JP2006196882A - Optical amplifier, laser oscillator, and mopa laser equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical amplifier capable of equalizing the temperature distribution of a solid-state laser medium of a slab profile using a simple/small structure. <P>SOLUTION: An optical amplifier 17 comprises a solid-state laser medium 31, excited light sources 32a and 32b, light absorbers 33c and 33d, heating light sources 34ac, 34ad, 34bc, and 34bd, rectifier objects 35c and 35d, a medium housing 36, and a controller 37. The active element of the solid-state laser medium 31 is excited when irradiated with excitation light outputted from the excited light sources 32a and 32b. The light absorbers 33c and 33d is provided in touch with the side surface of the solid-state laser medium 31. The light absorbers 33c and 33d absorb heating light and generate heat when irradiated with the heating light outputted from the heating light sources 34ac, 34bc, 34ad, and 34bd. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical amplifier capable of inducing and amplifying light of a predetermined wavelength, a laser oscillator including the optical amplifier in a resonator, and a MOPA (Master Oscillator Power Amplifier) laser apparatus including a light source and the optical amplifier. It is about.

  Laser oscillators are used in many fields such as measurement and manufacturing in modern society. Laser oscillators are classified into gas lasers, liquid lasers, solid-state lasers, and the like depending on the laser medium. Among them, a solid-state laser oscillator including a solid-state laser medium as an optical amplification medium can be easily handled because the volume of the laser medium can be reduced as compared with a gas or liquid laser oscillator.

  The solid-state laser oscillator excites the solid-state laser medium by irradiating the solid-state laser medium with excitation light output from a pump lamp such as a flash lamp or a semiconductor laser element (LD) with high energy utilization efficiency. Laser light is extracted from the solid-state laser medium. As a solid-state laser medium, a crystal (for example, Nd: YAG or Nd: YLF) or glass to which an active element (Nd or Yb rare earth element or transition metal element) is used is used.

  Solid laser oscillators are classified into rods, slabs (flat plates), and disks, depending on the form of the laser medium. For example, Patent Document 1 and Non-Patent Document 1 describe an optical amplifier including a slab-shaped solid-state laser medium, and a laser oscillator including such an optical amplifier and a resonator is known. A MOPA laser device including an optical amplifier and a light source is known.

  In the optical amplifiers described in these Patent Documents 1 and Non-Patent Document 1, the main surface of a slab-shaped solid laser medium is irradiated with excitation light to excite active elements contained in the solid laser medium. Then, light to be amplified having a predetermined wavelength is incident on the first end face of the solid-state laser medium, and the light to be amplified is optically amplified while being propagated in a zigzag manner while being repeatedly reflected on both main surfaces in the solid-state laser medium, The light amplified light is emitted from the other second end face of the solid-state laser medium. By disposing the slab-shaped solid laser medium between the output mirror constituting the resonator and the total reflection mirror, it is possible to obtain a solid laser oscillator for extracting laser oscillation light.

  By the way, when the solid-state laser medium is excited by irradiation of the excitation light output from the excitation light source, most of the excitation light absorbed in the solid-state laser medium becomes a heat load in the solid-state laser medium, and the temperature distribution in the solid-state laser medium is increased. Bring. This temperature distribution causes a thermal lens effect, a thermal birefringence effect, beam deflection, and the like, and causes a change in the mode pattern of laser light and a decrease in output. When the heat load is large, the laser medium may be destroyed.

  Therefore, it is necessary to cool the solid laser medium during operation of the optical amplifier. For this purpose, the solid laser medium is accommodated inside the medium accommodating portion, and water is allowed to flow inside the medium accommodating portion to cool the solid laser medium. Further, a transparent window portion is provided in the medium housing portion, the excitation light is transmitted from the outside to the inside through this window portion, and the excitation light is irradiated to the main surface of the solid laser medium.

Since an optical amplifier having a slab-shaped solid-state laser medium as described in Patent Document 1 or Non-Patent Document 1 can efficiently remove a heat load by water cooling, a large output energy can be taken out. In addition, by making the amplified light propagate in a zigzag manner in the slab-shaped solid laser medium, the thermal effect in the zigzag propagation optical path is averaged, so that a uniform output pattern can be obtained.
JP 2001-203410 A T. Kawashima, et al., "Design and Performance of a Diode-PumpedNd: Silica-Phosphate Glass Zig-Zag Slab Laser Amplifier for Inertial FusionEnergy", Jpn.J.Appl.Phys., Vol.40, Pt.1, No.11, pp.6415-6425 (2001)

  However, even in an optical amplifier that amplifies light by zigzag-propagating the amplified light in the slab-shaped solid-state laser medium as described above, the light that does not contribute to the pumping of the pumping light emitted from the pumping light source is converted into heat. As a result, the temperature of the solid-state laser medium increases, and a thermal effect occurs. Due to this temperature rise, the temperature in the zigzag propagation optical path surface of the slab solid-state laser medium shows a non-uniform distribution that is high in the center and low on the cooling surface, but is thermally averaged because the laser light propagates zigzag, There is no thermal effect in this plane. On the other hand, even in the vertical direction of the slab solid-state laser medium (the direction perpendicular to the zigzag propagation optical path surface), the temperature distribution becomes uneven in the center and lower on the upper and lower sides. This temperature distribution is averaged by zigzag propagation. It is not possible.

  In order to compensate for the thermal lens effect in the vertical direction, it may be possible to arrange a compensation lens outside the solid-state laser medium, but the configuration of the optical amplifier becomes complicated, and as the excitation light intensity increases, Since the focal length of the thermal lens is shortened, it is impossible to compensate for the thermal lens effect.

  Further, in the optical amplifier disclosed in Patent Document 1, a temperature distribution in the vertical direction of the solid-state laser medium is made uniform by providing a hot water channel on each side surface of the solid-state laser medium in the vertical direction. However, in this case, it is necessary to provide a mechanism for heating both sides of the solid laser medium in the vertical direction separately from the cooling mechanism for cooling the main surface of the solid laser medium. Complicated and enlarged. Further, since it takes time to adjust the temperature of the hot water, it is impossible to control the temperature of the laser medium in a short time.

