Solid-state laser device and method for manufacturing solid-state laser device

Abstract

A solid-state laser device (100) is provided with: a light-emitting element (140) that emits first light (L1); a laser crystal (150) that absorbs the first light (L1) and emits second light (L2); a nonlinear optical crystal (160) that absorbs the second light (L2) and emits third light (L3); a second selective transmission mirror (120) that is disposed between the laser crystal (150) and the nonlinear optical crystal (160) and transmits the second light (L2); and a third selective transmission mirror (130) that is disposed on the optical axis of the third light (L3) and transmits the third light (L3). A first selective transmission mirror (110) reflects the second light (L2), the second selective transmission mirror (120) reflects the third light (L3), and the third selective transmission mirror (130) reflects the second light (L2). The second selective transmission mirror (120) and the third selective transmission mirror (130) are spaced apart from the nonlinear optical crystal.

Description

Solid-state laser device and method for manufacturing solid-state laser device

[0001] The present disclosure relates to a solid-state laser device and a method for manufacturing a solid-state laser device.

[0002] For example, solid-state laser devices that emit light in a short wavelength region such as the ultraviolet region have attracted attention (see, for example, Patent Document 1). Patent Document 1 describes a wavelength conversion laser light source as an example of a solid-state laser device. The wavelength conversion laser light source described in Patent Document 1 includes a laser medium (in other words, a laser crystal) and a wavelength conversion element (in other words, a nonlinear optical crystal).

[0003] International Publication No. 2011 / 132414

[0004] The present disclosure aims to improve the efficiency of a solid-state laser device that includes a laser crystal and a nonlinear optical crystal.

[0005] In order to achieve the above object, a solid-state laser device according to one aspect of the present disclosure includes: a light-emitting element that emits first light having a first peak wavelength; a laser crystal that absorbs the first light and emits second light having a second peak wavelength; a nonlinear optical crystal that absorbs the second light and emits third light having a third peak wavelength; a first selective transmission mirror that is disposed on an optical axis of the first light between the light-emitting element and the laser crystal and transmits the first light; a second selective transmission mirror that is disposed on an optical axis of the second light between the laser crystal and the nonlinear optical crystal and transmits the second light; and a third selective transmission mirror that is disposed on an optical axis of the third light and transmits the third light, a laser crystal is disposed on the optical axis of the first light between the light-emitting element and the nonlinear optical crystal; the nonlinear optical crystal is disposed on the optical axis of the second light between the second selective transmission mirror and the third selective transmission mirror; the first selective transmission mirror reflects the second light; the second selective transmission mirror reflects the third light; the third selective transmission mirror reflects the second light; the first selective transmission mirror and the third selective transmission mirror form a resonator for the second light; the first selective transmission mirror and the second selective transmission mirror are parallel to each other; and the second selective transmission mirror and the third selective transmission mirror are spaced apart from the nonlinear optical crystal.

[0006] In order to achieve the above object, a manufacturing method for a solid-state laser device according to one aspect of the present disclosure is a manufacturing method for the solid-state laser device, comprising: a step of aligning at least one of the first selective transmission mirror, the laser crystal, the second selective transmission mirror, and the third selective transmission mirror; and a step of adjusting the tilt angle of the nonlinear optical crystal with respect to the optical axis of the second light while monitoring the third light emitted from the third selective transmission mirror.

[0007] According to the present disclosure, it is possible to improve the efficiency of a solid-state laser device equipped with a laser crystal and a nonlinear optical crystal.

[0008] 1 is a schematic top view showing the overall configuration of a solid-state laser device according to embodiment 1. FIG. 2 is a diagram showing the relationship between the crystal axes of a laser crystal and the polarization directions of a first light and a second light according to embodiment 1. FIG. 3 is a diagram showing the direction of the crystal axes of a nonlinear optical crystal according to embodiment 1. FIG. 4 is a graph showing an outline of an example of transmittance characteristics of a first selective transmission mirror according to embodiment 1. FIG. 5 is a graph showing an outline of an example of transmittance characteristics of a second selective transmission mirror according to embodiment 1. FIG. 6 is a graph showing an outline of an example of transmittance characteristics of a third selective transmission mirror according to embodiment 1. FIG. 7 is a graph showing an example of actual transmittance characteristics of a third selective transmission mirror according to embodiment 1. FIG. 8 is a graph showing an outline of an example of transmittance characteristics of an anti-reflection film according to embodiment 1. FIG. 9 is a diagram explaining the operation of a solid-state laser device according to embodiment 1. FIG. 10 is a diagram explaining the operation of a solid-state laser device of a comparative example. FIG. 11 is a flowchart showing the flow of a method for manufacturing the solid-state laser device according to embodiment 1. FIG. 12 is a schematic side view showing the overall configuration of a solid-state laser device according to modification 2 of embodiment 1. FIG. 13 is a diagram showing the direction of the crystal axes of a nonlinear optical crystal 160 according to modification 2 of embodiment 1. FIG. 14 is a diagram showing the configurations of solid-state laser devices according to embodiment 1 and its modifications. FIG. 15 is a schematic top view showing the overall configuration of a solid-state laser device according to embodiment 2. 1 is a perspective view showing the overall configuration of a solid-state laser device according to embodiment 2. FIG. 2 is a schematic top view showing the overall configuration of a solid-state laser device according to embodiment 3. FIG. 3 is a schematic side view showing the overall configuration of a solid-state laser device according to embodiment 3. FIG. 4 is a diagram showing an example of each parameter of the solid-state laser device according to embodiment 3. FIG. 5 is a schematic top view showing another configuration example of the solid-state laser device according to embodiment 3. FIG. 6 is a diagram comparing the dependency of output light L4 on light-emitting element drive current in solid-state laser devices according to embodiment 3 and a comparative example. FIG. 7 is a schematic side view showing a focusing mode of a first light by a focusing optical system of configuration example 1 according to embodiment 3. FIG. 8 is a schematic side view showing a laser crystal and the first light focused by the focusing optical system of configuration example 1 according to embodiment 3. FIG. 9 is a schematic side view showing a focusing mode of a first light L1 by the focusing optical system of configuration example 2 according to embodiment 3. FIG. 10 is a schematic side view showing a laser crystal and the first light L1 focused by the focusing optical system of configuration example 2 according to embodiment 3. FIG. 11 is a schematic top view showing the overall configuration of a solid-state laser device according to embodiment 4.10 is a diagram showing the optical axis direction of the second light in the nonlinear optical crystal according to embodiment 4, and the direction of the crystal axis of the nonlinear optical crystal. FIG. 11 is a schematic top view showing the overall configuration of a solid-state laser device according to embodiment 5. FIG. 12 is a perspective view showing the solid-state laser device according to embodiment 5. FIG. 13 is an exploded perspective view showing the configuration of the solid-state laser device according to embodiment 5. FIG. 14 is a diagram showing another contact mode between the positioning portion and the support member according to embodiment 5. FIG. 15 is a schematic top view showing the overall configuration of a solid-state laser device according to embodiment 6. FIG. 16 is a schematic side view showing the overall configuration of a solid-state laser device according to embodiment 6. FIG. 17 is a schematic top view showing the overall configuration of a solid-state laser device according to embodiment 7. FIG. 18 is a schematic side view showing the overall configuration of a solid-state laser device according to embodiment 7. FIG. 19 is a schematic top view showing the overall configuration of a solid-state laser device according to embodiment 8. FIG. 19 is a schematic side view showing the overall configuration of a solid-state laser device according to embodiment 8.

[0009] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, arrangement and connection of the components, steps, order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0010] Furthermore, each figure is a schematic diagram and is not necessarily an exact illustration. Therefore, for example, the scales of the figures do not necessarily match. Furthermore, in each figure, substantially the same components are given the same reference numerals, and redundant explanations are omitted or simplified.

[0011] Furthermore, in this specification, terms indicating the relationship between elements, such as "equal," terms indicating the shape of elements, such as "flat," "parallel," "vertical," "plate-shaped," and "curved," as well as numerical ranges, are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0012] Furthermore, in this specification, terms indicating the relationship between elements, such as parallel and perpendicular, terms indicating the shape of elements, such as rectangular parallelepiped and arc, and numerical ranges are not expressions that only express a strict meaning, but are expressions that also include a substantially equivalent range, for example, a difference of about a few percent.

[0013] First Embodiment A solid-state laser device and a manufacturing method thereof according to a first embodiment will be described.

[0014] [Overall Configuration] The overall configuration of the solid-state laser device according to this embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic top view showing the overall configuration of a solid-state laser device 100 according to this embodiment. Fig. 1 and other figures show an x-axis, a y-axis, and a z-axis that are orthogonal to each other. The x-axis, y-axis, and z-axis form a right-handed Cartesian coordinate system. Fig. 1 shows a top view of the solid-state laser device 100 as seen from the y-axis positive side.

[0015] The solid-state laser device 100 according to this embodiment includes a light-emitting element 140, a laser crystal 150, a nonlinear optical crystal 160, a first selective transmission mirror 110, a second selective transmission mirror 120, and a third selective transmission mirror 130. In this embodiment, the solid-state laser device 100 further includes anti-reflection films 171 to 173. The solid-state laser device 100 also has a main surface (not shown) that is parallel to the zx plane, and a fixing surface (not shown) that is parallel to or coincident with the main surface.

[0016] The light emitting element 140 emits light having a first peak wavelength λ １ In this embodiment, the light emitting element 140 is a nitride semiconductor light emitting element including a substrate and a semiconductor laminated film including an active layer laminated on the substrate. １ is, for example, 350 nm or more and 500 nm or less. The first peak wavelength λ1 may be 365 nm or more and 500 nm or less. In this embodiment, the light emitting element 140 includes an AlInGaN-based nitride semiconductor. This allows the light emitting element 140 to efficiently emit light with a wavelength of 350 nm or more and 500 nm or less. In this embodiment, the light emitting element 140 has a first peak wavelength λ １The light emitting element 140 is a semiconductor laser element that emits laser light having a wavelength of 444 nm as the first light L1. The light emitting element 140 may be a multimode semiconductor laser element that emits multi-transverse mode laser light.

[0017] The light emitting element 140 has an optical waveguide 140a in a semiconductor laminated film. The light emitting element 140 has an emission surface that emits the first light L1, and the emission surface has a light emitting portion 140e that is the portion from which the first light L1 is emitted. In this embodiment, the stacking direction of the semiconductor laminated film of the light emitting element 140 is parallel to the y-axis direction in FIG. 1, and the stacking surface of the semiconductor laminated film (a surface perpendicular to the stacking direction) is parallel to the xz plane. The end of the optical waveguide 140a has a light emitting portion 140e having an emission width 140w that corresponds to the width of the optical waveguide 140a in the x-axis direction in FIG. 1. The first light L1 is emitted from the light emitting portion 140e in the positive z-axis direction.

[0018] 1, the optical waveguide 140a extends in the z-axis direction, and the optical axis of the first light L1 is parallel to the z-axis direction. The slow axis direction of the first light L1 is parallel to the stacking plane of the semiconductor stacked film, and the fast axis direction is parallel to the stacking direction of the semiconductor stacked film. That is, the slow axis direction is parallel to the x-axis direction, and the fast axis direction is parallel to the y-axis direction. Therefore, the slow axis of the first light L1 is parallel to the principal surface.

[0019] Furthermore, in this embodiment, the first light L1 emitted from the light-emitting element 140 is polarized light in which the electric field component in the x-axis direction is sufficiently larger than the electric field component in the y-axis direction, and travels in the positive direction in the z-axis direction. In this embodiment, the light-emitting element 140 is mounted in a so-called junction-up manner on a submount or the like on the main surface, and the surface of the light-emitting element 140 perpendicular to the fast axis direction that is farther from the optical waveguide 140a (the surface on the negative side in the y-axis direction) is the mounting surface.

[0020] The laser crystal 150 absorbs the first light L1 and emits light having a second peak wavelength λ ２The laser crystal 150 is an element that emits second light L2 having a second peak wavelength λ. The laser crystal 150 is disposed on the optical axis of the first light L1 between the light emitting element 140 and the nonlinear optical crystal 160. The laser crystal 150 is also disposed on the optical axis of the first light L1 between the first selective transmission mirror 110 and the second selective transmission mirror 120. The laser crystal 150 is a crystal doped with at least one of Pr, Tb, and Dy, for example. ２ In this embodiment, the laser crystal 150 is made of Pr ３＋ : YLiF ４ In this embodiment, the laser crystal 150 has a second peak wavelength λ ２ The laser beam having a wavelength of 640 nm is emitted as the second light L2.

[0021] Pr ３＋ : YLiF ４ is an anisotropic uniaxial crystal. ３＋ : YLiF ４ The crystal axes of the laser crystal 150 in this case will be described with reference to Fig. 2. Fig. 2 is a diagram showing the relationship between the crystal axes of the laser crystal 150 according to this embodiment and the polarization directions of the first light L1 and the second light L2. Fig. 2 also shows the directions of the crystal axes (a-axis and c-axis) of the laser crystal 150.

