JP2020043278A - Solid-state laser device - Google Patents

Abstract

To provide a solid-state laser device capable of preventing deterioration of optical properties even when a periodic polarization inverse element is used.SOLUTION: The solid-state laser device includes: a semiconductor laser 1 for emitting excitation light; a laser medium 5, disposed between an incident mirror and an output mirror 7, excited by the excitation light from the semiconductor laser 1 to emit a fundamental laser beam; a periodic polarization inverse element 6, disposed between the laser medium 5 and the output mirror 7 to form a periodic polarization inverse structure and convert a fundamental wave into a harmonic; transparent materials 8a, 8b covering the periodic polarization inverse element 6; and metal holders 11c, 11d for covering the transparent materials 8a, 8b.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a solid-state laser device for holding a wavelength conversion element using a periodically poled element.

  Excitation light from a semiconductor laser is condensed by a condensing lens, the condensed excitation light is applied to a laser medium, and a fundamental wave induced and emitted from the laser medium is applied to a nonlinear crystal accommodated in an optical resonator. Thus, there is known a solid-state laser device that converts a fundamental wave into a second harmonic, oscillates the second harmonic in an optical resonator, and outputs the second harmonic to the outside via an emission mirror (Patent Document 1).

  A quasi-phase type periodically poled element such as MgSLT or MgLN may be used as a nonlinear crystal including a wavelength conversion element that converts a fundamental wave into a second harmonic. It is easy to widen the opening of the periodically poled element in the width direction of the element from the manufacturing method. However, it is difficult to widen the opening in the thickness direction.

  For example, the thickness of an element for outputting a second harmonic of 532 nm from a fundamental of 1064 nm is limited to about 1 mm. As shown in FIG. 7, a periodically poled element 6A having a thickness of about 1 mm is held by two metal holders 11a and 11b and inserted into a resonator.

JP-A-10-7997

  However, the aperture having a thickness of 1 mm is the smallest among the optical components constituting the resonator, and it has been difficult to adjust the resonator. In particular, since the periphery of the periodically poled element 6A is covered with the metal holders 11a and 11b, a part of the stimulated emission of the fundamental wave is blocked. For this reason, the temperature of the metal holders 11a and 11b rises, and the optical characteristics such as the rising characteristics of the laser deteriorate due to the heat caused by the temperature rise.

  An object of the present invention is to provide a solid-state laser device capable of preventing deterioration of optical characteristics even when a periodically poled element is used.

  In order to solve the above-mentioned problems, a solid-state laser device according to the present invention is arranged between a semiconductor laser that emits pump light and an incident mirror and an output mirror, and uses a pump light from the semiconductor laser. A laser medium that is excited and emits a fundamental-wave laser beam, and is disposed between the laser medium and the emission mirror, forms a periodically poled structure, and converts the fundamental wave into a harmonic. And a transparent material that covers the periodic polarization inversion element, and a metal holder that covers the transparent material.

  According to claim 2, the periodic domain inversion element has a rectangular parallelepiped shape, an opening in the width direction is wider than the thickness direction, and the transparent material is disposed so as to sandwich the two surfaces of the periodic domain inversion element in the thickness direction. It is characterized by that.

  A third aspect of the present invention is directed to a fast axis cylindrical lens which is directly attached to the semiconductor laser and converts parallel light into fast axis direction excitation light from the semiconductor laser, and parallels slow axis direction excitation light from the fast axis cylindrical lens. A slow-axis cylindrical lens that converts light into light, a λ / 2-wave plate (λ is a wavelength) provided between the slow-axis cylindrical lens and the laser medium, and that rotates a polarization direction by 90 degrees; , TM-polarized laser, wherein the slow axis direction of the semiconductor laser is made to coincide with the thickness direction of the periodically poled element.

  A fourth aspect of the present invention is directed to a fast axis cylindrical lens which is directly attached to the semiconductor laser and converts the fast axis excitation light from the semiconductor laser into parallel light, and a slow axis direction excitation light from the fast axis cylindrical lens in parallel. A slow-axis cylindrical lens for emitting light, wherein the semiconductor laser is a TE-polarized laser, and a slow-axis direction of the semiconductor laser is made to coincide with a thickness direction of the periodic polarization inversion element.