  The present invention has been made to solve the above problems, and an optical amplifier capable of uniformizing the temperature distribution of a slab-shaped solid-state laser medium with a simple and small configuration, and such an optical amplifier. An object of the present invention is to provide a laser oscillator and a MOPA laser apparatus including

  An optical amplifier according to the present invention includes (1) a slab-shaped solid laser medium capable of inducing and emitting light of a predetermined wavelength when irradiated with excitation light, and (2) a first side surface of the solid laser medium facing each other, and A light absorber that is in contact with each of the second side surfaces and generates heat by absorbing light; (3) an excitation light source that outputs excitation light to be irradiated on the solid-state laser medium; and (4) absorbed by the light absorber. A heating light source that outputs the heating light to be generated, and (5) a solid laser medium and a light absorber are housed inside, and water cooling means is provided for cooling the solid laser medium by flowing water therein. A window portion for transmitting the output excitation light and the heating light output from the heating light source from the outside to the inside; and the excitation light transmitted through the window portion is incident on the main surface of the solid-state laser medium; The heating light transmitted through And a medium accommodating portion to be incident on the absorber, characterized in that it comprises a. Further, the light having a predetermined wavelength incident on the first end face of the solid-state laser medium is optically amplified in the solid-state laser medium, and the light-amplified light is emitted from the second end face of the solid-state laser medium.

  In this optical amplifier, the pumping light output from the pumping light source passes through the window portion of the medium housing portion, enters the main surface of the solid laser medium housed inside the medium housing portion, and enters the solid laser medium. Excites the active element. The light having a predetermined wavelength incident on the first end surface of the solid-state laser medium is amplified while being propagated through the solid-state laser medium, and is emitted from the second end surface of the solid-state laser medium. Further, the heating light output from the heating light source is transmitted through the window portion of the medium storage portion and is in contact with each of the first and second side surfaces of the solid laser medium stored in the medium storage portion facing each other. Is incident on the light absorber and absorbed by the light absorber. By irradiating the solid laser medium with excitation light, part of the irradiation energy becomes thermal energy, and the temperature of the solid laser medium rises. In order to suppress this temperature increase, water is caused to flow inside the medium housing portion by the water cooling means, and the solid laser medium is water cooled. If the light absorber is not provided, the temperature in the vicinity of both sides is lower in the vertical temperature distribution of the solid laser medium than in the vicinity of the center. However, in the present invention, since the light absorber is provided in contact with both side surfaces of the solid-state laser medium, the heating light output from the heating light source is absorbed by the light absorber and the light absorber generates heat. The vertical temperature distribution in the solid-state laser medium is made uniform.

  In the optical amplifier according to the present invention, the light absorber preferably absorbs part of the emitted light generated in the solid-state laser medium and generates heat, or part of the excitation light output from the excitation light source. It is preferable that heat is also absorbed by absorbing. In these cases, the light absorber also generates heat by absorbing the emitted light or the excitation light. Therefore, the power of the heating light to be output from the heating light source may be small, and the power consumption may be small.

  In the optical amplifier according to the present invention, it is preferable that the host materials of the solid-state laser medium and the light absorber are the same. In this case, since the thermal expansion coefficients of the light absorber and the solid laser medium are equal to each other, they can be connected by fusion or strongly bonded.

  The optical amplifier according to the present invention includes (1) temperature measuring means for measuring the temperature of the solid-state laser medium, and (2) based on a measurement result by the temperature measuring means in a direction perpendicular to the first side surface of the solid-state laser medium. It is preferable to further include a control unit that feedback-controls the heating light irradiation to the light absorber by the heating light source so as to make the temperature distribution along the line uniform. Alternatively, the optical amplifier according to the present invention includes (1) output light quality measuring means for measuring the quality of light of a predetermined wavelength generated and output by stimulated radiation in the solid-state laser medium, and (2) this output light quality measurement. It is also preferable to further comprise a control means for feedback-controlling the heating light irradiation to the light absorber by the heating light source so as to improve the quality of the light output from the solid-state laser medium based on the measurement result by the means. It is. As described above, the heating light irradiation to the light absorber by the heating light source is feedback-controlled by the control means, so that the temperature distribution along the direction perpendicular to the side surface of the solid-state laser medium is effectively uniformed, The quality of the light output from the solid state laser medium is improved.

  The optical amplifier according to the present invention preferably further includes an electrical heating source for heating each of the first side surface and the second side surface of the solid-state laser medium. At this time, the optical amplifier according to the present invention includes (1) temperature measuring means for measuring the temperature of the solid laser medium, and (2) the first side surface of the solid laser medium based on the measurement result by the temperature measuring means. And a control means for feedback-controlling the heating light irradiation to the light absorber by the heating light source or the heating by the electric heating source so as to uniformize the temperature distribution along the direction perpendicular to the heating source. is there. Alternatively, the optical amplifier according to the present invention includes (1) output light quality measuring means for measuring the quality of light of a predetermined wavelength generated and output by stimulated radiation in the solid-state laser medium, and (2) this output light quality measurement. Control means for feedback control of heating light irradiation to the light absorber by the heating light source or heating by the electric heating source so as to improve the quality of the light output from the solid-state laser medium based on the measurement result by the means; It is also preferable to further include As described above, the light irradiation to the light absorber by the light source for heating or the heating by the electric heating source is feedback-controlled by the control means, so that it is effectively along the direction perpendicular to the side surface of the solid-state laser medium. The temperature distribution is made uniform, and the quality of light output from the solid-state laser medium is improved.

  Further, the optical amplifier according to the present invention is (1) a rectifier that rectifies the flow of water inside the medium housing portion provided on the side opposite to the surface in contact with the solid-state laser medium in the optical absorber; 2) It is preferable to further include a second light absorber provided between the light absorber and the rectifier so as to be in contact with the light absorber and having higher thermal conductivity than the light absorber and absorbing light. In addition, it is preferable to further include a second light absorber that is provided between the light absorber and the electric heating source so as to be in contact with the light absorber and has a higher thermal conductivity than the light absorber and absorbs light. Some of the light that should enter the light absorber and contribute to heat generation may pass through the light absorber without being absorbed by the light absorber. If the second absorber is not provided, a part of the light transmitted through the light absorber is reflected at the boundary with the rectifier or the electric heating source and is incident on the light absorber again. It is absorbed by the absorber and contributes to heat generation, and there is a possibility that the calorific value is larger than the intended calorific value. On the other hand, when the second absorber is provided, part of the light transmitted through the light absorber is absorbed by the second light absorber, so that the ratio of the light reflected to the light absorber is As a result, the desired calorific value can be easily obtained, and as a result, the temperature distribution of the solid-state laser medium can be more easily uniformized. In addition, by providing the second light absorber, parasitic oscillation is reduced and amplification efficiency is improved.