[0022] The shape of the laser crystal 150 is not particularly limited. In this embodiment, as shown in FIG. 2 , the laser crystal 150 has a rectangular parallelepiped shape. The laser crystal 150 has an a-axis and a c-axis as crystal axes. The laser crystal 150 is disposed on the principal surface so that the c-axis of the laser crystal 150 is parallel to the x-axis. In other words, the laser crystal 150 is disposed so that the c-axis of the laser crystal 150 is parallel to the slow axis of the first light L1. The laser crystal 150 has six end faces: a first face S1, a second face S2, a third face S3, a fourth face S4, a fifth face S5, and a sixth face S6. The first face S1 faces the light-emitting element 140 and is an end face perpendicular to the a-axis of the laser crystal 150. The second face S2 faces the first face S1. The third face S3 and the fourth face S4 are each end faces perpendicular to the c-axis. The fifth surface S5 and the sixth surface S6 are each an end surface perpendicular to both the first surface S1 and the third surface S3.

[0023] In this embodiment, the first light L1 incident on the laser crystal 150 is polarized light. Here, light polarized parallel to the c-axis is referred to as π-polarized light, and light polarized parallel to the a-axis (i.e., parallel to the y-axis in FIG. 2) is referred to as σ-polarized light. Similarly, when the second light L2 emitted from the laser crystal 150 is polarized light, light polarized parallel to the c-axis is referred to as π-polarized light, and light polarized parallel to the a-axis (i.e., parallel to the y-axis in FIG. 2) is referred to as σ-polarized light. In this embodiment, the laser crystal 150 emits light polarized in the y-axis direction (i.e., σ-polarized light) as the second light L2.

[0024] The nonlinear optical crystal 160 absorbs the second light L2 and emits light having a third peak wavelength λ ３ The nonlinear optical crystal 160 is disposed on the optical axis of the second light L2 between the second selective transmission mirror 120 and the third selective transmission mirror 130. In this embodiment, the nonlinear optical crystal 160 emits the second harmonic of the second light L2. That is, the nonlinear optical crystal 160 emits the second harmonic of the second light L2. ３ is the second peak wavelength λ ２ The third peak wavelength λ ３ In this embodiment, the third peak wavelength λ is, for example, 400 nm or less. ３ is 320 nm.

[0025] The material of the nonlinear optical crystal 160 is not particularly limited as long as it is a crystal that can emit second harmonic waves. The nonlinear optical crystal 160 is, for example, LBO (LiB ３ O ５ ), BBO (β-BaB ２ O ４ ), or KTP (KTiOPO ４ ) The transmission wavelength range of LBO is 160 nm or more. In other words, LBO can be used when the wavelength of the second harmonic is 160 nm or more. The transmission wavelength range of BBO is 190 nm or more. The transmission wavelength range of KTP is 350 nm or more. In this embodiment, LBO is used as the nonlinear optical crystal 160.

[0026] The nonlinear optical crystal 160 is fixed to a fixed surface (not shown). The direction of the crystal axis of the nonlinear optical crystal 160 is indicated by an arrow in the nonlinear optical crystal 160 in FIG. 1 . As described above, the direction of the crystal axis of the nonlinear optical crystal 160 is tilted with respect to the optical axis of the second light L2 (i.e., the z-axis direction). This tilt direction will be explained using FIG. 3 . FIG. 3 is a diagram showing the direction of the crystal axis of the nonlinear optical crystal 160 according to this embodiment. As shown in FIG. 3 , the direction of the crystal axis of the nonlinear optical crystal 160 is tilted by an angle α1 from the z-axis direction toward the x-axis direction, centered on the y-axis. Here, the angle α1 is an angle that satisfies the phase matching condition for maximizing the conversion efficiency of the second light L2 to the third light L3. At this angle α1, the refractive indexes of the second light L2 as the fundamental wave and the third light L3 as the second harmonic wave in the nonlinear optical crystal 160 are equal to each other. In this embodiment, the direction of the crystal axis of the nonlinear optical crystal 160 is adjusted during the manufacture of the solid-state laser device 100. The method for adjusting the direction of the crystal axis of the nonlinear optical crystal 160 will be described later.

[0027] The first selective transmission mirror 110 is a mirror that is disposed on the optical axis of the first light L1 between the light emitting element 140 and the laser crystal 150 and transmits the first light L1. In this embodiment, the first selective transmission mirror 110 is spaced apart from the light emitting element 140 and the laser crystal 150. Here, transmitting the first light L1 means transmitting at least a part of the first light L1. The first peak wavelength λ of the first selective transmission mirror 110 １ In this embodiment, the transmittance of the first selective transmission mirror 110 to the light of the first peak wavelength λ 2 may be, for example, 90% or more. １ The transmittance of the light is 95% or more.

[0028] The first selective transmission mirror 110 reflects the second light L2. Here, reflecting the second light L2 means reflecting at least a part of the second light L2. The second peak wavelength λ of the first selective transmission mirror 110 ２ In this embodiment, the reflectance of the first selective transmission mirror 110 with respect to the second peak wavelength λ ２ The reflectance of the film to light is 99% or more.

[0029] In this embodiment, the first selective transmission mirror 110 is a flat optical element and includes a light-transmitting substrate 112 and a dielectric multilayer film 114. The light-transmitting substrate 112 is a substrate that transmits the first light L1. The dielectric multilayer film 114 is a film that is disposed on the surface of the light-transmitting substrate 112 that faces the laser crystal 150, and transmits the first light L1 and reflects the second light L2. Note that an anti-reflection film for the wavelength of the first light L1 may be formed on the surface of the light-transmitting substrate 112 of the first selective transmission mirror 110 opposite to the surface on which the dielectric multilayer film 114 is disposed.

[0030] Here, the transmittance characteristics of the first selective transmission mirror 110 will be described with reference to Fig. 4. Fig. 4 is a graph showing an overview of an example of the transmittance characteristics of the first selective transmission mirror 110 according to this embodiment. The horizontal axis of Fig. 4 represents wavelength, and the vertical axis represents transmittance when a light ray is perpendicularly incident on the dielectric multilayer film 114 side of the first selective transmission mirror 110. As the transmittance on the vertical axis of Fig. 4 decreases, the reflectance increases. In other words, the reflectance is the value obtained by subtracting the transmittance from 1.

[0031] As shown in FIG. 4, the first selective transmission mirror 110 is configured to transmit light having a first peak wavelength λ １ wavelength λ shorter than Ｔ１Ｌ From the first peak wavelength λ １ wavelength λ Ｔ１Ｕ The transmittance is T Ａ１Ｌ Higher, second peak wavelength λ ２ wavelength λ shorter than Ｒ２Ｌ From the second peak wavelength λ ２ wavelength λ Ｒ２Ｕ High reflectivity at wavelengths up to T Ａ２Ｕ (lower). The first peak wavelength λ of the first selective transmission mirror 110 １ The transmittance at T Ａ１ (>T Ａ１Ｌ ) and the first peak wavelength λ １ The transmittance at T Ａ２ (<T Ａ２Ｕ ) For example, T Ａ１Ｌ is 0.95, and T Ａ２Ｕ is 0.05.

[0032] In this embodiment, the first selective transmission mirror 110 is configured to receive the light of wavelength λ Ｔ１Ｌ is 430 nm, and the wavelength λ Ｔ１Ｕ is 460 nm, and the wavelength λ Ｒ２Ｌ is 610 nm, and the wavelength λ Ｒ２Ｕ The first selective transmission mirror 110 has a transmittance of 95% or more in the wavelength range of 430 nm or more and 460 nm or less, and a transmittance of 5% or less (reflectance of about 95% or more) in the wavelength range of 610 nm or more and 660 nm or less.

[0033] The second selective transmission mirror 120 is disposed on the optical axis of the second light L2 between the laser crystal 150 and the nonlinear optical crystal 160, and transmits the second light L2. The first selective transmission mirror 110 and the second selective transmission mirror 120 are parallel to each other. The first selective transmission mirror 110 and the third selective transmission mirror 130 form a resonator for the second light L2. The second selective transmission mirror 120 is spaced apart from the nonlinear optical crystal 160.

[0034] The second peak wavelength λ of the second selective transmission mirror 120 ２ In this embodiment, the transmittance of the second selective transmission mirror 120 to the light of the second peak wavelength λ 2 may be, for example, 90% or more. ２ The transmittance of the light is 95% or more.

[0035] The second selective transmission mirror 120 reflects the third light L3. ３ In this embodiment, the reflectance of the second selective transmission mirror 120 with respect to the third peak wavelength λ ３ The reflectance of the film to light is 95% or more.

[0036] In this embodiment, the second selective transmission mirror 120 is disposed on the laser crystal 150. More specifically, the second selective transmission mirror 120 is a dielectric multilayer film disposed on an end face (second surface S2 shown in FIG. 2 ) of the laser crystal 150.

[0037] Here, the transmittance characteristics of the second selective transmission mirror 120 will be described with reference to Fig. 5. Fig. 5 is a graph showing an overview of an example of the transmittance characteristics of the second selective transmission mirror 120 according to this embodiment. The horizontal axis of Fig. 5 represents wavelength, and the vertical axis represents transmittance when a light ray is perpendicularly incident on the second selective transmission mirror 120. Note that Fig. 5 also shows, by a dotted line, the transmittance characteristics of the second selective transmission mirror 120 according to a first modified example of this embodiment, which will be described later. As shown in Fig. 5, the second selective transmission mirror 120 has a second peak wavelength λ ２ wavelength λ shorter than Ｔ２Ｌ From the second peak wavelength λ ２ wavelength λ Ｔ２Ｕ The transmittance is TＢ２Ｌ Higher, third peak wavelength λ ３ wavelength λ shorter than Ｒ３Ｌ From the third peak wavelength λ ３ wavelength λ Ｒ３Ｕ The reflectance is high at wavelengths up to T Ｂ３Ｕ The second peak wavelength λ of the second selective transmission mirror 120 ２ The transmittance at T Ｂ２ (>T Ｂ２Ｌ ) and the third peak wavelength λ ３ The transmittance at T Ｂ３ (<T Ｂ３Ｕ ) For example, T Ｂ２Ｌ is 0.95, and T Ｂ３Ｕ is 0.05.

[0038] In this embodiment, the second selective transmission mirror 120 is configured to receive the light of wavelength λ Ｔ２Ｌ is 610 nm, and the wavelength λ Ｔ２Ｕ is 660 nm, and the wavelength λ Ｒ３Ｌ is 310 nm, and the wavelength λ Ｒ３Ｕ The second selective transmission mirror 120 has a transmittance of 95% or more in the wavelength range of 610 nm or more and 660 nm or less, and a transmittance of 5% or less (reflectance of approximately 95% or more) in the wavelength range of 310 nm or more and 460 nm or less.

[0039] The third selective transmission mirror 130 is disposed on the optical axis of the third light L3 and transmits the third light L3. The third selective transmission mirror 130 transmits the third light L3. The third selective transmission mirror 130 is the output light L4 of the solid-state laser device 100. The third selective transmission mirror 130 is spaced apart from the nonlinear optical crystal 160. The third peak wavelength λ of the third selective transmission mirror 130 ３ In this embodiment, the transmittance of the third selective transmission mirror 130 to the light of the third peak wavelength λ 2 may be, for example, 90% or more. ３ The transmittance of the light is 95% or more.

[0040] The third selective transmission mirror 130 reflects the second light L2. ２ In this embodiment, the reflectance of the third selective transmission mirror 130 for the light having the second peak wavelength λ２ The reflectance for the second light L2 is 95% or more. The third selective transmission mirror 130 and the first selective transmission mirror 110 form a resonator for the second light L2.

[0041] In this embodiment, the third selective transmission mirror 130 is a concave mirror. In this embodiment, the third selective transmission mirror 130 includes a light-transmitting substrate 132, a dielectric multilayer film 134, and a dielectric multilayer film 133. The light-transmitting substrate 132 has a concave surface facing the nonlinear optical crystal 160, and the dielectric multilayer film 134 is disposed on the concave surface of the light-transmitting substrate 132. In this embodiment, the concave surface is a spherical concave surface, and condenses light reflected on the concave surface. The surface of the light-transmitting substrate 132 facing the surface on which the concave surface is formed is a flat surface. A dielectric multilayer film 133 that functions as an anti-reflection film for light with the wavelength of the third light L3 is disposed on this flat surface. Note that the surface of the light-transmitting substrate 132 on which the dielectric multilayer film 133 is formed may be made convex to condense the third light L3 that passes through the third selective transmission mirror 130.

[0042] Here, the transmittance characteristics of the third selective transmitting mirror 130 will be described with reference to Fig. 6. Fig. 6 is a graph showing an overview of an example of the transmittance characteristics of the third selective transmitting mirror 130 according to this embodiment. The horizontal axis of Fig. 6 represents wavelength, and the vertical axis represents transmittance when a light ray is perpendicularly incident on the bottom of the concave surface of the dielectric multilayer film 134 of the third selective transmitting mirror 130. Note that Fig. 6 also shows, by a dotted line, the transmittance characteristics of the third selective transmitting mirror 130 according to a first modified example of this embodiment, which will be described later. As shown in Fig. 6, the third selective transmitting mirror 130 has a third peak wavelength λ ３ wavelength λ shorter than Ｔ３Ｌ From the third peak wavelength λ ３ wavelength λ Ｔ３Ｕ The transmittance is T Ｃ３Ｌ Higher, second peak wavelength λ ２ wavelength λ shorter than Ｒ２Ｌ From the second peak wavelength λ ２ wavelength λ Ｒ２Ｕ The reflectance is high at wavelengths up to T Ｃ２Ｕ The second peak wavelength λ of the third selective transmission mirror 130 ２ The transmittance at TＣ２ (<T Ｃ２Ｕ ) and the third peak wavelength λ ３ The transmittance at T Ｃ３ (>T Ｃ３Ｌ ) For example, T Ｃ２Ｕ is 0.05, and T Ｃ３Ｌ is 0.05.