  According to the present invention, since the periodically poled element is covered with the transparent material and the transparent material is covered with the metal holder, the fundamental wave in the resonator is not blocked by the metal holder. Therefore, a rise in temperature of the metal holder can be reduced, deterioration of optical characteristics such as rising characteristics can be prevented, and high-quality laser light can be obtained.

FIG. 1A is a side view of a solid-state laser device according to a first embodiment of the present invention, and FIG. 1B is a top view of the solid-state laser device of the first embodiment of the present invention. FIG. 3 is a diagram illustrating an emitter of a semiconductor laser provided in the solid-state laser device according to the first embodiment of the present invention. FIG. 2 is a configuration diagram of a periodically poled element provided in the solid-state laser device according to the first embodiment of the present invention. FIG. 7 is a diagram illustrating a state in which a part of the stimulated emission beam is blocked by a metal holder that covers the periodically poled element. FIG. 9 is a diagram illustrating a state in which a stimulated emission beam is not blocked by a metal holder by providing a transparent material outside a periodically poled element. FIG. 6A is a side view of a solid-state laser device according to a second embodiment of the present invention, and FIG. 6B is a top view of the solid-state laser device of the second embodiment of the present invention. It is a figure showing the conventional periodically poled element directly covered with the metal holder.

(First embodiment)
Hereinafter, a solid-state laser device according to an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1A is a side view of a solid-state laser device according to a first embodiment of the present invention. FIG. 1B is a top view of the solid-state laser device according to the first embodiment of the present invention.

  The solid-state laser device includes a semiconductor laser 1, a fast axis cylindrical lens 2, a slow axis cylindrical lens 3, a λ / 2 wavelength plate 4, a laser medium 5, and a periodically poled element 6. λ is the wavelength of the laser light.

  The semiconductor laser 1 has an emitter 1a and emits excitation light having a wavelength of 808 nm composed of elliptical beams having different beam widths in a fast axis direction and a slow axis direction orthogonal to each other. In the semiconductor laser 1, as shown in FIG. 2, when a TM-polarized semiconductor laser is used, the thickness direction of the emitter 1a is the polarization direction of the TM-polarized semiconductor laser. When a TE-polarized semiconductor laser is used, the width direction of the emitter 1a is the polarization direction of the TE-polarized semiconductor laser. In the first embodiment, the semiconductor laser 1 is a TM-polarized laser, and the slow axis direction of the semiconductor laser 1 is made to coincide with the thickness direction of the periodically poled element 6.

  The fast axis cylindrical lens 2 is directly attached to the semiconductor laser 1 and converts the excitation light from the semiconductor laser 1 in the fast axis direction into parallel light. That is, a fast axis beam 111 of parallel light is output. Note that the slow axis direction beam 112 is output while being expanded. The slow axis cylindrical lens 3 converts the excitation light in the slow axis direction from the fast axis cylindrical lens 2 into parallel light.

  The λ / 2 wavelength plate 4 is provided between the slow axis cylindrical lens 3 and the laser medium 5, and rotates the polarization direction of the laser light from the slow axis cylindrical lens 3 by 90 degrees.

  The laser medium 5 is coated on its surface on the side of the semiconductor laser 1 with a coating that has low reflection with respect to the excitation light (wavelength of 808 nm) from the semiconductor laser 1 and high reflection with respect to the fundamental wave wavelength of 1064 nm. I have. A dielectric film is used as the coating. The coating corresponds to the entrance mirror of the invention.

  The laser medium 5 is disposed between the entrance mirror and the exit mirror 7, and is excited by light from the λ / 2 wavelength plate 4 to emit a fundamental laser beam. That is, the resonator fundamental mode beam 113 is output. As the laser medium 5, for example, an Nd: YVO4 crystal is used.

