Laser medium unit

Abstract

The present invention provides a laser medium unit that can improve the quality of laser light while suppressing parasitic oscillations. [Solution] The laser medium unit 10 comprises a laser medium 50 having a pair of end faces 51a, 51b and a side surface 51c intersecting the pair of end faces 51a, 51b, and a holder 60 that is positioned along the side surface 51c when viewed from a direction intersecting the pair of end faces 51a, 51b and holds the laser medium 50. The holder 60 has a recess 62 that opens towards the center of the laser medium 50 when viewed from a direction intersecting the pair of end faces 51a, 51b. The holder 60 holds the laser medium 50 such that a space S2 is formed between the side surface 51c and the inner surface 62c of the recess 62.

Description

Technical Field

[0001] The present invention relates to a laser medium unit.

Background Art

[0002] Patent Document 1 describes a laser medium unit including a laser medium and a clad material as a frame body that supports the laser medium so as to surround the side surface thereof. In such a laser medium unit, the entire side surface of the laser medium is fixed to the clad material by an adhesive, and spontaneous emission light generated in the laser medium is absorbed by the clad material. Thereby, parasitic oscillation in the laser medium unit is suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the laser medium unit as described above, heat is generated when the clad material absorbs spontaneous emission light. The generated heat is transmitted from the clad material to the laser medium, and the temperature of the laser medium rises. Although it is possible to cool the laser medium from the side surface of the laser medium, the temperature distribution in the excitation region of the laser medium may become non-uniform during cooling. The non-uniformity of the temperature distribution in the excitation region may cause a deterioration in the quality of the laser light emitted from the laser medium unit.

[0005] An object of the present invention is to provide a laser medium unit capable of improving the quality of laser light while suppressing parasitic oscillation.

Means for Solving the Problems

[0006] The laser medium unit of the present invention is a laser medium having a pair of end faces and a side surface intersecting the pair of end faces, and a holder that is arranged along the side surface when viewed from a direction intersecting the pair of end faces and holds the laser medium, wherein the holder has a recess formed therein that opens toward the center of the laser medium when viewed from the direction intersecting the pair of end faces, and the holder holds the laser medium such that a space is formed between the side surface and the inner surface of the recess.

[0007] In the above-described laser medium unit, the holder holds the laser medium such that a space is formed between the side surface of the laser medium and the inner surface of a recess formed in the holder. Parasitic oscillation occurs when spontaneously emitted light generated in the excitation region of the laser medium repeatedly passes through that excitation region. In the above-described laser medium unit, spontaneously emitted light generated in the excitation region of the laser medium is emitted from the side surface of the laser medium into the space between that side surface and the inner surface of the recess. The emitted spontaneously emitted light is scattered by repeated reflection from the inner surface of the recess and does not easily return to the excitation region of the laser medium. Therefore, parasitic oscillation is suppressed. Furthermore, in the above-described laser medium unit, even if heat is generated on the inner surface of the recess by absorbing spontaneously emitted light, the heat is not easily transferred to the laser medium because a space is formed between the inner surface of the recess and the side surface of the laser medium. Therefore, the non-uniformity of the temperature distribution in the excitation region of the laser medium can be suppressed, and the quality of the laser light can be improved. Thus, the above-described laser medium unit can improve the quality of the laser light while suppressing parasitic oscillation.

[0008] The laser medium unit of the present invention may also be [2] "the laser medium unit according to [1] above, wherein the holder is formed in a frame shape that surrounds the laser medium when viewed from the direction intersecting the pair of end faces." In this case, the holder can hold the laser medium in a more stable state.

[0009] The laser medium unit of the present invention may also be [3] "the laser medium unit according to [1] or [2] above, wherein the recess has a shape that tapers towards the bottom of the recess." In this case, the number of times the spontaneously emitted light emitted from the side of the laser medium is reflected on the inner surface of the recess increases, so that the spontaneously emitted light can be scattered efficiently in the recess. This further suppresses parasitic oscillation.

[0010] The laser medium unit of the present invention may also be [4] "the laser medium unit according to any one of [1] to [3] above, wherein the holder is in contact with the side surface." In this case, the laser medium can be held in a more stable state by the holder while suppressing parasitic oscillations.

[0011] The laser medium unit of the present invention may also be [5] "the laser medium unit according to any one of [1] to [4] above, wherein the proportion of the contact area between the side surface and the holder to the entire side surface is 90% or less." In this case, spontaneous emission light can be more reliably emitted from the side surface of the laser medium into the space between the side surface and the inner surface of the recess, and parasitic oscillation can be further suppressed.

[0012] The laser medium unit of the present invention may also be [6] "the laser medium unit according to any one of [1] to [5] above, wherein the proportion of the contact area between the side surface and the holder to the entire side surface is 5% or more." In this case, it is possible to prevent the stress applied from the holder to the side surface of the laser medium from concentrating locally. This makes it possible to hold the laser medium in a more stable state by the holder while suppressing parasitic oscillations.

[0013] The laser medium unit of the present invention may also be [7] "the laser medium unit according to any one of [1] to [6] above, wherein the recess is formed to be point-symmetric with respect to the center of the laser medium when viewed from the direction intersecting the pair of end faces." In this case, even if the temperature of the inner surface of the recess rises due to the absorption of spontaneously emitted light, since the recess is formed to be point-symmetric with respect to the center of the laser medium, it is possible to suppress non-uniformity of the temperature distribution in the excitation region of the laser medium and improve the quality of the laser light.

[0014] The laser medium unit of the present invention may also be [8] "the laser medium unit according to any one of [1] to [7] above, wherein the holder has a plurality of recesses, each of which is the recess." In this case, spontaneous emission light can be more reliably emitted into the plurality of spaces between the side surface of the laser medium and the inner surfaces of the plurality of recesses, and parasitic oscillation can be further suppressed. In addition, the area of ​​the contact region between the side surface of the laser medium and the holder can be reduced. As a result, the transfer of heat from the holder generated by the absorption of spontaneous emission light to the laser medium can be further suppressed, and the quality of the laser light can be improved.

[0015] The laser medium unit of the present invention may also be the laser medium unit described in [8] above, wherein the plurality of recesses are formed to be point-symmetric with respect to the center of the laser medium when viewed from the direction intersecting the pair of end faces. In this case, even if the temperature of the inner surfaces of the plurality of recesses rises due to the absorption of spontaneously emitted light, the plurality of recesses are formed to be point-symmetric with respect to the center of the laser medium, so that the non-uniformity of the temperature distribution in the excitation region of the laser medium can be suppressed and the quality of the laser light can be improved.

[0016] The laser medium unit of the present invention may also be

[10] "the laser medium unit according to [8] or [9] above, wherein a plurality of regions located between the openings of the plurality of recesses on the surface of the holder are in contact with the side surface." In this case, the laser medium can be held in a more stable state by the holder.

[0017] The laser medium unit of the present invention may also be

[11] "the laser medium unit according to any one of [1] to

[10] above, wherein the holder has a through hole formed therein that connects the space with the space outside the holder." In this case, spontaneously emitted light emitted from the side surface of the laser medium into the space between the side surface and the inner surface of the recess is emitted to the space outside the holder through the through hole. This further suppresses parasitic oscillation.

[0018] The laser medium unit of the present invention may also be

[12] "the laser medium unit according to any one of [1] to

[11] above, wherein the holder has a contact portion that contacts the laser medium, and the contact portion is made of resin." In this case, the contact portion that contacts the laser medium is made of a resin, which is generally more flexible than metal, for example, thereby reducing the stress applied from the holder to the laser medium. This allows the holder to hold the laser medium in a more stable state while suppressing parasitic oscillations. In addition, although resins generally have lower thermal conductivity than metals, in the above laser medium unit, the contact area between the holder and the laser medium is reduced by forming a recess. Therefore, heat generated in the holder is less likely to be transferred to the laser medium, which can suppress non-uniformity of the temperature distribution in the excitation region of the laser medium and improve the quality of the laser light.

[0019] The laser medium unit of the present invention may also be

[13] "the laser medium unit according to

[12] above, wherein the holder has a non-contact portion that does not come into contact with the laser medium, and the non-contact portion is made of metal." In this case, the contact portion that comes into contact with the laser medium is insulated from the laser medium, while the non-contact portion is made of metal, which has a higher thermal conductivity than resin, so that the heat transmitted from the laser medium to the holder through the space can be quickly released to the outside.

[0020] The laser medium unit of the present invention may also be

[14] "the laser medium unit according to any one of [1] to

[13] above, wherein the holder comprises a light absorbing portion formed in the recess and absorbing spontaneously emitted light generated in the laser medium." In this case, spontaneously emitted light emitted from the side surface of the laser medium into the space between the side surface and the inner surface of the recess is absorbed by the light absorbing portion. This further suppresses parasitic oscillation.

[0021] The laser medium unit of the present invention may also be

[15] "the laser medium unit according to

[14] above, wherein the light absorbing portion is formed of a light absorber, and the light absorber is arranged away from the laser medium in the recess." In this case, spontaneously emitted light emitted from the side surface of the laser medium into the space between the side surface and the inner surface of the recess is absorbed by the light absorber. This further suppresses parasitic oscillation. Furthermore, even if heat is generated in the light absorber due to the absorption of spontaneously emitted light, the heat generated is less likely to be transferred to the laser medium because the light absorber is arranged away from the laser medium. This suppresses non-uniformity of the temperature distribution in the excitation region of the laser medium and improves the quality of the laser light.

[0022] The laser medium unit of the present invention may also be

[16] "the laser medium unit described in

[14] above, wherein the light absorbing portion is formed of a light absorbing paint." In this case, the light absorbing portion can be easily formed.