[0043] In this embodiment, the third selective transmission mirror 130 Ｔ３Ｌ is 310 nm, and the wavelength λ Ｔ３Ｕ is 350 nm, and the wavelength λ Ｒ２Ｌ is 610 nm, and the wavelength λ Ｒ２Ｕ The third selective transmission mirror 130 has a transmittance of 95% or more for wavelengths of 310 nm or more and 350 nm or less, and a transmittance of 5% or less (reflectance of approximately 95% or more) for wavelengths of 610 nm or more and 660 nm or less.

[0044] An example of the actual transmittance characteristics of the third selective transmission mirror 130 according to this embodiment will be described with reference to FIG. 7. FIG. 7 is a graph showing an example of the actual transmittance characteristics of the third selective transmission mirror 130 according to this embodiment. The horizontal axis of FIG. 7 represents wavelength, and the vertical axis represents transmittance. As shown in FIG. 7, the above-described transmittance and reflectance characteristics are obtained in the actual transmittance characteristics. In the example shown in FIG. 7, the first peak wavelength λ １ The reflectance of the third selective transmission mirror 130 at the third peak wavelength λ (640 nm) is 99.8%. ３ The transmittance of the third selective transmission mirror 130 at (320 nm) is 95.5%.

[0045] Each of the antireflection films 171 to 173 is a film for reducing the reflectance of light at the end face of the laser crystal 150 or the nonlinear optical crystal 160. The antireflection films 171 to 173 are not limited to films that completely prevent the reflection of light. The antireflection films 171 to 173 may be any film that reduces the reflectance of light of a specific wavelength.

[0046] The anti-reflection coating 171 is disposed on the end face (first surface S1) of the laser crystal 150 facing the first selective transmission mirror 110. The anti-reflection coating 171 reduces the reflectance of the first surface S1 of the laser crystal 150 with respect to the first light L1 and the second light L2.

[0047] The antireflection coating 172 is disposed on the end face of the nonlinear optical crystal 160 that faces the second selective transmission mirror 120. The antireflection coating 172 reduces the reflectance of the end face of the nonlinear optical crystal 160 for the second light L2 and the third light L3.

[0048] The antireflection coating 173 is disposed on the end face of the nonlinear optical crystal 160 that faces the third selective transmission mirror 130. The antireflection coating 173 reduces the reflectance of the end face of the nonlinear optical crystal 160 for the second light L2 and the third light L3.

[0049] Here, an example of the transmittance characteristics of the antireflection films 172 and 173 will be described with reference to FIG. 8 as an example of the antireflection films 171 to 173. FIG. 8 is a graph showing an outline of an example of the transmittance characteristics of the antireflection films 172 and 173 according to this embodiment. The horizontal axis of FIG. 8 represents wavelength, and the vertical axis represents transmittance when light is perpendicularly incident on the antireflection films 172 and 173. Note that FIG. 8 also shows, by dotted lines, the transmittance characteristics of each antireflection film according to Modification 1 of this embodiment, which will be described later. As shown in FIG. 8, in the antireflection films 172 and 173, the transmittance characteristics of the antireflection films 172 and 173 at the second peak wavelength λ ２ Transmittance T Ｄ２ , and the third peak wavelength λ ３ Transmittance T Ｄ３ is a value close to 100%. That is, the reflectance of the antireflection films 172 and 173 for the second light L2 and the third light L3 is sufficiently reduced.

[0050] [Operation and Effects of Solid-State Laser Device] The operation and effects of the solid-state laser device 100 according to this embodiment will be described.

[0051] First, the operation of the solid-state laser device 100 according to this embodiment will be described with reference to Fig. 9. Fig. 9 is a diagram for explaining the operation of the solid-state laser device 100 according to this embodiment.

[0052] As shown in FIG. 9, a light emitting device 140 disposed outside the resonator formed by the first selective transmission mirror 110 and the third selective transmission mirror 130 emits a first peak wavelength λ １ The first light L1 having the wavelength .gtoreq.110 is emitted. The first light L1 is transmitted through the first selective transmission mirror 110 and then enters the laser crystal 150. In FIG. 9, the optical path of the first light L1 is indicated by a dotted arrow.

[0053] At least a portion of the first light L1 is absorbed by the laser crystal 150 and excites the laser crystal 150. A portion of the first light L1 is absorbed, for example, at a predetermined position A2 within the laser crystal 150. Another portion of the first light L1 reaches the second selective transmission mirror 120 without being absorbed by the laser crystal 150. Because the second selective transmission mirror 120 has a high reflectivity for the first light L1, most of the first light L1 that reaches the second selective transmission mirror 120 is reflected by the second selective transmission mirror 120 and propagates through the laser crystal 150 in the negative direction of the z-axis as reflected light L13. A portion of the first light L1 that reaches the second selective transmission mirror 120 travels toward the nonlinear optical crystal 160 as transmitted light L12 that passes through the second selective transmission mirror 120.

[0054] In the pumped laser crystal 150, the second peak wavelength λ ２ A second light L2 having a wavelength of 1000 nm is emitted. A part of the second light L2 propagates toward the nonlinear optical crystal 160 (in the positive direction of the z-axis), and another part propagates toward the light-emitting element 140 (in the negative direction of the z-axis). An emission position E2a of the second light L2 toward the nonlinear optical crystal 160 and an emission position E2b of the second light L2 toward the light-emitting element 140 are the same as position A2. In FIG. 9 , in order to distinguish the first light L1 from the second light L2, positions E2a and E2b are shown at positions away from position A2 in the x-axis direction.

[0055] Most of the second light L2 emitted from position E2a (position A2) is incident on the second selective transmission mirror 120. Because the second selective transmission mirror 120 has a high transmittance for the second light L2, most of the second light L2 incident on the second selective transmission mirror 120 passes through the second selective transmission mirror 120 and is incident on the antireflection coating 172. Because the antireflection coating 172 has a high transmittance for the second light L2, most of the second light L2 incident on the antireflection coating 172 passes through the antireflection coating 172 and is incident on the nonlinear optical crystal 160.

[0056] The second light L2 emitted from position E2b (position A2) toward the light emitting element 140 is incident on the first selective transmission mirror 110. Because the first selective transmission mirror 110 has a high reflectivity for the second light L2, most of the second light L2 incident on the first selective transmission mirror 110 is reflected by the first selective transmission mirror 110, returns to the laser crystal 150, transmits through the second selective transmission mirror 120 and the anti-reflection film 172, and is incident on the nonlinear optical crystal 160.

[0057] At least a portion of the second light L2 incident on the nonlinear optical crystal 160 passes through the nonlinear optical crystal 160 and enters the antireflection coating 173. Because the antireflection coating 173 has a high transmittance for the second light L2, most of the second light L2 incident on the antireflection coating 173 passes through the antireflection coating 173 and enters the third selective transmission mirror 130. Because the third selective transmission mirror 130 has a high reflectance for the second light L2, most of the second light L2 reaching the third selective transmission mirror 130 is reflected by the third selective transmission mirror 130 and returns to the nonlinear optical crystal 160. At least a portion of the second light L2 returning to the nonlinear optical crystal 160 passes through the antireflection coating 172 and the second selective transmission mirror 120, returns to the laser crystal 150, and is amplified by the laser crystal 150, which is continuously pumped by the first light L1. By repeating this operation, the second light L2 is repeatedly amplified in the laser crystal 150. In this way, the second light L2 resonates while being amplified within the resonator formed by the first selective transmission mirror 110 and the third selective transmission mirror 130, whereby the second light L2 is amplified.

[0058] At least a portion of the second light L2 that is incident on the nonlinear optical crystal 160 and propagates in the positive direction along the z axis is absorbed by the nonlinear optical crystal 160. A portion of the second light L2 that propagates in the positive direction along the z axis is absorbed at a position A3a within the nonlinear optical crystal 160. From the position A3a where the second light L2 that propagates in the positive direction along the z axis is absorbed, a third peak wavelength λ , which is the second harmonic of the second light L2, is absorbed. ３ A third light L3a having the above-mentioned characteristic is emitted in the positive direction in the z-axis direction. In Fig. 9, in order to distinguish between the second light L2 and the third light L3a, the emission position of the third light L3a is represented as position E3a. Position A3a and position E3a are the same position, but are shown shifted in the x-axis direction in Fig. 9.

[0059] The third light L3a is incident on the antireflection film 173. Because the antireflection film 173 has a high transmittance for the third light L3a, most of the third light L3a incident on the antireflection film 173 passes through the antireflection film 173 and is incident on the third selective transmission mirror 130. Because the third selective transmission mirror 130 has a high transmittance for the third light L3a, most of the third light L3a that reaches the third selective transmission mirror 130 passes through the third selective transmission mirror 130 and is output from the solid-state laser device 100 as output light L4.

[0060] At least a portion of the second light L2 propagating in the negative z-axis direction within the nonlinear optical crystal 160 is absorbed by the laser crystal 150. A portion of the second light L2 propagating in the negative z-axis direction is absorbed at a predetermined position A3b within the nonlinear optical crystal 160. From position A3b where the second light L2 propagating in the negative z-axis direction is absorbed, third light L3b, which is the second harmonic of the second light L2, is emitted in the negative z-axis direction. In FIG. 9 , in order to distinguish between the second light L2 and the third light L3b, the emission position of the third light L3b is represented as position E3b. Position A3a and position E3b are the same position, but are shown shifted in the x-axis direction in FIG. 9 .

[0061] The third light L3b is incident on the antireflection coating 172. Because the antireflection coating 172 has a high transmittance for the third light L3b, most of the third light L3b incident on the antireflection coating 172 passes through the antireflection coating 172 and is incident on the second selective transmission mirror 120. Because the second selective transmission mirror 120 has a high reflectance for the third light L3b, most of the third light L3b that reaches the second selective transmission mirror 120 is reflected by the second selective transmission mirror 120, passes through the antireflection coating 172, and propagates through the nonlinear optical crystal 160 in the positive direction in the z-axis direction. Like the third light L3a described above, most of the third light L3b propagating through the nonlinear optical crystal 160 in the positive direction in the z-axis direction is output from the third selective transmission mirror 130 as output light L4. In this way, in this embodiment, not only the third light L3a emitted from the nonlinear optical crystal 160 in the positive direction of the z-axis, but also the third light L3b emitted in the negative direction of the z-axis can be output, thereby increasing the intensity of the output light.

[0062] As described above, according to the solid-state laser device 100 of this embodiment, the third peak wavelength λ ３The third light L3 having the above-mentioned characteristic can be output as output light. In this embodiment, the second selective transmission mirror 120 and the third selective transmission mirror 130 are spaced apart from the nonlinear optical crystal 160. In order for the nonlinear optical crystal 160 to efficiently convert the second light L2 into the third light L3, which is a second harmonic, it is necessary to satisfy a phase matching condition. A simple method for satisfying the phase matching condition in the nonlinear optical crystal 160 is to set the relative angle between the crystal axis of the nonlinear optical crystal 160 and the optical axis of the second light L2 to a phase matching angle α1 at which the refractive indexes of the second light L2 and the third light L3 (second harmonic) are equal. The end face of the nonlinear optical crystal 160 is formed so as to satisfy the phase matching condition based on the configuration of the solid-state laser device 100, the expected environmental temperature, and the like. However, in reality, the phase matching condition is not satisfied due to manufacturing errors in the nonlinear optical crystal 160 or slight deviations in the incident angle of the second light L2. Therefore, in order to satisfy the phase matching condition, it is necessary to adjust the installation angle of the nonlinear optical crystal 160 within a range of approximately ±1°. Furthermore, the angle range in which the phase matching condition is satisfied is a narrow range of ±0.1° or less centered on α1, so the angle of nonlinear optical crystal 160 must be adjusted with high precision.

[0063] In the solid-state laser device 100 according to the present embodiment, the third selective transmission mirror 130 constituting the resonator and the second selective transmission mirror 120 reflecting the third light L3 are spaced apart from the nonlinear optical crystal 160. This makes it possible to suppress fluctuations in the resonance conditions of the resonator even when the installation angle of the nonlinear optical crystal 160 is adjusted. Furthermore, it is possible to suppress interference with the superposition of the third light L3 reflected by the second selective transmission mirror 120 and propagating in the positive direction of the z-axis with the third light L3 emitted from the nonlinear optical crystal 160 in the positive direction of the z-axis. Therefore, according to the solid-state laser device 100 according to the present embodiment, highly efficient wavelength conversion can be achieved in the nonlinear optical crystal 160 by satisfying the phase matching condition while suppressing misalignment of the optical axes of the resonator and the like.

[0064] Furthermore, the second selective transmission mirror 120 according to the present embodiment reflects the third light L3. The effect of such a second selective transmission mirror 120 will be described in comparison with a solid-state laser device of a comparative example shown in Fig. 10. Fig. 10 is a diagram illustrating the operation of the solid-state laser device 1000 of the comparative example. The solid-state laser device 1000 of the comparative example shown in Fig. 10 differs from the solid-state laser device 100 according to the present embodiment in the configurations of the first selective transmission mirror 1010 and the second selective transmission mirror 1020, but is the same in other configurations.

