WO2005093914A1

WO2005093914A1 - Device and method for controlling pumping distribution of solid laser medium

Info

Publication number: WO2005093914A1
Application number: PCT/JP2005/005504
Authority: WO
Inventors: Takashi Sekine; Osamu Matsumoto; Toshiyuki Kawashima; Takashi Kurita; Tadashi Kanabe
Original assignee: Hamamatsu Photonics K.K.
Priority date: 2004-03-26
Filing date: 2005-03-25
Publication date: 2005-10-06
Also published as: JP4473617B2; JP2005285812A

Abstract

A pumping distribution controller (10) comprising a moving unit (40), a measuring section (50) and a control section (60) in addition to a solid laser medium (31) and a pumping light source (32). The moving unit can alter the distance between the solid laser medium and the pumping light source by moving the pumping light source. The measuring section measures the pumping distribution of the solid laser medium. The control section drives the moving unit depending on the measured pumping distribution to adjust the distance between the solid laser medium and the pumping light source. When a plurality of unit light sources (33) are stacked in the pumping light source, the intensity distribution of the pumping light with which the solid laser medium is irradiated depends on the distance between the solid laser medium and the pumping light source. Consequently, the pumping distribution of the solid laser medium is controlled appropriately by adjusting the distance and the thermal effect can be lessened.

Description

Specification

Apparatus and method for controlling excitation distribution of solid-state laser medium

Technical field

The present invention relates to control of an excitation distribution of a solid-state laser medium used in a solid-state laser system.

Background art

[0002] In recent years, attention has been paid to LD-pumped solid-state lasers. In the case of LD pumping, unlike the flash lamp pumping, the wavelength of the pumping light can be matched to the absorption wavelength of the laser medium. Therefore, heat generated in the laser medium is reduced, and the laser efficiency is improved.

[0003] In order to increase the output of the LD-excited solid-state laser, the area of the laser medium irradiated with the excitation light may be increased. Japanese Patent Application Laid-Open No. 2003-78194 discloses a laser array module having a plurality of laser array units arranged in a line as an excitation light source. In each laser array unit, a plurality of LD bar packages having a plurality of LDs arranged in a row are stacked. Each LD bar package is fitted with a heat sink to cool the LD.

In designing a solid-state laser system, compensation of a thermal effect (for example, thermal lens effect ゃ thermal birefringence effect) generated in a laser medium is a major issue! This is because the thermal effect significantly reduces the beam quality of the laser beam. If the beam pattern of the laser beam deteriorates due to the thermal effect, the optical components may be damaged. In addition, since the laser light focusing characteristics are also deteriorated, it becomes difficult for the laser light to pass through the pinhole of the spatial filter arranged in the system, and as a result, the output power is reduced.

[0005] Against this background, Toshiyuki Kawashima Horik "Quasi-CW 丄丄 OkW AlGaAs Laser Diode Array Module for Inertial Fusion Energy Laser Driver for Inertial Fusion Energy Laser Driver" , Japan Journal of Applied Physics, The Japan Society of Applied Physics, December 2001, Vol. 40, Part 1, Issue 12, pages 6852-6858. Adjust the irradiation angle to reduce the thermal lens effect in the laser medium It discloses a method for doing so.

Disclosure of the invention

[0006] In developing a high-power solid-state laser system, the present inventors are studying the use of an excitation light source in which a plurality of laser array modules are stacked. However, the technique disclosed in JP-A-2003-78194 is not suitable for a configuration in which a large number of unit light sources are stacked. In this method, it is necessary to arrange the unit light sources so that the excitation light of all unit light sources is irradiated on the laser medium and each unit light source can be rotated. Therefore, when a large number of unit light sources are stacked, it is necessary to arrange these unit light sources in a sector around the laser medium. However, in such an arrangement, the number of stacked unit light sources is naturally limited, so that it is difficult to stack and use a large number of unit light sources.

[0007] Therefore, the present invention provides an apparatus and a method capable of appropriately controlling the excitation distribution of a solid-state laser medium and reducing a thermal effect even when using an excitation light source having a structure in which a number of unit light sources are stacked. As an issue.

[0008] One aspect of the present invention relates to an apparatus for controlling an excitation distribution of a solid-state laser medium. This device is a solid-state laser medium that is excited by irradiation with excitation light and can stimulate and emit light of a predetermined wavelength, an excitation light source that irradiates the solid-state laser medium with excitation light, and an excitation light source. A moving device that can change the distance between the solid-state laser medium and the excitation light source by moving the solid-state laser medium, a measuring unit that measures the excitation distribution of the solid-state laser medium, and a moving unit that moves according to the excitation distribution measured by the measuring unit A control unit that controls the excitation distribution of the solid-state laser medium by driving the device and adjusting the distance between the solid-state laser medium and the excitation light source.

[0009] When a plurality of unit light sources are stacked in an excitation light source, the intensity distribution of the excitation light applied to the solid-state laser medium depends on the distance between the solid-state laser medium and the excitation light source. Therefore, by adjusting this distance, the excitation distribution of the solid-state laser medium can be controlled. The adjustment of the distance can be performed without being affected by the number of unit light sources to be stacked. Therefore, even when using an excitation light source with a structure in which many unit light sources are stacked, it is necessary to appropriately control the excitation distribution of the solid-state laser medium and reduce the thermal effect. Can do.

[0010] In this excitation distribution control device, the solid-state laser medium includes first and second end faces, a long upper surface and a bottom surface extending between the end surfaces, and a first and a second surface between the upper surface and the bottom surface. And one end of the second end face having two sides extending to the other and having a length along a direction substantially parallel to the top, bottom and two sides, and substantially parallel to the top and bottom. The medium may be a slab-shaped medium having a height along a direction substantially perpendicular to the direction and a thickness along a direction substantially perpendicular to the two side surfaces. Further, the excitation light source may include first and second unit light sources stacked along the height direction of the solid-state laser medium.

[0011] The measurement unit has an imaging device that acquires an image of the spontaneous emission light emitted from the first or second end surface of the solid-state laser medium when the excitation light source is irradiated with the excitation light! / ヽYou can! / The control unit uses the image to determine the intensity distribution of the spontaneous emission light in the height direction of the solid-state laser medium, and finds the intensity distribution between the two peaks corresponding to the emission of the first and second unit light sources, respectively. The moving device may be driven such that the depth of the valley located at the location is minimized.

[0012] The intensity distribution of spontaneous emission light emitted from the end face of the solid-state laser medium reflects the excitation distribution in the thickness and height directions of the solid-state laser medium. The deeper the valley, the more the excitation light from each unit light source is separated, and the higher the non-uniformity of the excitation distribution in the height direction of the solid-state laser medium. Therefore, if the distance between the solid-state laser medium and the excitation light source is adjusted so that the depth of the valley is minimized, the uniformity of the excitation distribution in the height direction of the solid-state laser medium is increased, and the thermal effect is reduced. .

[0013] The measuring unit includes a condensing device that condenses the light having the predetermined wavelength, which enters the solid-state laser medium through the first end face, propagates on the zigzag optical path, and emits from the second end face. An imaging device for acquiring an image of the beam pattern of the light thus condensed may be provided. The control unit may calculate the area of the beam pattern when the solid-state laser medium is irradiated with the excitation light, and may drive the moving device so that the area is minimized.

[0014] When the solid-state laser medium is irradiated with the excitation light, the light propagating on the zigzag optical path receives a thermal effect from the heat generated in the solid-state laser medium. For this reason, the light focusing property depends on the excitation distribution of the solid laser medium. Therefore, the light collected by the The light beam pattern reflects the excitation distribution of the solid-state laser medium. The larger the area of the beam pattern, the poorer the light collection. Therefore, if the distance between the solid-state laser medium and the excitation light source is adjusted so that the area of the beam pattern is minimized, the uniformity of the excitation distribution in the height direction of the solid-state laser medium is increased, and the thermal effect is reduced.

[0015] The measurement unit is configured to split the inspection light into first and second lights, emit the inspection light into the solid-state laser medium through the first end face, and propagate the first light into the solid-state laser medium and propagate the light on the zigzag optical path. An interference optical system that emits a second end face force and interferes with the second light to generate an interference fringe having a rectangular pattern along the thickness direction and the height direction of the solid-state laser medium. And an imaging device for acquiring an image of interference fringes. The control unit sets a reference line parallel to the height direction of the solid-state laser medium in the image of the interference fringe acquired when the excitation light is irradiated on the solid-state laser medium, and sets an image on the reference line. Alternatively, the moving device may be driven such that the number of vibrations of the luminance is counted and the number of vibrations is minimized.

[0016] The interference fringes reflect the refractive index distribution of the solid-state laser medium along the zigzag optical path. This refractive index distribution is formed by irradiating the solid-state laser medium with excitation light. Therefore, the pattern of interference fringes reflects the excitation distribution of the solid-state laser medium. The greater the number of oscillations of the brightness of the interference fringe image on the reference line, the higher the non-uniformity of the excitation distribution in the height direction of the solid-state laser medium. Therefore, if the distance between the solid-state laser medium and the excitation light source is adjusted so as to minimize the number of oscillations, the uniformity of the excitation distribution in the height direction of the solid-state laser medium is increased, and the thermal effect is reduced.