[0023] The laser medium unit of the present invention may also be "

[17] the laser medium unit according to any one of [1] to

[16] above, wherein the laser medium is configured not to include a light absorption region having an absorption rate of 90% or more with respect to spontaneous emission light generated in the laser medium". When the laser medium includes a light absorption region having an absorption rate of 90% or more with respect to spontaneous emission light, the high heat generated when the light absorption region absorbs the spontaneous emission light is directly transmitted to the excitation region of the laser medium. In the above laser medium unit, since the laser medium is configured not to include a light absorption region having an absorption rate of 90% or more with respect to spontaneous emission light, such direct transmission of heat is suppressed. Therefore, it is possible to suppress the non-uniformity of the temperature distribution in the excitation region of the laser medium and improve the quality of the laser light. Further, when forming (bonding) a light absorption region in the laser medium, there is a possibility that stress distortion may occur in the laser medium, but in the above laser medium unit, the occurrence of such stress distortion is suppressed. Therefore, it is possible to suppress the deterioration of the characteristics of the laser medium and improve the quality of the laser light.

[0024] The laser medium unit of the present invention may also be "

[18] the laser medium unit according to any one of [1] to

[17] above, wherein the laser medium includes a light absorption region having an absorption rate of less than 90% with respect to spontaneous emission light generated in the laser medium". In this case, the spontaneous emission light generated in the laser medium is appropriately absorbed by the light absorption region having an absorption rate of less than 90% with respect to the spontaneous emission light, and the spontaneous emission light transmitted through the light absorption region is emitted, for example, from the side surface of the laser medium to the space between the side surface and the inner surface of the concave portion, and parasitic oscillation is suppressed. Further, excessive temperature rise of the light absorption region due to absorption of the spontaneous emission light is suppressed, it is possible to suppress the non-uniformity of the temperature distribution in the excitation region of the laser medium, and improve the quality of the laser light.

[0025] The laser medium unit of the present invention may be "

[19] the laser medium unit according to any one of [1] to

[18] above, wherein the holder is in contact with each of the pair of end faces". In this case, the laser medium can be held in a more stable state by the holder.

[0026] The laser medium unit of the present invention may be "

[20] the laser medium unit according to

[19] above, wherein the holder has a restricting portion that contacts the side surface and restricts the movement of the laser medium in a direction perpendicular to the direction intersecting the pair of end faces". In this case, the movement of the laser medium is restricted by the restricting portion, and a predetermined space can be more reliably formed between the side surface of the laser medium and the concave portion of the holder.

Advantages of the Invention

[0027] According to the present invention, it is possible to provide a laser medium unit that can improve the quality of laser light while suppressing parasitic oscillation.

Brief Description of the Drawings

[0028] [Figure 1] It is a diagram showing the overall configuration of a laser device according to an embodiment. [Figure 2] It is a perspective view showing the laser medium unit shown in FIG. 1. [Figure 3] It is a perspective view showing the laser medium and the holder shown in FIG. 2. [Figure 4] It is a plan view showing the laser medium and the holder shown in FIG. 2. [Figure 5] It is a cross-sectional view of the laser medium and the holder along the line V-V shown in FIG. 4. [Figure 6] It is a diagram showing the internal configuration of the laser medium and the holder shown in FIG. 2. [Figure 7] It is a diagram showing the configuration of the holder shown in FIG. 2. [Figure 8] It is a diagram schematically showing the path of spontaneous emission light in the laser medium of the laser medium unit according to Comparative Example 1. [Figure 9] This figure schematically shows the path of spontaneously emitted light in the laser medium of the laser medium unit according to the first embodiment. [Figure 10] This is a plan view showing the laser medium and holder according to the first modified example. [Figure 11] Figure 10 is a cross-sectional view of the laser medium and holder along the line XI-XI shown. [Figure 12] Figure 10 shows the internal configuration of the laser medium and the holder. [Figure 13] This is a plan view showing the laser medium and holder according to the second modified example. [Figure 14] Figure 13 is a cross-sectional view of the laser medium and holder along the line XIV-XIV shown. [Figure 15] This figure shows the temperature distribution in the laser medium of the laser medium unit according to Comparative Example 2. [Figure 16] This figure shows the temperature distribution in the laser medium of the laser medium unit according to Example 1. [Figure 17] This figure shows the temperature distribution in the laser medium of the laser medium unit according to Example 2. [Figure 18] This is a perspective view showing the laser medium and holder according to the second embodiment. [Figure 19] Figure 18 is a plan view showing the laser medium and holder. [Figure 20] Figure 19 shows a cross-sectional view of the laser medium and holder along the line XX-XX. [Figure 21] This is a plan view showing the laser medium and holder according to the third modified example. [Figure 22] Figure 21 is a cross-sectional view of the laser medium and holder along the line XXII-XXII shown. [Figure 23] This is a diagram showing a modified example of the holder. [Figure 24] This figure shows a modified example of a laser medium. [Figure 25] Figure 24 schematically shows the path of spontaneously emitted light in a laser medium. [Figure 26] This figure shows a modified example of a laser medium. [Modes for carrying out the invention]

[0029] An example of the present invention will be described in detail below with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant explanations are omitted. [First Embodiment] [Laser device]

[0030] As shown in Figure 1, the laser apparatus 1 of the first embodiment comprises a plurality of laser medium units 10, a chamber 2, a laser light source 3, and a plurality of excitation light sources 4. Each laser medium unit 10 is arranged with gaps between them along the Z-axis direction. Hereinafter, one direction intersecting the Z-axis direction will be referred to as the X-axis direction, and the direction intersecting the Z-axis direction and the X-axis direction will be referred to as the Y-axis direction. In this embodiment, the X-axis direction, the Y-axis direction, and the Z-axis direction are orthogonal to each other.

[0031] Chamber 2 comprises a main body 21, a pair of window sections 22, an introduction section 25, and an exit section 26. The main body 21 has a space S1 for housing a plurality of laser medium units 10. The main body 21 has a pair of openings 21a and a pair of openings 21b. The pair of openings 21a face each other in the Z-axis direction. The pair of openings 21b face each other in the Y-axis direction.

[0032] Each window section 22 is attached to the main body section 21 so as to close each opening 21a. Each window section 22 includes a frame 23 and a window member 24 held by the frame 23. The window member 24 transmits the laser light L1 and excitation light L2, which will be described later.

[0033] The introduction section 25 has an introduction passage 25a. The introduction section 25 is attached to the main body 21 such that the introduction passage 25a communicates with space S1 through an opening 21b. The introduction section 25 introduces a refrigerant M (for example, a cooling gas such as low-temperature helium gas) into space S1. The refrigerant M flows in space S1 through a gap formed between adjacent laser medium units 10. The outlet section 26 has an outlet passage 26a. The outlet section 26 is attached to the main body 21 such that the outlet passage 26a communicates with space S1 through an opening 21b. The outlet section 26 discharges the refrigerant M from space S1.

[0034] The laser light source 3 is positioned on one side in the Z-axis direction relative to the chamber 2 (multiple laser medium units 10). The laser light source 3 emits a seed laser beam L1 to the multiple laser medium units 10. The laser diameter of the laser beam L1 is, for example, about 60 mm. The laser beam L1 emitted from the laser light source 3 enters the multiple laser medium units 10 through the window member 24 of the window portion 22, which is positioned on one side in the Z-axis direction relative to the multiple laser medium units 10. The laser beam L1 is amplified by each laser medium unit 10.

[0035] The multiple excitation light sources 4 include a pair of first excitation light sources 41 and a pair of second excitation light sources 42. In this example, each of the pair of first excitation light sources 41 and the pair of second excitation light sources 42 has a configuration in which multiple (about 10) laser diode (LD) bars, each having multiple light-emitting regions arranged in an array, are stacked. The pair of first excitation light sources 41 are located on one side in the Z-axis direction with respect to the chamber 2 (multiple laser medium units 10). Each first excitation light source 41 emits excitation light L2 to the multiple laser medium units 10. The excitation light L2 emitted from each first excitation light source 41 is incident on the multiple laser medium units 10 through a window member 24 of a window portion 22 located on one side in the Z-axis direction with respect to the multiple laser medium units 10. The pair of second excitation light sources 42 are located on the other side in the Z-axis direction with respect to the chamber 2 (multiple laser medium units 10). Each second excitation light source 42 emits excitation light L2 to the multiple laser medium units 10. The excitation light L2 emitted from each second excitation light source 42 enters the multiple laser medium units 10 through the window member 24 of the window portion 22, which is located on the other side in the Z-axis direction relative to the multiple laser medium units 10. The excitation light L2 excites the laser medium 50, which will be described later. [Laser medium unit]

[0036] The details of the laser medium unit 10 will be described with reference to Figures 2 to 7. Figure 6 is a diagram showing the internal configuration of the laser medium 50 and the holder 60, which will be described later, and is a half-cross-sectional view in which a part of the laser medium 50 and the holder 60 is cut in a cross-section along the X and Y axes. The laser medium unit 10 comprises the laser medium 50, the holder 60, and the frame 70. The laser medium 50 has a pair of end faces 51a, 51b and a side surface 51c. The laser medium 50 has thickness in the Z-axis direction and has a plate-like shape with the pair of end faces 51a, 51b as its main surfaces. In this example, the laser medium 50 has a disc-like shape. The pair of end faces 51a, 51b intersect in the Z-axis direction. End face 51b is located on the opposite side from end face 51a in the Z-axis direction.