[0065] The first selective transmission mirror 1010 of the comparative example differs from the first selective transmission mirror 110 of the present embodiment in that it transmits the third light L3. The second selective transmission mirror 1020 of the comparative example differs from the second selective transmission mirror 120 of the present embodiment in that it transmits the third light L3.

[0066] In the solid-state laser device 1000 of this comparative example, the third light L3b propagating from the nonlinear optical crystal 160 in the negative direction of the z-axis passes through the second selective transmission mirror 1020 and propagates through the laser crystal 150. At this time, the laser crystal 150 absorbs at least a portion of the third light L3b. In particular, in the region where the first light L1, which is the excitation light, is focused on the laser crystal 150, a state with a high exciton density is formed due to optical absorption of the first light L1, which is the excitation light. When the third light L3b passes through this region, the third light L3b is absorbed by the excited laser crystal 150, thereby generating an even higher level of electronic excitation state in the laser crystal 150. This resonant multiphoton absorption process is more likely to occur in the focused region of the first light L1, which is the excitation light, and heat is generated from the laser crystal 150 in a high-energy state. This heat generation can cause crystal damage to the laser crystal 150, fluctuations in the resonance conditions due to the thermal lens effect in the laser crystal 150, and a decrease in amplification efficiency.

[0067] Furthermore, the third light L3b propagating in the negative direction of the z-axis within the laser crystal 150 passes through the first selective transmission mirror 1010 and becomes stray light, and therefore does not contribute to the output light L4. Furthermore, if part of the third light L3b that has become stray light is irradiated onto the light-emitting element 140, this may cause deterioration of the light-emitting element 140.

[0068] Compared to the solid-state laser device 1000 of the comparative example, in the solid-state laser device 100 of the present embodiment, the second selective transmission mirror 120 reflects the third light L3b, thereby suppressing optical damage caused by resonant multiphoton absorption of the third light L3b in a high excitation density region inside the laser crystal 150, and the third light L3b can be extracted as output light L4 by being superimposed with the third light L3a. Therefore, according to the solid-state laser device 100 of the present embodiment, the extraction efficiency of the third light L3 can be increased compared to the solid-state laser device 1000 of the comparative example.

[0069] In the solid-state laser device 100 according to this embodiment, the second selective transmission mirror 120 is disposed on the laser crystal 150. More specifically, the second selective transmission mirror 120 is a dielectric multilayer film formed on the end face of the laser crystal 150 facing the nonlinear optical crystal 160. This reduces the number of parts in the solid-state laser device 100. Furthermore, since the positions of the second selective transmission mirror 120 and the laser crystal 150 can be adjusted simultaneously, the position adjustment can be simplified.

[0070] [Manufacturing Method] A manufacturing method for the solid-state laser device 100 according to this embodiment will be described with reference to Fig. 11. Fig. 11 is a flowchart showing the flow of the manufacturing method for the solid-state laser device 100 according to this embodiment.

[0071] As shown in FIG. 11, first, the components that make up the solid-state laser device 100 are prepared (S10).

[0072] Next, each component is placed in a predetermined position (S20), with the nonlinear optical crystal 160 placed on a fixed surface parallel to the main surface.

[0073] Next, the first light L1 is emitted from the light-emitting element 140 (S30). Next, alignment of at least one of the first selective transmission mirror 110, the laser crystal 150, the second selective transmission mirror 120, and the third selective transmission mirror 130 of the solid-state laser device 100 is performed (S40). In this embodiment, the components of the solid-state laser device 100, namely the light-emitting element 140, the laser crystal 150, the nonlinear optical crystal 160, the first selective transmission mirror 110, the second selective transmission mirror 120, and the third selective transmission mirror 130, are aligned to a predetermined base or the like. In this embodiment, the first light L1 is emitted from the light-emitting element 140, and alignment of each component (so-called active alignment) is performed while measuring the intensity of the third light L3 (output light L4) emitted from the third selective transmission mirror 130. In step S40, only the position of the nonlinear optical crystal 160 is adjusted, and adjustment of the tilt angle with respect to the second light L2 is not required.

[0074] Next, the tilt angle of the nonlinear optical crystal 160 with respect to the optical axis of the second light L2 is adjusted (S50) while monitoring the third light L3 emitted from the third selective transmission mirror 130. In this step, as shown in FIG. 3 , the crystal axis of the nonlinear optical crystal 160 is tilted by an angle α1 with respect to the direction of the optical axis of the second light L2 (the z-axis direction shown in FIG. 3 ), thereby satisfying the phase matching condition. At this time, the nonlinear optical crystal 160 is rotated or tilted along a fixed plane. In this embodiment, by finely adjusting the tilt angle of the nonlinear optical crystal 160 while monitoring the third light L3 emitted from the third selective transmission mirror 130, the phase matching condition can be satisfied with greater precision. This allows the wavelength conversion efficiency of the nonlinear optical crystal 160 to be improved.

[0075] After steps 40 and 50 are performed, the optical output of the third light L3 (output light L4) is measured to determine whether it has reached a predetermined optical output value (S60). If the optical output of the third light L3 (output light L4) has not reached the predetermined optical output value (No in S60), the process returns to step S40 and alignment is performed again. Steps S40 to S60 are repeated, and if the predetermined optical output value is reached (Yes in S60), the components are fixed (S70).

[0076] Through the above-described steps, a highly efficient solid-state laser device 100 can be manufactured.

[0077] In this embodiment, the light emitting element 140 is mounted on a submount or the like in a junction-up manner, but the mounting manner of the light emitting element 140 is not limited to this. It may also be mounted in a so-called junction-down manner, in which the surface of the light emitting element 140 closer to the optical waveguide 140 a is the mounting surface.

[0078] [First Modification of First Embodiment] A solid-state laser device according to a first modification of the present embodiment will be described with reference to Figures 5, 6, 8, and 9. The solid-state laser device according to this modification differs from the solid-state laser device 100 according to the first embodiment in the transmittance characteristics of the second selective transmission mirror 120, the third selective transmission mirror 130, and the antireflection films 172 and 173, but is the same in other configurations.

[0079] As shown by the dotted line in FIG. 5, in the transmittance characteristics of the second selective transmission mirror 120 of the solid-state laser device according to this modification, the first peak wavelength λ １ In this case, the transmittance is lower (that is, the reflectance is higher) than that of the second selective transmission mirror 120 according to the first embodiment. Ｂ３Ｕ Specifically, T Ｂ３Ｕ is 0.05. Accordingly, the transmitted light L12 (see FIG. 9 ) that passes through the second selective transmission mirror 120 is reduced, and the reflected light L13 (see FIG. 9 ) that is reflected by the second selective transmission mirror 120 is increased. As a result, in the solid-state laser device according to this modification, the first light L1 that passes through the second selective transmission mirror 120 and enters the nonlinear optical crystal 160 can be reduced. Therefore, it is possible to prevent the first light L1 from reaching the nonlinear optical crystal 160 and the third selective transmission mirror 130 and causing a malfunction. Furthermore, the reflected light L13 reflected by the second selective transmission mirror 120 passes through the laser crystal 150 again, and a portion of it is absorbed by the laser crystal 150. Therefore, the reflected light L13 that is absorbed by the laser crystal 150 and becomes the second light L2 increases, and the third light L3 can be emitted more efficiently from the solid-state laser device.

[0080] In this modification, the antireflection films 172 and 173 and the third selective transmission mirror 130 also have the first peak wavelength λ１ The transmittance characteristics of the antireflection films 172 and 173 are shown by dotted lines in Fig. 8. The transmittance characteristics of the third selective transmission mirror 130 are shown by dotted lines in Fig. 6. As shown by the dotted lines in Fig. 6 and Fig. 8, in the transmittance characteristics of the antireflection films 172 and 173 and the third selective transmission mirror 130 of the solid-state laser device according to this modification, １ In this case, the transmittance is lower (i.e., the reflectance is higher) than the antireflection films 172, 173 and the third selective transmission mirror 130 according to the first embodiment. Specifically, it is 0.7 or less. This makes it possible to suppress malfunctions in the solid-state laser device caused by the first light L1 being emitted from the third selective transmission mirror 130, that is, by the emission of light other than the third light L3 from the solid-state laser device.

[0081] [Modification 2 of Embodiment 1] A solid-state laser device according to Modification 2 of this embodiment will be described. The solid-state laser device according to this modification differs from the solid-state laser device 100 according to this embodiment in the polarization direction of the second light L2 emitted by the laser crystal 150. The solid-state laser device according to this modification will be described below with reference to FIGS. 12 and 13. FIG. 12 is a schematic side view showing the overall configuration of a solid-state laser device 100a according to this modification. FIG. 12 shows a side view of the solid-state laser device 100a as seen from the x-axis direction. In other words, FIG. 12 shows a side view as seen from a direction different by 90° from FIG. 1. FIG. 13 is a diagram showing the direction of the crystal axis of a nonlinear optical crystal 160 according to this modification.

[0082] The light-emitting element 140 according to this modification is mounted in a so-called junction-down manner, with the surface closer to the optical waveguide 140a as the mounting surface. The light-emitting element 140 is mounted on a surface parallel to a principal surface (not shown) that is parallel to the zx plane. As with the first light L1 according to the present embodiment, the first light L1 of the light-emitting element 140 according to this modification has an optical axis parallel to the z-axis direction, a slow-axis direction parallel to the x-axis direction, and a fast-axis direction parallel to the y-axis direction.

[0083] In this modification, the second light L2 emitted from the laser crystal 150 is π-polarized (see FIG. 2). That is, the polarization direction of the second light L2 is parallel to the x-axis direction. In addition, in this modification, the second peak wavelength λ of the second light L2 is ２ is 490 nm.

[0084] The direction of the crystal axis of the nonlinear optical crystal 160 is set based on the polarization direction of the second light L2 emitted from the laser crystal 150, etc. In this modification, the crystal axis of the nonlinear optical crystal 160 is an axis parallel to the yz plane. The direction of the crystal axis of the nonlinear optical crystal 160 is tilted from the z-axis direction toward the y-axis direction by an angle β1, centered on the x-axis. That is, while the crystal axis of the nonlinear optical crystal 160 in the solid-state laser device 100 according to this embodiment shown in FIG. 1 is parallel to a plane formed by the propagation direction of the first light L1 and the slow axis direction, the crystal axis of the nonlinear optical crystal 160 according to this modification is parallel to a plane formed by the propagation direction of the first light L1 and the fast axis direction. Here, the angle β1 is an angle that satisfies the phase matching condition for maximizing the conversion efficiency of the second light L2 to the third light L3 in the solid-state laser device 100a according to this modification. In this modification, the third peak wavelength λ of the third light L3 is ３ is 245 nm.

[0085] In this modification, the fixing surface of the solid-state laser device 100a is perpendicular to the main surface. The nonlinear optical crystal 160 is fixed to the fixing surface. This allows the tilt of the crystal axis of the nonlinear optical crystal 160 to be easily adjusted while the nonlinear optical crystal 160 is placed on the fixing surface.

[0086] The solid-state laser device 100a according to this modification also has the same effects as those of the solid-state laser device 100 according to the present embodiment.

[0087] [Modifications 3 to 12 of Embodiment 1] Solid-state laser devices according to Modifications 3 to 12 of this embodiment will be described with reference to Fig. 14. Fig. 14 is a diagram showing the configuration of the solid-state laser devices according to this embodiment and its modifications.

[0088] In FIG. 14, the first peak wavelength λ １ , second peak wavelength λ ２, third peak wavelength λ ３ 14 shows the materials of the laser crystal 150 and the nonlinear optical crystal 160, the polarization direction of the first light L1 absorbed in the laser crystal 150 (absorption polarization direction), the polarization direction of the second light L2 emitted from the laser crystal 150 (second light polarization direction), the transmittance characteristics of the first selective transmission mirror 110, the transmittance characteristics of the second selective transmission mirror 120, and the transmittance characteristics of the third selective transmission mirror 130. In FIG. Ｔ１Ｌ Above, the wavelength λ Ｔ１Ｕ In the following range, the transmittance for the first light L1 is high, and the wavelength λ Ｒ２Ｌ Above, the wavelength λ Ｒ２Ｕ It is shown that the reflectance for the second light L2 is high in the following range: Ｒ３Ｌ Above, the wavelength λ Ｒ３Ｕ In the following range, the reflectance for the third light L3 is high, and the wavelength λ Ｔ２Ｌ Above, the wavelength λ Ｔ２Ｕ It is shown that the transmittance for the second light L2 is high in the following range: Ｔ３Ｌ Above, the wavelength λ Ｔ３Ｕ In the following range, the transmittance for the third light L3 is high, and the wavelength λ Ｒ２Ｌ Above, the wavelength λ Ｒ２Ｕ It is shown that the reflectance for the second light L2 is high in the following range.

[0089] As shown in FIG. 14, the solid-state laser devices according to these modifications have a first peak wavelength λ １ , second peak wavelength λ ２ , third peak wavelength λ ３ , the material of the laser crystal 150, the polarization direction of the second light L2, the transmittance characteristics of the first selective transmission mirror 110, the transmittance characteristics of the second selective transmission mirror 120, and the transmittance characteristics of the third selective transmission mirror 130.

[0090] The solid-state laser devices according to these modifications can also output light having a wavelength of 400 nm or less as the output light L4, and can achieve the same effects as the solid-state laser device 100 according to the present embodiment.