[0017] Before counting the number of vibrations, the control unit may determine that an image of interference fringes acquired when the solid-state laser medium is not irradiated with the excitation light is substantially parallel to the height direction of the solid-state laser medium. The interference optical system may be adjusted so as to have a bright line.

[0018] Another aspect of the present invention relates to a method for controlling an excitation distribution of a solid-state laser medium that is excited by irradiation with an excitation light source and is capable of stimulated emission of light having a predetermined wavelength. The method includes measuring an excitation distribution of a solid-state laser medium, moving an excitation light source according to the measured excitation distribution, and adjusting a distance between the solid-state laser medium and the excitation light source.

When a plurality of unit light sources are stacked in the excitation light source, the solid-state laser medium The intensity distribution of the excitation light applied to the laser beam depends on the distance between the solid-state laser medium and the excitation light source. Therefore, by adjusting this distance, the excitation distribution of the solid-state laser medium can be controlled. The adjustment of the distance can be performed without being affected by the number of unit light sources to be stacked. Therefore, even when an excitation light source having a structure in which many unit light sources are stacked is used, it is possible to appropriately control the excitation distribution of the solid-state laser medium and reduce the thermal effect.

[0020] In this excitation distribution control method, the solid-state laser medium includes first and second end faces, a long upper surface and a bottom surface extending between the end surfaces, and the first and second end surfaces. One of the first and second end faces has two side faces extending to the other, and has a length along a direction substantially parallel to the top face, the bottom face and the two side faces, and a length along the top face and the bottom face. It may be a slab-shaped medium having a height along a direction substantially perpendicular to the two sides and a thickness along a direction substantially perpendicular to the two side surfaces. Further, the excitation light source may include first and second unit light sources stacked along the height direction of the solid-state laser medium.

[0021] The measurement of the excitation distribution may include acquiring an image of the spontaneous emission light that also emits the first or second end face force when the excitation light source power is being irradiated with the excitation light. To adjust the distance, the intensity distribution of the spontaneous emission light in the height direction of the solid-state laser medium is obtained using the image, and the intensity distribution is calculated between the two peaks respectively corresponding to the emission of the first and second unit light sources. The distance may be adjusted so that the depth of the valley located at is minimum.

[0022] The intensity distribution of the spontaneous emission light emitted from the end face of the solid-state laser medium reflects the excitation distribution in the thickness direction and the height direction of the solid-state laser medium. The deeper the valley, the more the excitation light from each unit light source is separated, and the higher the non-uniformity of the excitation distribution in the height direction of the solid-state laser medium. Therefore, if the distance between the solid-state laser medium and the excitation light source is adjusted so that the depth of the valley is minimized, the uniformity of the excitation distribution in the height direction of the solid-state laser medium is increased, and the thermal effect is reduced. .

In the measurement of the excitation distribution, when the excitation light is irradiated on the solid-state laser medium, the excitation light enters the solid-state laser medium through the first end face, propagates on a zigzag optical path, and emits the second end face force. Light of the wavelength ^^, and obtain an image of the beam pattern of the collected light May be included. Adjusting the distance may include calculating the area of the beam pattern and adjusting the distance so that the area is minimized.

When the solid-state laser medium is irradiated with the excitation light, the light propagating on the zigzag optical path receives a thermal effect from the heat generated in the solid-state laser medium. For this reason, the light focusing property depends on the excitation distribution of the solid laser medium. Therefore, the beam pattern of the collected light reflects the excitation distribution of the solid-state laser medium. The larger the area of the beam pattern, the poorer the light focusing. Therefore, if the distance between the solid-state laser medium and the excitation light source is adjusted so that the beam pattern area is minimized, the uniformity of the excitation distribution in the height direction of the solid-state laser medium is improved, and the thermal effect is reduced. Is done.

[0025] In the measurement of the excitation distribution, the inspection light emitted from a predetermined inspection light source is split into first and second lights, the first light is made incident on the first end face of the solid-state laser medium, and a zigzag optical path is formed. Propagation causes the second end face force to be emitted, interferes with the second light, and generates interference fringes having a rectangular pattern along the thickness and height directions of the solid-state laser medium, and the interference fringes are generated. Acquiring a fringe image may be included. To adjust the distance, a reference line parallel to the height of the solid-state laser medium is set in the interference fringe image acquired when the solid-state laser medium is irradiated with the excitation light, and the image on the reference line is adjusted. It may also include counting the number of vibrations of the luminance and adjusting the distance so that the number of vibrations is minimized.

[0026] The interference fringes reflect the temperature distribution of the solid-state laser medium along the zigzag optical path. This temperature distribution is formed by irradiating the solid-state laser medium with excitation light. Therefore, the interference fringe pattern reflects the excitation distribution of the solid-state laser medium. The greater the number of vibrations of the interference fringe image on the reference line, the higher the non-uniformity of the excitation distribution in the height direction of the laser medium. Therefore, if the distance between the solid-state laser medium and the excitation light source is adjusted so as to minimize the number of oscillations, the uniformity of the excitation distribution in the height direction of the solid-state laser medium is increased, and the thermal effect is reduced.

[0027] The measurement of the excitation distribution may include generating interference fringes using an interference optical system. In this excitation distribution control method, an image of interference fringes obtained when the excitation light is irradiated on the solid-state laser medium before the adjustment of the distance is substantially parallel to the height direction of the solid-state laser medium. Adjusting the interference optical system to have a clear bright line. [0028] The understanding of the present invention will be better understood from the following detailed description and the accompanying drawings. It should be noted that the attached drawings are merely examples, and are not intended to limit the scope of the present invention.

Brief Description of Drawings

FIG. 1 shows a configuration of a MOPA system according to a first embodiment.

FIG. 2 is an enlarged plan view of an excitation light source.

FIG. 3 shows the front and back of the excitation light source.

FIG. 4 is a cross-sectional view of the main amplifier.

FIG. 5 schematically shows amplified light propagating in a solid-state laser medium.

FIG. 6 shows excitation distributions in the Y and Z directions.

FIG. 7 is a diagram for explaining changes in the shape of the wavefront of the light to be amplified.

FIG. 8 schematically shows images of ASE light obtained under various light source distances.

FIG. 9 shows Z-direction profiles under various light source distances.

FIG. 10 shows a configuration of a MOPA system according to a second embodiment.

FIG. 11 schematically shows images of a light-converging pattern obtained under various light source distances.

FIG. 12 shows a configuration of a MOPA system according to a third embodiment.

[Figure 13] Images of various interference fringes are schematically shown!

FIG. 14 shows one-dimensional profiles of interference fringes under various light source distances.

Explanation of symbols

[0030] 1, la and lb: MOPA system, 10, 10a and 10b: excitation distribution control device, 31: solid-state laser medium, 32: excitation light source, 40: actuator (moving device), 50: measuring unit, 52: CCD Camera (Imaging device), 54: Condensing lens (Condensing device), 55: Inspection light source, 56: Matsuhatsu Honda interference system (interference optical system), 57: Screen, 60: Control unit, 62: Computer, 64: Camera Actuator controller, 66: Drive for excitation light source.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. [0032] First Embodiment

Hereinafter, a first embodiment according to the present invention will be described with reference to FIGS. FIG. 1 shows a configuration of a MOPA (Master Oscillator Power Amplifier) system including the excitation distribution control device of the present embodiment. The MOPA system 1 consists of a laser light source 11, a preamplifier 12, a beam expander 13, an optical mask 14, a spatial filter 15, a Faraday rotator 16, a main amplifier 17, and a spatial filter in addition to the excitation distribution controller 10. 18 and a polarizer 19. The MOPA system 1 amplifies and outputs laser light emitted from the laser light source 11.

[0033] The laser light source 11 is a master oscillator that emits laser light to be amplified. The laser light that also emits power has a wavelength that can be amplified by each of the preamplifier 12 and the main amplifier 17. The laser light source 11 is, for example, a diode-pumped Nd: YLF laser device. This laser device uses a continuous-wave laser diode to excite the Nd: YLF laser medium, amplifies the seed light by Q-switching, and generates a laser beam with energy ΙΙΏ :, beam diameter lmm, and wavelength 1.053 m. Generate

[0034] The preamplifier 12 receives the amplified light emitted from the laser light source 11, and amplifies the amplified light to 300mi. Light emitted from the preamplifier 12 is reflected by the mirror 21 and sent to the beam eta spanner 13. The beam expander 13 enlarges the beam diameter of the light and emits the light toward the mirror 22. This light is reflected by the mirror 22 and goes to the optical mask 14. The optical mask 14 has an opening for beam shaping. When the light expanded by the beam expander 13 passes through this opening, the spatial distribution shape of the light is shaped into a rectangular shape.

