressure distribution of the photoacoustic wave generated by the photoacoustic effect in the subject can be imaged (hereinafter referred to as a photoacoustic image). Based on the photoacoustic image obtained in this way, the optical characteristic distribution in the subject, particularly the absorption coefficient distribution, can be acquired. Such information can also be used for quantitative measurement of a specific substance in the subject, for example, glucose or hemoglobin contained in blood. In recent years, research on a photoacoustic imaging apparatus aimed at imaging a blood vessel image of a small animal using PAT or applying it to diagnosis of breast cancer or the like has been actively promoted.

  In vivo substances such as glucose and hemoglobin have different absorption rates depending on the wavelength of incident light. Therefore, the distribution of the substance in the living body can be measured more accurately by irradiating light having different wavelengths and analyzing the difference in the absorption coefficient distribution. Generally, light having a wavelength of 500 nm to 1200 nm is used as irradiation light. In particular, when it is necessary to avoid absorption of melanin or water, near infrared light having a wavelength of 700 nm to 900 nm is used as incident light.

  The alexandrite laser is a tunable solid-state laser having a gain band in the above wavelength range. It is known that the gain of alexandrite crystals is temperature-dependent, and the gain increases as the crystal temperature increases (Non-patent Document 1). Therefore, high gain is achieved by heating the alexandrite crystals by circulating hot water of about 60 ° C. to 80 ° C. On the other hand, in general, a flash lamp used for crystal excitation needs water cooling. For this reason, water of about 30 ° C. to 40 ° C. is circulated for cooling the lamp. An example in which the circulation of water for crystallization and the circulation of water for lamps are independently provided is disclosed in Patent Document 1. An example of heating a laser crystal with a heater is disclosed in Patent Document 2.

JP-A-5-13840 JP 2012-33818 A

IEEE J. Quantum Electron., Vol.QE-19, pp.480-483, Mar. 1983

  When the circulation of water for crystallization and the circulation of water for lamps are provided independently as in Patent Document 1, a temperature adjustment mechanism and a pump for circulation are necessary for each, and the apparatus becomes large and expensive. There is a problem to do. Further, when the laser crystal is heated with water, the temperature cannot be raised to 100 ° C. or higher, and there is a limit to further increasing the gain. Further, Patent Document 2 irradiates the crystal with excitation light from a semiconductor laser along the resonance direction, and cannot be applied to an apparatus that irradiates excitation light from the side surface of the crystal, such as flash lamp excitation.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a flash lamp-pumped solid-state laser device capable of high-efficiency and stable laser oscillation.

The present invention employs the following configuration. That is,
A resonator that outputs laser light;
A solid-state laser medium disposed inside the resonator;
A flash lamp for irradiating the laser medium with excitation light;
A heating means for heating the laser medium provided to cover at least a part of the laser medium;
Is a solid-state laser device.

  According to the present invention, it is possible to provide a flash lamp-pumped solid-state laser device capable of high-efficiency and stable laser oscillation.

The schematic diagram explaining a 1st Example. The figure explaining the shape of the resistive film in a 1st Example. The schematic diagram explaining the 2nd Example. Schematic diagram illustrating a third embodiment. The schematic diagram explaining a 4th Example. FIG. 10 is a schematic diagram for explaining a fifth embodiment. Schematic diagram illustrating a sixth embodiment. FIG. 10 is a schematic diagram for explaining a seventh embodiment. The schematic diagram explaining the 8th Example. The schematic diagram explaining the 9th Example.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described below should be changed as appropriate according to the configuration of the apparatus to which the invention is applied and various conditions. It is not intended to limit the following description.

The present invention can be applied to a solid-state laser device. The present invention can also be applied to an object information acquisition apparatus that acquires photoacoustic waves generated from an object by pulse laser irradiation and generates characteristic information in the object.
Hereinafter, each component of the solid-state laser device according to the present invention and the mechanism of laser output will be described.

(Laser medium)
The laser medium absorbs excitation light from the flash lamp and emits light having a desired wavelength.
In the following examples, examples using Alexandrite crystals are shown, but other crystals may be used.