  A laser oscillator according to the present invention includes the optical amplifier according to the present invention described above, and a resonator having a solid-state laser medium included in the optical amplifier on a resonant optical path. Further, a MOPA laser device according to the present invention comprises a light source that outputs light, and the optical amplifier according to the present invention that receives the light output from the light source, and amplifies and outputs the light. To do.

  According to the present invention, the temperature distribution of a slab-shaped solid-state laser medium can be made uniform with a simple and small configuration, and high-quality output light can be obtained.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. For convenience of explanation, an xyz rectangular coordinate system is set.

  First, the MOPA laser apparatus 1 according to this embodiment will be described. FIG. 1 is a configuration diagram of a MOPA laser device 1 according to the present embodiment. The MOPA laser apparatus 1 shown in this figure includes a laser light source 11, an optical amplifier 12, a beam expander 13, an optical mask 14, a spatial filter 15, a Faraday rotator 16, an optical amplifier 17, a spatial filter 18 and a polarizer 19. .

  The laser light source 11 outputs laser light. The wavelength of the light output from the laser light source 11 is a wavelength that can be optically amplified in each of the optical amplifier 12 and the optical amplifier 17. The optical amplifier 12 receives the light output from the laser light source 11, optically amplifies it, and outputs it. The beam expander 13 receives the light output from the optical amplifier 12 and reflected by the mirror 21, and outputs the light with a larger beam diameter. The optical mask 14 has an opening, receives light that is output from the beam expander 13 and reflected by the mirror 22, and transmits light only through the opening. The spatial distribution shape of this light is rectangular. To output. The opening of the optical mask 14 is preferably a rectangular serrated aperture.

  The spatial filter 15 includes a lens 15a, a lens 15b, and a pinhole 15c. The spatial filter 18 also has a lens 18a, a lens 18b, and a pinhole 18c. The lens 15a and the lens 15b constitute a confocal optical system of Kepler type reverse telephoto system, and the lens 18a and the lens 18b also constitute a confocal optical system of Kepler type reverse telephoto system. The beam cross-sectional shape of the light at the position is transferred one after another.

  The pinhole 15c is at a focal position between the lens 15a and the lens 15b, and the pinhole 18c is at a focal position between the lens 18a and the lens 18b. These pinhole 15c and pinhole 18c are provided to remove spatial harmonic components. In addition, since each of the pinhole 15c and the pinhole 18c is provided at a light condensing position, the pinhole 15c and the pinhole 18c are preferably made of a material having high thermal shock resistance and high hardness, and are preferably made of ceramics. It is preferably made of silicon nitride, carbon nitride or boron nitride, or a mixture thereof. Moreover, it is preferable that the opening shape of each of the pinhole 15c and the pinhole 18c is substantially similar to the shape obtained by Fourier transforming the opening shape of the optical mask 14.

  The optical amplifier 17 includes a solid-state laser medium 31, a pumping light source 32a, and a pumping light source 32b. The excitation light source 32a and the excitation light source 32b that output excitation light to be irradiated to the solid-state laser medium 31 may include a flash lamp, and preferably include a laser diode array or a laser diode array stack. The solid-state laser medium 31 is made of slab-shaped glass, and can emit light having a predetermined wavelength by irradiating both main surfaces with excitation light. The light to be amplified is incident obliquely on the end face of the solid-state laser medium 31 and is zigzagged in the solid-state laser medium 31 while being repeatedly reflected by both main surfaces of the solid-state laser medium 31, and after the light amplification, It is emitted from the end face. The optical amplifier 17 amplifies the light input from the mirror 23 to the first end face of the solid-state laser medium 31 in the solid-state laser medium 31 and outputs the light after the light amplification to the mirror 24 from the second end face. Further, the optical amplifier 17 amplifies the light input from the mirror 24 to the second end face of the solid-state laser medium 31 in the solid-state laser medium 31 and outputs the light after the light amplification to the mirror 25 from the first end face. . A reflection reducing film is formed on each of the first end face and the second end face of the solid-state laser medium 31.

  The Faraday rotator 16 is provided on the optical path between the spatial filter 15 and the mirror 26, rotates the polarization direction of light by 90 degrees in two passes, and compensates for thermal birefringence. The polarizer 19 selectively reflects light having a polarization component in a specific direction out of the light output from the spatial filter 15 and arrives at it, and uses the reflected light as output light of the MOPA laser device 1.

  The MOPA laser device 1 operates as follows. The light output from the laser light source 11 is optically amplified by the optical amplifier 12, the beam diameter is expanded by the beam expander 13, and is input to the optical mask 14. The light whose cross-sectional shape is made rectangular by the optical mask 14 is a spatial filter 15, a mirror 23, an optical amplifier 17, a mirror 24, a spatial filter 18, a mirror 27, a mirror 28, a spatial filter 18, and a mirror 25. The optical amplifier 17, the mirror 26, the Faraday rotator 16, and the spatial filter 15 are sequentially passed to reach the mirror 29. The light path from the optical mask 14 to the mirror 29 is defined as the forward path, and the light that has reached the mirror 29 and is reflected passes through the return path that is the same optical path as the forward path, and reaches the polarizer 19.

  Since the light passes through the Faraday rotator 16 twice between the forward path (optical path from the optical mask 14 to the mirror 29) and the backward path (optical path from the mirror 29 to the polarizer 19), a total of 90 The polarization direction of the light rotates by the degree. Therefore, the light that has reached the polarizer 19 on the return path is reflected by the polarizer 19, and this reflected light becomes the output light of the MOPA laser device 1.