The spatial filter 15 has a lens 15a, a lens 15b, and a pinhole plate 15c. Similarly, the spatial filter 18 has a lens 18a, a lens 18b, and a pinhole plate 18c. The lens 15a and the lens 15b form a confocal optical system of a Keplera inverse telephoto system, and the lens 18a and the lens 18b also form a confocal optical system of a Keplera inverse telephoto system. These confocal optical systems transfer the pattern (beam pattern) of the cross section of the amplified light formed by the optical mask 14 as an optical image. In the present embodiment, amplification transfer is performed a total of eight times in four round trips. Bead formed by optical mask 14 By repeatedly transferring the system pattern, the amplified light propagates without causing diffraction.

[0036] The pinhole 15c is at the focal position between the lens 15a and the lens 15b, and the pinhole plate 18c is at the focal position between the lens 18a and the lens 18b. These pinhole plates 15c and 18c are provided for removing spatial harmonic components. Since the pinhole plates 15c and 18c are provided at the condensing position of the amplified laser light, it is desirable that the material has a high thermal shock resistance and a high material strength. Examples of such a material include ceramics, and among them, alumina, silicon nitride, carbon nitride or boron nitride, or a mixture thereof is particularly preferable. The shape of each of the openings of the pinhole plates 15c and 18c is preferably substantially similar to the shape obtained by Fourier transforming the shape of the opening of the optical mask 14.

The main amplifier 17 has a solid-state laser medium 31 and a pair of pumping light sources 32 arranged so as to sandwich the solid-state laser medium 31. Each excitation light source 32 generates excitation light and irradiates the solid laser medium 31 to excite the solid laser medium 31. Hereinafter, the configuration of the main amplifier 17 will be described in detail.

[0038] The solid-state laser medium 31 can form a population inversion in response to the irradiation of the excitation light, and can stimulate and emit light of a specific wavelength. The amplified light that also emits the power of the laser light source 11 has a wavelength that the solid-state laser medium 31 can induce and emit. In the present embodiment, the solid-state laser medium 31 is Nd-doped glass having a long slab shape.

FIG. 5 schematically shows the amplified light 70 propagating in the solid-state laser medium 31. As shown in FIG. 5, the solid-state laser medium 31 is a parallelepiped having three end faces 3 la and 3 lb, a long top surface 31c and a bottom surface 31d, and long side surfaces 31e and 31f. The amplified light 70 enters the solid-state laser medium 31 through the end faces 3 la and 3 lb parallel to each other, or the amplified light 70 exits from the solid-state laser medium 31. Each of the end face 31a and the end face 31b of the solid-state laser medium 31 is provided with a reflection reduction film. The top surface 31c and the bottom surface 31d extend in parallel between the end surfaces 31a and 31b. The side surfaces 31e and 31f extend in parallel from the end surface 31a to the end surface 31b between the top surface 31c and the bottom surface 31d. The solid-state laser medium 31 has a length along a direction parallel to the top surface 31c, the bottom surface 31d, and the two side surfaces 3le and 3If. The solid-state laser medium 31 has a top surface 31c and a bottom surface 3c. It has a height along a direction substantially perpendicular to Id and a thickness along a direction substantially perpendicular to sides 31e and 31. The X, Y and Z axes shown in the drawing indicate the length direction, thickness direction and height direction of the solid-state laser medium 31, respectively.

The amplified light 70 is obliquely incident on the end face 31 a or 31 b of the solid-state laser medium 31, and is repeatedly reflected on the side faces 31 e and 31 f of the solid-state laser medium 31 and travels on a zigzag optical path in the solid-state laser medium 31. proceed. The zigzag optical path extends substantially parallel to the top surface 31c and the bottom surface 31d of the solid-state laser medium 31. The zigzag optical path has a shape that is substantially symmetric with respect to the center line of the thickness of the solid-state laser medium 31. During the propagation of the amplified light 70 along the zigzag optical path, stimulated emission occurs according to the pumping profile (Pump Profile) in the solid-state laser medium 31, and the amplified light 70 is amplified. This excitation distribution is formed according to the intensity distribution of the excitation light.

Hereinafter, the excitation light source 32 will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is an enlarged plan view of the excitation light source 32, and FIGS. 3A and 3B show a front surface and a rear surface of the excitation light source 32, respectively. As shown in FIG. 3, each excitation light source 32 has two laser array modules 33 stacked. In each laser array module 33, a plurality of laser array units 34 are arranged one-dimensionally along the length direction (X direction) of the solid-state laser medium 31. Each laser array unit 34 has a plurality of LD bar packages and a heat sink attached to the LD bar packages. Further, as shown in FIG. 3B, the laser array unit 34 has extraction electrodes 36 and 37 electrically connected to the anode and the cathode of the LD bar package, respectively.

[0042] Each LD bar package has a structure in which LD bars are mounted on a metal heat sink. The LD bar is a laser array including a plurality of LDs (laser diodes) arranged one-dimensionally in a certain direction (the Z direction in FIG. 3), and therefore, a plurality of laser emission spots arranged in a line. Have. In the present embodiment, an LD bar in which a plurality of LDs are monolithically integrated is used. In such an LD bar, a plurality of stripe waveguides are usually provided by dividing an active layer and an electrode into a plurality of stripes and arranging them in parallel. In the present invention, instead of the LD bar having such a structure, an LD bar having a structure in which a plurality of independent LD chips are arranged in a line can be used. In each laser array unit 34, a plurality of LD bar packages are stacked in a direction perpendicular to the arrangement direction of the LDs (the X direction in FIG. 1). That is, the laser array unit 34 is a laser array having a plurality of LDs and laser emission spots two-dimensionally arranged in a matrix. The substantially rectangular area formed by assembling the light emitting surfaces of the LD bar packages is the light emitting section 34a of the laser array unit 34. In the excitation light source 32, the plurality of light emitting parts 34a are arranged so as to form substantially one plane. The excitation light source 32 is arranged such that the light emitting portions 34a face the side surfaces 3 le or 3 If of the solid-state laser medium 31.

At the rear of the laser array unit 34, a cooling manifold is attached.

The cooling manifold supplies a coolant to a flow path in a heat sink of the laser array unit 34 to cool the laser array unit 34. The laser array unit 34 and the cooling manifold are housed in housings 38 and 39.

As shown in FIG. 2, the excitation light source 32 is provided with an actuator 40 for moving the laser array unit 34 back and forth in the Y direction. The structure of the actuator 40 will be described later.

In general, a fast axis (Fast Axis) and a slow axis (Slow Axis) are defined for an LD. The fast axis is perpendicular to the pn junction of the LD and the slow axis is parallel to the pn junction. LD force The divergence angle of the emitted laser light in the fast axis direction is larger than the divergence angle in the slow axis direction

[0047] All LDs included in each laser array unit 34 are arranged with the directions of the fast axis and the slow axis mutually aligned. Since the solid-state laser medium 31 is long in the X direction, the laser array unit 34 must be extended along the length direction (X-direction) of the solid-state laser medium 31 in order to increase the irradiation area of the solid-state laser medium 31 with the excitation light. Are preferably arranged. Further, it is preferable that each laser array unit 34 is arranged so that the fast axis direction matches the length direction of the solid-state laser medium 31. This is because the spread angle of the LD light in the fast axis direction is larger than that in the slow axis direction. That is, if the fast axis direction is matched with the length direction of the solid-state laser medium 31, the force does not need to correct a large spread of the laser light in the fast axis direction. For the above reasons, in the present embodiment, the excitation light source 32 is arranged so that the fast axis direction of the laser array unit 34 matches the X direction and the slow axis direction matches the Z direction. ing.

FIG. 4 is a cross-sectional view of the main amplifier 17. This figure shows a cross section perpendicular to the length direction of the solid-state laser medium 31.

The main amplifier 17 has a medium storage section 80 in addition to the solid-state laser medium 31, the pumping light source 32, and the housings 38 and 39 described above. The medium storage section 80 stores the solid-state laser medium 31 inside. A refrigerant passage 80a is also provided inside the medium storage section 80. When the cooling water supplied from the outside flows through the coolant channel 80a, the solid-state laser medium 31 is cooled. Inside the medium accommodating section 80, a pair of windows 35 are arranged in parallel with each other with the solid-state laser medium 31 interposed therebetween. Each window 35 is a transparent flat plate. These windows 35 are parallel to the side surfaces 31 e and 31 f of the solid-state laser medium 31. The excitation light source 32 is arranged to face the solid-state laser medium 31 through the window 35.

[0050] The housings 38 and 39 house the excitation light source 32 therein. An opening 38a is provided at the front end of the housing 38. The excitation light emitted from the excitation light source 32 passes through the opening 38a and the window 35 and irradiates the solid-state laser medium 31. In response, the active elements contained in solid laser medium 31 are excited. Thereafter, when light of a predetermined wavelength enters the solid-state laser medium 31, stimulated emission occurs, and the incident light is amplified. The housing 39 holds the laminated laser array unit 34 and the cooling manifold 36 with a vertical force interposed therebetween. A cooling medium passage (not shown) is provided inside the cooling manifold 36.