  The emission mirror 7 is formed of a concave mirror, and is coated with a coating that reflects high at 1064 nm and low at 532 nm, which is the second harmonic wavelength.

  The periodic polarization inversion element 6 is disposed between the laser medium 5 and the emission mirror 7, and as shown in FIG. 3, the polarization inversion parts 6a and the polarization inversion parts 6b are alternately arranged and periodically arranged in the same direction. It comprises a wavelength conversion element that forms a periodically poled periodic polarization inversion structure and converts a fundamental wave into a harmonic.

  The periodic domain inversion element 6 is PPMgSLT, PPMgLN, PPLN, or the like. In this example, PPMgSLT was used. The crystal Z direction of the periodically poled element 6 is arranged so as to coincide with the polarization direction of the semiconductor laser 1 as shown in FIG. The period of the periodic polarization inversion is such that a fundamental wave having a wavelength of 1064 nm is converted into a second harmonic light having a wavelength of 532 nm at a desired temperature. The periodically poled element 6 is formed in the shape of a rectangular parallelepiped. As shown in FIG. 5, the opening in the width direction is wider than the thickness direction. The size in the width direction of the periodically poled element 6 is, for example, 2 mm in L3, and the size in the thickness direction is, for example, 1 mm in L4.

  The transparent members 8a and 8b are arranged so as to sandwich the two surfaces of the periodically poled element 6 in the thickness direction, and cover the periodically poled element 6. The size of the transparent material 8a in the width direction is, for example, 2 mm in L3, and the size in the thickness direction is, for example, 0.5 mm in L5. The size in the width direction of the transparent material 8b is, for example, 2 mm in L3, and the size in the thickness direction is, for example, 0.5 mm in L6.

  The material of the transparent materials 8a and 8b is desirably a material that is transparent to the fundamental wave, in the example, 1064 nm light, and has high thermal conductivity. For example, as the material of the transparent members 8a and 8b, there may be used Sirfire, MgSLT or the like. When MgSLT is used as the transparent materials 8a and 8b, it is not necessary to perform the polarization inversion processing.

  The metal holders 11c and 11d are made of, for example, aluminum and cover and hold the transparent members 8a and 8b and the periodically poled element 6, and are inserted into the resonator.

  Next, the operation of the solid-state laser device will be described. First, in the conventional solid-state laser device, as shown in FIG. 4, a periodically poled element 6A having a width direction size L1 (eg, 1 mm) and a thickness direction size L2 (eg, 1 mm) is covered with metal holders 11a and 11b. ing. In this case, a part of the stimulated emission beam BM is blocked by the metal holders 11a and 11b as shown by the dotted lines.

  On the other hand, in the solid-state laser device of the first embodiment, as shown in FIG. 5, the periodically poled element 6 is covered with transparent materials 8a and 8b, and the transparent materials 8a and 8b are covered with metal holders 11c and 11d. Therefore, the fundamental wave (beam BM) in the resonator is not blocked by the metal holders 11c and 11d. Therefore, a rise in the temperature of the metal holders 11c and 11d can be reduced, deterioration of optical characteristics such as rising characteristics can be prevented, and high-quality laser light can be obtained.

  The solid-state laser device according to the first embodiment shown in FIG. 1 shows an example in which a TM-polarized semiconductor laser 1 is used when the laser beam condensing position of the semiconductor laser 1 can be adjusted only in one direction. I have.

  Since the fast-axis cylindrical lens 2 is directly attached to the semiconductor laser 1, the fast-axis cylindrical lens 2 cannot be finely adjusted in the fast-axis direction.

  On the other hand, the position of the slow axis cylindrical lens 3 can be adjusted by adjusting in the slow axis direction.

  Further, since the TM-polarized semiconductor laser 1 is used, the thickness direction of the emitter 1a is the polarization direction of the TM-polarized semiconductor laser 1, as shown in FIG. In FIG. 1A, the polarization direction of the TM-polarized semiconductor laser 1 is a vertical direction. Therefore, by passing the TM-polarized laser light from the semiconductor laser 1 through the λ / 2 wavelength plate 4, the polarization direction is rotated by 90 degrees.