[0037] The side surface 51c of the laser medium 50 intersects with a pair of end faces 51a and 51b. The side surface 51c is aligned with the Z-axis direction. When viewed from the direction intersecting the pair of end faces 51a and 51b (Z-axis direction), the side surface 51c defines the outer edge of the laser medium 50. That is, the side surface 51c has a circular shape when viewed from the Z-axis direction. When viewed from the Z-axis direction, the center of the circle defined by the side surface 51c coincides with the center C of the laser medium 50. The side surface 51c has a predetermined width in the Z-axis direction. The thickness of the laser medium 50 (width of the side surface 51c in the Z-axis direction) is, for example, several millimeters to several tens of millimeters. The diameter of the laser medium 50 (width in the direction perpendicular to the Z-axis direction) is, for example, about 100 mm.

[0038] The laser medium 50 is a solid-state laser medium. The material of the laser medium 50 is, for example, YAG doped with an active element such as Yb or Nd. In this example, the entire laser medium 50 is formed of YAG doped with the active element. The laser medium 50 is constructed without including a light absorption region where the absorptive absorption rate for spontaneously emitted light generated in the laser medium 50 is 90% or more. That is, the absorptive absorption rate for spontaneously emitted light in the laser medium 50 is less than 90%. The spontaneously emitted light generated in the laser medium 50 may be, for example, light between 1000 nm and 1100 nm. Absorptive absorption rate is the absorptive absorption rate per 1 cm of absorption length.

[0039] The laser medium 50 is excited by the excitation light L2 and emits light. Figure 4 shows the region (excitation region 52) irradiated by the excitation light L2. As described above, the first excitation light source 41 and the second excitation light source 42 each have a configuration in which multiple laser diode (LD) bars are stacked. As a result, rectangular excitation light L2 is irradiated onto the laser medium 50. Therefore, when viewed from the Z-axis direction, the excitation region 52 has a rectangular shape. In this example, the width of the excitation region 52 in the X-axis direction is wider than the width in the Y-axis direction. The width of the excitation region 52 in the X-axis direction is, for example, about 80 mm. The width of the excitation region 52 in the Y-axis direction is, for example, about 60 mm. From the viewpoint of energy efficiency, it is preferable that the width of the excitation region 52 is close to the laser diameter of the seed light, the laser beam L1, but it does not have to be the same. The emitted light that is output is, for example, stimulated emission light. The stimulated emission light contributes to the optical amplification of the laser beam L1.

[0040] The holder 60 is positioned along the side surface 51c of the laser medium 50 when viewed from the Z-axis direction and holds the laser medium 50. In this example, the holder 60 is formed in a frame shape that surrounds the side surface 51c of the laser medium 50 when viewed from the Z-axis direction. The surface 61 of the holder 60 has an inner surface 61a, an outer surface 61b, and a pair of sides 61c, 61d.

[0041] The inner surface 61a extends along the side surface 51c of the laser medium 50 when viewed from the Z-axis direction. In this example, the inner surface 61a is circular when viewed from the Z-axis direction. The outer surface 61b is rectangular when viewed from the Z-axis direction. Each of the inner surface 61a and outer surface 61b of the holder 60 has a predetermined width in the Z-axis direction (the thickness direction of the holder 60). The thickness of the holder 60 (i.e., the width of each of the inner surface 61a and outer surface 61b in the Z-axis direction) is, for example, several millimeters to several tens of millimeters. The thickness of the holder 60 is approximately the same as the thickness of the laser medium 50. The pair of sides 61c and 61d intersect in the Z-axis direction. Side 61c is located on the opposite side from side 61d in the Z-axis direction.

[0042] As an example, the material of the holder 60 may be resin or metal. The resin may be, for example, a fluororesin such as polytetrafluoroethylene (PTFE). The metal may be, for example, aluminum. As another example, the material of the holder 60 may be a ceramic (such as black alumina) that absorbs light in the wavelength range of spontaneously emitted light generated in the excitation region 52 (for example, about 1000 nm to 1100 nm). In this example, the entire holder 60, including the contact portion 63 that contacts the laser medium 50, is made of the same material. Specifically, the entire holder 60, including the contact portion 63, is made of resin (PTFE). In this example, the contact portion 63 is in contact with the side surface 51c of the laser medium 50.

[0043] The holder 60 has a plurality of recesses 62 formed therein. The plurality of recesses 62 are formed on the inner surface 61a. As shown in Figure 4, the plurality of recesses 62 are formed at a constant distance from each other in the direction A (the direction along the side surface 51c of the laser medium 50) surrounding the center C of the laser medium 50 when viewed from the Z-axis direction. The plurality of recesses 62 are formed to be point-symmetric with respect to the center C of the laser medium 50 when viewed from the Z-axis direction. That is, when the plurality of recesses 62 are rotated 180° with respect to the center C, the arrangement of the plurality of recesses 62 matches the arrangement before rotation. The plurality of recesses 62 are formed to be line-symmetric with respect to a straight line L passing through the center C and the bottom 62b when viewed from the Z-axis direction. Each recess 62 opens toward the center C side (towards the inner region) of the laser medium 50 when viewed from the Z-axis direction. The recesses 62 have an opening 62a on the inner surface 61a.

[0044] The recess 62 has a shape that tapers from the opening 62a towards the bottom 62b. That is, the internal space of the recess 62 narrows as it approaches the bottom 62b from the opening 62a. Specifically, the recess 62 has a conical shape. In this example, the recess 62 has an elliptical conical shape. The inner surface 62c of the recess 62 corresponds to the side surface of the cone. As shown in Figure 7, the opening 62a of the recess 62 has an elliptical shape with a minor axis along the Z-axis direction. The recess 62 is formed to be symmetric with respect to a line passing through the center C (line L in this example) when viewed from the Z-axis direction (see Figure 4). In this example, the shape of the recess 62 when viewed from the Z-axis direction is an isosceles triangle with the bottom 62b as the vertex and the base (the part corresponding to the inner surface 61a) curving inward.

[0045] The holder 60 further comprises a plurality of locking portions (claw portions) 69. The locking portions 69 are shown in Figures 2, 3, and 6, and are not shown in the other drawings. A pair of locking portions 69 is provided on the side surface 61c of the holder 60. Similarly, a pair of locking portions 69 is provided on the side surface 61d of the holder 60. On both the side surface 61c and the side surface 61d of the holder 60, each locking portion 69 protrudes inward from the inner surface 61a when viewed from the Z-axis direction. Each of the pair of locking portions 69 provided on the side surface 61c faces (overlaps with) the corresponding locking portion 69 of the pair of locking portions 69 provided on the side surface 61d in the Z-axis direction.

[0046] The holder 60 surrounds the laser medium 50 when viewed from the Z-axis direction. In other words, the laser medium 50 is located inside the holder 60. When viewed from the Z-axis direction, the diameter of the laser medium 50 is approximately the same as the diameter of the inner surface 61a of the holder 60. The movement of the laser medium 50 in the direction perpendicular to the Z-axis direction is restricted by the holder 60. The laser medium 50 is held in place by a plurality of locking parts 69 in the Z-axis direction. The movement of the laser medium 50 in the Z-axis direction is restricted by a plurality of locking parts 69. Thus, the laser medium 50 is held inside the holder 60 by the holder 60.

[0047] The laser medium 50 and the holder 60 are in contact with each other. The laser medium 50 and the holder 60 are in direct contact without any other components in between. Specifically, the side surface 51c of the laser medium 50 and the inner surface 61a of the holder 60 are in contact with each other. The holder 60 holds the laser medium 50 such that a space S2 is formed between the side surface 51c of the laser medium 50 and the inner surface 62c of each recess 62. In this example, air is present in space S2, and no solid or liquid substances are placed there. The side surface 51c includes a region R1 that is in contact with the holder 60 (inner surface 61a) and a region R2 that is not in contact with the holder 60. In this example, region R2 is the region facing space S2.

[0048] The holder 60 has multiple spaces S2 corresponding to multiple recesses 62. The multiple spaces S2 are formed at a constant distance from each other in the direction A surrounding the center C when viewed from the Z-axis direction. As shown in Figure 4, multiple regions R3 located between the openings 62a of the multiple recesses 62 on the surface 61 (inner surface 61a) of the holder 60 are in contact with the side surface 51c of the laser medium 50. That is, multiple regions R3 aligned in direction A on the inner surface 61a are in contact with the side surface 51c.

[0049] The laser medium 50 and the holder 60 are in continuous and gapless contact in region R1. The laser medium 50 and the holder 60 are in close contact with each other in region R1. On the other hand, the laser medium 50 and the holder 60 are not in contact in region R2. The laser medium 50 and the holder 60 are spatially separated in region R2 via space S2. The proportion of region R1 to the entire surface 51c of the laser medium 50 (sum of regions R1 and R2) (contact ratio) is, for example, 5% or more and 90% or less. The upper limit of the contact ratio is preferably 90% or less, more preferably 70% or less, even more preferably 50% or less, and even more preferably 30% or less. By reducing the contact ratio, spontaneous emission light can be more reliably emitted from the surface 51c of the laser medium 50 into the space between the surface 51c and the inner surface 62c of the recess 62, and heat insulation between the laser medium 50 and the holder 60 can be more reliably achieved. The lower limit of the contact ratio is preferably 5% or more, and more preferably 10% or more. Increasing the contact ratio prevents localized concentration of stress applied from the holder 60 to the side surface 51c of the laser medium 50. In this example, the proportion of region R1 to the entire side surface 51c is about 10%.

[0050] The frame 70 is formed in a frame shape that surrounds the outer surface 61b of the holder 60 when viewed from the Z-axis direction. In this example, the frame 70 is formed in a rectangular frame shape when viewed from the Z-axis direction. The frame 70 holds the holder 60. The holder 60 is held by the frame 70 by being fitted inside the frame 70. That is, the inner edge of the frame 70 when viewed from the Z-axis direction coincides with the outer edge (outer surface 61b) of the holder 60.