FIG. 1 is referred to again. The amplified light that has entered the end face 31a of the solid-state laser medium 31 from the mirror 23 is amplified while propagating in the solid-state laser medium 31, and then exits from the end face 31b toward the mirror 24. This light is reflected by mirror 24, passes through spatial filter 18, is reflected by mirrors 27 and 28, and travels to mirror 25. The amplified light reflected by the mirror 25 and incident on the end face 31b of the solid-state laser medium 31 is amplified while propagating in the solid-state laser medium 31, and then is emitted from the end face 31a toward the mirror. This light is reflected by mirror 26 and travels to Faraday rotator 16.

The Faraday rotator 16 is arranged on the optical path between the spatial filter 15 and the mirror 26. The Faraday rotator 16 is an optical unit that rotates the plane of polarization of the incident light. Goods. In the present embodiment, the Faraday rotator 16 has a rotation angle of 45 degrees. The Faraday rotator 16 also compensates for thermal birefringence.

The polarizer 19 selectively reflects a polarized light component of a specific direction in the light that has passed through the spatial filter 15 from the mirror 23. This reflected light is the output light of MOPA system 1.

[0054] This MOPA system 1 operates as follows. The amplified light output from the laser light source 11 is amplified by the preamplifier 12, the beam diameter is expanded by the beam expander 13, and is input to the optical mask 14. The light whose beam cross-section is made rectangular by the optical mask 14 is converted into a spatial filter 15, a mirror 23, a main amplifier 17, a mirror 24, a spatial filter 18, a mirror 27, a mirror 28, a spatial filter 18, and a mirror. 25, the main amplifier 17, the mirror 26, the Faraday rotator 16, and the spatial filter 15 arrive at the mirror 29 in this order. The light reflected by the mirror 29 travels in the optical path until the optical mask 14 reaches the mirror 29 in the opposite direction, and reaches the volatilizer 19. In the following, the optical path from the optical mask 14 to the mirror 29 will be referred to as the “outbound path”, and the optical path from the mirror 29 to the polarizer 19 will be referred to as the “return path”.

[0055] The amplified light passes through the Faraday rotator 16 having a rotation angle of 45 degrees twice when traveling on the outward path and the return path. Therefore, the plane of polarization of the light rotates by 90 degrees in total. Therefore, the light that travels on the return route and reaches the volatilizer 19 is reflected by the volatilizer 19. This reflected light is the output light of the MOPA system 1.

When the amplified light travels on the outward path and the return path, the beam pattern of the amplified light at the position of the optical mask 14 is transferred eight times by the spatial filters 15 and 18. At this time, the pinhole plates 15c and 18c in the spatial filters 15 and 18 remove spatial harmonic components due to thermal distortion and the like, and thus eliminate spike noise. As a result, damage to the optical components in the MOPA system 1 due to the amplified light can be reduced.

The light to be amplified passes through the main amplifier 17 four times while passing through the forward path and the return path. The amplified light passes through the solid-state laser medium 31 excited by the excitation light source 32 and causes stimulated emission. Thus, the amplified light is amplified each time it passes through the main amplifier 17. Solid ray The total energy of the excitation light applied to the medium 31 is 48 J, and the excitation efficiency is 0.5. At this time, the energy of the output light radiated through the volatilizer 19 is 10J.

In the MOPA system 1 of the present embodiment, a device 10 for controlling the excitation distribution of the solid-state laser medium 31 is provided. This is to eliminate the problem caused by inappropriate excitation distribution of the solid-state laser medium 31. Hereinafter, this problem will be described with reference to FIGS.

As shown in FIG. 5, the amplified light 70 travels zigzag in the solid-state laser medium 31.

The side surfaces 31e and 31f of the solid-state laser medium 31 are irradiated with excitation light from the excitation light source 32 along the thickness direction (Y direction) of the solid-state laser medium 31. As a result, the solid-state laser medium 31 is excited and emits spontaneous emission (Amplified Spontaneous Emission: ASE) light. Reference numeral 71 in FIG. 5 schematically shows a pattern of the ASE light emitted from the end face of the solid-state laser medium 31. The ASE pattern 71 shows the intensity distribution in the cross section of the ASE light beam, and reflects the excitation distribution of the solid-state laser medium 31. The ASE pattern 71 of FIG. 5 is taken along a cross section substantially perpendicular to the length direction (X direction) of the solid-state laser medium 31. The ASE pattern 71 has regions 71a-71d of different intensities. These regions have higher intensity in the order of regions 71a, 71b, 71c and 71d. The higher the intensity, the higher the excitation intensity. The excitation intensity corresponds to the intensity distribution of the excitation light applied to the solid-state laser medium 31.

As described above, the excitation light source 32 has a structure in which two laser array modules 33 are stacked along the height direction (Z direction) of the solid-state laser medium 31. There is usually a gap of 1 mm or more between the light emitting portions 34a included in the upper and lower laser array modules 33. Due to this interval, the solid-state laser medium 31 may have a non-uniform excitation distribution along the height direction. The excitation light emitted from the upper and lower laser array modules 33 travels toward the solid-state laser medium 31 while diffusing in the Z direction. Therefore, the intensity distribution of the excitation light applied to the solid-state laser medium 31 and the excitation distribution of the solid-state laser medium 31 change according to the distance between the solid-state laser medium 31 and the excitation light source 32. If this distance is too short, the excitation light from the upper and lower laser array modules 33 is separated in the Z direction and is irradiated on the solid-state laser medium 31. As a result, as shown in the ASE pattern 71, In the high region 71b, a region 71c having a relatively low intensity is generated and extends so as to divide the region 71b. In addition, two high-strength regions 71a respectively appear in the upper and lower portions of the ASE pattern 71 in the Y direction.

[0061] A region having a higher excitation intensity is irradiated with excitation light having a higher intensity. Therefore, a region having a high excitation intensity generates a large amount of heat and accordingly has a high temperature. The heat generated in the solid-state laser medium 31 may exert a thermal effect on the amplified light 70 such as a thermal lens effect and a thermal birefringence effect.

FIGS. 6A and 6B show the excitation distributions in the Y and Z directions corresponding to the ASE pattern 71 shown in FIG. 5, respectively. As shown in FIG. 6, two peaks appear in both excitation distributions. As described above, since the amplified light 70 propagates in the solid-state laser medium 31 along the zigzag optical path parallel to the XY plane, it is affected by the entire Y-direction excitation distribution. Therefore, the two peaks of the Y-direction excitation distribution and the valley located therebetween cancel out the thermal effects on the amplified light 70, and as a result, the thermal effects of the Y-direction excitation distribution are averaged. On the other hand, the effect of the excitation distribution in the Z direction perpendicular to the zigzag optical path on the amplified light 70 is integrated as the amplified light 70 propagates. Therefore, the amplified light 70 emitted from the solid-state laser medium 31 receives a non-uniform thermal effect in the Z direction, and the beam quality is significantly deteriorated.

FIG. 7 is a diagram for explaining a change in the shape of the wavefront of the light 70 to be amplified. FIG. 7 (a) schematically shows the shape of the wavefront of the amplified light 70 before passing through the solid-state laser medium 31, and FIG. 7 (c) shows the amplified light after passing through the solid-state laser medium 31. 70 schematically shows the shape of the 70 wavefront. FIG. 7B shows an equivalent excitation distribution for the amplified light 70 traveling along the zigzag optical path in the solid-state laser medium 31. In FIG. 7 (b), the above-mentioned averaging caused by the zigzag optical path makes the excitation distribution in the Y direction uniform. On the other hand, two peaks 82 of the excitation intensity are arranged along the Z direction. This is the sum of the two peaks in Fig. 6 (b). The thermal lens effect due to such non-uniform excitation distribution along the Z direction causes the flat wavefront 90 of the amplified light 70 shown in FIG. 7 (a) to become uneven as shown in FIG. 7 (c). To a wavefront 91 with

[0064] When the beam quality deteriorates in this manner, the amplified signals in the pinhole plates 15c and 18c are amplified. The MOPA system 1 has a low transmittance of the light 70, damage to optical components in the MOPA system 1 has increased, and the output of the MOPA system 1 has decreased due to the elliptically polarized light 70 to be amplified. Performance may be greatly reduced. Therefore, in the MOPA system 1 of the present embodiment, a device 10 for controlling the excitation distribution of the solid-state laser medium 31 is provided. The excitation distribution control device 10 achieves an appropriate excitation distribution by adjusting the distance between the solid-state laser medium 31 and the excitation light source 32. As described above, the excitation light emitted from each of the upper and lower laser array modules 33 travels toward the solid-state laser medium 31 while diffusing. Therefore, if the distance between the laser array module 33 and the solid-state laser medium 31 changes, the intensity distribution of the excitation light changes, and the excitation distribution of the solid-state laser medium 31 changes accordingly. The excitation distribution control device 10 controls the excitation distribution using this mechanism.

In the following, the configuration of the excitation distribution control device 10 will be described with reference to FIGS. 1 and 2 again. The excitation distribution control device 10 includes an actuator 40, a measurement unit 50, and a control unit 60 in addition to the main amplifier 17.

The actuator 40 is attached to the excitation light source 32. The actuator 40 can change the distance between the solid-state laser medium 31 and the excitation light source 32 by moving the excitation light source 32 in the thickness direction (Y direction) of the solid-state laser medium 31.