[0091] In addition, in Figure 14, the absorption polarization direction and the second light polarization direction are not shown for Modifications 10 to 12 of Embodiment 1, but these polarization directions may be set appropriately in accordance with the characteristics of the laser crystal 150.

[0092] (Embodiment 2) A solid-state laser device according to embodiment 2 will be described. The solid-state laser device according to this embodiment differs from the solid-state laser device 100 according to embodiment 1 mainly in the configuration of the first selective transmission mirror and in that a package is provided. The solid-state laser device according to this embodiment will be described below with reference to FIGS. 15 and 16, focusing on the differences from the solid-state laser device 100 according to embodiment 1. FIG. 15 is a schematic top view showing the main components of the solid-state laser device 200 according to this embodiment. FIG. 16 is a perspective view showing the overall configuration of the solid-state laser device 200 according to this embodiment.

[0093] 15 and 16 , a solid-state laser device 200 according to this embodiment includes a light-emitting element 140, a laser crystal 150, a nonlinear optical crystal 160, a first selective transmission mirror 210, a second selective transmission mirror 120, a third selective transmission mirror 130, and anti-reflection films 172 and 173. In this embodiment, the solid-state laser device 200 further includes a package 290 and a submount 246. The package 290 is composed of a base 291 and a lid (not shown).

[0094] The first selective transmission mirror 210 according to the present embodiment differs from the first selective transmission mirror 110 according to the first embodiment in that it is disposed in the laser crystal 150. The first selective transmission mirror 210 is a dielectric multilayer film formed on the end face (first surface S1) of the laser crystal 150 that faces the light emitting element 140. The first selective transmission mirror 210 has transmittance characteristics similar to those of the dielectric multilayer film 114 of the first selective transmission mirror 110 according to the first embodiment. The two opposing first surfaces S1 and second surfaces S2 of the laser crystal 150 are parallel to each other.

[0095] The base 291 according to this embodiment is a housing that houses the light emitting element 140, the laser crystal 150, the nonlinear optical crystal 160, the first selective transmission mirror 210, the second selective transmission mirror 120, and the third selective transmission mirror 130. In this embodiment, the base 291 further houses anti-reflection films 172 and 173 and a submount 246, and is hermetically sealed together with the above-mentioned components by a lid (not shown).

[0096] The base 291 has a flat bottom plate 292 , a frame 298 arranged so as to surround the center of the bottom plate 292 , and a plurality of terminals 293 arranged on a portion of the surface of the frame 298 .

[0097] In this embodiment, the bottom plate 292 is a rectangular plate-shaped member made of a material with high thermal conductivity, such as copper. The submount 246 and laser crystal 150 are disposed on the main surface of the bottom plate 292 (the surface located inside the base 291). In this embodiment, the bottom plate 292 also serves as a pedestal 294. The pedestal 294 has a fixing surface 294a, and the nonlinear optical crystal 160 is disposed on the fixing surface 294a. In this embodiment, the fixing surface 294a is the main surface of the bottom plate 292.

[0098] Frame body 298 is a plate-like member that stands on bottom plate 292. In the present embodiment, frame body 298 is a rectangular frame-like (in other words, rectangular cylindrical) member that has side walls 298a, 298b, 298c, and 298d and is disposed along the edge of bottom plate 292. Frame body 298 has a rectangular through-hole, and bottom plate 292 is disposed so as to cover one end of the through-hole.

[0099] The terminals 293 are conductive members that penetrate the frame body and are insulated from the frame body 298 by an insulating ring (not shown). In this embodiment, two terminals are arranged on the side wall 298c that is close to the light emitting element 140.

[0100] The lid is a plate-like member that is disposed on the upper surface of the frame body 298 (i.e., one of the two ends of the through-hole of the frame body 298 opposite the end where the bottom plate 292 is disposed). In the present embodiment, the lid is a rectangular plate-like member similar to the bottom plate 292. The lid is disposed so as to cover the opening of the frame body 298, thereby sealing the package 290.

[0101] The light emitting element 140 is fixed by solder or the like onto a submount 246 that is fixed onto the bottom plate 292. The submount 246 is made of a material with high thermal conductivity, for example, a thermal conductivity of 100 W / mK or more. The submount 246 is made of a ceramic such as AlN or SiC, and a metal film such as Au is formed on the surface facing the light emitting element 140.

[0102] The metal film formed on the submount 246 and the light emitting element 140 are electrically connected to one terminal 293 and the other terminal 293, respectively, by metal wires or the like (not shown). This makes it possible to supply power to the light emitting element 140 from outside the package 290 via the terminal 293. While the light emitting element 140 according to the first embodiment is mounted in a junction-up position, this embodiment uses a junction-down position. That is, of the surfaces of the light emitting element 140 perpendicular to the fast axis direction, the surface closer to the optical waveguide 140a is the mounting surface.

[0103] With the positions and inclinations of the laser crystal 150 and the nonlinear optical crystal 160 adjusted, they are fixed to the bottom plate 292 or the fixing surface 294a using an adhesive layer such as solder.

[0104] The third selective transmission mirror 130 is fixed to the inner surface of the frame 298. An opening (not shown) is formed in a side wall 298d of the frame 298 on which the third selective transmission mirror 130 is disposed, and the third selective transmission mirror 130 is disposed so as to cover the opening. Then, the output light L4 transmitted through the third selective transmission mirror 130 is emitted to the outside of the package 290.

[0105] The solid-state laser device 200 according to this embodiment also achieves the same effects as the solid-state laser device 100 according to the first embodiment.

[0106] Furthermore, in the solid-state laser device 200 according to the present embodiment, the number of parts constituting the solid-state laser device 200 can be reduced by providing the first selective transmission mirror 210 disposed in the laser crystal 150. Therefore, the solid-state laser device 200 can be made smaller and less expensive.

[0107] Furthermore, since the first selective transmission mirror 210 is disposed on the end face of the laser crystal 150, alignment of the first selective transmission mirror 210 can be performed simultaneously by aligning the laser crystal 150. In this way, alignment can be simplified in the solid-state laser device 200 according to this embodiment.

[0108] Furthermore, since the solid-state laser device 200 according to the present embodiment has the package 290, the light-emitting element 140 and the like can be disposed in the sealed package 290. Therefore, it is possible to reduce adhesion of foreign matter and the like to each component such as the light-emitting element 140.

[0109] (Embodiment 3) A solid-state laser device according to embodiment 3 will be described. The solid-state laser device according to this embodiment differs from the solid-state laser device 100 according to embodiment 1 mainly in that it includes a focusing optical system and in the configuration of the resonator. The solid-state laser device according to this embodiment will be described below with reference to FIGS. 17 to 19, focusing on the differences from the solid-state laser device 100 according to embodiment 1. FIGS. 17 and 18 are schematic top and side views, respectively, showing the overall configuration of a solid-state laser device 300 according to this embodiment. FIGS. 17 and 18 show schematic diagrams of the solid-state laser device 300 as viewed from the fast axis direction and the slow axis direction of the first light L1, respectively. FIG. 19 is a diagram showing an example of each parameter of the solid-state laser device 300 according to this embodiment.

[0110] The solid-state laser device 300 according to this embodiment further includes a focusing optical system 380 in addition to the components of the solid-state laser device 100 according to the first embodiment.

[0111] The focusing optical system 380 is an optical system arranged on the optical axis of the first light L1 between the light emitting element 140 and the first selective transmission mirror 210. The focusing optical system 380 focuses the first light L1. In this embodiment, a focusing point F1 of the first light L1 focused by the focusing optical system 380 is located inside the laser crystal 150. The focusing point F1 is a position where the beam diameter of the first light L1 focused by the focusing optical system 380 is minimum. The beam diameter is a value obtained by dividing the optical density (in other words, optical power density) of the first light L1 in a cross section perpendicular to the optical axis by 1 / e of the maximum value. ２The focusing optical system 380 is defined as the diameter (i.e., total width) of a region where the diameter is at least 1 / 100 of the focusing optical system 380. For example, a focusing lens such as an aspherical lens or a spherical lens can be used as the focusing optical system 380. The shapes of both surfaces of the lens used as the focusing optical system 380 may be different or the same. In the lens used as the focusing optical system 380 shown in FIG. 17, the radius of curvature of the surface facing the laser crystal 150 is smaller than that of the surface facing the semiconductor laser 140, but this relationship in magnitude of the radii of curvature may be reversed. The radii of curvature of both surfaces of the lens used as the focusing optical system 380 may be the same.

[0112] By providing such focusing optical system 380, it is possible to increase the overlap between first light L1 and second light L2 in laser crystal 150 compared to a case where focusing optical system 380 is not provided. Therefore, it is possible to increase the efficiency of conversion from first light L1 to second light L2 in laser crystal 150.

[0113] The lens magnification, defined as the ratio of the distance d1 from the light-emitting portion 140e of the light-emitting element 140 to the focusing optical system 380 to the distance d2 from the focusing optical system 380 to the focusing point F1, may be determined, for example, as shown in Figure 19.

[0114] In this embodiment, the third selective transmission mirror 130 is a concave mirror. The cavity length L between the first selective transmission mirror 110, which is a plane mirror, and the third selective transmission mirror 130, which is a concave mirror, the radius of curvature R of the third selective transmission mirror 130, the length T1 of the laser crystal 150 in the optical axis direction of the second light L2, the length T2 of the gap between the laser crystal 150 and the nonlinear optical crystal 160 on the optical axis of the second light L2, the length T3 of the nonlinear optical crystal 160 on the optical axis of the second light L2, and the Rayleigh length z of the second light L2 resonating in the cavity are Ｒ satisfies the following relationship:

[0115]

[0116] Here, g is a parameter determined by the cavity length L and the curvature radius R of the third selective transmission mirror 130, as shown in the above relational expression (1). An example of each parameter of the solid-state laser device 300 according to this embodiment is as shown in FIG. 19. In the example shown in FIG. 19, the Rayleigh length z of the second light L2 Ｒ is 22.0 mm, the beam diameter (beam waist) ω0 is 0.067 mm, and the divergence angle θd is 0.17°.

[0117] As shown in the above relational expression (1), in this embodiment, the Rayleigh length z Ｒ The laser crystal 150 and the nonlinear optical crystal 160 are arranged within this range. This makes it possible to suppress divergence of the second light L2 in the nonlinear optical crystal 160. Here, the wavelength conversion by the nonlinear optical crystal 160 strongly depends on the angle of incidence of the second light L2 with respect to the crystal axis. Therefore, in order to maximize the energy conversion efficiency in the nonlinear optical crystal 160, it is better that the light incident on the nonlinear optical crystal 160 is close to parallel light. In this embodiment, the Rayleigh length z Ｒ By arranging the laser crystal 150 and the nonlinear optical crystal 160 within this range, it is possible to realize substantially parallel incidence of the second light L2 on the nonlinear optical crystal 160. Therefore, it is possible to increase the wavelength conversion efficiency in the nonlinear optical crystal 160.

[0118] Furthermore, the configuration of the solid-state laser device 300 according to this embodiment is not limited to the above-described configuration example. Another configuration example of the solid-state laser device 300 according to this embodiment will be described below with reference to Fig. 20. Fig. 20 is a schematic top view showing another configuration example of the solid-state laser device 300 according to this embodiment.

[0119] As shown in FIG. 20 , the light emitting element 140 may be mounted in a TO-CAN package 348. The TO-CAN package 348 has a base 348a, electrode pins 348b, a cap 348c, a light-transmitting window 348d, and a heat sink 348e. The base 348a is a plate-shaped member that serves as the base of the TO-CAN package 348. The electrode pins 348b are conductive members that penetrate the base 348a. The cap 348c is a substantially cylindrical member that is fixed to the base 348a. The heat sink 348e, to which the light emitting element 140 is fixed, is disposed in a space surrounded by the base 348a and the cap 348c. The heat sink 348e is a member that stands on the base 348a, and the light emitting element 140 is mounted on the heat sink 348e directly or via a submount. The light-transmitting window 348d is a plate-shaped light-transmitting member disposed in the opening of the cap 348c. The first light L1 emitted from the light-emitting element 140 passes through the light-transmitting window 348d and is emitted to the outside of the TO-CAN package 348.

[0120] By hermetically sealing light emitting element 140 in such TO-CAN package 348, it is possible to prevent foreign matter from adhering to light emitting element 140. In particular, when light emitting element 140 is a short-wavelength semiconductor laser element with an oscillation wavelength of 500 nm or less, as in the present embodiment, impurities may adhere to the light-emitting end surface with high light density due to the optical tweezers effect, causing a decrease in optical output. In the present embodiment, by hermetically sealing light emitting element 140, it is possible to prevent such a decrease in optical output.

[0121] Here, the optical output of the solid-state laser device 300 will be described using FIG. 21 . FIG. 21 is a graph comparing the dependency of the output light L4 on the light-emitting element drive current in the solid-state laser devices according to the third embodiment and the comparative example. FIG. 21 shows the relationship between the drive current value of the light-emitting element 140 included in the solid-state laser device 300 and the measured optical output value of the third light L3 (output light L4) when the configuration of the solid-state laser device 300 shown in FIG. 20 is actually constructed. FIG. 21 also shows the relationship in a solid-state laser device according to a comparative example of this embodiment. The solid-state laser device according to the comparative example differs from the solid-state laser device 300 according to this embodiment in that the second selective transmission mirror transmits the third light L3b without reflecting it, but is otherwise identical. In this embodiment, the optical output value of the third light L3 (output light L4) is approximately twice as high at all operating currents as in the comparative example. As such, this embodiment can increase the extraction efficiency compared to the comparative example.