(Flash lamp)
The flash lamp emits light that serves as excitation light for the laser medium. The flash lamp is usually cooled with water by circulating water at 30 ° C. to 40 ° C. from the viewpoint of life.

(Heating means)
The heating means heats the laser medium. The heating means is installed so as to cover at least a part of the laser medium.
In one form, a heating means is transparent with respect to excitation light, and excitation light passes through a heating means and is irradiated to a laser medium. As the heating means, for example, a quartz glass with a resistance film mainly composed of ITO or ZnO, or a resistance film directly formed on the side surface of a laser medium can be used. The transmittance of the heating means for the excitation light is desirably 75% or more. If the transmittance is smaller than this, it is not practical because it is necessary to increase the input power of the flash lamp or excessively heat the laser medium in order to obtain laser light with a desired output. Even in this form, the heating means does not necessarily need to cover the entire laser medium. Further, the resistance film of the heating means does not necessarily need to cover the entire glass.

  In another embodiment, the heating means covers a part of the laser medium, and the excitation light is irradiated to the laser medium through a region not covered with the heating means. In this case, the heating means does not need to be transparent to the excitation light. In order to return the light that has passed through the laser medium to the laser medium again, it is desirable that the surface of the heating means is covered with a material having a high reflectance or a high diffuse reflectance with respect to light having a wavelength that excites the laser medium. . For example, it is preferable to arrange a white ceramic such as alumina on the surface.

(Lamp chamber)
The lamp chamber efficiently transmits light from the flash lamp to the laser medium. The lamp chamber has a hollow structure in which a flash lamp and a laser medium are arranged. The surface of the lamp chamber is covered with a material having a high diffuse reflectance (for example, barium sulfate) or a metal having a high reflectance (for example, gold). In addition, ceramics such as macerite (registered trademark of Nippon Coke Kogyo Co., Ltd.) may be processed into a hollow structure.

(Output coupler)
The output coupler extracts part of the light inside the resonator to the outside of the resonator and returns the rest to the inside of the resonator. The output coupler is composed of a mirror having an appropriate reflectance for light of a desired wavelength.

(Wavelength selection means)
The wavelength selection means selectively resonates light having a desired wavelength. The wavelength selection means is composed of one birefringent plate or a plurality of birefringent plates made of a uniaxial crystal (for example, quartz) processed so that the optical axis is parallel to the plate surface. Or what uses the wavelength dispersion of a prism may be used.

(Rear mirror)
The rear mirror reflects light inside the resonator and returns it to the inside of the resonator. The rear mirror is generally composed of a dielectric multilayer film having a reflectance of 95% or more.

(Power control means)
The power control means adjusts the input power to the heating means in accordance with the output from the measurement means, and performs control so as to keep the output from the temperature measurement means constant.

(Temperature measuring means)
The temperature measuring unit measures the temperature of the laser medium or the heating unit. The temperature measuring means is composed of, for example, a thermistor.

(Light intensity measuring means)
The light quantity measuring means is provided outside the laser resonator and monitors the laser output (light quantity).

(Wavelength detection means)
The wavelength detection means detects the wavelength selected by the wavelength selection means. When there is a correlation between the wavelength selection means state (for example, position and angle) and the wavelength, the state may be detected.

(Control of the entire device)
Light irradiation by the flash lamp, operation of the wavelength selection means, measurement by the temperature measurement means, monitoring by the light quantity measurement means, measurement by the wavelength detection means, etc. are performed by hardware such as a control circuit or software in which various controls are pre-programmed. Be controlled. In the case of hardware control, a control circuit for each component, including a control circuit for each component and a circuit for controlling the operation timing thereof, may be considered as control means for the entire laser apparatus. In the case of software control, an information processing device such as a CPU and software operating on the information processing device may be considered as control means. In the control, the operation of each component is executed in conjunction with each other according to a predetermined flow or timing chart. Further, at that time, input regarding numerical setting or operation instruction from the operator may be received and reflected in the operation. In addition, adjustment of input power by the above-described power control unit may be included in the control of the entire apparatus.
A more detailed configuration will be described in the following examples.