[0051] The frame 70 has a pair of first parts 71 extending along the X-axis and a pair of second parts 72 extending along the Y-axis. The width of the first parts 71 in the Y-axis direction is wider than the width of the second parts 72 in the X-axis direction. Each of the pair of first parts 71 has a wedge-shaped fin 73 formed thereon. The fins 73 are formed such that their width in the Z-axis direction decreases as they move away from the center C of the laser medium 50 along the Y-axis direction. In this example, the fins 73 are formed in a triangular prism shape. The presence of the fins 73 in the frame 70 allows the coolant M introduced into the space S1 to flow smoothly between the multiple laser medium units 10. The width of the frame 70 in the Y-axis direction (the width of the entire laser medium unit 10 in the Y-axis direction) is, for example, about 30 cm to 40 cm. The thickness of the frame 70 in the Z-axis direction is, for example, about a few millimeters to several tens of millimeters. The thickness of the frame 70 is approximately the same as the thickness of the laser medium 50. The material of the frame 70 may be, for example, metal. The metal may be, for example, aluminum. In this example, the entire frame 70 is made of the same material. Specifically, the entire frame 70 is made of aluminum. [Mechanism of Action and Effects]

[0052] In the laser medium unit 10, the holder 60 holds the laser medium 50 such that a space S2 is formed between the side surface 51c of the laser medium 50 and the inner surface 62c of the recess 62 formed in the holder 60. Parasitic oscillation occurs when spontaneously emitted light generated in the excitation region of the laser medium repeatedly passes through that excitation region. In the laser medium unit 10, spontaneously emitted light generated in the excitation region 52 is emitted from the side surface 51c of the laser medium 50 into space S2. The emitted spontaneously emitted light is scattered by repeated reflection from the inner surface 62c of the recess 62 and does not easily return to the excitation region 52. Therefore, parasitic oscillation is suppressed. In addition, in the laser medium unit 10, even if heat is generated on the inner surface 62c of the recess 62 by absorbing spontaneously emitted light, the heat is not easily transferred to the laser medium 50 because a space S2 is formed between the inner surface 62c of the recess 62 and the side surface 51c of the laser medium 50. Therefore, the non-uniformity of the temperature distribution in the excitation region 52 can be suppressed, and the quality of the laser light L1 can be improved. Thus, the laser medium unit 10 can improve the quality of the laser light L1 while suppressing parasitic oscillations.

[0053] Furthermore, the laser medium unit 10 can suppress parasitic oscillations without forming (or joining) cladding materials or other components to the laser medium 50 itself to absorb spontaneously emitted light. Therefore, there is no need to consider the yield when forming such components in the laser medium 50, and material costs are reduced. Thus, the laser medium unit 10 can improve manufacturing efficiency.

[0054] Here, the operation and effects of the laser medium unit 10 will be described in more detail with reference to Figures 8 and 9. Figure 8 is a schematic diagram showing the path of spontaneously emitted light L10 in the laser medium 550 of the laser medium unit according to Comparative Example 1. Figure 9 is a schematic diagram showing the path of spontaneously emitted light L10 in the laser medium 50 of the laser medium unit 10 according to the first embodiment. In the example shown in Figure 8, no recess is formed in the holder 560, and the entire side surface 551c of the laser medium 550 is in contact with the holder 560.

[0055] In the example shown in Figure 8, since no recess is formed in the holder 560 (because space S2 does not exist), the spontaneously emitted light L10 generated in the excitation region 552 of the laser medium 50 is reflected at the interface between the side surface 51c of the laser medium 50 and the holder 60, without being emitted to the outside from the laser medium 50. As a result, the spontaneously emitted light L10 repeatedly passes through the excitation region 52, making parasitic oscillation likely to occur. In contrast, in the example shown in Figure 9, the spontaneously emitted light L10 generated in the excitation region 52 is emitted from the side surface 51c of the laser medium 50 into space S2. The emitted spontaneously emitted light L10 is scattered by repeated reflection at the inner surface 62c of the recess 62, as shown in Figure 9, and is unlikely to return to the excitation region 52. Therefore, according to the laser medium unit 10 of this embodiment, parasitic oscillation is suppressed.

[0056] The holder 60 is formed in a frame shape that surrounds the laser medium 50 when viewed from the Z-axis direction. This allows the holder 60 to hold the laser medium 50 in a more stable state.

[0057] The recess 62 has a shape that tapers towards the bottom 62b of the recess 62. This increases the number of times the spontaneously emitted light emitted from the side surface 51c of the laser medium 50 is reflected by the inner surface 62c of the recess 62, thereby efficiently scattering the spontaneously emitted light in the recess 62. This further suppresses parasitic oscillations.

[0058] The proportion of the contact area (region R1) with the holder 60 on the side surface 51c of the laser medium 50 to the entire side surface 51c is 50% or less. This allows for more reliable emission of spontaneously emitted light from the side surface 51c of the laser medium 50 into space S2, further suppressing parasitic oscillations.

[0059] The holder 60 is in contact with the side surface 51c of the laser medium 50. This allows the holder 60 to hold the laser medium 50 in a more stable state while suppressing parasitic oscillations.

[0060] The proportion of region R1 to the entire surface 51c of the laser medium 50 is 5% or more. This prevents localized concentration of stress from the holder 60 on the surface 51c of the laser medium 50. As a result, parasitic oscillations are suppressed, and the laser medium 50 can be held in a more stable state by the holder 60.

[0061] Multiple recesses 62 are formed in the holder 60. This allows spontaneous emission light to be more reliably emitted from the side surface 51c of the laser medium 50 into multiple spaces S2, further suppressing parasitic oscillation. In addition, the area of ​​the contact region (region R1) between the holder 60 and the side surface 51c can be reduced. This further suppresses the transfer of heat from the holder 60, generated by the absorption of spontaneous emission light, to the laser medium 50, thereby improving the quality of the laser light L1.

[0062] Multiple recesses 62 are formed so as to be point-symmetric with respect to the center C of the laser medium 50 when viewed from the Z-axis direction. As a result, even if the temperature of the inner surface 62c of the multiple recesses 62 rises due to the absorption of spontaneously emitted light, the non-uniformity of the temperature distribution in the excitation region 52 of the laser medium 50 can be suppressed because the multiple recesses 62 are formed so as to be point-symmetric with respect to the center C of the laser medium 50, thereby improving the quality of the laser light L1.

[0063] Multiple regions R3 located between the openings 62a of multiple recesses 62 on the surface of the holder 60 are in contact with the side surface 51c of the laser medium 50. This allows the holder 60 to hold the laser medium 50 in a more stable state.

[0064] The holder 60 has a contact portion 63 that contacts the laser medium 50. The contact portion 63 is made of resin. Because the contact portion 63 is made of resin, which is generally more flexible than metal, the stress applied from the holder 60 to the laser medium 50 is reduced. This allows the holder 60 to hold the laser medium 50 in a more stable state while suppressing parasitic oscillations. In addition, although resin generally has lower thermal conductivity than metal, in the laser medium unit 10, the contact area between the holder 60 and the side surface 51c is reduced by the formation of a recess 62. Therefore, heat generated in the holder 60 is less likely to be transferred to the laser medium 50, which can suppress non-uniformity of the temperature distribution in the excitation region 52 of the laser medium 50 and improve the quality of the laser light L1.

[0065] The laser medium 50 is configured without including a light-absorbing region where the absorptive efficiency for spontaneously emitted light is 90% or more. When a laser medium includes a light-absorbing region where the absorptive efficiency for spontaneously emitted light is 90% or more, the high heat generated when the light-absorbing region absorbs the spontaneously emitted light is directly transferred to the excitation region of the laser medium. In the laser medium unit 10, since the laser medium 50 is configured without including a light-absorbing region where the absorptive efficiency for spontaneously emitted light is 90% or more, such direct heat transfer is suppressed. Therefore, the non-uniformity of the temperature distribution in the excitation region 52 of the laser medium 50 can be suppressed, and the quality of the laser light L1 can be improved. In addition, when a light-absorbing region is formed (bonded) to the laser medium, stress strain may occur in the laser medium, but the occurrence of such stress strain is suppressed in the laser medium unit 10. Therefore, the deterioration of the properties of the laser medium 50 can be suppressed, and the quality of the laser light L1 can be improved. [Modified version of the first embodiment]

[0066] Next, a modified example of the laser medium unit 10 according to the first embodiment will be described. First, the laser medium unit 10 according to the first modified example will be described with reference to Figures 10, 11, and 12. Figure 12 is a diagram showing the internal configuration of the laser medium 50 and the holder 60, and is a half-cross-sectional view in which a part of the laser medium 50 and the holder 60 is cut in a cross-section along the X and Y axes. In Figures 10 to 12, the locking portion 69 is not shown.

[0067] In the first modified example, multiple through-holes 64 are formed in the holder 60, connecting multiple spaces S2 with the external space of the holder 60. Each through-hole 64 connects the corresponding space S2 with the external space of the holder 60. Each through-hole 64 opens to the side surfaces 61c and 61d. The through-holes 64 are formed to penetrate the recess 62 in the Z-axis direction (passing through the space S2 inside the recess 62). Air is present inside the through-holes 64, and no solid or liquid substances are placed there.

[0068] The inner surface 64a of the through-hole 64, which defines the through-hole 64, is circular when viewed from the Z-axis direction. An opening 64b is formed in the inner surface 64a. The space inside the through-hole 64 is in communication with space S2 through the opening 64b. As a result, space S2 is spatially connected to the space outside the laser medium unit 10 through the through-hole 64. The refrigerant M (see Figure 1) introduced into space S1 enters space S2 through the through-hole 64.