[0122] [Concentrating optical system of configuration example 1] The focusing optical system of configuration example 1 according to the present embodiment will be described with reference to Fig. 22 and Fig. 23. Fig. 22 is a schematic side view showing the focusing of the first light L1 by the focusing optical system 380a of configuration example 1 according to the present embodiment. Fig. 23 is a schematic side view showing the first light L1 focused by the focusing optical system 380a of configuration example 1 according to the present embodiment and laser crystal 150.

[0123] The focusing optical system 380a is an example of an optical system arranged on the optical axis of the first light L1 between the light-emitting element 140 and the first selective transmission mirror 210. The focusing optical system 380a focuses the first light L1. The focusing optical system 380a of Configuration Example 1 is an aspherical lens with little aberration. By using an aspherical lens with little aberration as the focusing optical system 380a, it is possible to shorten the length of the high light density region L1D in the traveling direction of the first light L1 (i.e., the z-axis direction), as shown in FIG. 22 . Here, the high light density region L1D is, for example, a region where the beam diameter of the first light L1 is 0.2 mm or less.

[0124] 22, the beam end is indicated by a broken line. The beam end is a point where the light density is 1 / e of the maximum value in a cross section of the first light L1 perpendicular to the z-axis direction.２ 22, a light ray L1C of the first light L1 that passes through a position near the optical axis is indicated by a dashed line, and a light ray L1E of the first light L1 that passes through a position away from the optical axis (i.e., near the beam end) is indicated by a dotted line.

[0125] By including such focusing optical system 380a in solid-state laser device 300, as described above, it is possible to increase length L1F in the z-axis direction of the overlap region between high-density region L1D of first light L1 and second light L2 in laser crystal 150, compared to a case where focusing optical system 380a is not included. Therefore, it is possible to increase the efficiency of conversion from first light L1 to second light L2 in laser crystal 150.

[0126] [Concentrating optical system of configuration example 2] The focusing optical system of configuration example 2 according to the present embodiment will be described with reference to Fig. 24 and Fig. 25. Fig. 24 is a schematic side view showing a mode of focusing of the first light L1 by focusing optical system 380b of configuration example 2 according to the present embodiment. Fig. 25 is a schematic side view showing the first light L1 focused by focusing optical system 380b of configuration example 2 according to the present embodiment and laser crystal 150.

[0127] The focusing optical system 380b is an example of an optical system arranged on the optical axis of the first light L1 between the light-emitting element 140 and the first selective transmission mirror 210. The focusing optical system 380b focuses the first light L1. The focusing optical system 380b of configuration example 2 is a spherical lens. In other words, the focusing optical system 380b is a convex lens having a spherical surface.

[0128] The manner in which the first light L1 is collected by the collecting optical system 380b, which is a spherical lens, will be described with reference to Fig. 24. In Fig. 24, a ray L1C of the first light L1 that passes through a position near the optical axis is indicated by a dashed-dotted line, and a ray L1E of the first light L1 that passes through a position away from the optical axis (i.e., near the beam end) is indicated by a dotted line.

[0129] Since the surface curvature of a spherical lens is constant, so-called spherical aberration occurs. Figure 24 shows a point F1C at which a light ray L1C (indicated by a dashed-dotted line in Figure 24 ) of the first light L1 that passes through a position near the center of the focusing optical system 380b (i.e., the spherical lens) is focused, and a point F1E at which a light ray L1E (indicated by a dotted line in Figure 24 ) of the first light L1 that passes through a position away from the center of the focusing optical system 380b is focused. As shown in Figure 24 , points F1E and F1C are located at different positions in the z-axis direction, with point F1E being closer to the focusing optical system 380b than point F1C. Therefore, the high-light-density region L1D of the first light L1 focused by the focusing optical system 380b, which is a spherical lens, is longer in the z-axis direction than the high-light-density region L1D of the first light L1 focused by the focusing optical system 380a, which is an aspherical lens with the same focal length and no aberration. Furthermore, the change in the beam diameter in the z-axis direction near the focal point F1 in the high light density region L1D in the second configuration example is gentler than that in the first configuration example.

[0130] In Configuration Example 2, due to the above-described characteristics, it is possible to increase the length L1F in the z-axis direction of the overlap region where the high light density region L1D and the second light L2 overlap within the laser crystal 150, compared to Configuration Example 1. This makes it possible to increase the length in the z-axis direction of the region in the laser crystal 150 where amplification efficiency is high. Therefore, it is possible to increase the efficiency of conversion from the first light L1 to the second light L2 in the laser crystal 150. Furthermore, when the position of the high light density region L1D in the z-axis direction coincides with the position of the laser crystal 150 in the z-axis direction, the conversion efficiency can be further increased.

[0131] 25 , in this configuration example, the length of the high light density region L1D of the first light L1 in the laser crystal 150 in the optical axis direction of the first light L1 is longer than the interaction length Le, which is the propagation distance required from the end face of the laser crystal 150 on which the first light L1 is incident until 80% of the first light L1 is absorbed by the laser crystal 150, and is shorter than the length Lc of the first light L1 in the optical axis direction of the laser crystal 150. This makes it possible to reduce the proportion of the first light L1 that is transmitted through the laser crystal 150 without being absorbed by the laser crystal 150. Therefore, it is possible to increase the utilization efficiency of the first light L1.

[0132] In this configuration example, the length of the high light density region L1D of the first light L1 in the laser crystal 150 in the optical axis direction of the first light L1 corresponds to the length L1F of the overlapping region in the z axis direction described above. The interaction length Le is the distance from the end face of the laser crystal 150 onto which the first light L1 is incident to the position where the power of the first light L1 is 20% of the power before incidence on the laser crystal 150. The interaction length Le can be calculated using the absorbance A0 of the first light L1 in the laser crystal 150 by the following formula (2):

[0133] Le=-ln(0.2) / A0 (2)

[0134] In this configuration example, the conversion efficiency of the first light L1 to the second light L2 can be increased by making the length L1F of the overlapping region between the high light density region L1D of the first light L1 and the second light L2 longer than the interaction length Le.

[0135] Here, the absorbance A0 of the first light L1 in the laser crystal 150 is 1.5 cm －１ or less. As a result, the laser crystal 150 gradually absorbs the first light L1 along the optical axis direction, and the heat generation region in the laser crystal 150 can be dispersed in the optical axis direction. Therefore, destruction of the laser crystal 150 can be suppressed, and the thermal lens effect caused by heat generation in the laser crystal 150 can be reduced. In particular, the visible laser light (first light L1 and second light L2) used in this embodiment has a large energy per photon, and therefore the effect of suppressing heat generation by suppressing the light density is significant. The absorbance A0 of the laser crystal 150 is 1.0 cm －１This can further suppress damage to the laser crystal 150 and can further reduce the thermal lens effect caused by heat generation in the laser crystal 150.

[0136] Furthermore, the beam diameter of the second light L2 between the first selective transmission mirror 210 and the dielectric multilayer film 134 may be 50 μm or more and 200 μm or less.

[0137] In addition, the aberration Δf of the focusing optical system 380b, which is a spherical lens, ｔｈ The following equation (3) may hold for

[0138]

[0139] This allows the first light L1 focused inside the laser crystal 150 to efficiently contribute to the oscillation of the solid-state laser device 300 due to the aberration of the focusing optical system 380b, which is a spherical lens.

[0140] Furthermore, when a spherical lens with little aberration is used as the focusing optical system 380b, the magnification of the focusing optical system 380b may be 2 times or more and 4 times or less.

[0141] Furthermore, as shown in FIG. 25, the following equation (4) may hold for the distance a1 from the light-emitting portion 140e of the light-emitting element 140 to the surface of the spherical lens that constitutes the focusing optical system 380b that faces the light-emitting element 140, and the radius of curvature R1 and refractive index n1 of the spherical lens.

[0142]

[0143] This allows the first light L1 emitted by the light emitting element 140 to be focused within the beam diameter of the second light L2 in the slow axis direction, thereby improving the oscillation efficiency of the solid-state laser device 300.

[0144] (Embodiment 4) A solid-state laser device according to embodiment 4 will be described. The solid-state laser device according to this embodiment differs from the solid-state laser device 300 according to embodiment 3 mainly in that the nonlinear optical crystal 160 is inclined with respect to the incident optical axis of the second light L2. The solid-state laser device according to this embodiment will be described below with reference to Figs. 26 and 27, focusing on the differences from the solid-state laser device 300 according to embodiment 3. Fig. 26 is a schematic top view showing the overall configuration of the solid-state laser device 400 according to this embodiment. Fig. 27 shows the optical axis direction z of the second light L2 in the nonlinear optical crystal 160 according to this embodiment. １ 10A and 10B are diagrams showing the directions of the crystal axes of the nonlinear optical crystal 160.

[0145] 26, the nonlinear optical crystal 160 has a rectangular parallelepiped shape and is tilted from the z-axis direction toward the x-axis direction by an inclination angle θn around the y-axis direction. In other words, the normal direction of the end face of the nonlinear optical crystal 160 facing the second selective transmission mirror 120 is tilted by the inclination angle θn with respect to the optical axis of the second light L2.

[0146] More specifically, the normal to the end face of nonlinear optical crystal 160 facing laser crystal 150 is inclined from the z-axis direction toward the x-axis direction by an inclination angle θn, with the y-axis direction as the center. In this case, if the refractive index of nonlinear optical crystal 160 is n, then the optical axis direction z of second light L2 in nonlinear optical crystal 160 is １ is tilted from the z-axis direction toward the x-axis direction by θn(1−1 / n) (see FIG. 27). Therefore, in order to satisfy the phase matching condition, the crystal axis of nonlinear optical crystal 160 is inclined in the optical axis direction z １ , the direction is set to be tilted by α1 toward the x-axis direction.

[0147] In this embodiment, the tilt angle θn with respect to the optical axis of the second light L2 in the normal direction of the end face of the nonlinear optical crystal 160 facing the second selective transmission mirror 120, the length T1 of the laser crystal 150 in the optical axis direction of the second light L2, the length T2 of the gap between the laser crystal 150 and the nonlinear optical crystal 160 in the optical axis of the second light L2, and the beam diameter ω0 in the slow axis direction of the second light L2 at the end face of the laser crystal 150 facing the light emitting element 140 satisfy the following relationship.

[0148]

[0149] The end face of the nonlinear optical crystal 160 facing the laser crystal 150 has the property of transmitting the second light L2, but actually reflects a portion of the light. Of the second light L2, reflected light L21 reflected by this end face propagates toward the laser crystal 150, and when it reaches the population inversion region inside the laser crystal 150, it consumes energy through stimulated emission. When the reflected light L21 reaches the gain region that contributes to the laser oscillation of the second light L2, competition for stimulated emission energy consumption (i.e., mode competition) occurs between the reflected light L21 and the second light L2 that contributes to the conversion to the third light L3. As a result, the intensity of the output light L4 becomes unstable.

[0150] In this embodiment, by satisfying the above relational expression, the reflected light L21 is prevented from propagating to the high gain density region 151 that contributes to the oscillation of the second light L2. Here, since the absorption amount of the first light L1 in the laser crystal 150 decreases exponentially with the propagation distance of the first light L1, the gain density is particularly high near the first surface S1 of the laser crystal 150. For this reason, the tilt angle θn of the nonlinear optical crystal 160 is set to an angle that prevents the beam of the second light L2 on the first surface S1 of the laser crystal 150 from overlapping with the reflected light L21. In other words, the following relational expression is satisfied:

[0151]

[0152] From this relational expression, the above relational expression (5) is derived.

[0153] Although beam overlap occurs in the region closer to the third selective transmission mirror 130 than the first surface S1 of the laser crystal 150, the overlap occurs in a region where the beam intensity is low and the gain density is low, so the effect of mode competition is suppressed.

[0154] As described above, according to this embodiment, in addition to the same effects as those of the solid-state laser device 300 according to the third embodiment, an effect of being able to stabilize the output light intensity is achieved.

[0155] (Embodiment 5) A solid-state laser device according to embodiment 5 will be described. The solid-state laser device according to this embodiment differs from the solid-state laser device 400 according to embodiment 4 mainly in the configuration of the support member for the nonlinear optical crystal 160. The solid-state laser device according to this embodiment will be described below with reference to FIGS. 28 to 30, focusing on the differences from the solid-state laser device 400 according to embodiment 4. FIG. 28 is a schematic top view showing the main components of the solid-state laser device 500 according to this embodiment. FIG. 29 is a perspective view showing the solid-state laser device 500 according to this embodiment. FIG. 30 is an exploded perspective view showing the configuration of the solid-state laser device 500 according to this embodiment.

[0156] 28, a solid-state laser device 500 according to this embodiment includes a light-emitting element 140, a laser crystal 150, a nonlinear optical crystal 160, a first selective transmission mirror 210, a second selective transmission mirror 120, a third selective transmission mirror 130, antireflection films 172 and 173, a focusing optical system 380, and a TO-CAN package 348. In this embodiment, as shown in FIG. 29, the solid-state laser device 500 further includes a package 590, a lens holder 593, and a support member 599 (see FIG. 30). The package 590 includes a base 591, a laser holder 592, and a lid (not shown).