  Thus, in FIG. 1A, the polarization direction of the laser beam from the semiconductor laser 1 having the TM polarization is perpendicular to the plane of the drawing by passing the laser beam through the λ / 2 wave plate 4. FIG. 1B is a diagram rotated by 90 degrees with respect to FIG. 1A. Therefore, in FIG. 1B, the polarization direction of the laser beam from the semiconductor laser 1 of TM polarization is λ. The light passes through the half-wave plate 4 to be in the vertical direction.

  By adjusting the polarization direction of the semiconductor laser 1 after passing through the λ / 2 wavelength plate 4, that is, the slow axis direction, to the thickness direction (Z direction) of the periodically poled element 6, the adjustment of the semiconductor laser 1 is performed. It will be easier.

(Second embodiment)
FIG. 6A is a side view of a solid-state laser device according to a second embodiment of the present invention, and FIG. 6B is a top view of the solid-state laser device of the second embodiment of the present invention. The solid-state laser device of the second embodiment uses a semiconductor laser 1 of TE polarization. As shown in FIG. 6A, the direction perpendicular to the paper surface of the semiconductor laser 1 of TE polarization is the polarization direction of the semiconductor laser 1.

  In this case, there is no need to provide the λ / 2 wavelength plate 4 between the slow axis cylindrical lens 3 and the laser medium 5.

  That is, since FIG. 6B is a view rotated 90 degrees with respect to FIG. 6A, in FIG. 6B, the polarization direction of the TE-polarized laser light from the semiconductor laser 1 is the vertical direction. Becomes

  By adjusting the polarization direction of the semiconductor laser 1, that is, the slow axis direction, to the thickness direction (Z direction) of the periodically poled element 6, the adjustment of the semiconductor laser 1 becomes easy.

  The present invention is applicable to a laser oscillator.

Reference Signs List 1 semiconductor laser 1a emitter of semiconductor laser 2 fast axis cylindrical lens 3 slow axis cylindrical lens 4 λ / 2 wavelength plate 5 laser medium 6, 6A periodic polarization inversion element 7 emission mirrors 8a, 8b transparent materials 11a to 11d metal holder 111 fast axis Directional beam 112 Slow axial beam 113 Resonator fundamental mode beam

Claims (4)

A semiconductor laser for emitting excitation light,
A laser medium disposed between the entrance mirror and the exit mirror, and excited by excitation light from the semiconductor laser to emit a fundamental laser beam;
A periodically poled element disposed between the laser medium and the emission mirror to form a periodically poled structure, and to convert the fundamental wave into a harmonic;
A transparent material covering the periodically poled element,
A metal holder covering the transparent material,
A solid-state laser device comprising:   The periodic domain inversion element has a rectangular parallelepiped shape, an opening in the width direction is wider than the thickness direction, and the transparent material is arranged so as to sandwich the two surfaces of the periodic domain inversion element in the thickness direction. The solid-state laser device according to claim 1. A fast-axis cylindrical lens that is directly attached to the semiconductor laser, and makes parallel excitation light in the fast-axis direction from the semiconductor laser;
A slow axis cylindrical lens that converts excitation light in the slow axis direction from the fast axis cylindrical lens into parallel light,
A λ / 2 wavelength plate (λ is a wavelength) that is provided between the slow axis cylindrical lens and the laser medium and rotates the polarization direction by 90 degrees;
The solid-state laser device according to claim 2, wherein the semiconductor laser is a TM-polarized laser, and a slow axis direction of the semiconductor laser is made to coincide with a thickness direction of the periodically poled element. A fast-axis cylindrical lens that is directly attached to the semiconductor laser, and makes parallel excitation light in the fast-axis direction from the semiconductor laser;
A slow axis cylindrical lens that converts excitation light in the slow axis direction from the fast axis cylindrical lens into parallel light,
The semiconductor laser is a TE-polarized laser,
3. The solid-state laser device according to claim 2, wherein a slow axis direction of the semiconductor laser is made to coincide with a thickness direction of the periodically poled element.

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