<First embodiment>
FIG. 1 is a schematic view for explaining a first embodiment of the laser apparatus of the present invention. FIG. 1A shows a cross-sectional view in a plane parallel to the resonance direction, and FIG. 1B shows a cross-sectional view in a plane perpendicular to the resonance direction.

(Device configuration)
In the figure, reference numeral 101 denotes a laser medium made of a cylindrical alexandrite crystal having a diameter of 6.25 mm. Reference numeral 103 denotes a heating means, which includes a quartz glass tube 105 having an inner diameter of 8.5 mm and a resistance film 107 made of an ITO thin film formed on the entire surface of the quartz glass tube 105. The thickness of the resistance film 107 is adjusted so that the sheet resistance is about 150Ω. The visible light transmittance of the heating means 103 is approximately 75 to 80%. Reference numeral 109 denotes electrodes made of Al provided at both ends of the resistance film 107. Although not shown in the drawing, the electrode 109 is electrically connected to a current source. By passing a desired current through the resistance film 107, the quartz glass tube 105 is heated to about 120 ° C., and the laser medium 101 provided inside the quartz glass tube 105 is also heated to a similar temperature.

Reference numeral 113 denotes a flash lamp, which is disposed in a glass tube 115 made of quartz. Although not shown in the drawing, the flash lamp 113 is connected to a pulse power source and emits excitation light. Reference numeral 117 denotes cooling water. Although not shown in the drawing, the glass tube 115 is connected to a pump and a thermostatic bath, and the cooling water 117 is adjusted to about 40 ° C. and circulates. Reference numeral 111 denotes a lamp chamber whose inner wall is covered with a diffuse reflector made of barium sulfate. Excitation light emitted from the flash lamp 113 is emitted from the lamp chamber 111.
Is diffusely reflected on the surface of the laser beam, passes through the heating means 103 and reaches the laser medium 101.

  Reference numeral 119 denotes a housing. The laser medium 101 and the heating means 103 are fixed to the housing 119 by support members 121 and 123 made of fluorine resin having excellent heat resistance. The glass tube 115 is fixed to the housing 119 by sealing materials 125 and 127 that seal the cooling water 117. The flash lamp 113 is supported by a housing 119 and is sealed by rubber O-rings 129 and 131 provided at both ends.

  Reference numeral 133 denotes a rear mirror having a reflectance of 99%. Reference numeral 135 denotes an output coupler having a reflectance of 50%. Reference numeral 137 denotes a wavelength selection means composed of three birefringent plates. The wavelength selection unit 137 rotates around an axis perpendicular to the birefringent plate, so that only light having a desired wavelength can be selectively transmitted.

(Device operation)
An operation example of such an apparatus will be described. A pulse having an energy of 70 J and a pulse width of 150 μs was applied to the flash lamp 113. The selection wavelength of the wavelength selection means 137 was set to 750 nm, and the temperature of the laser medium was set to about 120 ° C. In this case, a laser beam having a pulse energy of about 200 mJ was obtained.
In another example of operation, the input energy to the lamp is the same, the wavelength selected by the wavelength selector 133 is set to 780 nm, and the temperature of the laser medium is set to about 135 ° C. In this case, a laser beam having a pulse energy of about 200 mJ was obtained.

(effect)
In the present embodiment, the presence of the heating means 103 allows the alexandrite crystal to be heated to a high temperature of 100 ° C. or higher, so that a high gain can be achieved. Therefore, a large laser output can be obtained with a small input power compared to a method using warm water. Further, since the high gain region is used, it is possible to reduce variations in laser output for each pulse. Furthermore, since a warm water circulation mechanism is not required, the apparatus can be miniaturized. As described above, according to the present invention, highly efficient and stable laser oscillation is possible.