[0157] The base 591 is a component formed by processing a metal such as an aluminum alloy with high thermal conductivity. The base 591 has a pedestal 594 located in the center, a frame 598 located so as to surround the pedestal 594, and a fixing flange 595 located on the outside of the frame 598. The laser holder 592 is a component for fixing the TO-CAN package 348 including the light-emitting element 140. The lid is a plate-like member that is located in the opening of the base 591 shown in FIG. 29 and seals the package 590.

[0158] Base 591 has a pedestal 594 to which nonlinear optical crystal 160 is fixed. In this embodiment, pedestal 594 has a fixing surface 594a, a positioning portion 594b, and a laser crystal holding portion 594c. Frame 598 has side walls 598a, 598b, and 598c.

[0159] Fixing surface 594a is a surface to which nonlinear optical crystal 160 is fixed, and is the bottom surface of first recess 594d formed in the central portion of pedestal 594. In this embodiment, fixing surface 594a is a flat surface parallel to the zx plane.

[0160] The positioning portion 594b is a side surface of the first recess 594d of the base 594, and is a portion that contacts the nonlinear optical crystal 160 or the support member 599 in a plan view of the fixing surface 594a. The positioning portion 594b positions the nonlinear optical crystal 160 so that the tilt angle of the nonlinear optical crystal 160 with respect to the optical axis of the second light L2 can be adjusted. In this embodiment, the positioning portion 594b has a pair of arc-shaped recesses in a plan view of the fixing surface 594a. The outer shape of the support member 599 also has arc-shaped convex portions. The support member 599 is rotatably disposed on the fixing surface 594a while contacting the recesses. This allows the tilt angle of the support member 599 with respect to the optical axis of the second light L2 to be adjusted.

[0161] Laser crystal holding part 594c is a part that holds laser crystal 150. Laser crystal holding part 594c is a second recess formed on the laser holder 592 side of pedestal 594. Laser crystal holding part 594c spatially connects first recess 594d and the area where laser holder 592 is arranged. Laser crystal 150 is fixed to laser crystal holding part 594c.

[0162] The frame 598 has side walls 598a, 598b, and 598c. The side walls 598a, 598b, and 598c are plate-like members that are erected so as to surround the base 594. The side walls 598a and 598b are arranged parallel to the yz plane. The side wall 598c is connected to the ends of the side walls 598a and 598b (the ends on the positive side in the z-axis direction). A through hole is formed in the side wall 598c, and the third selective transmission mirror 130 is arranged to cover the through hole.

[0163] Laser holder 592 is a plate-like member connected to the ends (the ends on the negative side in the z-axis direction) of side walls 598a, 598b. In this embodiment, TO-CAN package 348 and lens holder 593 are disposed in laser holder 592. Laser holder 592 may include a connector into which electrode pin 348b of TO-CAN package 348 is inserted.

[0164] The lens holder 593 is a holder that supports the condensing optical system 380. The lens holder 593 is fixed to the laser holder 592 using screws or the like. The lens holder 593 covers the TO-CAN package 348.

[0165] The support member 599 is a member that supports the nonlinear optical crystal 160. In this embodiment, the support member 599 has an arc-shaped end in a plan view of the fixing surface 594a, and is positioned by the end contacting the positioning portion 594b. The support member 599 is disposed on the fixing surface 594a, and its position parallel to the zx plane is restricted by the positioning portion 594b. The support member 599 is positioned on the fixing surface 594a so as to be rotatable about an axis parallel to the y-axis direction. The tilt angle of the support member 599 with respect to the optical axis of the second light L2 is adjusted, for example, as described in the first embodiment, while monitoring the third light L3 emitted from the third selective transmission mirror 130. After the tilt angle of the support member 599 is adjusted, the support member 599 is fixed to the fixing surface 594a using an adhesive or the like.

[0166] The solid-state laser device 500 according to this embodiment includes the package 590, which can reduce adhesion of foreign matter to the components such as the light-emitting element 140.

[0167] In this embodiment, support member 599 is positioned on fixed surface 594a so as to be rotatable about an axis parallel to the y-axis direction, thereby making it possible to adjust only the tilt angle of support member 599 while suppressing movement of support member 599 (i.e., nonlinear optical crystal 160) in each of the x, y, and z-axis directions. Therefore, the tilt angle of nonlinear optical crystal 160 can be easily adjusted.

[0168] Furthermore, in this embodiment, light emitting element 140 is hermetically sealed in TO-CAN package 348, thereby preventing foreign matter from adhering to light emitting element 140. Furthermore, in this embodiment, a decrease in the optical output of light emitting element 140 due to the optical tweezers effect can be prevented.

[0169] In the present embodiment, the positioning portion 594b and the support member 599 are in continuous contact with each other at their respective arc-shaped portions, but the manner of contact between the positioning portion 594b and the support member 599 is not limited to this. The positioning portion 594b may be in contact with the support member 599 at two locations. Other modes of contact between the positioning portion 594b and the support member 599 will be described below with reference to FIG. 31 .

[0170] Fig. 31 is a diagram showing another contact state between the positioning portion 594b and the support member 599 according to the present embodiment. Fig. 31 shows the shapes of the positioning portion 594b and the support member 599 in a plan view of the fixing surface 594a.

[0171] Positioning portion 594b formed on base 594 is two flat surfaces. The angle between these two flat surfaces is, for example, 90° or more. Support member 599 is a cylindrical member. The support member has a recess in its center, to which nonlinear optical crystal 160 is fixed. Support member 599 contacts each of the two flat surface positioning portions 594b at one point. Base 594 also has pressing member 594e that presses support member 599 toward two positioning portions 594b. Pressing member 594e is a plate-like member having spring properties, such as a leaf spring. This configuration increases the degree of freedom in setting the position of the rotation center of nonlinear optical crystal 160.

[0172] The positioning portion 594b and the support member 599 having such shapes also have the same effects as the positioning portion 594b and the support member 599 shown in FIGS.

[0173] (Embodiment 6) A solid-state laser device according to embodiment 6 will be described. The solid-state laser device according to this embodiment differs from the solid-state laser device 400 according to embodiment 4 mainly in the tilt direction of the nonlinear optical crystal 160. Hereinafter, the solid-state laser device according to this embodiment will be described with reference to FIGS. 32 and 33, focusing on the differences from the solid-state laser device 400 according to embodiment 4. FIGS. 32 and 33 are schematic top and side views, respectively, showing the overall configuration of a solid-state laser device 600 according to this embodiment. FIG. 32 is a schematic diagram of the solid-state laser device 600 as viewed from the fast axis direction of the first light L1, and FIG. 33 is a schematic diagram of the solid-state laser device 600 as viewed from the slow axis direction of the first light L1.

[0174] The solid-state laser device 600 according to this embodiment includes a light-emitting element 140, a laser crystal 150, a nonlinear optical crystal 160, a first selectively transmitting mirror 210, a second selectively transmitting mirror 120, a third selectively transmitting mirror 130, anti-reflection films 172 and 173, a focusing optical system 380, a base 694, a heat sink 647, a submount 646, and an inclined base 693.

[0175] Pedestal 694 is a base on which light-emitting element 140, laser crystal 150, and nonlinear optical crystal 160 are placed. In this embodiment, pedestal 694 is a rectangular plate-shaped member made of a material with high thermal conductivity, such as aluminum nitride ceramic or alumina ceramic. Light-emitting element 140, laser crystal 150, and nonlinear optical crystal 160 are placed on a main surface 694m of pedestal 694, and heat generated by light-emitting element 140, laser crystal 150, and nonlinear optical crystal 160 is efficiently dissipated to the outside via pedestal 694.

[0176] The submount 646 is a member on which the light emitting element 140 is mounted. In this embodiment, the submount 646 is a rectangular parallelepiped member. The heat sink 647 is a member on which the submount 646 is mounted. In this embodiment, the heat sink 647 is a rectangular parallelepiped member. The light emitting element 140 is fixed to the main surface 694m of the base 694 via the heat sink 647 and the submount 646.

[0177] The tilting table 693 is a member that supports the nonlinear optical crystal 160 at an angle relative to a main surface 694m of the pedestal 694. In this embodiment, as shown in FIG. 33, the tilting table 693 has a fixing surface 694a on which the nonlinear optical crystal 160 is placed, and the fixing surface 694a is tilted relative to the main surface of the pedestal 694. The height of the fixing surface 694a from the main surface 694m of the pedestal 694 increases as it approaches the third selective transmission mirror 130. The side of the tilting table 693 has, for example, a triangular shape. As shown in FIGS. 32 and 33, in this embodiment, the main surface 694m is a surface parallel to the zx plane. The axes tilted relative to the y-axis direction and the z-axis direction are respectively referred to as y-axis and z-axis directions. ２ Axial and z directions ２ axial direction, the fixing surface 694a is xz ２ The normal direction of the fixed surface 694a is y ２ The fixing surface 694a is parallel to the axial direction. In other words, the fixing surface 694a is inclined with respect to the main surface 694m. The nonlinear optical crystal 160 according to this embodiment is inclined with the slow axis direction (x-axis direction) of the first light L1 as the rotation axis. In other words, the normal to the end face of the nonlinear optical crystal 160 facing the second selective transmission mirror 120 is inclined with the slow axis direction (x-axis direction) of the first light L1 as the rotation axis.

[0178] In addition, when viewed from above on the main surface 694m, the crystal axis of the nonlinear optical crystal 160 is y ２ The solid-state laser device 600 is manufactured by tilting the y-axis of the nonlinear optical crystal 160 from the z-axis direction toward the x-axis direction. ２ The tilt direction with the axial direction as the rotation axis is defined as the fixed surface 694a (z ２On the other hand, the incident angle of the second light L2 emitted from the laser crystal 150 and incident on the anti-reflection film 172 of the nonlinear optical crystal 160 can be adjusted in the z-axis direction and then fixed. ２ It can be tilted at an angle to the axial direction.

[0179] As a result, similarly to the fourth embodiment, it is possible to reduce mode competition caused by the inclination of the end face of nonlinear optical crystal 160 causing reflected light L21 of second light L2 reflected by the end face of nonlinear optical crystal 160 to enter the gain region in laser crystal 150. At this time, similarly to relational expression (5) of the fourth embodiment, the length of laser crystal 150 in the optical axis direction of second light L2, the length of the gap between laser crystal 150 and nonlinear optical crystal 160 in the optical axis of second light L2, and the beam diameter (beam waist) in the fast axis direction of second light L2 at the end face of laser crystal 150 facing light emitting element 140 are calculated based on the relationship between the z-axis direction and the z-axis direction. ２ The angle between the axes can be determined.

[0180] Furthermore, in this embodiment, the direction in which the phase matching angle is adjusted is different from the direction in which the reflection direction of the second light L2 is controlled, so that the degree of freedom in adjusting the phase matching angle increases, making it easier to improve efficiency.

[0181] (Seventh Embodiment) A solid-state laser device according to the seventh embodiment will be described. The solid-state laser device according to the present embodiment differs from the solid-state laser device 400 according to the fourth embodiment mainly in that the focusing optical system has a diverging lens. Hereinafter, the solid-state laser device according to the present embodiment will be described with reference to FIGS. 34 and 35, focusing on the differences from the solid-state laser device 400 according to the fourth embodiment. FIGS. 34 and 35 are schematic top and side views, respectively, showing the overall configuration of the solid-state laser device 700 according to the present embodiment. FIGS. 34 and 35 show schematic views of the solid-state laser device 700 as seen from the fast axis direction and the slow axis direction of the first light L1, respectively.

[0182] As shown in FIGS. 34 and 35, a solid-state laser device 700 according to this embodiment includes a focusing optical system 780 .

[0183] The focusing optical system 780 according to the present embodiment includes a focusing lens 781 and a diverging lens 782. The focusing lens 781 is a lens that focuses the first light L1. As with the focusing optical system 380 according to the third embodiment, for example, an aspherical lens, a spherical lens, or the like can be used as the focusing lens 781. The diverging lens 782 is a lens disposed between the focusing lens 781 and the first selective transmission mirror 210. The diverging lens 782 collimates the first light L1 emitted from the focusing lens 781. Here, "collimate" not only means completely collimating the first light L1, but also means bringing the first light L1 closer to parallel light. Furthermore, "collimate" means bringing at least one of the fast axis direction and the slow axis direction of the first light L1 closer to parallel light. In the present embodiment, the diverging lens 782 is a cylindrical lens having a cylindrical concave surface. In this embodiment, both the incident surface and the exit surface of the diverging lens 782 for the first light L1 are concave, but only one of them may be concave.

[0184] The effects of the light collecting optical system 780 according to this embodiment will be described.

[0185] In order to increase the efficiency of converting the energy of the first light L1 into the energy of the second light L2, it is necessary to match the propagation position of the first light L1 with the propagation position of the second light L2. The mode matching efficiency η is an index that indicates the spatial overlap of the two beams, and is expressed as follows using the magnitudes E1 and E2 of the electric fields of the first light L1 and the second light L2, respectively.