[0069] In this modified example, the holder 60 has through-holes 64 that connect the space S2 with the space outside the holder 60. As a result, spontaneously emitted light from the side surface 51c of the laser medium 50 into space S2 is emitted into the space outside the holder 60 through the through-holes 64. Therefore, parasitic oscillation can be further suppressed. In addition, the coolant M enters space S2 through the through-holes 64 and comes into contact with the side surface 51c. This allows the laser medium 50 to be cooled efficiently.

[0070] Next, with reference to Figures 13 and 14, a second modified example of the laser medium unit 10 will be described. In the second modified example, the holder 60 includes a light-absorbing section 65a formed by a light-absorbing material 65. The light-absorbing section 65a is formed in a recess 62. The light-absorbing section 65a absorbs spontaneously emitted light generated in the laser medium 50. The absorption rate of the light-absorbing section 65a with respect to spontaneously emitted light is 0.1% or more, more preferably 1% or more, even more preferably 5% or more, even more preferably 10% or more, and even more preferably 50% or more. In this example, the absorption rate of the light-absorbing section 65a with respect to spontaneously emitted light is 80% or more. By having an absorption rate of 0.1% or more for the light-absorbing section 65a with respect to spontaneously emitted light, the spontaneously emitted light is attenuated each time it is incident on (hits) the light-absorbing section 65a, ultimately preventing parasitic oscillation. The material of the light-absorbing section 65a (light-absorbing material 65) may be, for example, Cr-doped YAG.

[0071] The light absorber 65 extends in an annular shape when viewed from the Z-axis direction. In this example, the light absorber 65 extends continuously in an annular shape. The center of the light absorber 65 when viewed from the Z-axis direction coincides with the center C of the laser medium 50. The light absorber 65 is arranged to pass through a plurality of recesses 62. Specifically, the light absorber 65 is continuously arranged in the portion between the plurality of recesses 62 in the holder 60, and within the interior of the plurality of recesses 62 (space S2). The light absorber 65 is fitted into an annular groove formed in the holder 60 (space that opens on the sides 61c, 61d of the holder 60). The light absorber 65 is exposed to the external space of the holder 60 on the sides 61c, 61d. In the recesses 62, the light absorber 65 is located away from the side 51c of the laser medium 50. That is, there is space S2 between the light absorber 65 and the side 51c. In this example, the light absorber 65 is located inside the bottom 62b of each recess 62 when viewed from the Z-axis direction (there is a space between the light absorber 65 and the bottom 62b).

[0072] In this modified example, the holder 60 is provided with a light-absorbing section 65a formed in the recess 62, which absorbs spontaneously emitted light generated in the laser medium 50. As a result, spontaneously emitted light emitted from the side surface 51c of the laser medium 50 into space S2 is absorbed by the light-absorbing section 65a. This further suppresses parasitic oscillation.

[0073] The light-absorbing section 65a is formed by a light-absorbing body 65, which is positioned away from the laser medium 50 in the recess 62. As a result, even if heat is generated in the light-absorbing body 65 due to the absorption of spontaneously emitted light, the heat generated is less likely to be transferred to the laser medium 50 because the light-absorbing body 65 is positioned away from the laser medium 50. This suppresses the non-uniformity of the temperature distribution in the excitation region 52 of the laser medium 50, thereby improving the quality of the laser light L1.

[0074] In this modified example, the light absorber 65 is located inside the bottom 62b of each recess 62 when viewed from the Z-axis direction, but the light absorber 65 may be positioned so as to overlap with the bottom 62b when viewed from the Z-axis direction. Also, in this modified example, the holder 60 has one continuous light absorber 65, but the holder 60 may have multiple light absorbers 65 (separate light absorbers 65) each positioned in the corresponding recess 62. [Examples]

[0075] The temperature distribution in the laser medium 50 will be explained with reference to Figures 15, 16, and 17. Figure 15 is a diagram showing the temperature distribution in the laser medium 650 of the laser medium unit according to Comparative Example 2. Figure 16 is a diagram showing the temperature distribution in the laser medium 50 of the laser medium unit 10 according to Example 1. Figure 17 is a diagram showing the temperature distribution in the laser medium 50 of the laser medium unit 10 according to Example 2. Figures 15 to 17 show the simulation results of the temperature distribution in the laser medium.

[0076] In Comparative Example 2, shown in Figure 15, a light-absorbing region 655 formed by Cr-doped YAG is formed on the outer edge of the laser medium 650. Also in Comparative Example 2, no recesses are formed in the holder 660, and the entire side surface 651c of the laser medium 650 is in contact with the holder 660. Example 1, shown in Figure 16, has the configuration of the first embodiment described above. That is, a plurality of recesses 62 are formed in the holder 60, and a plurality of spaces S2 are formed between the side surface 51c of the laser medium 50 and the inner surface 62c of the plurality of recesses 62. Example 2, shown in Figure 17, has the configuration of the first modified example described above. That is, in Example 2, in addition to the plurality of recesses 62, a plurality of through holes 64 are formed in the holder 60. In all of Comparative Example 2 and Examples 1 and 2, the material of the holder was PTFE resin.

[0077] Other simulation conditions were as follows: In Comparative Example 2 shown in Figure 15, it was assumed that 67 W of heat was generated in the excitation region 652 and 210 W of heat was generated in the light absorption region 655. In Examples 1 and 2 shown in Figures 16 and 17, it was assumed that 67 W of heat was generated in the excitation region 52 and 210 W of heat was generated on the inner surface 62c of the recess 62. In both Comparative Example 2 and Examples 1 and 2, the incoming refrigerant was cooling helium gas, the refrigerant flow rate was 30 m / s, the pressure was 0.5 MPa, and the temperature was 150 K.

[0078] As shown in Figures 15 to 17, the temperature distributions of Examples 1 and 2 were simpler, closer to concentric circles with respect to the center of the laser medium, compared to the temperature distribution of Comparative Example 2. Furthermore, the specific simulation results in the excitation region (width 80 mm in the X-axis direction × width 60 mm in the Y-axis direction) are as follows. First, in Comparative Example 2, in excitation region 652, the center temperature was 159.9 K, the average temperature was 161.3 K, the temperature difference (PV value) was 10.2 K, and the temperature difference (standard deviation) was 1.650 K (rms 1.02%). In Example 1, in excitation region 52, the center temperature was 158.2 K, the average temperature was 156.7 K, the temperature difference (PV value) was 4.2 K, and the temperature difference (standard deviation) was 0.982 K (rms 0.62%). In Example 2, in the excitation region 52, the center temperature was 158.3K, the average temperature was 156.8K, the temperature difference (PV value) was 3.7K, and the temperature difference (standard deviation) was 0.897K (rms 0.57%). In other words, in Examples 1 and 2, the temperature difference (PV value) decreased by about 6K compared to Comparative Example 2. Also, in Examples 1 and 2, the standard deviation of the temperature distribution decreased by about 0.4% compared to Comparative Example 2. From these simulation results, it was confirmed that the laser medium unit 10 suppresses the non-uniformity of the temperature distribution in the excitation region 52 of the laser medium 50.

[0079] Furthermore, even in a range narrower than the excitation region (60 mm in width along the X axis × 60 mm in width along the Y axis), the temperature distributions in Examples 1 and 2 were simpler, closer to concentric circles with respect to the center of the laser medium, compared to the temperature distribution in Comparative Example 2. The specific simulation results in this range are as follows: In Comparative Example 2, the center temperature was 159.9 K, the average temperature was 160.6 K, the temperature difference (PV value) was 5.6 K, and the temperature difference (standard deviation) was 0.867 K. In Example 1, the center temperature was 158.2 K, the average temperature was 157.0 K, the temperature difference (PV value) was 3.7 K, and the temperature difference (standard deviation) was 0.870 K. In other words, in the above range narrower than the excitation region, it was confirmed that the temperature difference (PV value) in Example 1 decreased by approximately 2 K compared to Comparative Example 2. [Second Embodiment]

[0080] Next, the laser medium unit 10A according to the second embodiment will be described with reference to Figures 18, 19, and 20. The laser medium unit 10A comprises a laser medium 50, a holder 160, and a frame 70. However, in Figures 18 to 20, the frame 70 is not shown, and only the laser medium 50 and the holder 160 are depicted. The laser medium unit 10A according to the second embodiment may be used in place of the laser medium unit 10 in the laser device 1. The laser medium unit 10A according to the second embodiment differs from the laser medium unit 10 according to the first embodiment in the configuration of the holder. Therefore, in the following description, the holder 160 will be mainly described, and the common points between the second embodiment and the first embodiment may be omitted from the description.

[0081] The holder 160 is positioned along the side surface 51c of the laser medium 50 when viewed from the Z-axis direction and holds the laser medium 50. In this example, the holder 160 is formed in the shape of a circular frame that surrounds the side surface 51c of the laser medium 50 when viewed from the Z-axis direction. The surface 161 of the holder 160 has an inner surface 161a, an outer surface 161b, and a pair of sides 161c, 161d.

[0082] The inner surface 161a extends along the side surface 51c of the laser medium 50 when viewed from the Z-axis direction. In this example, the inner surface 161a has a circular shape when viewed from the Z-axis direction. When viewed from the Z-axis direction, the inner surface 161a is located inside (towards the center C) of the side surface 51c of the laser medium 50. The outer surface 161b has a rectangular shape when viewed from the Z-axis direction. Each of the inner surface 161a and outer surface 161b of the holder 160 has a predetermined width in the Z-axis direction (the thickness direction of the holder 160). The thickness of the holder 160 (i.e., the width of each of the inner surface 161a and outer surface 161b in the Z-axis direction) is, for example, several mm to several tens of mm. The thickness of the holder 160 is greater than the thickness of the laser medium 50. The pair of sides 161c and 161d intersect in the Z-axis direction. Side 161c is located on the opposite side from side 161d in the Z-axis direction.