  Further, during the forward path and the backward path, the beam cross-sectional shape of the light at the position of the optical mask 14 is subjected to image transfer eight times by the spatial filter 15 or the spatial filter 18 and is caused by thermal distortion or the like. Spatial harmonic components are removed. As a result, the output light of the MOPA laser device 1 has reduced diffraction. Further, the light passes through the optical amplifier 17 four times during the forward path and the backward path, and the light is amplified in the optical amplifier 17 each time the light passes.

  An example of a more specific configuration of the MOPA laser apparatus 1 is as follows. The laser light source 11 includes a single vertical and horizontal seed laser light source that excites Nd: YLF with a continuous oscillation laser diode, and a Q-switch optical amplifier that excites Nd: YLF with a laser diode, and has a wavelength of 1053 nm. Feedback control is performed with an algorithm that minimizes the rise time of the output pulse light to stabilize the single mode. The optical amplifier 12 is configured to excite rod-shaped Nd: YLF with a laser diode. The solid-state laser medium 31 included in the optical amplifier 17 is slab-shaped Nd-doped glass, and both end surfaces in the longitudinal direction serve as light incident / exit surfaces for light amplification. Each of the excitation light source 32a and the excitation light source 32b includes a laser diode array stack. The total energy of the excitation light irradiated to the solid-state laser medium 31 is 48 J, and the excitation efficiency is 0.5. At this time, the energy of the light output from the polarizer 19 is 10J.

Next, the optical amplifier 17 according to the present embodiment will be described in detail. FIG. 2 is a three-way view of the solid-state laser medium 31 included in the optical amplifier 17 according to the present embodiment. FIG. 2A is a view of the solid-state laser medium 31 viewed in the y direction, and FIG. Is a diagram of the solid laser medium 31 viewed in the z direction, and FIG. 10C is a diagram of the solid laser medium 31 viewed in the x direction. Figure 3 is a perspective view showing a state of propagation of the amplified light L ₀ in the solid-state laser medium 31 included in the optical amplifier 17 according to the present embodiment.

  The solid-state laser medium 31 has a slab shape, and has a main surface 31a and a main surface 31b facing each other, a side surface 31c and a side surface 31d facing each other, and an end surface 31e and an end surface 31f facing each other. . Here, the direction perpendicular to the main surfaces 31a and 31b is defined as the x direction, the direction perpendicular to the side surfaces 31c and 31d is defined as the y direction, and the direction perpendicular to the end surfaces 31e and 31f is defined as the z direction.

Excitation light L _P having a wavelength capable of exciting the active element contained in the solid-state laser medium 31 is applied to each of the main surface 31a and the main surface 31b. The amplified light L ₀ incident on the end surface 31e is the major surface 31a in the solid-state laser medium 31, and repeatedly reflected while zigzag propagated 31b, is emitted from the end face 31f to the outside. In contrast, in the configuration shown in FIG. 1, the amplified light L ₀ incident on the end surface 31f propagates in a zigzag manner while being repeatedly reflected by the main surfaces 31a and 31b in the solid-state laser medium 31, and is externally transmitted from the end surface 31e. Is emitted. The zigzag propagation optical path surface of the amplified light in the solid-state laser medium 31 is parallel to the xz plane.

  FIG. 4 is a cross-sectional view of the optical amplifier 17 according to the present embodiment, showing a cross section parallel to the xy plane. FIG. 5 is a perspective view of a main part of the optical amplifier 17 according to the present embodiment. The optical amplifier 17 includes a solid-state laser medium 31, a pumping light source 32a, a pumping light source 32b, a light absorber 33c, a light absorber 33d, a heating light source 34ac, a heating light source 34ad, a heating light source 34bc, a heating light source 34bd, and a rectifier. 35c, a rectifier 35d, a medium storage unit 36, and a control unit 37. Among these, the solid-state laser medium 31, the light absorber 33 c, the light absorber 33 d, the rectifier 35 c, and the rectifier 35 d are housed inside the medium housing portion 36. The excitation light source 32a, the excitation light source 32b, the heating light source 34ac, the heating light source 34ad, the heating light source 34bc, the heating light source 34bd, and the control unit 37 are arranged outside the medium storage unit 36.

  Each of the light absorber 33c and the light absorber 33d has a rectangular parallelepiped shape, the width in the x direction is approximately the same as the width of the solid laser medium 31, and the length in the z direction is equal to the length of the solid laser medium 31. It is about the same. The light absorber 33c. It is provided in contact with the side surface 31c of the solid-state laser medium 31, and when the heating light output from the heating light sources 34ac and 34bc is irradiated, it absorbs the heating light and generates heat. The light absorber 33d is provided in contact with the side surface 31d of the solid-state laser medium 31, and generates heat by absorbing the heating light when irradiated with the heating light output from the heating light sources 34ad and 34bd.

  Each of the light absorber 33c and the light absorber 33d preferably absorbs part of the emitted light generated in the solid-state laser medium 31 and generates heat, and the excitation light output from the excitation light sources 32a and 32b. It is preferable to generate a heat by absorbing a part of these. Furthermore, the host material of each of the light absorber 33c and the light absorber 33d is preferably the same as the host material of the solid-state laser medium 31. For example, the host materials of the light absorbers 33c and 33d and the solid laser medium 31 are glass having the same composition, and an active element such as a rare earth element is added to the solid laser medium 31, and the light absorber 33c and the light absorber are absorbed. A light absorbing element (for example, Cu element) is added to each of the bodies 33d instead of the active element.

  Each of the rectifier 35c and the rectifier 35d is an isosceles triangle and has a triangular prism shape extending in the z direction, and the width of the base of the isosceles triangle is approximately the same as the width of the solid-state laser medium 31. , The length in the z direction is about the same as the length of the solid-state laser medium 31. The rectifier 35c is provided such that the base of the isosceles triangle is in contact with the light absorber 33c. The rectifier 35d is provided such that the base of the isosceles triangle is in contact with the light absorber 33d. The rectifier 35c, the light absorber 33c, the solid-state laser medium 31, the light absorber 33d, and the rectifier 35d are stacked in this order in the y direction, and are provided in the same region when projected onto the xy plane. It is stored inside the storage unit 36.