  When the solid-state laser according to this embodiment is applied to a PAT apparatus, the pulse width is desirably 100 ns or less from the viewpoint of resolution. In order to narrow the pulse width, a so-called Q switch structure may be adopted in which a Pockels cell is inserted into the laser resonator and a giant pulse is generated by switching ON / OFF of a high voltage applied to the Pockels cell.

(Modification)
In this example, a heating means provided with a resistor having a pattern as shown in FIG. However, the shape of the resistive film is not limited to this. For example, as shown in FIGS. 2B to 2D, a region where no resistive film is present may be provided. Thereby, the further improvement of the transmittance | permeability of excitation light can be anticipated. The structure of FIG. 2B is relatively easy to manufacture. On the other hand, since the structure is constant in the resonance direction and periodic in the circumferential direction, there is a possibility of inducing higher-order mode oscillation of the laser light. 2C and 2D, there is an effect that the gain is averaged when propagating in the resonance direction.

  Further, in the present embodiment, an example in which the wavelength selecting means is provided in the laser resonator is shown, but the means may not be provided. In this case, oscillation occurs in the vicinity of 755 nm, which is the wavelength region with the largest gain, but it goes without saying that there is an effect of increasing the gain by improving the crystal temperature.

<Second embodiment>
FIG. 3 is a schematic view for explaining a second embodiment of the laser apparatus of the present invention. The description of the parts common to the first embodiment is omitted, and the same drawing numbers are added. The difference from the first embodiment is that a temperature control mechanism is provided.

  In FIG. 3, reference numeral 201 denotes a current source capable of current control (corresponding to a control unit), which injects a current into the heating unit 103 via the electric wirings 205 and 207. Reference numeral 203 denotes a temperature measuring means comprising a thermistor, and the sensor unit is fixed to the inner wall of the heating means 103.

  In this embodiment, the temperature of the laser medium 101 can be kept constant by controlling the input power to the heating means in accordance with the output from the temperature measuring means. For example, if the measured temperature is lower than a predetermined value, heating is performed, and heating is stopped when the predetermined value is reached. Further, the degree of heating may be controlled according to the difference from the predetermined value. As a result of such control, the laser output can be stabilized.

<Third embodiment>
FIG. 4 is a schematic view for explaining a third embodiment of the laser apparatus of the present invention. The description of the parts common to the first embodiment is omitted, and the same drawing numbers are added. The difference from the first embodiment is that a laser output control mechanism is provided.

  In FIG. 4, reference numeral 241 denotes a current source (corresponding to a control unit) capable of current control, and injects a current into the heating unit 103 via the electric wirings 205 and 207. Reference numeral 243 denotes a beam sampler, which extracts laser light. The laser light extracted by the beam sampler 243 is detected by a light amount measuring unit 245 including a pyroelectric sensor.

  There is a monotonically increasing relationship between the gain and temperature of the alexandrite crystal, where the gain increases as the temperature increases. Therefore, the crystal temperature may be increased when the laser output is increased, and the crystal temperature may be decreased when the laser output is decreased.

  Therefore, in this embodiment, it is possible to keep the laser output constant by controlling the input power to the heating means in accordance with the output from the light quantity measuring means. For example, if the measured light quantity is lower than a predetermined value, heating is performed to increase the crystal temperature, and heating is stopped when the predetermined value is reached. As a result of such control, the laser output can be stabilized.

<Fourth embodiment>
FIG. 5 is a schematic view for explaining a fourth embodiment of the laser apparatus of the present invention. The description of the parts common to the first embodiment is omitted, and the same drawing numbers are added. The difference from the first embodiment is that a laser output stabilization mechanism that does not require a laser output monitor is provided.

In FIG. 5, reference numeral 261 denotes a current source capable of current control (corresponding to a control unit), and injects a current into the heating unit 103 via the electric wirings 205 and 207. Reference numeral 263 denotes a rotation stage serving as a wavelength detection unit, and also has a function of detecting the angle of the wavelength selection unit 137. The relationship between the angle of the wavelength selection means 137 and the transmitted wavelength is almost linear, and the wavelength of the laser beam can be grasped by monitoring the angle.
The relationship between the angle of the wavelength selection means 137 (that is, the oscillation wavelength) and the crystal temperature for obtaining a desired laser output is previously measured and tabulated.