As shown in FIG. 2, the actuator 40 is a screw feed mechanism having a main body 42, a pair of screw components 44, and a pair of motors 46. The main body 42 is attached to the rear of the excitation light source 32. Each screw component 44 has a head portion 44a provided with a gear, and a shaft portion 44b extending in the Y direction from the head portion 44a. A male screw is provided on the outer periphery of the shaft portion 44b. The shaft portion 44b extends into the housing 38 while being screwed with a screw hole provided in the main body 42. The tip of the shaft portion 44b is rotatably supported by a support member 48 provided in the housing 38. The motor 46 has a pinion 46a that engages with the head 44a of the screw product 44, and a shaft portion 46b that extends from the pinion 46a in the Y direction. The drive signal of the motor 46 is supplied from the control unit 60. This drive signal instructs the motor 46 on the amount and direction of rotation. When the motor 46 is driven, the pin 46a rotates around the shaft portion 46b, and the screw component 44 rotates around the shaft portion 44b in conjunction therewith. As the screw component 44 rotates, the main body 42 and the excitation light source 32 translate along the Y direction. Thereby, the distance between the excitation light source 32 and the solid-state laser medium 31 is increased. The separation changes. This distance increases or decreases depending on the direction of rotation of the motor 46.

The measuring section 50 according to the present embodiment includes a CCD camera 52. The CCD camera 52 acquires an image of the ASE light 88 emitted from one end face (the end face 31b in the present embodiment) of the solid-state laser medium 31. The CCD camera 52 has an imaging surface, and converts an optical image incident on the imaging surface into an electrical output signal. In the present embodiment, the CCD camera 52 is arranged so that its imaging surface is substantially perpendicular to the length direction (X direction) of the solid-state laser medium 31. The CCD camera 52 generates an output signal representing an image of the ASE light 88 and sends it to the control unit 60.

The control section 60 has a personal computer 62, an actuator controller 64, and a driving device 66 for the excitation light source 32. The computer 62 performs an operation using the output signal of the measuring section 50, and controls the operation of the actuator controller 64 according to the result. The actuator controller 64 transmits a drive signal to the motor 46 of the actuator 40 under the control of the computer 62 to drive the actuator 40. Actuator controller 64 controls the direction and amount of movement of actuator 40 by instructing the direction and amount of rotation of motor 46. The driving device 66 supplies driving power to the excitation light source 32 under the control of the computer 62, and causes the excitation light source 32 to emit excitation light. Therefore, the computer 62 can excite the solid-state laser medium 31 at a desired timing.

[0070] The MOPA system 1 of the present embodiment first adjusts the excitation distribution in the solid-state laser medium 31 using the excitation distribution control device 10, and then emits light from the laser light source 11, and converts the light. Amplify. The excitation distribution control device 10 controls the excitation distribution by adjusting the distance between the solid-state laser medium 31 and the excitation light source 32. This adjustment of the distance is performed based on an image of the ASE light emitted from the solid-state laser medium 31. Hereinafter, the adjustment of the distance will be described in detail.

First, the excitation distribution control device 10 acquires an ASE light image using the CCD camera 52. As described above, the intensity distribution of the excitation light applied to the solid-state laser medium 31 changes according to the distance between the excitation light source 32 and the solid-state laser medium 31. An excitation distribution is formed in the solid-state laser medium 31 according to the intensity distribution, and ASE light is emitted from the excited part. Excitation intensity The larger the is, the stronger the ASE light is emitted. Therefore, the intensity distribution of the ASE light emitted from the end face of the solid-state laser medium 31 reflects the excitation distribution of the solid-state laser medium 31 in the thickness direction (Y direction) and the height direction (Z direction).

FIG. 8 schematically shows ASE light images acquired by the CCD camera 52 when the light emitting section 34a of the excitation light source 32 is arranged at various distances from the solid-state laser medium 31. The ASE light image 72 is a two-dimensional image of the solid-state laser medium 31 along the thickness direction (Y direction) and the height direction (Z direction). The ASE light image 72 has regions 72a to 72d of different luminances. These areas have higher brightness in the order of the areas 72a, 72b, 72c and 72d. The higher the brightness, the higher the intensity of the ASE light. That is, the luminance distribution of the ASE light image 72 indicates the intensity distribution of the ASE light on the YZ plane.

FIG. 8A shows an ASE light image 72 when the distance between the light emitting section 34a of the excitation light source 32 and the solid-state laser medium 31 (hereinafter, referred to as “light source distance”) is short. In this image, a region 72c having a relatively low luminance is generated in a region 72b having a relatively high luminance, and extends so as to divide the region 72b. This indicates that non-uniform excitation occurs near the center of the solid-state laser medium 31. When the light source distance increases, the ASE light image 72 shown in FIG. 8B is detected, and when the light source distance further increases, the ASE light image 72 shown in FIG. 8C is detected. In these images, the region 72b is not divided by the region 72c, and near the center of the solid-state laser medium 31, the uniformity of excitation is increased.

As described above, the non-uniformity of the excitation distribution in the Y direction does not cause any problem because it is averaged. The non-uniformity in the Z direction is integrated, so that the quality of the output beam of the MOPA system 1 deteriorates. Let it. Therefore, in the present embodiment, the non-uniformity of the excitation distribution in the Z direction is evaluated based on the ASE light image 72, and the light source distance is adjusted according to the result.

The output signal of the CCD camera 52 is sent to the computer 62 in the control unit 60. The computer 62 converts the output signal into two-dimensional text data. The two-dimensional text data contains the brightness of the ASE light image acquired by the CCD camera 52 in association with each pixel. Each pixel is assigned a pair of Y and Z direction pixel numbers. That is, the output signal of the CCD camera 52 includes the two-dimensional luminance distribution data of the ASE light emitted from the end face of the solid-state laser medium 31. The computer 62 integrates the luminance distribution of the ASE light image in the Y direction to create the luminance distribution of the ASE light in the Z direction in order to evaluate the non-uniformity of the excitation distribution in the Z direction. Specifically, the computer 62 uses the above-described two-dimensional text data to calculate the total luminance for each of the pixel rows parallel to the Y direction. Each pixel column has a single Z-direction pixel number. The computer 62 plots the total brightness calculated for each pixel column, and creates a brightness distribution of the ASE light image in the height direction (Z direction) of the solid-state laser medium 31. Hereinafter, this luminance distribution is referred to as a “Z-direction profile”.

FIG. 9 shows Z-direction profiles under various light source distances. In FIG. 9, the horizontal axis represents coordinates in the height direction (Z direction) of the solid-state laser medium 31, and the vertical axis represents luminance integrated in the thickness direction (Y direction) of the solid-state laser medium 31.

FIGS. 9 (a)-(c) correspond to FIGS. 8 (a) -1 (c), respectively. As shown in FIG. 9A, at the shortest light source distance, two peaks 84 and a valley 85 located between the peaks 84 appear in the Z-direction profile. These peaks 84 correspond to the emission centers of the laser array modules 33 in the Z direction. In the following, the depth of the valley 85 of the Z-direction profile is denoted as ΔΙ. The valley 85 indicates the magnitude of the non-uniformity of the excitation distribution in the Z direction. When the light source distance is longer, ΔΙ is reduced as shown in FIGS. 9 (b) and 9 (c). This means that the non-uniformity of the excitation distribution has been reduced. Therefore, the computer 62 adjusts the light source distance so that ΔI is minimized.

First, the computer 62 controls the actuator controller 64 to drive the actuator 40 to bring the excitation light source 32 sufficiently close to the solid-state laser medium 31 so that a valley 85 appears in the Z-direction profile. Subsequently, the computer 62 controls the driving device 66 to drive the excitation light source 32 to irradiate the solid-state laser medium 31 with the excitation light. The CCD camera 52 acquires an image of the ASE light emitted from the end face 31b of the solid-state laser medium 31, and sends an output signal to the computer 62. The computer 62 uses this output signal to create a Z-direction profile according to the procedure described above.

In order to evaluate the depth Δ 深 of the valley 85 appearing in the Z-direction profile, the computer 62 calculates the reference coordinates ζθ corresponding to the bottom of the valley 85 and the reference coordinates zl corresponding to the top of the valley 85. Is calculated. ζθ and zl can be determined using any waveform analysis method . The reference coordinates zl are determined according to the brightness 10 corresponding to the top of the valley 85. The luminance 10 may be, for example, the average value of the heights of the two peaks 84 appearing in the Z-direction profile, or may be the height of the peak 84! / ,.

Next, the computer 62 moves the excitation light source 32 away from the solid-state laser medium 31 by a predetermined distance, and then drives the excitation light source 32 to irradiate the solid-state laser medium 31 with excitation light. Get profile. The computer 62 calculates the depth ΔΙ based on the acquired Z-direction profile. Specifically, in the Z-direction profile, the luminances corresponding to the reference coordinates 基準 θ and zl are respectively specified, and the difference between the specified luminances is calculated as ΔΙ. Thereafter, the computer 62 repeats the operation of moving the excitation light source 32 away from the solid-state laser medium 31 by a predetermined distance, acquiring a Z-direction profile, and calculating ΔΙ.