  The medium storage unit 36 includes a window portion 36a, a window portion 36b, a water supply / drain port 36c, and a water supply / drain port 36d. The water supply / drain ports 36 c and 36 d are for supplying and draining water flowing into the medium storage unit 36 and cooling the solid laser medium 31 with water. One or a plurality of water supply / drain ports 36c are provided on the −y direction side of the medium storage portion 36 along the z direction. Further, one or a plurality of water supply / drain ports 36d are provided on the + y direction side of the medium storage unit 36 along the z direction. The cooling water injected into the inside through the water supply / drain port 36c flows in the medium storage portion 36 in the approximately + y direction and is discharged from the water supply / drain port 36d to the outside. The rectifying bodies 35c and 35d are arranged in order to allow the cooling water to flow without delay in the medium storage unit 36.

  The window portion 36a is provided as a wall surface on the + x direction side of the medium storage portion 36, and internally outputs light output from the excitation light source 32a, the heating light source 34ac, and the heating light source 34ad disposed outside the medium storage portion 36. To penetrate. The window unit 36a causes the excitation light output from the excitation light source 32a to enter the main surface 31a of the solid-state laser medium 31, and causes the heating light output from the heating light source 34ac to enter the light absorber 33c. Heating light output from the heating light source 34ad is made incident on the light absorber 33d.

  The window portion 36b is provided as a wall surface on the −x direction side of the medium storage portion 36, and receives light output from the excitation light source 32b, the heating light source 34bc, and the heating light source 34bd arranged outside the medium storage portion 36. Permeate inside. And the window part 36b makes the excitation light output from the excitation light source 32b inject into the main surface 31b of the solid-state laser medium 31, makes the heating light output from the light source 34bc for heating enter into the light absorber 33c, Heating light output from the heating light source 34bd is made incident on the light absorber 33d.

  Each of the heating light sources 34ac and 34bc outputs heating light to be absorbed by the light absorber 33c. Each of the heating light sources 34ad and 34bd outputs heating light to be absorbed by the light absorber 33d. Each of these heating light sources 34ac, 34bc, 34ad, 34bd may include a flash lamp, and preferably includes a laser diode array or a laser diode array stack.

  The control unit 37 controls the power of the heating light output from the heating light sources 34ac and 34bc and applied to the light absorber 33c, and is output from the heating light sources 34ad and 34bd and applied to the light absorber 33d. The power of the heating light to be controlled is controlled. At this time, the control unit 37 may adjust the power of the heating light output from each heating light source, or may adjust the distance between each heating light source and each light absorber, In addition, the direction of the heating light output from each heating light source may be adjusted, and in any case, the power of the heating light applied to each light absorber can be controlled.

FIG. 6 is a diagram illustrating temperature measurement and temperature distribution of the solid-state laser medium 31 and the like included in the optical amplifier 17 according to the present embodiment. FIG. 6A is a diagram of the solid laser medium 31 and the like viewed in the x direction, and FIG. 5B is a diagram illustrating the temperature distribution of the solid laser medium 31 and the like in the y direction. As shown in FIG. 6 (a), the temperature measuring device 38 ₁ to 38 ₅ is provided in the solid-state laser medium 31 and the like on the main surface side in a in the parallel one straight line in the y-direction.

The temperature measuring element 38 _{1-38 5} respectively, for example, the platinum resistor, a thermocouple or thermistor, and is connected to the control unit 37. Temperature measuring elements 38 ₁ measures the temperature in the vicinity of the boundary between the light absorber 33c and the straightening member 35c. Thermometric element 38 ₂ measures the temperature in the vicinity of the boundary between the solid-state laser medium 31 and the light absorber 33c. Temperature measuring element 38 ₃ measures the temperature in the vicinity of the center of the y-direction of the solid-state laser medium 31. Temperature measuring elements 38 ₄ measures the temperature in the vicinity of the boundary between the solid-state laser medium 31 and the light absorber 33d. The temperature measuring element 38 ₅ measures the temperature in the vicinity of the boundary between the light absorber 33d and the rectifying member 35d.

Then, the control unit 37, so as to equalize the been y-direction temperature distribution measured by the temperature measuring device 38 ₁ to 38 _5, is preferred to feedback control the power of the heating light to be irradiated to the optical absorber is there. In FIG. 6B, the solid line shows the y-direction temperature distribution in the solid-state laser medium 31 in the case of the present embodiment in which the light absorbers 33c and 33d are provided. The broken line indicates the y-direction temperature distribution in the solid-state laser medium 31 in the comparative example in which the light absorbers 33c and 33d are not provided.

  The optical amplifier 17 according to this embodiment operates as follows. The excitation light output from the excitation light source 32 a passes through the window portion 36 a of the medium housing portion 36 and is irradiated on the main surface 31 a of the solid-state laser medium 31. Further, the excitation light output from the excitation light source 32 b passes through the window portion 36 b of the medium housing portion 36 and is irradiated onto the main surface 31 b of the solid-state laser medium 31. In this way, the excitation light output from the excitation light sources 32 a and 32 b is irradiated onto the solid-state laser medium 31, whereby the active element contained in the solid-state laser medium 31 is excited. Then, the light to be amplified enters the end face 31e and is amplified while propagating through the solid-state laser medium 31, and the light amplified light is emitted from the end face 31f to the outside.

  At this time, due to the irradiation of the excitation light onto the solid-state laser medium 31, a part of the irradiation energy becomes thermal energy, and the temperature of the solid-state laser medium 31 rises. In order to suppress this temperature rise, cooling water is injected into the medium storage unit 36 from the water supply / drain port 36c, and the cooling water flows in the medium storage unit 36 in approximately the + y direction. The heat is taken away and discharged from the water supply / drain port 36d to the outside.

  However, in the case where no light absorber is provided, in the y-direction temperature distribution of the solid-state laser medium 31, the side surfaces 31c and 31d are closer than the center, as indicated by the broken line in FIG. The temperature is low. On the other hand, in the case of the present embodiment in which the light absorbers 33c and 33d are provided, the heating light output from each heating light source is absorbed by the light absorbers 33c and 33d, and the light absorbers 33c and 33c. Since 33d generates heat, the temperature distribution in the y direction in the solid-state laser medium 31 is made uniform as shown by the solid line in FIG.