  In this embodiment, the laser output is kept constant even when the wavelength is changed by controlling the input power to the heating means using the table according to the output (angle information) from the wavelength detecting means. It becomes possible. As a result of such control, the laser output can be stabilized. Therefore, it is particularly effective when obtaining the concentration distribution of the substance in the subject based on the measurement results of a plurality of wavelengths using a wavelength tunable laser.

<Fifth embodiment>
FIG. 6 is a schematic view for explaining a fifth embodiment of the laser apparatus of the present invention. The description of the parts common to the first embodiment is omitted, and the same drawing numbers are added. The difference from the first embodiment is that the laser medium has a direct heating mechanism.
6A shows a cross section along a plane parallel to the resonance direction, and FIG. 6B shows a cross section along a plane perpendicular to the resonance direction.

  In the figure, reference numeral 301 denotes a laser medium made of a cylindrical alexandrite crystal having a diameter of 6.25 mm. Reference numeral 303 denotes a heating means, which includes a resistance film 307 made of an ITO thin film formed on the entire surface of the laser medium 301. The thickness of the resistance film 307 is adjusted so that the sheet resistance is about 150Ω. Reference numeral 309 denotes an electrode made of Al provided at both ends of the resistance film 307. Although not shown in the figure, the electrode 309 is electrically connected to a current source. The laser medium 301 is heated to about 120 ° C. by applying a desired current to the resistance film 307. Reference numeral 311 denotes a lamp chamber whose inner wall is covered with a diffuse reflector made of barium sulfate. The excitation light emitted from the flash lamp 113 is diffusely reflected on the surface of the lamp chamber 311, passes through the heating means 303, and reaches the laser medium 301.

  Reference numeral 319 denotes a housing. The laser medium 101 is fixed to the housing 319 by support members 321 and 323 made of fluorine resin having excellent heat resistance. The glass tube 115 is fixed to the housing 319 by sealing materials 125 and 127 that seal the cooling water 117. The flash lamp 113 is supported by a housing 319 and is sealed by rubber O-rings 129 and 131 provided at both ends.

  In this embodiment, since the heating means is directly attached to the laser medium, there is an advantage that the response characteristic when heated is quick. Therefore, the effect that a high gain is obtained when the heating means raises the temperature of the laser medium is quickly exhibited. The advantages of reducing variations in laser output, downsizing the apparatus, and highly efficient and stable laser oscillation can be enjoyed as they are.

<Sixth embodiment>
FIG. 7 is a schematic view for explaining a sixth embodiment of the laser apparatus of the present invention. The description of the parts common to the first embodiment is omitted, and the same drawing numbers are added.
FIG. 7A shows a cross section in a plane parallel to the resonance direction, and FIG. 7B shows a cross section in a plane perpendicular to the resonance direction.

  In the figure, reference numeral 401 denotes a laser medium made of a cylindrical alexandrite crystal having a diameter of 6.25 mm. Reference numeral 403 denotes a heating means, which is composed of a sintered body of aluminum oxide in which a heating wire is embedded. The heating means 403 is disposed so as to surround the laser medium 401 except for the side where the flash lamp 113 is present. Although not shown in the figure, the heating means 403 is electrically connected to a current source. Reference numeral 411 denotes a lamp chamber whose inner wall is covered with a diffuse reflector made of barium sulfate.

  Reference numeral 419 denotes a housing. The laser medium 401 is fixed to the housing 419 by support members 421 and 423 made of a fluorine resin having excellent heat resistance. Further, the glass tube 115 is fixed to the housing 419 by sealing materials 125 and 127 that seal the cooling water 117. The flash lamp 113 is supported by a housing 419 and is sealed by rubber O-rings 129 and 131 provided at both ends.