[0186]

[0187] A semiconductor laser element such as the light-emitting element 140 generally has a characteristic that the beam quality in the slow axis direction is low and the beam quality in the fast axis direction is high. Therefore, when focusing is performed using a single lens as in embodiment 3, the divergence angle in the slow axis direction is small, resulting in a large beam diameter. On the other hand, the divergence angle in the fast axis direction is large, resulting in a small beam diameter. In the configuration using a single focusing lens in embodiment 3, considering the spatial overlap between the first light L1 and the second light L2, the divergence angle in the slow axis direction is small, so as long as the beam diameter is not too large, the overlap with the beam of the second light L2 is likely to be large. On the other hand, the divergence angle in the fast axis direction is large, and even if the beam diameter at the focusing point is appropriate, the divergence angle is large before and after the focusing point, resulting in a rapid increase in the beam diameter of the second light L2. This causes a decrease in the overlap integral of the electric fields of the first light L1 and the second light L2, thereby reducing the mode matching efficiency η. The mode matching efficiency η is maximized when the first light L1 and the second light L2 have exactly the same shape and size, but in this embodiment, by placing diverging lens 782 between condensing lens 781 and laser crystal 150, it is possible to shape the beam shape of first light L1 and bring it closer to the beam shape of second light L2. Diverging lens 782 is placed at a position within the region where first light L1 is condensed by condensing lens 781 so that the beam diameter is exactly the same as the beam diameter (beam waist) ω0 of second light L2. The radius of curvature of the concave surface of diverging lens 782 and the lens material are appropriately set so that the first light L1 emitted from diverging lens 782 becomes a parallel light when viewed from the slow axis direction.

[0188] Another effect of the seventh embodiment is that the light density can be reduced. There is an upper limit to the number of excitons that can form a population inversion inside the laser crystal 150. Therefore, even if the light density of the first light L1 is increased above a predetermined upper limit, it cannot contribute to laser oscillation. Therefore, when the energy of the first light L1 is high, it is necessary to reduce the light density of the first light L1 so that the light density of the first light L1 does not become too high.

[0189] In this embodiment, the diverging lens 782 can effectively increase the beam cross-sectional area of ​​the first light L1 and reduce the light density. Furthermore, by reducing the light density of the first light L1, damage to the end face and inside of the laser crystal 150 can be suppressed. The light density p is calculated by multiplying the total power P [W] of the first light L1, the infinitesimal distance Δz [m] in the optical axis direction of the first light L1, and the beam diameter ω in the fast axis direction. ｆ [m] and the beam diameter ω in the slow axis direction ｓ It can be calculated using the following formula using [m].

[0190]

[0191] In the solid-state laser device 300 according to the third embodiment, the mode matching efficiency η is 53% and the optical density p is 6.3 kW / mm ３ However, in the solid-state laser device 700 according to this embodiment, the mode matching efficiency η is 82% and the optical density p is 0.126 kW / mm ３ were improved respectively.

[0192] In this way, in the solid-state laser device 700 according to this embodiment, high efficiency can be achieved and damage to the laser crystal 150 can be suppressed.

[0193] (Embodiment 8) A solid-state laser device according to embodiment 8 will be described. The solid-state laser device according to this embodiment differs from the solid-state laser device 700 according to embodiment 7 mainly in that the focusing optical system has a converging lens instead of a diverging lens. The solid-state laser device according to this embodiment will be described below with reference to FIGS. 36 and 37, focusing on the differences from the solid-state laser device 700 according to embodiment 7. FIGS. 36 and 37 are schematic top and side views, respectively, showing the overall configuration of the solid-state laser device 800 according to this embodiment. FIGS. 36 and 37 show schematic views of the solid-state laser device 800 as seen from the fast axis direction and the slow axis direction of the first light L1, respectively.

[0194] As shown in FIGS. 36 and 37, a solid-state laser device 800 according to this embodiment includes a focusing optical system 880 .

[0195] The focusing optical system 880 according to this embodiment includes a focusing lens 781 and a converging lens 882. The focusing lens 781 has a configuration similar to that of the focusing lens 781 according to the seventh embodiment. The converging lens 882 is a lens disposed between the focusing lens 781 and the first selective transmission mirror 210. The converging lens 882 collimates the first light L1 emitted from the focusing lens 781. In this embodiment, the converging lens 882 is a cylindrical lens having a convex cylindrical surface. In this embodiment, both the entrance surface and exit surface of the converging lens 882 for the first light L1 are convex surfaces, but only one of them may be convex. Furthermore, the converging lens 882 is disposed between the focal point F1 of the first light L1 by the focusing lens 781 and the laser crystal 150. The converging lens 882 is positioned in a region where the first light L1 diverges again after being focused by the focusing lens 781, so that the beam diameter is exactly the same as the beam diameter (beam waist) ω0 of the second light L2.

[0196] In the solid-state laser device 800 according to the present embodiment, it is also possible to collimate the first light L1 incident on the laser crystal 150 in the fast axis direction. Therefore, the same effects as those of the solid-state laser device 700 according to the seventh embodiment can be achieved.

[0197] Furthermore, since the converging lens 882 according to this embodiment has a convex surface, it is easier to process than the diverging lens 782, which has a concave surface. Accordingly, the use of the converging lens 882 can reduce costs.

[0198] The converging lens 882 is disposed at a position where the beam diameter of the first light L1 in the region where it diverges again after being condensed by the condensing lens 781 is exactly the same as the beam diameter (beam waist) ω0 of the second light L2. This maximizes the spatial overlap between the first light L1 and the second light L2 in the fast axis direction. However, in the slow axis direction, the diverging region of the first light L1 overlaps with the second light L2, so the mode matching efficiency is lower than in the seventh embodiment. In the solid-state laser device 800 according to this embodiment, the mode matching efficiency η is 70% and the optical density is 0.126 kW / mm ３and in the third embodiment (η=53%, p=6.3 kW / mm ３ ) has been significantly improved compared to

[0199] (Other Embodiments) While the solid-state laser device according to the present disclosure has been described above based on the embodiments and modifications thereof, the present disclosure is not limited to these embodiments and modifications thereof. As long as the modifications do not deviate from the gist of the present disclosure, various modifications conceivable by a person skilled in the art to the embodiments and other forms constructed by combining some of the components of the embodiments and modifications thereof are also included in the scope of the present disclosure.

[0200] For example, in the fifth embodiment, support member 599 is positioned by positioning portion 594b, but nonlinear optical crystal 160 may be directly positioned by positioning portion 594b. That is, the solid-state laser device may not include support member 599, and nonlinear optical crystal 160 may be disposed on fixing surface 594a. Furthermore, positioning portion 594b may contact nonlinear optical crystal 160 at two or more locations in a plan view of fixing surface 594a.

[0201] Furthermore, in the third and fifth embodiments, the light emitting element 140 is mounted in the TO-CAN package 348 , but the light emitting elements according to the other embodiments may also be mounted in the TO-CAN package 348 .

[0202] Furthermore, the above-described embodiments can be modified, substituted, added, omitted, and the like in various ways within the scope of the claims or their equivalents.

[0203] The solid-state laser device according to the present disclosure is particularly useful as a short-wavelength laser light source having a wavelength of 400 nm or less, for example.

[0204] 100, 100a, 200, 300, 400, 500, 600, 700, 800, 1000 solid-state laser device 110, 210, 1010 first selective transmission mirror 112, 132 light-transmitting substrate 114, 133, 134 dielectric multilayer film 120, 1020 second selective transmission mirror 130 third selective transmission mirror 140 light-emitting element 140a optical waveguide 140e light-emitting section 140w light-emitting width 150 laser crystal 151 high gain density region 160 nonlinear optical crystal 171, 172, 173 anti-reflection film 246, 646 submount 290, 590 package 291, 591 base 292 bottom plate 293 terminal 294, 594, 694 pedestal 294a, 594a, 694a Fixing surface 298, 598 Frame body 298a, 298b, 298c, 298d, 598a, 598b, 598c Side wall 348 TO-CAN package 348a Base 348b Electrode pin 348c Cap 348d Light-transmitting window 348e, 647 Heat sink 380, 380a, 380b, 780, 880 Condensing optical system 592 Laser holder 593 Lens holder 594b Positioning portion 594c Laser crystal holding portion 594d First recess 594e Pressing member 595 Flange 599 Support member 693 Inclined base 694m Main surface 781 Condenser lens 782 Diverging lens 882 Converging lens

Claims

a laser crystal that absorbs the first light and emits a second light having a second peak wavelength; a nonlinear optical crystal that absorbs the second light and emits a third light having a third peak wavelength; a first selective transmission mirror that is arranged on the optical axis of the first light between the light-emitting element and the laser crystal and transmits the first light; a second selective transmission mirror that is arranged on the optical axis of the second light between the laser crystal and the nonlinear optical crystal and transmits the second light; and a third selective transmission mirror that is arranged on the optical axis of the third light and transmits the third light, wherein the laser crystal is arranged on the optical axis of the first light between the light-emitting element and the nonlinear optical crystal, and the nonlinear optical crystal is arranged on the optical axis of the second light between the second selective transmission mirror and the third selective transmission mirror, the first selective transmission mirror reflects the second light, the second selective transmission mirror reflects the third light, and the third selective transmission mirror reflects the second light, and the first selective transmission mirror and the third selective transmission mirror form a resonator for the second light, a first selective transmission mirror and a second selective transmission mirror which are parallel to each other; and a second selective transmission mirror and a third selective transmission mirror which are spaced apart from the nonlinear optical crystal.

2. The solid-state laser device according to claim 1, wherein the first selective transmission mirror is disposed on the laser crystal.

3. The solid-state laser device according to claim 1 or 2, wherein the second selective transmission mirror is disposed on the laser crystal.

4. The solid-state laser device according to any one of claims 1 to 3, wherein the third peak wavelength is 400 nm or less.

5. The solid-state laser device according to any one of claims 1 to 4, wherein the second peak wavelength is not less than 400 nm and not more than 800 nm.

6. The solid-state laser device according to any one of claims 1 to 5, wherein the first peak wavelength is not less than 350 nm and not more than 500 nm.

7. A solid-state laser device according to any one of claims 1 to 6, wherein the third peak wavelength is half the second peak wavelength.

8. The solid-state laser device according to any one of claims 1 to 7, wherein the light-emitting element is a nitride semiconductor light-emitting element.

9. The solid-state laser device according to any one of claims 1 to 8, wherein the laser crystal is a crystal doped with at least one of Pr, Tb, and Dy.

10. The solid-state laser device according to any one of claims 1 to 9, wherein the nonlinear optical crystal is LBO, BBO, or KTP.

11. The third selective transmission mirror is a concave mirror, and a resonator length L between the first selective transmission mirror and the third selective transmission mirror, a radius of curvature R of the third selective transmission mirror, a length T1 of the laser crystal in the optical axis direction of the second light, a length T2 of the gap between the laser crystal and the nonlinear optical crystal on the optical axis of the second light, and a length T3 of the nonlinear optical crystal on the optical axis of the second light, and a Rayleigh length z of the second light resonating in the resonator Ｒ The following relationship is true: The solid-state laser device according to any one of claims 1 to 10, which satisfies the following:

12. The solid-state laser device according to any one of claims 1 to 11, further comprising a focusing optical system arranged on the optical axis of the first light between the light-emitting element and the first selective transmission mirror, and a focusing point of the first light focused by the focusing optical system is located within the laser crystal.

13. The solid-state laser device according to claim 12, wherein the focusing optical system is a spherical lens.

14. The solid-state laser device described in claim 13, wherein the length in the optical axis direction of the first light in the region in the laser crystal where the beam diameter of the first light is 0.2 mm or less is longer than the propagation distance required from the end face of the laser crystal where the first light is incident until 80% of the first light is absorbed by the laser crystal, and is shorter than the length of the laser crystal in the optical axis direction of the first light.

15. The solid-state laser device according to claim 12, wherein the focusing optical system comprises a focusing lens and a diverging lens, the diverging lens is disposed between the focusing lens and the first selective transmission mirror, and the diverging lens collimates the first light emitted from the focusing lens.

16. The solid-state laser device according to any one of claims 1 to 15, further comprising an anti-reflection film disposed on the end face of the nonlinear optical crystal facing the second selective transmission mirror.

17. A solid-state laser device according to any one of claims 1 to 16, wherein the normal direction of the end face of the nonlinear optical crystal facing the second selective transmission mirror is inclined with respect to the optical axis of the second light.

18. The inclination angle θn of the normal direction with respect to the optical axis of the second light, the length T1 of the laser crystal in the optical axis direction of the second light, the length T2 of the gap between the laser crystal and the nonlinear optical crystal in the optical axis of the second light, and the beam diameter ω0 of the second light at the end face of the laser crystal facing the light emitting element are related by the following formula: The solid-state laser device according to claim 17 , which satisfies the above.

19. The solid-state laser device according to any one of claims 1 to 18, further comprising a base having a fixing surface to which the nonlinear optical crystal is fixed, the nonlinear optical crystal or a support member supporting the nonlinear optical crystal being disposed on the fixing surface, the base having a positioning portion contacting the nonlinear optical crystal or the support member at two points in a plan view of the fixing surface, the positioning portion positioning the nonlinear optical crystal so as to adjust the inclination angle of the nonlinear optical crystal relative to the optical axis of the second light.

20. A method for manufacturing a solid-state laser device as defined in any one of claims 1 to 19, comprising the steps of: aligning at least one of the first selective transmission mirror, the laser crystal, the second selective transmission mirror, and the third selective transmission mirror; and adjusting the inclination angle of the nonlinear optical crystal with respect to the optical axis of the second light while monitoring the third light emitted from the third selective transmission mirror.

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