In particular, the control unit 37, so that the y-direction temperature distribution in the solid-state laser medium 31 measured by the temperature measuring device 38 ₁ to 38 ₅ are made uniform, the power of the heating light is feedback irradiated on the optical absorber It is preferred that it be controlled. By doing so, for example, when the amount of heat taken by the cooling water from the solid-state laser medium 31 fluctuates or when the amount of heat generated in the solid-state laser medium 31 fluctuates, the y-direction temperature in the solid-state laser medium 31 also varies. The distribution is made uniform.

  As described above, in the present embodiment, the temperature distribution of the slab-shaped solid laser medium 31 can be made uniform with a simple and small configuration. And since the influence of a thermal effect is suppressed, the stable operation | movement is attained and high quality output light can be obtained.

  The light absorbers 33c and 33d preferably generate heat by absorbing a part of the emitted light generated in the solid-state laser medium 31, and absorb a part of the excitation light output from the excitation light sources 32a and 32b. It is also preferable to generate heat. In the latter case, it is preferable that an optical system is provided in front of the excitation light sources 32a and 32b so that a part of the excitation light is incident on the light absorbers 33c and 33d by this optical system. In these cases, the light absorbers 33c and 33d also generate heat by absorbing the emitted light or the excitation light, so that the power of the heating light to be output from each of the heating light sources 34ac, 34ad, 34bc, and 34bd is small. Well, less power consumption.

  Furthermore, the host material of each of the light absorber 33c and the light absorber 33d is preferably the same as the host material of the solid-state laser medium 31. In this case, since the thermal expansion coefficients of the light absorbers 33c and 33d and the solid-state laser medium 31 are equal to each other, they can be connected by fusion or strongly bonded. In the case where the thermal expansion coefficients of the light absorbers 33c and 33d and the solid laser medium 31 are different from each other, an adhesive (for example, a transparent silicon adhesive) that can absorb the strain is used in order to prevent destruction when the temperature changes. Preferably used and adhered to each other.

In the above description, the control unit 37, when the feedback control of the power of the heating light to be irradiated to the optical absorber, y-direction temperature of the solid laser medium 31 measured by the temperature measuring device 38 ₁ to 38 ₅ The distribution was made uniform. However, the control unit 37 irradiates each light absorber based on the result obtained by monitoring the quality of the light generated and output by the induced radiation in the solid-state laser medium 31 by the output light quality measuring means. The power of the heating light may be feedback controlled. Hereinafter, such output light quality measuring means will be described with reference to FIGS.

  FIG. 7 is a diagram illustrating a first configuration example of the output light quality measurement unit included in the optical amplifier 17 according to the present embodiment. The output light quality measuring means shown in this figure includes a beam splitter 41 and a CCD camera 42. The beam splitter 41 transmits a part of the light amplified by the solid-state laser medium 31 and output from the end face 31f, and reflects the remaining part. The CCD camera 42 receives the light transmitted through the beam splitter 41 and monitors the intensity distribution in the cross section of the light. Then, the control unit 37 heats the light absorbers 33c and 33d by each heating light source so that the cross-sectional intensity distribution of light monitored by the CCD camera 42 approaches a uniform (or ideal Gaussian distribution). Feedback control of light irradiation.

  FIG. 8 is a diagram illustrating a second configuration example of the output light quality measurement unit included in the optical amplifier 17 according to the present embodiment. The output light quality measuring means shown in this figure includes a beam splitter 41, a cylindrical lens 43, a cylindrical lens 44, and a quadrant photodiode 45. The beam splitter 41 transmits a part of the light amplified by the solid-state laser medium 31 and output from the end face 31f, and reflects the remaining part. The cylindrical lens 43 inputs the light transmitted through the beam splitter 41 and converges the light with respect to the y direction. The cylindrical lens 44 receives the light output from the cylindrical lens 43 and converges the light in the direction perpendicular to the y direction. The condensing position by each of the cylindrical lenses 43 and 44 is on the light receiving surface of the quadrant photodiode 45.

As shown in FIG. 9A, the four-divided photodiode 45 is divided into four, and is arranged so that the angle between the division boundary line and the y-direction is 45 degrees. Four of the divided photodiode four in 45 photodiode _PD 1 -PD _4, two photodiodes _PD 1, PD ₂ are arranged in the y-direction, two photodiodes _PD 3, PD ₄ is perpendicular to the y-direction Is arranged. The output value from the photodiode PD ₁ and _{I 1,} the output value from the photodiode PD ₂ and _{I 2,} the output value from the photodiode PD ₃ and _{I 3,} the output value from the photodiode PD _{4 I 4} Then, an output value ((I ₁ + I ₂ ) − (I ₃ + I ₄ )) can be obtained from the quadrant photodiode 45.

When spot light is incident on the light receiving surface of the quadrant photodiode 45, the output value ((I ₁ + I ₂ ) − (I ₃ + I ₄ )) represents the spot light incident position on the light receiving surface. Therefore, as shown in FIG. 9B, the output value ((I ₁ + I ₂ ) − (I ₃ + I ₄ )) becomes zero when the thermal lens effect is not generated in the solid-state laser medium 31. If the quadrant photodiode 45 is arranged, the thermal lens effect in the solid-state laser medium 31 can be monitored from the output value ((I ₁ + I ₂ ) − (I ₃ + I ₄ )). Therefore, the control unit 37 performs feedback control of heating light irradiation to the light absorbers 33c and 33d by the respective light sources for heating so that the output value ((I ₁ + I ₂ ) − (I ₃ + I ₄ )) approaches 0. To do.

  FIG. 10 is a diagram illustrating a third configuration example of the output light quality measurement unit included in the optical amplifier 17 according to the present embodiment. The output light quality measuring means shown in this figure includes a beam splitter 41, a lens array 46, and a CCD camera 42, and constitutes a Shack-Hartmann wavefront sensor. The beam splitter 41 transmits a part of the light amplified by the solid-state laser medium 31 and output from the end face 31f, and reflects the remaining part. The lens array 46 is formed by two-dimensionally arranging microlenses on a plane perpendicular to the optical axis, and each microlens transmits light incident through the beam splitter 41 onto the imaging surface of the CCD camera 42. Condensate. The CCD camera 42 receives light collected by each microlens included in the lens array 46 and monitors the light collection position. Then, the control unit 37 absorbs light by each heating light source so that the condensing position monitored by the CCD camera 42 approaches a predetermined position (condensing position when the thermal lens effect is not generated in the solid-state laser medium). The heating light irradiation to the bodies 33c and 33d is feedback controlled.