Each shape is determined so that the inner wall of the heating means 403 and the inner wall of the lamp chamber 411 are connected almost continuously. The excitation light emitted from the flash lamp 113 is diffusely reflected on the surface of the lamp chamber 411 and reaches the laser medium 401. Further, the light hitting the inner wall of the heating means 403 is also diffusely reflected on the surface and reaches the laser medium 401.

An operation example of such an apparatus will be described. A pulse having an energy of 70 J and a pulse width of 150 μs was applied to the flash lamp 113. The selection wavelength of the wavelength selection means 133 was set to 750 nm, and the temperature of the laser medium was set to about 120 ° C. In this case, a laser beam having a pulse energy of about 150 mJ was obtained.
In another example of operation, the input energy to the lamp is the same, the wavelength selected by the wavelength selector 133 is set to 780 nm, and the temperature of the laser medium is set to about 135 ° C. In this case, a laser beam having a pulse energy of about 150 mJ was obtained.

  According to the present embodiment, it is possible to provide a laser device capable of both heating the laser medium with a heater that does not transmit light and exciting the laser medium with flash lamp light.

<Seventh embodiment>
FIG. 8 is a schematic view for explaining a seventh embodiment of the laser apparatus of the present invention. Descriptions of parts common to the sixth embodiment are omitted, and the same drawing numbers are added. The difference from the sixth embodiment is that the housing is not required and miniaturization is possible.
8A shows a cross section along a plane parallel to the resonance direction, and FIG. 8B shows a cross section along a plane perpendicular to the resonance direction.

  In the figure, reference numeral 501 denotes a laser medium made of a cylindrical alexandrite crystal having a diameter of 6.25 mm. Reference numeral 503 denotes a heating means, which is composed of a sintered body of aluminum oxide in which a heating wire is embedded. The heating means 503 is arranged so as to surround the laser medium 501 except for the side where the flash lamp 513 exists. Although not shown in the figure, the heating means 503 is electrically connected to a current source. Reference numeral 511 denotes a lamp chamber, and the inner wall is covered with a diffuse reflector made of barium sulfate.

  The laser medium 501 is fixed to the heating means 503 or the lamp chamber 511 by support members 521 and 523 made of a fluorine resin having excellent heat resistance. Reference numeral 515 denotes a glass plate made of quartz, and the glass plate 515 is fixed to the lamp chamber 511 by a sealing material 527 for sealing the cooling water 517. The sealing material 527 is provided on the entire circumference of the glass plate 515. The flash lamp 513 is supported by the lamp chamber 511 and is sealed by rubber O-rings 529 and 531 provided at both ends.

  Each shape is determined so that the inner wall of the heating means 503 and the inner wall of the lamp chamber 511 are connected substantially continuously. The excitation light emitted from the flash lamp 513 is diffusely reflected on the surface of the lamp chamber 511 and reaches the laser medium 501. Further, the light hitting the inner wall of the heating means 503 is diffusely reflected on the surface and reaches the laser medium 501.

  This embodiment is suitable for downsizing compared to the sixth embodiment.

<Eighth embodiment>
FIG. 9 is a schematic view for explaining an eighth embodiment of the laser apparatus of the present invention. Description of the parts common to the seventh embodiment is omitted, and the same drawing numbers are added. The difference from the seventh embodiment is that there are two flash lamps.
FIG. 9A shows a cross section along a plane parallel to the resonance direction, and FIG. 9B shows a cross section along a plane perpendicular to the resonance direction.

  In the figure, reference numeral 601 denotes a laser medium made of a prismatic alexandrite crystal whose cross section is a square having a side of 7 mm. Reference numeral 603 denotes a heating means, which is composed of a sintered body of aluminum oxide in which a heating wire is embedded. The heating means 603 is arranged so that the laser medium 601 can be heated from above and below. Although not shown in the figure, the heating means 603 is electrically connected to a current source. Reference numerals 511 and 611 denote lamp chambers whose inner walls are covered with a diffuse reflector made of barium sulfate.