[0083] The holder 160 has a pair of plate members 170. The holder 160 is composed of a pair of stacked plate members 170. Each plate member 170 includes a main body portion 171 and a wall portion 172. The main body portion 171 is plate-shaped with an opening 173 formed therein. In this example, the main body portion 171 is rectangular. The opening 173 is formed in the center of the main body portion 171 when viewed from the Z-axis direction. The main body portion 171 has an inner surface 171a that defines the opening 173. The opening 173 (inner surface 171a) is circular when viewed from the Z-axis direction. When the pair of plate members 170 are stacked, the inner surface 171a of one plate member 170 and the inner surface 171a of the other plate member 170 constitute the inner surface 161a of the holder 160. When viewed from the Z-axis direction, the shape of the inner surface 171a is identical to the shape of the inner surface 161a.

[0084] The wall portion 172 extends along the outer edge of the main body portion 171 when viewed from the Z-axis direction. The wall portion 172 has an inner surface 172a, an outer surface 172b, and a top surface 172c. The inner surface 172a extends along the side surface 51c of the laser medium 50 when viewed from the Z-axis direction. In this example, the inner surface 172a is circular when viewed from the Z-axis direction. When viewed from the Z-axis direction, the inner surface 172a is located outside the side surface 51c of the laser medium 50. The outer surface 172b is rectangular when viewed from the Z-axis direction. When a pair of plate members 170 are stacked, the outer surface 172b of one plate member 170 and the outer surface 172b of the other plate member 170 constitute the outer surface 161b of the holder 160.

[0085] The pair of plate members 170 are stacked on top of each other such that the top surface 172c of one plate member 170 contacts the top surface 172c of the other plate member 170. A gap is formed between one main body portion 171 and the other main body portion 171, corresponding to the height of the two wall portions 172 in the Z-axis direction. The material of the holder 160 (each plate member 170) may be the same as the material of the holder 60 according to the first embodiment.

[0086] A recess 162 is formed in the holder 160. The recess 162 is formed on the inner surface 161a. As shown in Figure 19, the recess 162 is formed in a continuous annular shape along direction A surrounding the center C of the laser medium 50 when viewed from the Z-axis direction. The recess 162 is formed to be point-symmetric with respect to the center C of the laser medium 50 when viewed from the Z-axis direction. That is, when the recess 162 is rotated 180° with respect to the center C, the arrangement (shape) of the recess 162 matches the arrangement (shape) before rotation. The recess 162 is formed to be line-symmetric with respect to the straight line LA passing through the center C when viewed from the Z-axis direction. The recess 162 opens toward the center C side (towards the inner region) of the laser medium 50 when viewed from the Z-axis direction. The recess 162 has an opening 162a on the inner surface 161a. The bottom 162b of the recess 162 is composed of the inner surfaces 172a of two wall portions 172. The width of the recess 162 in the Z-axis direction is constant. That is, the width of the recess 162 in the Z-axis direction does not change as you move from the opening 162a towards the bottom 162b.

[0087] The holder 160 surrounds the laser medium 50 when viewed from the Z-axis direction. When viewed from the Z-axis direction, the diameter of the laser medium 50 is larger than the diameter of the inner surface 161a of the holder 160 and smaller than the diameter of the bottom 162b of the recess 162 (inner surface 172a of the wall portion 172). When viewed from the Z-axis direction, the outer edge of the laser medium 50 is located between the pair of plate members 170 (main body portion 171). The holder 160 holds the laser medium 50 by sandwiching it between the pair of plate members 170 in the Z-axis direction. The holder 160 is in contact with each of the pair of end faces 51a and 51b of the laser medium 50. Specifically, one plate member 170 is in direct contact with end face 51a, and the other plate member 170 is in direct contact with end face 51b. The laser medium 50 is held between the holder 160 (a pair of plate members 170), thereby restricting the movement of the laser medium 50 in the Z-axis direction and in a direction perpendicular to the Z-axis direction.

[0088] The holder 60 has a pair of restricting portions 163, as shown in Figure 20. Each restricting portion 163 is integrally formed with the main body portion 171 of the corresponding plate member 170. The restricting portions 163 extend in an annular shape when viewed from the Z-axis direction. In this example, the restricting portions 163 extend along the side surface 51c of the laser medium 50 when viewed from the Z-axis direction. The restricting portion 163 is a convex portion that projects from the inner surface 162c of the recess 162 toward space S2 (inside the recess 62). The restricting portion 163 is in contact with the side surface 51c of the laser medium 50. The restricting portion 163 restricts the movement of the laser medium 50 in a direction perpendicular to the Z-axis direction.

[0089] The holder 160 holds the laser medium 50 such that a space S2 is formed between the side surface 51c of the laser medium 50 and the inner surface 162c of the recess 162. The side surface 51c does not include a region that contacts the holder 160 (inner surface 161a) (contact region). That is, the side surface 51c includes only a region that does not contact the holder 160 (non-contact region).

[0090] In this embodiment, the holder 160 includes a light-absorbing portion 165a formed by a light-absorbing body 165. The light-absorbing portion 165a is formed in the recess 162. The light-absorbing portion 165a absorbs spontaneously emitted light generated in the laser medium 50. The absorption rate of the light-absorbing portion 165a for spontaneously emitted light is 0.1% or more, more preferably 1% or more, even more preferably 5% or more, even more preferably 10% or more, and even more preferably 50% or more. The material of the light-absorbing portion 165a (light-absorbing body 165) may be, for example, Cr-doped YAG. The light-absorbing body 165 extends in an annular shape when viewed from the Z-axis direction. In this example, the light-absorbing body 165 extends in an annular shape. The center of the light-absorbing body 165 when viewed from the Z-axis direction coincides with the center C of the laser medium 50. The light-absorbing body 165 is continuously arranged on the bottom 162b of the recess 162. The light absorber 165 is located in the recess 162, away from the side surface 51c of the laser medium 50. A space S2 exists between the light absorber 165 and the side surface 51c. Air is present in the space S2 between the light absorber 165 and the side surface 51c, and no solid or liquid substances are present.

[0091] In the laser medium unit 10A according to the second embodiment, the holder 160 holds the laser medium 50 such that a space S2 is formed between the side surface 51c of the laser medium 50 and the inner surface 162c of the recess 162 formed in the holder 160. As a result, the laser medium unit 10A can improve the quality of the laser light L1 while suppressing parasitic oscillations, for the same reasons as the laser medium unit 10 according to the first embodiment.

[0092] The recess 162 is formed to be point-symmetric with respect to the center C of the laser medium 50 when viewed from the Z-axis direction. As a result, even if the temperature of the inner surface 162c of the recess 162 rises due to the absorption of spontaneously emitted light, the non-uniformity of the temperature distribution in the excitation region 52 of the laser medium 50 can be suppressed because the recess 162 is formed to be point-symmetric with respect to the center C of the laser medium 50, thereby improving the quality of the laser light L1.

[0093] The holder 160 is equipped with a light-absorbing section 165a formed in the recess 162, which absorbs spontaneously emitted light generated in the laser medium 50. As a result, spontaneously emitted light emitted from the side surface 51c of the laser medium 50 into space S2 is absorbed by the light-absorbing section 165a. This further suppresses parasitic oscillation.

[0094] The light-absorbing section 165a is formed by a light-absorbing body 165, which is positioned away from the laser medium 50 in the recess 162. As a result, even if heat is generated in the light-absorbing body 165 due to the absorption of spontaneously emitted light, the heat generated is less likely to be transferred to the laser medium 50 because the light-absorbing body 165 is positioned away from the laser medium 50. This suppresses the non-uniformity of the temperature distribution in the excitation region 52 of the laser medium 50, thereby improving the quality of the laser light L1.

[0095] The holder 60 is in contact with each of the pair of end faces 51a and 51b of the laser medium 50. This allows the holder 60 to hold the laser medium 50 in a more stable state.

[0096] The holder 160 has a restricting portion 163 that contacts the side surface 51c of the laser medium 50 and restricts the movement of the laser medium 50 in a direction perpendicular to the Z-axis direction. The restricting portion 163 restricts the movement of the laser medium 50, making it possible to more reliably form a predetermined space S2 between the side surface 51c of the laser medium 50 and the recess 62 of the holder 60. [Modified version of the second embodiment]

[0097] Next, a modified example of the laser medium unit 10A according to the second embodiment will be described. First, with reference to Figures 21 and 22, the laser medium unit 10A according to the third modified example will be described. In the third modified example, the shape of the laser medium and the holder differs from the shape of the laser medium 50 and the holder 160 according to the second embodiment described above. The laser medium 250 and the holder 260 according to the third modified example will be described below, but the common points with the laser medium 50 and the holder 160 according to the second embodiment described above may be omitted from the explanation.

[0098] The laser medium 250 has a pair of end faces 251a, 251b and a side surface 251c. The laser medium 250 has thickness in the Z-axis direction and is plate-shaped with the pair of end faces 251a, 251b as its main surfaces. In this example, the laser medium 250 is rectangular plate-shaped. The pair of end faces 251a, 251b intersect in the Z-axis direction. End face 251b is located on the opposite side from end face 251a in the Z-axis direction.

[0099] The side surface 251c of the laser medium 250 intersects with a pair of end faces 251a and 251b. The side surface 251c is aligned with the Z-axis direction. When viewed from the direction intersecting the pair of end faces 251a and 251b (Z-axis direction), the side surface 251c defines the outer edge of the laser medium 250. That is, the side surface 251c has a rectangular shape when viewed from the Z-axis direction. When viewed from the Z-axis direction, the center of the rectangle defined by the side surface 251c coincides with the center C of the laser medium 250. The length of one side of the laser medium 250 when viewed from the Z-axis direction is, for example, about 100 mm. The material of the laser medium 250 may be the same as the material of the laser medium 50.