  In the above description, in order to heat the side surfaces 31c and 31d of the solid-state laser medium 31, the light absorbers 33c and 33d are provided in contact with the side surfaces 31c and 31d, and the heating light output from each heating light source is provided. Is irradiated to the light absorbers 33c and 33d, so that the light absorbers 33c and 33d generate heat. However, in addition to these, an electric heating source may be further provided to heat the side surfaces 31 c and 31 d of the solid-state laser medium 31. The configuration in this case will be described with reference to FIG.

  FIG. 11 is a cross-sectional view of an optical amplifier 17A according to another embodiment, showing a cross section parallel to the xy plane. Compared with the configuration of the optical amplifier 17 shown in FIG. 4, the optical amplifier 17A shown in FIG. 11 is provided with a heater 39c between the optical absorber 33c and the rectifier 35c, and is aligned with the optical absorber 33d. The difference is that a heater 39d is provided between the fluid 35d and a control unit 37A instead of the control unit 37.

The heaters 39c and 39d as electric heating sources are controlled by the control unit 37A to generate heat. Then, the control unit 37A, so as to equalize the measured y-direction temperature distribution by the temperature measuring device 38 ₁ to 38 _5, as shown in FIG. 6, the power of the heating light to be irradiated to the optical absorber Alternatively, the heating by each heater may be feedback controlled. Alternatively, the output light quality measuring means as shown in FIGS. 7 to 10 is used to determine the quality of the light generated and output by the induced radiation in the solid-state laser medium 31 by the control unit 37A. On the basis of the result obtained by monitoring, the power of the heating light applied to each light absorber or the heating by each heater may be feedback controlled.

  It is also preferable that the second light absorbers 40c and 40d are provided in contact with the light absorbers 33c and 33d. FIG. 12 is a cross-sectional view of an optical amplifier 17B according to still another embodiment, showing a cross section parallel to the xy plane. Compared with the configuration of the optical amplifier 17 shown in FIG. 4, the optical amplifier 17B shown in FIG. 12 includes a second optical absorber 40c between the optical absorber 33c and the rectifier 35c, and The difference is that a second light absorber 40d is provided between the light absorber 33d and the rectifier 35d. FIG. 13 is a cross-sectional view of an optical amplifier 17C according to still another embodiment, showing a cross section parallel to the xy plane. Compared to the configuration of the optical amplifier 17A shown in FIG. 11, the optical amplifier 17C shown in FIG. 13 includes a second light absorber 40c between the light absorber 33c and the heater 39c, and light absorption. The difference is that a second light absorber 40d is provided between the body 33d and the heater 39d.

  The second light absorbers 40c and 40d newly added in the configurations shown in FIGS. 12 and 13 have higher thermal conductivity than the light absorbers 33c and 33d and absorb light. The second light absorber 40c is provided in contact with the light absorber 33c. The second light absorber 40d is provided in contact with the light absorber 33d. A graphite sheet is preferably used as the second light absorbers 40c and 40d.

  Some of the light that should enter the light absorbers 33c and 33d and contribute to heat generation may pass through the light absorbers 33c and 33d without being absorbed by the light absorbers 33c and 33d. If the second absorbers 40c and 40d are not provided, part of the light transmitted through the light absorbers 33c and 33d is reflected at the boundary with the rectifier or the heater, and again the light absorbers 33c and 33d. 33d and absorbed by the light absorbers 33c and 33d to contribute to heat generation, and there is a possibility that the heat generation amount is larger than the intended heat generation amount.

  On the other hand, when the second absorbers 40c and 40d are provided, part of the light transmitted through the light absorbers 33c and 33d is absorbed by the second light absorbers 40c and 40d. The ratio of the light reflected to the bodies 33c and 33d is reduced, the desired amount of heat generation can be easily obtained, and the temperature distribution of the solid-state laser medium 31 can be made uniform more easily. Further, by providing the second light absorbers 40c and 40d, parasitic oscillation is reduced and amplification efficiency is improved.

  Further, the optical amplifiers 17, 17A, 17B, and 17C according to the present embodiment are not only used as one of the components included in the MOPA laser device 1 as shown in FIG. 1, but are also included in the laser oscillator. It can also be used as one of the components. Hereinafter, a laser oscillator including the optical amplifier 17 will be described.

  FIG. 14 is a configuration diagram of the laser oscillator 2 according to the present embodiment. The laser oscillator 2 shown in this figure includes the optical amplifier 17 described above and a resonator having a solid-state laser medium 31 included in the optical amplifier 17 on a resonant optical path. The mirror 51 and the mirror 52 constitute a resonator. One mirror 51 has a high reflectivity with respect to the wavelength of light naturally emitted from the solid-state laser medium 31. The other mirror 52 has a relatively low reflectance with respect to its wavelength.

  In the laser oscillator 2, when the excitation light output from the excitation light sources 32a and 32b is irradiated onto the solid-state laser medium 31, the active element contained in the solid-state laser medium 31 is excited and light having a predetermined wavelength is emitted. The light is reflected by the mirror 51 and the mirror 52, and reciprocates in the resonator. As a result, stimulated radiation is generated in the solid-state laser medium 31, and the light of the predetermined wavelength is optically amplified. A part of the light amplified in the resonator passes through the mirror 52 and is output to the outside as output light of the laser oscillator 2.

  Since the optical amplifier 17 included in the laser oscillator 2 has the above-described configuration, the laser oscillator 2 can obtain high-quality laser output light.