  The laser medium 601 is fixed to the heating means 603 or the lamp chambers 511 and 611 by support members 621 and 623 made of fluorine resin having excellent heat resistance. Reference numerals 515 and 615 denote glass plates made of quartz, and the glass plates 515 and 615 are fixed to the lamp chambers 511 and 611 by sealants 527 and 627 that seal the cooling water 517 and 617. The sealing materials 527 and 627 are provided on the entire circumference of the glass plates 515 and 615. The flash lamps 513 and 613 are supported by lamp chambers 511 and 611 and are sealed by rubber O-rings 529, 531, 629 and 631 provided at both ends.

  Each shape is determined so that the inner wall of the heating means 603 and the inner walls of the lamp chambers 511 and 611 are connected substantially continuously. The excitation light emitted from the flash lamp 513 is diffusely reflected on the surface of the lamp chamber 511 and reaches the laser medium 601. The excitation light emitted from the flash lamp 613 is diffusely reflected on the surface of the lamp chamber 611 and reaches the laser medium 601. Light hitting the inner wall of the heating means 603 is also diffusely reflected on the surface and reaches the laser medium 601.

  In the present embodiment, as compared with the seventh embodiment, excitation is performed by two flash lamps, so that the output of laser light can be increased. In addition, since the structure is symmetric, laser light with excellent mode stability can be obtained.

<Ninth embodiment>
FIG. 10 shows an example in which the laser device according to the present invention is incorporated in a photoacoustic image apparatus.
In the figure, reference numeral 1001 denotes a laser device using the alexandrite crystal shown in the first embodiment. Reference numeral 1003 denotes an optical transmission means composed of a bundle fiber, and reference numeral 1005 denotes a light irradiation means. Reference numeral 1007 denotes a subject, and reference numerals 1009 and 1011 denote holding plates that hold the subject in between. The holding plates 1009 and 1011 are made of, for example, a polymethylpentene resin having a thickness of 10 mm.

  Reference numeral 1013 denotes an acoustic wave detector in which elements are arranged in a two-dimensional array. Reference numeral 1006 denotes irradiation light emitted from the light irradiation means 105. The irradiation area is adjusted by an optical system (not shown) such as a lens provided inside the light irradiation means 1005 so that the irradiation light 1006 strikes the subject 1007 in front of the acoustic wave detector 1013. Further, water is filled between the acoustic wave detector 1013 and the holding plate 1011 to facilitate propagation of acoustic waves (not indicated in the figure).

In this embodiment, the laser device 1001 is configured to be able to oscillate laser light having a pulse width of about 80 nsec and a pulse energy of about 200 mJ by setting an optimum temperature of the laser medium for each wavelength in a wavelength range of 740 nm to 780 nm. It is.
As the acoustic wave detector 1013, a transducer in which a piezoelectric element having an element size of 2 mm square, an element pitch of 2 mm, and a center detection frequency of 1 MHz is arranged in a two-dimensional array of 10 horizontal elements and 15 vertical elements is used.

  A time-series received signal received by the acoustic wave detector 1013 is converted into characteristic information inside the subject by the signal processing unit 1015 using, for example, a delay and sum algorithm. Further, image data is generated based on the distribution of the characteristic information inside the subject. And an operator becomes observable by displaying a photoacoustic image on a display (not shown in a figure). Here, when there is an information processing apparatus serving as a control unit for the entire laser apparatus, the information processing apparatus may be operated as a signal processing unit.

  This photoacoustic image represents the sound pressure distribution inside the subject, and since the sound pressure distribution is proportional to the light absorption rate, two photoacoustic images acquired using light of two wavelengths are compared and calculated. For example, it is possible to discriminate a site where the wavelength dependence of the absorption rate is large and a site where the wavelength dependence is small within the subject.

  In this example, a living body simulation sample (phantom) is arranged as a subject 1007 at a depth of 30 mm from the surface of the living body. Specifically, a tube simulating a blood vessel containing oxidized hemoglobin and reduced hemoglobin is used as the sample. First, a laser beam is irradiated to a sample at a repetition frequency of 10 Hz with an oscillation wavelength of the laser device 1001 being 750 nm, and a photoacoustic image is acquired. Next, the photoacoustic image is acquired by switching the oscillation wavelength to 780 nm. As a result of comparing and calculating the two acquired photoacoustic images, it is possible to visualize the difference in the concentration of oxidized hemoglobin.