As described above, the computer 62 repeats the calculation of ΔΙ while increasing the light source distance by a predetermined distance, and checks a change in ΔΙ according to the light source distance. As shown in FIGS. 9 (b) and 9 (c), when the light source distance increases, Δ Ι first decreases and then increases. When the depth Δ の of the valley 85 is the smallest, the non-uniformity of the excitation distribution in the Z direction is minimized. The computer 62 derives a light source distance that minimizes Δ Ι from Δ 算出 calculated under various light source distances. Then, the computer 62 drives the actuator 40 to arrange the excitation light source 32 at the calculated light source distance. Thereby, the unevenness of the excitation distribution of the solid-state laser medium 31 in the Z direction can be minimized. When the laser light source 11 emits amplified light, the amplified light is amplified by the main amplifier 17 and output from the MOPA system 1. Since the non-uniformity of the excitation distribution in the Z direction is suppressed, the thermal effect on the amplified light can be reduced, and a high-quality output beam can be obtained.

In the above embodiment, two unit light sources, ie, the laser array module 33, are stacked in the excitation light source 32. However, more laser array modules 33 may be stacked. The number of the laser array modules 33 stacked along the height direction (Z direction) of the solid-state laser medium 31 does not affect the adjustment of the distance between the solid-state laser medium 31 and the excitation light source 32. Therefore, even when an excitation light source having a structure in which a larger number of laser array modules 33 are stacked is used, the same method as in the present embodiment is used. By using this, the excitation distribution of the solid-state laser medium 31 can be controlled to reduce the thermal effect.

[0084] Second embodiment

Hereinafter, a second embodiment of the present invention will be described. FIG. 10 shows the configuration of the MO PA system according to the present embodiment. This MOPA system la has an excitation distribution control device 10a. The excitation distribution control device 10a controls the excitation distribution of the solid-state laser medium 31 by measuring the condensing pattern 74 of the light amplified by the solid-state laser medium 31 instead of the ASE light image 72. The excitation distribution control device 10a has an actuator 40, a measurement unit 50a, and a control unit 60. The excitation distribution control device 10a differs from the excitation distribution control device 10 of the first embodiment in the configuration of the measurement unit 50a and the operation of the control unit 60. The other configuration is the same as that of the first embodiment, and a duplicate description will be omitted.

The measuring section 50a has a condenser lens 54 and a mirror 25 in addition to the CCD camera 52. The mirror 25 forms a part of the optical system for optical amplification as described above. The mirror 25 has a sufficiently high reflectivity. A part of the amplified light passes through the mirror 25. The condenser lens 54 is arranged so as to condense the light to be amplified transmitted through the mirror 25 and emit the light to the CCD camera 52. The CCD camera 52 acquires a beam pattern of the amplified light condensed by the condenser lens 54, that is, an image of the condenser pattern. In the present embodiment, the CCD camera 52 is arranged so that its imaging surface is substantially perpendicular to the optical axis of the condenser lens 54.

[0086] In the present embodiment, the control unit 60 controls the light emission timing of the laser light source 11. That is, the laser light source 11 emits amplified light when receiving the light emission command signal from the computer 62.

FIG. 11 schematically shows a converging pattern image 74 obtained by the CCD camera 52 when the excitation light source 32 is arranged at various distances from the solid-state laser medium 31. The focusing pattern image 74 is a two-dimensional image of the solid-state laser medium 31 along the thickness direction (Y direction) and the height direction (Z direction). The converging pattern appearing in the image 74 reflects the beam pattern of the amplified light that has been amplified by the solid-state laser medium 31. Since the amplified light is amplified according to the excitation distribution of the solid-state laser medium 31, the beam pattern of the amplified light reflects the excitation distribution. After all, the condensing pattern of the amplified light reverses the excitation distribution of the solid-state laser medium 31. To be reflected.

FIG. 11A shows a light-collecting pattern image 74 when the light source distance is too short. In this focusing pattern, a number of light emitting spots 74a are arranged along the Z direction. This indicates that the light collecting property is good. This is due to the non-uniformity of the excitation distribution of the solid-state laser medium 31 in the Z direction. When the light source distance is further increased, as shown in FIG. 11B, the number and area of the light-emitting spots 74a in the light-collecting pattern image 74 are reduced, and the light-collecting property is improved. However, if the light source distance is too large, as shown in FIG. 11C, the area of the light emitting spot 74a is enlarged, and the light collecting property is reduced.

As described above, the non-uniformity of the excitation distribution in the Z direction lowers the light collecting property of the amplified light.

Therefore, in the present embodiment, the non-uniformity of the excitation distribution in the Z direction is evaluated based on the converging pattern image 74, and the light source distance is adjusted according to the result.

The output signal of the CCD camera 52 is sent to the computer 62 in the control unit 60. The computer 62 converts the output signal into two-dimensional text data. In the two-dimensional text data, the brightness of the converging pattern image acquired by the CCD camera 52 is stored in association with each pixel. Each pixel is assigned a pair of pixel numbers in the Y and Z directions. That is, the output signal of the CCD camera 52 includes the two-dimensional luminance distribution data of the amplified light collected by the condenser lens 54.

[0091] The computer 62 calculates the area of the converging pattern measured using the CCD camera 52 in order to evaluate the non-uniformity of the excitation distribution in the Z direction. Specifically, the computer 62 uses the two-dimensional text data to count pixels having a luminance equal to or higher than a threshold. In the present embodiment, a luminance corresponding to 10% of the maximum luminance in the converging pattern image 74 is used as the threshold. The ratio of the threshold to the maximum luminance can be set arbitrarily. The computer 62 stores the number of pixels obtained by the counting as the area S of the light-converging pattern.

[0092] The computer 62 drives the excitation light source 32 while changing the light source distance by a predetermined distance to irradiate the solid-state laser medium 31 with the excitation light, and further sends an emission command signal to the laser light source 11 to emit the amplified light. Let it. As a result, a condensing pattern image 74 of the amplified light amplified by the solid-state laser medium 31 is obtained, and condensed based on the condensing pattern image 74. The area of the pattern, that is, the number of pixels having a luminance equal to or greater than the threshold is obtained. For example, with respect to the light-collecting pattern images 74 in FIGS.

[0093] As described above, the computer 62 repeatedly measures the area S of the light-condensing pattern under various light source distances, and examines a change in the area S according to the light source distance. When the area S is the smallest, the non-uniformity of the excitation distribution in the Z direction is most suppressed. The computer 62 derives a light source distance that minimizes the area S from the area S obtained under various light source distances. Then, the computer 62 drives the actuator 40 to dispose the excitation light source 32 at the calculated light source distance. Thereby, the non-uniformity of the excitation distribution of the solid-state laser medium 31 in the Z direction can be minimized. When the laser light source 11 emits light to be amplified, the light to be amplified is amplified by the main amplifier 17 and output from the MOPA system la. Since the non-uniformity of the excitation distribution in the Z direction is suppressed, thermal effects on the amplified light can be reduced, and a high-quality output beam can be obtained.

In the above embodiment, two unit light sources, ie, the laser array module 33, are stacked in the excitation light source 32. However, more laser array modules 33 may be stacked. The number of the laser array modules 33 stacked along the height direction (Z direction) of the solid-state laser medium 31 does not affect the adjustment of the distance between the solid-state laser medium 31 and the excitation light source 32. Therefore, even when an excitation light source having a structure in which a larger number of laser array modules 33 are stacked is used, the excitation distribution of the solid-state laser medium 31 is controlled using the same method as in the present embodiment to reduce the thermal effect. can do.

[0095] Third Embodiment

Hereinafter, a third embodiment of the present invention will be described. FIG. 12 shows the configuration of the MOPA system according to the present embodiment. This MOPA system lb has an excitation distribution controller 10b. The excitation distribution control device 10b measures the excitation distribution of the solid-state laser medium 31 by measuring the interference fringe pattern with the light transmitted through the solid-state laser medium 31 instead of the ASE light image 72. Control. The excitation distribution control device 10b includes an actuator 40, a measurement unit 50b, and a control unit 60. The excitation distribution control device 10b differs from the excitation distribution control device 10 of the first embodiment in the configuration of the measurement unit 50b and the operation of the control unit 60. The other configuration is the same as that of the first embodiment, and a duplicate description will be omitted.

The measuring section 50b has an inspection light source 55, a Mach-Zehnder interference system 56, and a screen 57 in addition to the CCD camera 52. The inspection light source 55 is a He—Ne laser device that emits inspection light in response to a light emission command signal from the computer 62. The Matsuhatsu Donda interference system 56 is an optical system for generating interference fringes using the inspection light. The Matsuhatsu Honda interferometer 56 includes a beam splitter 56a, a dichroic mirror 56b, a high reflection mirror 56c, a beam splitter 56d, a beam expander 56e, and an optical mask 56f. The Mach-Zehnder interference system 56 propagates the inspection light substantially parallel to the XY plane. As will be described later, the computer 62 can adjust the positions of the high reflection mirror 56c and the beam splitter 56d.