[0100] The holder 260 is positioned along the side surface 251c of the laser medium 250 when viewed from the Z-axis direction, and holds the laser medium 250. In this example, the holder 260 is formed in the shape of a rectangular frame that surrounds the side surface 251c of the laser medium 250 when viewed from the Z-axis direction. The surface 261 of the holder 260 has an inner surface 261a, an outer surface 261b, and a pair of sides 261c, 261d. The inner surface 261a extends along the side surface 251c of the laser medium 250 when viewed from the Z-axis direction. In this example, the inner surface 261a is rectangular when viewed from the Z-axis direction. When viewed from the Z-axis direction, the inner surface 261a is located inside (towards the center C) of the side surface 251c of the laser medium 250. The outer surface 261b is rectangular when viewed from the Z-axis direction.

[0101] The holder 260 has a pair of plate members 270. The holder 260 is composed of a stacked pair of plate members 270. Each plate member 270 includes a main body portion 271 and a wall portion 272. The main body portion 271 is plate-shaped with an opening 273 formed therein. In this example, the main body portion 271 is rectangular. The main body portion 271 has an inner surface 271a that defines the opening 273. The opening 273 (inner surface 271a) is rectangular when viewed from the Z-axis direction. When the pair of plate members 270 are stacked, the inner surface 271a of one plate member 270 and the inner surface 271a of the other plate member 270 constitute the inner surface 261a of the holder 260.

[0102] The wall portion 272 extends along the outer edge of the main body portion 271 when viewed from the Z-axis direction. The wall portion 272 has an inner surface 272a, an outer surface 272b, and a top surface 272c. The inner surface 272a extends along the side surface 251c of the laser medium 250 when viewed from the Z-axis direction. In this example, the inner surface 272a has a rectangular shape when viewed from the Z-axis direction. When viewed from the Z-axis direction, the inner surface 272a is located outside the side surface 251c of the laser medium 250. The outer surface 272b has a rectangular shape when viewed from the Z-axis direction. When a pair of plate members 270 are stacked, the outer surface 272b of one plate member 270 and the outer surface 272b of the other plate member 270 constitute the outer surface 261b of the holder 260. The material of the retainer 260 (each plate member 270) may be the same as the material of the retainer 160 (i.e., the retainer 60).

[0103] A recess 262 is formed in the holder 260. The recess 262 is formed on the inner surface 261a. As shown in Figure 21, the recess 262 is formed continuously in a rectangular ring shape along direction A surrounding the center C of the laser medium 250 when viewed from the Z-axis direction. The recess 262 has an opening 262a on the inner surface 261a. The bottom 262b of the recess 262 is formed by the inner surfaces 272a of two wall portions 272.

[0104] The holder 260 surrounds the laser medium 250 when viewed from the Z-axis direction. When viewed from the Z-axis direction, the size of the laser medium 250 is larger than the rectangle defined by the inner surface 261a of the holder 260 and smaller than the rectangle defined by the bottom 262b of the recess 262 (inner surface 272a of the wall portion 272). The holder 260 holds the laser medium 250 by sandwiching it in the Z-axis direction with a pair of plate members 270. The holder 260 is in contact with each of the pair of end faces 251a and 251b of the laser medium 250. Specifically, one plate member 270 is in direct contact with end face 251a, and the other plate member 270 is in direct contact with end face 251b.

[0105] The holder 260 has a pair of restricting portions 263, as shown in Figure 22. Each restricting portion 263 is integrally formed with the main body portion 271 of the corresponding plate member 270. The restricting portions 263 extend in a rectangular annular shape when viewed from the Z-axis direction. In this example, the restricting portions 263 extend along the side surface 251c of the laser medium 250 when viewed from the Z-axis direction. The restricting portions 263 are convex portions that project from the inner surface 262c of the recess 262 toward space S2 (inside the recess 262). The restricting portions 263 are in contact with the side surface 251c of the laser medium 250. The restricting portions 263 restrict the movement of the laser medium 250 in a direction perpendicular to the Z-axis direction. The holder 260 holds the laser medium 250 such that space S2 is formed between the side surface 251c of the laser medium 250 and the inner surface 262c of the recess 262.

[0106] In this embodiment, the holder 260 includes a light-absorbing portion 265a formed by a light-absorbing element 265. The light-absorbing portion 265a is formed in the recess 262. The light-absorbing portion 265a absorbs spontaneously emitted light generated in the laser medium 250. The absorption rate of the light-absorbing portion 265a for spontaneously emitted light is 0.1% or more, more preferably 1% or more, even more preferably 5% or more, even more preferably 10% or more, and even more preferably 50% or more. The light-absorbing element 265 extends in a rectangular ring shape when viewed from the Z-axis direction. The center of the light-absorbing element 265 when viewed from the Z-axis direction coincides with the center C of the laser medium 250. The light-absorbing element 265 is continuously arranged on the bottom 262b of the recess 262. In the recess 262, the light-absorbing element 265 is located away from the side surface 251c of the laser medium 250. A space S2 exists between the light absorber 265 and the side surface 251c.

[0107] In the third modified laser medium unit 10A, the holder 260 holds the laser medium 250 such that a space S2 is formed between the side surface 251c of the laser medium 250 and the inner surface 262c of the recess 262 formed in the holder 260. This makes it possible to improve the quality of the laser light L1 while suppressing parasitic oscillations, for the same reasons as in the laser medium unit 10A according to the second embodiment. [Differentiation]

[0108] The present invention is not limited to the embodiments and modifications described above. For example, as shown in Figure 23, the holder may have a light-absorbing paint 365 applied to the inner surface of the recess as a light-absorbing portion 365a. That is, the light-absorbing portion 365a is formed of the light-absorbing paint 365. Part (a) of Figure 23 shows a configuration in which the holder 60 according to the first embodiment has a light-absorbing paint 365. The light-absorbing paint 365 absorbs spontaneously emitted light generated in the laser medium 50. The absorption rate of the light-absorbing portion 365a (light-absorbing paint 365) for spontaneously emitted light is 0.1% or more, more preferably 1% or more, even more preferably 5% or more, even more preferably 10% or more, and even more preferably 50% or more. The light-absorbing paint 365 is, for example, a black paint containing a metal oxide, carbon black, etc. The light-absorbing paint 365 is applied to the inner surface 62c of the recess 62. In this example, the light-absorbing paint 365 is applied to the entire inner surface 62c, but it may also be applied to only a portion of the inner surface 62c. A space S2 is formed between the light-absorbing paint 365 and the side surface 51c of the laser medium 50. Because the light-absorbing paint 365 is applied to the inner surface 62c, spontaneously emitted light emitted from the side surface 51c of the laser medium 50 into space S2 is absorbed (attenuated) by the light-absorbing paint 365. Therefore, parasitic oscillation can be further suppressed. Also, because a space S2 is formed between the light-absorbing paint 365 and the side surface 51c of the laser medium 50, even if heat is generated in the light-absorbing paint 365 due to the absorption of spontaneously emitted light, the heat is less likely to be transferred from the light-absorbing paint 365 to the excitation region 52. Therefore, the non-uniformity of the temperature distribution in the excitation region 52 can be suppressed, and the quality of the laser light L1 can be improved. Because the light-absorbing portion 365a is formed by the light-absorbing paint 365, the light-absorbing portion 365a can be easily formed.

[0109] Part 23(b) of Figure 23 shows a configuration in which the holder 160 according to the second embodiment has a light-absorbing paint 365 instead of a light absorber 165. Similar to the example shown in Part 23(a), the light-absorbing paint 365 is applied to the inner surface 162c of the recess 162 as a light-absorbing portion 365a. In this example, the light-absorbing paint 365 is applied to the entire inner surface 162c, but it may also be applied to only a part of the inner surface 162c. A space S2 is formed between the light-absorbing paint 365 and the side surface 51c of the laser medium 50. In the example shown in Part 23(b), parasitic oscillations can be further suppressed and the quality of the laser light L1 can be improved, similar to the example shown in Part 23(a). Since the light-absorbing portion 365a is formed by the light-absorbing paint 365, the light-absorbing portion 365a can be easily formed.

[0110] As shown in Figure 24, the laser medium 50 (including the laser medium 250) may have a light-transmitting region 55 in which the absorption rate for spontaneously emitted light generated in the laser medium 50 is 10% or less. The light-transmitting region 55 is undoped YAG (Yb or Nd). The light-transmitting region 55 is provided in an annular shape along the side surface 51c of the laser medium 50 when viewed from the Z-axis direction. In the laser medium 50, the light-transmitting region 55 is located outside (away from the center C) of the region 56 formed by doped YAG.

[0111] Figure 25 schematically shows the path of spontaneous emission light L10 in a laser medium 50 having a configuration similar to that shown in Figure 24. In Figure 25, the spontaneous emission light L10 is shown with a dashed line, but for ease of explanation, a portion of the spontaneous emission light L10 is shown with a thick solid line. In the example shown in Figure 25, the spontaneous emission light L10 generated in the excitation region 52 is incident on the side surface 51c. When viewed from the Z-axis direction, if the spontaneous emission light L10 is incident on the side surface 51c at an angle greater than the total reflection angle with respect to the normal to the side surface 51c, the spontaneous emission light L10 is reflected at the side surface 51c. Since the side surface 51c is circular when viewed from the Z-axis direction, the spontaneous emission light L10 reflected at the side surface 51c continues to be reflected at the same angle thereafter (looping in the laser medium 50).