  In this embodiment, when generating a photoacoustic image based on the characteristic information obtained by the PAT as described above, the high gain laser apparatus according to the present invention is used. Therefore, photoacoustic waves can be generated with high efficiency. Further, when calculating the initial sound pressure value from the intensity of the photoacoustic wave, a light amount value at a site to be examined such as a light absorber in the subject is used. Here, in the present invention, since the light intensity output from the laser device is stable, the accuracy of light quantity estimation at a position such as a light absorber is improved, and the initial sound pressure value or the absorption coefficient obtained therefrom is further increased. Accurate calculation is possible.

  101: Laser medium, 103: Heating means, 113: Flash lamp, 133: Rear mirror, 135: Output coupler

Claims (20)

A resonator that outputs laser light;
A laser medium disposed inside the resonator;
A flash lamp for irradiating the laser medium with excitation light;
A heating means for heating the laser medium provided to cover at least a part of the laser medium;
Having a solid state laser device. The solid-state laser apparatus according to claim 1, wherein the heating unit is made of a material that transmits the excitation light. The solid-state laser device according to claim 2, wherein a transmittance of the heating unit with respect to the excitation light is 75% or more. 4. The solid-state laser device according to claim 2, wherein the heating unit includes glass and a resistance film made of a material that transmits the excitation light and is provided so as to cover at least a part of the glass. . The solid-state laser device according to claim 4, wherein the glass is quartz glass. 4. The solid-state laser device according to claim 2, wherein the heating unit includes a resistance film made of a material that transmits the excitation light and is provided so as to cover at least a part of the laser medium. The solid-state laser device according to claim 4, wherein the resistance film is made of a material that transmits the excitation light. The solid-state laser device according to claim 7, wherein ITO or ZnO is used as a material of the resistance film. 9. The solid-state laser device according to claim 4, wherein the heating unit covers the entire circumference of the laser medium in a cross section perpendicular to the resonance direction of the resonator. 10. The solid-state laser device according to claim 1, wherein the heating unit has a portion that does not cover the laser medium in a cross section perpendicular to the resonance direction of the resonator. The solid-state laser apparatus according to claim 10, wherein the flash lamp irradiates the laser medium with the excitation light through a portion where the heating unit does not cover the laser medium. The solid-state laser device according to claim 11, wherein the heating unit is covered with a material that reflects the excitation light. The solid-state laser device according to claim 12, wherein the heating means is made of ceramic in which a heating wire is embedded. The solid-state laser device according to any one of claims 1 to 13, further comprising power control means for controlling power input to the heating means. A temperature measuring means for measuring the temperature of the laser medium;
The solid-state laser apparatus according to claim 14, wherein the power control unit controls power so as to keep a temperature of the laser medium constant. The solid-state laser according to claim 14, further comprising a light amount measuring unit that measures a light amount of the laser light output from the resonator, wherein the power control unit controls the power so as to keep the light amount of the laser light constant. apparatus. The solid-state laser device according to any one of claims 1 to 16, further comprising wavelength selection means for selecting a wavelength of the laser light. The power control unit controls the input power at the wavelength selected by the wavelength selection unit based on the relationship between the input power to the heating unit and the laser output at each wavelength selected by the wavelength selection unit. Item 18. A solid-state laser device according to Item 17. The solid-state laser apparatus according to claim 17 or 18, further comprising wavelength detection means for detecting a wavelength selected by the wavelength selection means. A solid-state laser device according to any one of claims 1 to 19,
An acoustic wave detector for detecting an acoustic wave propagating from a subject irradiated with the laser light from the solid-state laser device;
A signal processing unit for generating characteristic information in the subject based on the acoustic wave;
A subject information acquisition apparatus having:

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