It is a block diagram of the MOPA laser apparatus 1 which concerns on this embodiment. It is a three-way figure of the solid-state laser medium 31 contained in the optical amplifier 17 which concerns on this embodiment. It is a perspective view which shows the mode of propagation of the to-be-amplified light in the solid-state laser medium 31 contained in the optical amplifier 17 which concerns on this embodiment. It is sectional drawing of the optical amplifier 17 which concerns on this embodiment. It is a perspective view of the principal part of the optical amplifier 17 concerning this embodiment. It is a figure which shows temperature measurement and temperature distribution of the solid-state laser medium 31 grade | etc., Contained in the optical amplifier 17 which concerns on this embodiment. It is a figure which shows the 1st structural example of the output light quality measurement means contained in the optical amplifier 17 which concerns on this embodiment. It is a figure which shows the 2nd structural example of the output light quality measurement means contained in the optical amplifier 17 which concerns on this embodiment. It is explanatory drawing of the four division | segmentation photodiode 45. FIG. It is a figure which shows the 3rd structural example of the output light quality measurement means contained in the optical amplifier 17 which concerns on this embodiment. It is sectional drawing of the optical amplifier 17A which concerns on other embodiment. It is sectional drawing of the optical amplifier 17B which concerns on other embodiment. It is sectional drawing of the optical amplifier 17C which concerns on other embodiment. It is a block diagram of the laser oscillator 2 which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... MOPA laser apparatus, 2 ... Laser oscillator, 11 ... Laser light source, 12 ... Optical amplifier, 13 ... Beam expander, 14 ... Optical mask, 15 ... Spatial filter, 16 ... Faraday rotator, 17, 17A, 17B, 17C DESCRIPTION OF SYMBOLS ... Optical amplifier, 18 ... Spatial filter, 19 ... Polarizer, 21-29 ... Mirror, 31 ... Solid laser medium, 31a, 31b ... Main surface, 31c, 31d ... Side surface, 31e, 31f ... End surface, 32a, 32b ... Excitation Light source, 33c, 33d ... light absorber, 34ac, 34ad, 34bc, 34bd ... heating light source, 35c, 35d ... rectifier, 36 ... medium storage, 36a, 36b ... window, 36c, 36d ... water supply / drain port, 37 , 37A ... control unit, ₃₈ 1-38 5 _... temperature measuring element, 39c, 39d ... heater, 40c, 40d ... 2nd light absorber, 41 ... beam splitter, 42 ... CCD camera, 43, 44 ... cylindrical lens, 45 ... quadrant photodiode, 46 ... lens array, 51, 52 ... mirror.

Claims (13)

A slab-shaped solid laser medium capable of inducing and emitting light of a predetermined wavelength by being irradiated with excitation light; and
A light absorber that is provided in contact with each of the first side surface and the second side surface of the solid-state laser medium facing each other and absorbs light to generate heat;
An excitation light source that outputs excitation light to be irradiated to the solid-state laser medium;
A heating light source that outputs heating light to be absorbed by the light absorber;
The solid-state laser medium and the light absorber are housed inside, and water cooling means is provided for cooling the solid-state laser medium by flowing water therein, and is also output from the excitation light and the heating light source output from the excitation light source. A window portion that transmits the heated light from the outside to the inside, excitation light that has been transmitted through the window portion is incident on the main surface of the solid-state laser medium, and the light that has been transmitted through the window portion is the light absorber. A medium storage unit that is incident on
With
The light of the predetermined wavelength incident on the first end face of the solid-state laser medium is optically amplified in the solid-state laser medium, and the light-amplified light is emitted from the second end face of the solid-state laser medium;
An optical amplifier characterized by that.   2. The optical amplifier according to claim 1, wherein the light absorber absorbs part of emitted light generated by the solid-state laser medium and generates heat.   2. The optical amplifier according to claim 1, wherein the light absorber also absorbs part of the excitation light output from the excitation light source and generates heat.   2. The optical amplifier according to claim 1, wherein host materials of the solid-state laser medium and the light absorber are the same. Temperature measuring means for measuring the temperature of the solid-state laser medium;
Irradiation of heating light to the light absorber by the heating light source so as to uniformize the temperature distribution along the direction perpendicular to the first side surface of the solid-state laser medium based on the measurement result by the temperature measuring means. Control means for feedback control,
The optical amplifier according to claim 1, further comprising: Output light quality measuring means for measuring the quality of the light of the predetermined wavelength generated and output by stimulated radiation in the solid-state laser medium;
Control means for feedback controlling heating light irradiation to the light absorber by the heating light source so as to improve the quality of the light output from the solid-state laser medium based on the measurement result by the output light quality measuring means When,
The optical amplifier according to claim 1, further comprising:   2. The optical amplifier according to claim 1, further comprising an electric heating source for heating each of the first side surface and the second side surface of the solid-state laser medium. Temperature measuring means for measuring the temperature of the solid-state laser medium;
Irradiation of heating light to the light absorber by the heating light source so as to uniformize the temperature distribution along the direction perpendicular to the first side surface of the solid-state laser medium based on the measurement result by the temperature measuring means. Or control means for feedback control of heating by the electric heating source;
The optical amplifier according to claim 7, further comprising: Output light quality measuring means for measuring the quality of the light of the predetermined wavelength generated and output by stimulated radiation in the solid-state laser medium;
Based on the measurement result by the output light quality measuring means, the light absorber is irradiated with heating light by the heating light source or the electric heating source so as to improve the quality of light output from the solid-state laser medium. Control means for feedback control of heating by
The optical amplifier according to claim 7, further comprising: A rectifier that rectifies the flow of water inside the medium housing portion provided on the side opposite to the surface in contact with the solid-state laser medium in the light absorber;
A second light absorber that is provided between and in contact with the light absorber between the light absorber and the rectifier, and has a higher thermal conductivity than the light absorber and absorbs light;
The optical amplifier according to claim 1, further comprising:   It further comprises a second light absorber that is provided between the light absorber and the electrical heating source so as to be in contact with the light absorber and absorbs light with higher thermal conductivity than the light absorber. The optical amplifier according to claim 7. The optical amplifier according to any one of claims 1 to 11,
A resonator having a solid-state laser medium included in the optical amplifier on a resonant optical path;
A laser oscillator comprising: A light source that outputs light;
The optical amplifier according to any one of claims 1 to 11, wherein the light output from the light source is input, optically amplified and output.
A MOPA laser device comprising:

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