[0112] As shown in the modified examples in Figures 24 and 25, the presence of a light-transmitting region 55 in the laser medium 50 increases the distance from the excitation region 52 to the side surface 51c compared to a configuration without a light-transmitting region 55. This reduces the distance the looping spontaneously emitted light L10 travels through the excitation region 52, thereby suppressing parasitic oscillations. Furthermore, the low absorption rate of the light-transmitting region 55 for spontaneously emitted light suppresses heat generation in the light-transmitting region 55 due to absorption of spontaneously emitted light. Even if the holder 60 absorbs the spontaneously emitted light L10 that has passed through the light-transmitting region 55, generating heat in the holder 60, the light-transmitting region 55 acts as a buffer, making it difficult for heat to transfer from the holder 60 to the excitation region 52. Therefore, non-uniformity of the temperature distribution in the excitation region 52 can be suppressed, improving the quality of the laser light L1. When viewed from the Z-axis direction, the outer edge of the light-transmitting region 55 is not limited to a circular shape, but may also have a polygonal shape. For example, the laser medium 250 shown in Figure 21 may have a light-transmitting region 55 with a rectangular outer edge. If the outer edge of the light-transmitting region 55 is polygonal, it is preferable that the outer edge of the light-transmitting region 55 be a polygon other than a square (a polygon with many vertices close to a circle) from the viewpoint of suppressing spontaneous emission light L10 from passing through the excitation region 52.

[0113] As shown in Figure 26, the laser medium 50 (including the laser medium 250) may have an optical absorption region 57 in which the absorption rate for spontaneously emitted light generated in the laser medium 50 is 0.1% or more and less than 90%. In this example, the absorption rate is about 30%. The optical absorption region 57 is, for example, YAG doped with Cr. The absorption rate of the optical absorption region 57 is adjusted by the rate of the additive (the amount of Cr doped into the YAG). The optical absorption region 57 is provided in an annular shape along the side surface 51c of the laser medium 50 when viewed from the Z-axis direction. The absorption rate for spontaneously emitted light in the optical absorption region 57 is higher than the absorption rate for spontaneously emitted light in the region 58 located inside the optical absorption region 57 when viewed from the Z-axis direction.

[0114] As shown in the modified example in Figure 26, when the laser medium 50 has a light-absorbing region 57, the spontaneously emitted light generated in the excitation region 52 is moderately absorbed by the light-absorbing region 57, and the spontaneously emitted light that passes through the light-absorbing region 57 is emitted into space S2, for example, thereby suppressing parasitic oscillation. Furthermore, the absorptivity of the light-absorbing region 57 for spontaneously emitted light is less than 90%. In this case, excessive heating of the light-absorbing region 57 due to the absorption of spontaneously emitted light is suppressed, non-uniformity of the temperature distribution in the excitation region 52 can be suppressed, and the quality of the laser light L1 can be improved. The upper limit of the absorptivity of the light-absorbing region 57 for spontaneously emitted light is less than 90%, more preferably 70% or less, and even more preferably 50% or less. The lower limit of the absorptivity of the light-absorbing region 57 for spontaneously emitted light is 0.1% or more, more preferably 1% or more, even more preferably 5% or more, even more preferably 10% or more, and even more preferably 20% or more. Because the absorption rate is 0.1% or higher, spontaneously emitted light is gradually absorbed by the light absorption region 57, and as a result, parasitic oscillation can be suppressed.

[0115] The inner surface 62c of the recess 62 (including inner surfaces 162c and 262c) may be a rough surface (sandy ground) with irregularities. This makes it easier for spontaneously emitted light emitted from the side surface 51c of the laser medium 50 into space S2 to be scattered on the inner surface 62c, further suppressing parasitic oscillation. The side surface 51c of the laser medium 50 (including side surface 251c) may be a mirror surface, a mirror surface with an AR coating (an anti-reflective film formed on it), or a rough surface.

[0116] The holder 60 (including the holders 160 and 260) does not have to completely surround the laser medium 50 when viewed from the Z-axis direction, and may be positioned along only a portion of the side surface 51c of the laser medium 50 (including the side surface 251c of the laser medium 250). For example, in the third modified example shown in Figure 21, the holder 260 may have only a pair of portions 268 along a pair of regions of the side surface 251c that extend in the X-axis direction, and these portions 268 may be positioned to sandwich the laser medium 250 in the Y-axis direction.

[0117] The proportion of region R1 to the entire surface 51c is not limited to the examples described above. The proportion of region R1 to the entire surface 51c may be between 30% and 40%. The proportion of region R1 to the entire surface 51c may be greater than 90% or less than 5%.

[0118] The shape of the recess 62 is not limited to an elliptical cone shape. The recess 62 may, for example, be conical or pyramidal. Pyramid shapes include, for example, triangular pyramidal shapes, square pyramidal shapes, and pentagonal pyramidal shapes.

[0119] As shown in Figure 6, the holder 60 has a non-contact portion 66 that does not come into contact with the laser medium 50, and the non-contact portion 66 may be made of a different material than the contact portion 63. For example, the contact portion 63 may be made of resin, and the non-contact portion 66 may be made of metal. In this case, the contact portion 63 that comes into contact with the laser medium 50 is insulated from the laser medium 50, while the non-contact portion 66 is made of a metal that has a higher thermal conductivity than resin, so that the heat transferred from the laser medium 50 to the holder 60 through the space S2 can be quickly released to the outside.

[0120] The holder 160 may not have one of the pair of restricting portions 163, or it may not have both restricting portions 163. Each restricting portion 163 may be formed discontinuously. That is, each plate member 170 may have multiple restricting portions 163 (protrusions). The holder 260 may not have one of the pair of restricting portions 263, or it may not have both restricting portions 263. Each restricting portion 263 may be formed discontinuously. That is, each plate member 270 may have multiple restricting portions 263 (protrusions).

[0121] The light absorber 165 may be discontinuously arranged on the bottom 162b of the recess 162. That is, multiple light absorbers 165 may be arranged on the bottom 162b of the recess 162 with spacing between them. The light absorber 265 may be discontinuously arranged on the bottom 262b of the recess 262. That is, multiple light absorbers 265 may be arranged on the bottom 262b of the recess 262 with spacing between them. [Explanation of Symbols]

[0122] 10,10A...Laser medium unit, 50,250...Laser medium, 51a,51b,251a,251b...End face, 51c,251c...Side side, 60,160,260...Holder, 61,161,261...Surface, 62,162,262...Recess, 62a...Opening, 62b...Bottom, 62c,162c,262c...Inner surface, 63...Contact portion, 64...Through hole, 65,165,265...Light absorber, 65a,165a,265a...Light absorbing portion, 163,263...Restricting portion, 365...Light absorbing paint, R1...Region (contact region), R3...Region, S2...Space.

Claims

1. A laser medium having a pair of end faces and side surfaces intersecting the pair of end faces, A holder is provided which is arranged along the side surface when viewed from a direction intersecting the pair of end faces and which holds the laser medium, The holder has a recess formed therein that opens towards the center of the laser medium when viewed from the direction intersecting the pair of end faces. The holder holds the laser medium such that a space is formed between the side surface and the inner surface of the recess. Laser medium unit.

2. The holder is formed in a frame shape that surrounds the laser medium when viewed from the direction intersecting the pair of end faces. The laser medium unit according to claim 1.

3. The recess has a shape that tapers towards the bottom of the recess. The laser medium unit according to claim 1 or 2.

4. The retainer is in contact with the side surface, The laser medium unit according to claim 1 or 2.

5. The proportion of the side surface that is in contact with the retainer is 90% or less of the entire side surface. The laser medium unit according to claim 1 or 2.

6. The proportion of the side surface that is in contact with the retainer is 5% or more of the entire side surface. The laser medium unit according to claim 1 or 2.

7. The recess is formed such that it is point-symmetric with respect to the center of the laser medium when viewed from the direction intersecting the pair of end faces. The laser medium unit according to claim 1 or 2.

8. The retainer has a plurality of recesses, each of which is the recess. The laser medium unit according to claim 1 or 2.

9. The plurality of recesses are formed such that they are point-symmetric with respect to the center of the laser medium when viewed from the direction intersecting the pair of end faces. The laser medium unit according to claim 8.

10. Multiple regions on the surface of the retainer that are located between the openings of the multiple recesses are in contact with the side surface. The laser medium unit according to claim 8.

11. The holder has a through hole that connects the space and the external space of the holder. The laser medium unit according to claim 1 or 2.

12. The holder has a contact portion that contacts the laser medium, The aforementioned contact portion is formed of resin. The laser medium unit according to claim 1 or 2.

13. The holder has a non-contact portion that does not come into contact with the laser medium, The aforementioned non-contact portion is formed of metal. The laser medium unit according to claim 12.

14. The holder comprises a light-absorbing portion formed in the recess that absorbs spontaneously emitted light generated in the laser medium. The laser medium unit according to claim 1 or 2.

15. The aforementioned light-absorbing portion is formed by a light-absorbing material. The light absorber is positioned away from the laser medium in the recess. The laser medium unit according to claim 14.

16. The light-absorbing portion is formed by a light-absorbing paint. The laser medium unit according to claim 14.

17. The laser medium is configured without including a light-absorbing region in which the absorption rate for spontaneously emitted light generated in the laser medium is 90% or more. The laser medium unit according to claim 1 or 2.

18. The laser medium unit according to claim 1 or 2, wherein the laser medium includes a light-absorbing region in which the absorption rate for spontaneously emitted light generated in the laser medium is less than 90%.

19. The retainer is in contact with each of the pair of end faces. The laser medium unit according to claim 1 or 2.

20. The holder has a restricting portion that contacts the side surface and restricts the movement of the laser medium in a direction perpendicular to the direction intersecting the pair of end faces. The laser medium unit according to claim 19.

Images