[0097] The beam expander 56e enlarges the beam diameter of the inspection light and emits it toward the optical mask 56f. The optical mask 56f has an opening for beam shaping. When the inspection light enlarged by the beam expansor 56e passes through this opening, the wavefront of the inspection light is shaped into a rectangular shape. This wavefront has a short side extending in the Y direction and a long side extending in the Z direction, similarly to the amplified light shown in FIG.

[0098] The beam splitter 56a receives the inspection light from the optical mask 56f, and splits into the first light 86 and the second light 87. The beam splitter 56a transmits the first split light 86 toward the high reflection mirror 56b, and reflects the second split light 87 toward the high reflection mirror 56c. The mirror 56b reflects the first split light beam 86 toward the dichroic mirror 26a. The dichroic mirror 26a reflects the amplified light while transmitting the inspection light. Therefore, the first branch light 86 passes through the dichroic mirror 26a and travels to the solid-state laser medium 31. The first branch light 86 enters the solid-state laser medium 31 through the end face 3 la, propagates on the zigzag optical path of the amplified light, and then exits from the end face 31 b.

[0099] In the present embodiment, the dichroic mirror 25b is used as a mirror for receiving the amplified light emitted from the end face 3lb. The first branched light 86 emitted from the solid-state laser medium 31 travels on the optical path of the amplified light and reaches the dichroic mirror 25b. The dichroic mirror 25b reflects the amplified light to the spatial filter 18 while transmitting the first split light 86. The beam splitter 56d is the first branch that has passed through the dichroic mirror 25b. Half of the light 86 reflects off the screen 57.

[0100] On the other hand, the second split light beam 87 reflected by the beam splitter 56a is reflected by the high reflection mirror 56c and travels to the beam splitter 56d. Half of the second split beam 87 passes through the beam splitter 56d and goes to the screen 57. As a result, the inspection light that has passed through the solid-state laser medium 31 along the zigzag optical path (that is, the first branch light 86) and the inspection light that has not passed through the solid-state laser medium 31 (that is, the second branch light 87) ) And an interference beam 92 is formed.

[0101] The interference beam 92 is projected onto the projection surface of the screen 57. As a result, interference fringes 75 are formed on the projection surface. The projection surface of the screen 57 is arranged substantially perpendicular to the propagation direction of the interference beam 92. As described above, the inspection light and the branched lights 86 and 87 that also generate the inspection light power have rectangular wavefronts along the thickness direction (Y direction) and the height direction (Z direction) of the solid-state laser medium 31. Having. Therefore, the interference fringe 75 also has a rectangular pattern along the Y and Z directions.

[0102] The CCD camera 52 acquires an image of the interference fringe 75 projected on the projection surface of the screen 57. In the present embodiment, the non-uniformity of the excitation distribution in the Z direction is evaluated based on the interference fringe image, and the light source distance is adjusted according to the result. Hereinafter, this adjustment procedure will be described in detail.

[0103] First, the computer 62 in the control unit 60 adjusts the Mach-Zehnder interference system 56. The computer 62 sends a light emission command signal to the inspection light source 55 without driving the excitation light source 32 to emit inspection inspection light, and forms interference fringes 75. The CCD camera 52 obtains an image of the interference fringes 75 and generates an output signal corresponding to the image. This output signal is sent to the computer 62.

FIG. 13 (a) schematically shows the interference fringe image 76 thus obtained. The interference fringe image 76 is a two-dimensional image of the solid-state laser medium 31 along the thickness direction (Y direction) and the height direction (Z direction). FIG. 13 (a) also depicts a virtual reference line 77 parallel to the Z direction. The reference line 77 is a center line of the interference fringe image 76 extending parallel to the height direction (Z direction) of the solid-state laser medium 31. The reference line 77 corresponds to the center axis of the zigzag optical path of the amplified light in the solid-state laser medium 31. When the high-reflection mirror 56c and the beam splitter 56d are properly arranged when the solid-state laser medium 31 is not irradiated with the excitation light, as shown in FIG. It is possible to obtain an interference fringe image 76 in which bright lines 76a parallel to each other are arranged in the Y direction. The computer 62 adjusts the positions of the high reflection mirror 56c and the beam splitter 56d so as to obtain such an interference fringe image 76. When the interference fringe image 76 shown in FIG. 13A is obtained, the positions of the high reflection mirror 56c and the beam splitter 56d are fixed. Thus, the preprocessing is completed.

Next, the computer 62 drives the excitation light source 32 to irradiate the solid-state laser medium 31 with the excitation light, and sends a light emission command signal to the inspection light source 55 to emit the inspection light. From this, the interference fringes 75 are formed again and are acquired by the CCD camera 52. FIGS. 13 (b)-(d) schematically show interference fringe images 76 acquired by the CCD camera 52 when the solid-state laser medium 31 is irradiated with excitation light under various light source distances. .

When the solid-state laser medium 31 is irradiated with the excitation light, the temperature inside the solid-state laser medium 31 rises, and a temperature distribution is formed. This temperature distribution reflects the intensity distribution of the excitation light, and therefore reflects the excitation distribution of the solid-state laser medium 31. Since the refractive index of the solid-state laser medium 31 changes according to the temperature, a refractive index distribution according to the temperature distribution is formed in the solid-state laser medium 31. That is, the refractive index distribution of the solid-state laser medium 31 reflects the excitation distribution. The non-uniform refractive index distribution distorts the wavefront of the inspection light (first branch light 86) transmitted through the solid-state laser medium 31. This wavefront distortion affects the pattern of the interference fringes 75.

If the light source distance is too small, the excitation distribution shown in FIGS. 6A and 6B and the refractive index distribution corresponding to this excitation distribution are formed in the solid-state laser medium 31. Since the inspection light propagates in the solid-state laser medium 31 along a zigzag optical path parallel to the XY plane, the influence of the refractive index distribution in the Y direction on the inspection light is averaged. On the other hand, the influence of the refractive index distribution in the Z direction perpendicular to the zigzag optical path on the inspection light is integrated without friction of the inspection light. As a result, as shown in FIGS. 13B and 13D, the bright line 76a in the interference fringe image 76 is curved so as to cross the Z direction. The higher the non-uniformity of the refractive index distribution in the Z direction, the greater the curvature of the bright line 76a, and the more easily the bright line 76a intersects the reference line 77.

FIG. 13B shows an interference fringe image 76 when the light source distance is too short. In this interference fringe, A number of bright lines 76a cross the reference line 77. In other words, the luminance of the interference fringe image 76 vibrates many times on the reference line 77. This is due to the non-uniformity of the refractive index distribution of the solid-state laser medium 31 in the Z direction. As the light source distance becomes larger, the number of times of luminance oscillation on the reference line 77 decreases as shown in FIG. This means that the non-uniformity of the refractive index distribution in the Z direction has been reduced. However, if the light source distance is too large, the number of luminance oscillations on the reference line 77 increases as shown in FIG.

As described above, the smaller the number of oscillations of the luminance of the interference fringe image 76 on the reference line 77, the more uniform the refractive index distribution power of the solid-state laser medium 31 along the negative direction. As described above, this refractive index distribution corresponds to the excitation distribution of the solid-state laser medium 31. Therefore, in the present embodiment, the nonuniformity of the excitation distribution in the Z direction is evaluated based on the interference fringe image 76, and the light source distance is adjusted according to the result.

When the CCD camera 52 acquires an image of the interference fringe 75, it sends an output signal corresponding to the image to the computer 62. Computer 62 converts the output signal into two-dimensional text data. The two-dimensional text data contains the luminance of the interference fringe image 76 acquired by the CCD camera 52 in association with each pixel. Each pixel is assigned a pair of pixel numbers in the Y and Z directions. That is, the output signal of the CCD camera 52 includes the two-dimensional luminance distribution data of the interference fringe generated by the Mach-Zehnder interferometer 56.

[0112] The computer 62 sets a reference line 77 in the interference fringe image 76 measured using the CCD camera 52, and evaluates the non-uniformity of the excitation distribution in the Z direction. Count the number of brightness oscillations. Specifically, the computer 62 extracts a pixel row located on the reference line 77 from the two-dimensional text data. Subsequently, the computer 62 plots the luminance of each pixel included in the pixel column, and creates a luminance distribution of the interference fringe pattern along the reference line 77. Hereinafter, this luminance distribution is referred to as “one-dimensional profile of interference fringes”.

[0113] Fig. 14 shows one-dimensional profiles of interference fringes under various light source distances. In FIG. 14, the horizontal axis indicates the luminance of the interference fringe image 76 on the reference line 77, and the vertical axis indicates the fixed value. The coordinates in the height direction (Z direction) of the body laser medium 31 are shown. Figures 14 (a)-(c) correspond to Figures 13 (a)-(c), respectively. As shown in these figures, in the one-dimensional profile of the interference fringes, a waveform corresponding to the luminance fluctuation on the reference line 77 appears.

[0114] The computer 62 counts the number of luminance oscillations appearing in the one-dimensional profile. This counting is performed using any method. For example, a peak having a luminance equal to or higher than the predetermined threshold II may be detected in the one-dimensional profile, and the peak may be counted. Peak detection is performed using any waveform analysis method.

It is preferable that portions of the interference fringe image 76 that are included in the upper and lower 5% of the entire range of the Z coordinate be excluded from the counting of the number of luminance oscillations. Therefore, in the present embodiment, as shown in FIG. 14, the number of luminance oscillations is counted within the range from the coordinate zl to the coordinate z2 in the one-dimensional profile. In addition, a pixel included in the upper and lower 5% of the entire range of the Z coordinate of the interference fringe image 76 is excluded to create a one-dimensional profile, and the luminance of the one-dimensional profile is calculated over the entire range of the Z coordinate. The number of vibrations may be counted.

[0116] The computer 62 drives the excitation light source 32 while changing the light source distance by a predetermined distance to irradiate the solid-state laser medium 31 with the excitation light, and further sends a light emission command signal to the inspection light source 55 to emit the inspection light. Let it. As a result, the interference fringe image 76 is obtained, and the number of vibrations of the luminance on the reference line 77 along the height direction (Z direction) of the solid-state laser medium 31 is counted. For example, with respect to the interference fringe image 76 shown in FIGS. 13B to 13D, the number of vibrations of 5, 2, and 10, respectively, is obtained.

[0117] As described above, the computer 62 repeatedly counts the number of vibrations of the luminance along the Z direction in the interference fringe image 76 under various light source distances, and checks a change in the number of vibrations. At the lowest frequency, the non-uniformity of the excitation distribution in the Z direction is minimized. The computer 62 derives the light source distance that minimizes the number of vibrations from the number of vibrations obtained under various light source distances. Then, the computer 62 drives the actuator 40 to arrange the excitation light source 32 at the calculated light source distance. Thereby, the non-uniformity of the excitation distribution of the solid-state laser medium 31 in the Z direction can be minimized. When the laser light source 11 emits the amplified light, the amplified light is amplified by the main amplifier 17 and output from the MOPA system lb. Since the non-uniformity of the excitation distribution in the Z direction is suppressed, a high-quality output You can get the game.

In the above embodiment, two unit light sources, ie, the laser array module 33, are stacked in the excitation light source 32. However, more laser array modules 33 may be stacked. The number of the laser array modules 33 stacked along the height direction (Z direction) of the solid-state laser medium 31 does not affect the adjustment of the distance between the solid-state laser medium 31 and the excitation light source 32. Therefore, even when an excitation light source having a structure in which a larger number of laser array modules 33 are stacked is used, the excitation distribution of the solid-state laser medium 31 is controlled using the same method as in the present embodiment, and the thermal effect is reduced. can do.

As described above, the present invention has been described in detail based on the embodiments. However, the present invention is not limited to the above embodiment. The present invention can be variously modified without departing from the gist thereof.

[0120] In the third embodiment, an interference fringe is formed using the Mach-Zehnder interferometer 56. However, interference fringes may be formed using any other interference optical system.

As is apparent from the above-described invention, the embodiments of the present invention may be modified in various ways. All such modifications are intended to be included within the scope of the following claims, as will be apparent to those skilled in the art, such modifications do not depart from the scope of the invention.

Industrial applicability

[0122] According to the present invention, even when an excitation light source having a structure in which a number of unit light sources are stacked is used, the excitation distribution of the solid-state laser medium can be appropriately controlled, thereby compensating for the thermal effect.

Claims

The scope of the claims

[1] a solid-state laser medium that is excited by irradiation with the excitation light and is capable of stimulated emission of light of a predetermined wavelength;

An excitation light source for irradiating the solid-state laser medium with the excitation light,

A moving device capable of changing the distance between the solid-state laser medium and the excitation light source by moving the excitation light source;

A measuring unit for measuring an excitation distribution of the solid-state laser medium,

A control unit that controls the excitation distribution of the solid-state laser medium by driving the moving device according to the excitation distribution measured by the measurement unit and adjusting a distance between the solid-state laser medium and the excitation light source.

An excitation distribution control device comprising:

[2] The solid-state laser medium includes first and second end surfaces, a long upper surface and a bottom surface extending between the end surfaces, and the first and second end surfaces between the upper surface and the bottom surface. One force has two side surfaces extending to the other, and has a length along a direction substantially parallel to the top surface, the bottom surface and the two side surfaces, and a direction substantially perpendicular to the top surface and the bottom surface. A slab-shaped medium having a height along the direction and a thickness along a direction substantially perpendicular to the two side surfaces,

The excitation light source includes first and second unit light sources stacked along a height direction of the solid-state laser medium.

The excitation distribution control device according to claim 1.

[3] The measurement unit has an imaging device for acquiring an image of spontaneous emission light generated by the first or second end face force of the solid-state laser medium when the excitation light source irradiates the excitation light. And

The control unit obtains a luminance distribution of the spontaneous emission light in a height direction of the solid-state laser medium using the image, and two luminance distributions corresponding to the light emission of the first and second unit light sources, respectively. Driving the moving device so that the depth of the valley located between the peaks is minimized;

3. The excitation distribution control device according to claim 2.

[4] The measuring unit is configured to collect the light having the predetermined wavelength, which is incident on the solid-state laser medium through the first end face, propagates on the zigzag optical path, and emits from the second end face. An imaging device for acquiring an image of a beam pattern of light condensed by the light condensing device,

The pump according to claim 2, wherein the control unit calculates an area of the beam pattern when the solid-state laser medium is irradiated with the excitation light, and drives the moving device to minimize the area. Distribution control device.

[5] The measurement unit may include an inspection light source that emits inspection light, split the inspection light into first and second lights, and make the first light incident on the solid-state laser medium through the first end surface. The solid-state laser medium has a rectangular pattern along the thickness direction and the height direction of the solid-state laser medium by propagating on the zigzag optical path, emitting from the second end face, and interfering with the second light. An interference optical system that generates interference fringes, and an imaging device that acquires an image of the interference fringes,

The control unit sets a reference line parallel to the height direction in an image of the interference fringe acquired when the excitation light is applied to the solid-state laser medium, and sets the reference line on the reference line. Counting the number of vibrations of the brightness of the image, and driving the moving device so that the number of vibrations is minimized;

3. The excitation distribution control device according to claim 2.

[6] Before counting the number of vibrations, the control unit may control the image of the interference fringes acquired when the excitation light is not irradiated on the solid-state laser medium, substantially in the height direction. Adjusting the interference optics to have parallel bright lines,

6. The excitation distribution control device according to claim 5.

[7] Excitation light source power A method for controlling the excitation distribution of a solid-state laser medium that is excited by irradiation with excitation light and is capable of stimulated emission of light of a predetermined wavelength,

Measuring the excitation distribution of the solid state laser medium,

The excitation light source is moved according to the measured excitation distribution, and the distance between the solid-state laser medium and the excitation light source is adjusted. A method comprising:

[8] The solid-state laser medium includes first and second end faces, elongated upper and lower faces extending between the end faces, and the first and second end faces between the upper and bottom faces. One force has two side surfaces extending to the other, and has a length along a direction substantially parallel to the top surface, the bottom surface and the two side surfaces, and a direction substantially perpendicular to the top surface and the bottom surface. A slab-shaped medium having a height along the direction and a thickness along a direction substantially perpendicular to the two side surfaces,

The method of claim 7.

[9] The measurement of the excitation distribution includes acquiring an image of the spontaneous emission light generated by the first or second end face force of the solid-state laser medium when the excitation light is irradiated from the excitation light source. And

The adjustment of the distance is performed by obtaining an intensity distribution of the spontaneous emission light in a height direction of the solid-state laser medium using the image, and determining the intensity distribution of the spontaneous emission light corresponding to the emission of the first and second unit light sources. 9. The method according to claim 8, comprising adjusting the distance such that the depth of a valley located between two peaks is minimized.

[10] The measurement of the excitation distribution is such that, when the solid-state laser medium is irradiated with the excitation light, the excitation light is incident on the solid-state laser medium through the first end face and propagates on a zigzag optical path to form the second end face. Condensing the light of the predetermined wavelength emitted from the device, and acquiring an image of a beam pattern of the condensed light.

Adjusting the distance includes calculating the area of the beam pattern and adjusting the distance so that the area is minimized! / Puru,

A method according to claim 8.

[11] In the measurement of the excitation distribution, the inspection light emitted from a predetermined inspection light source is branched into first and second lights, and the first light is made incident on a first end face of the solid-state laser medium, and zigzag light is emitted. Propagation on the road, emission from the second end face, interference with the second light, interference having a rectangular pattern along the thickness direction and the height direction of the solid laser medium Generating fringes and obtaining an image of the interference fringes, wherein the adjusting of the distance includes adjusting the distance in the images of the interference fringes obtained when the excitation light is applied to the solid-state laser medium. Setting a reference line parallel to the height direction, counting the number of vibrations of the brightness of the image on the reference line, and adjusting the distance such that the number of vibrations is minimized. ,

A method according to claim 8.

The measurement of the excitation distribution includes generating the interference fringes using an interference optical system,

Before the adjustment of the distance, an image of the interference fringe obtained when the excitation light is not irradiated on the solid-state laser medium has a bright line substantially parallel to the height direction. The method of claim 11, further comprising adjusting the interference optics.