JP2007305733A - Solid laser apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a solid laser apparatus capable of fixing a laser medium so that the medium cannot move, and reducing distortion in laser operation. <P>SOLUTION: The solid laser apparatus is provided with a thin plate-like laser medium 1 for absorbing an excitation light to generate a gain, a heat sink 3 for discharging heat of the laser medium 1 to the outside, and a bonding agent 2 for bonding the laser medium 1 to the heat sink 3. The apparatus has a relation of Ts≥Td≥Th and a relation of α(Ts-Td)≈η(Ts-Th), where α is a linear expansion coefficient in a junction surface of the laser medium 1, η is a linear expansion coefficient of the heat sink 3, Ts is a curing temperature of the bonding agent 2, Td is an operation temperature of the laser medium 1, and Th is an operation temperature of the heat sink 3. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thin plate-like solid-state laser device suitable for a laser device for laser radar and a laser device for processing.

  The thin plate type laser medium is obtained by processing a laser medium into a thin plate shape. Laser light is incident from one of the surfaces having the largest area among the surfaces constituting the plate shape, reflected by a reflecting surface facing the incident surface, and amplified while propagating the laser light in the thickness direction of the plate. Therefore, when distortion occurs on the reflecting surface of the thin plate type laser medium, the beam quality of the amplified laser beam is deteriorated (the luminance of the beam is low), or the efficiency of the solid-state laser device is reduced due to diffraction loss. A problem occurs. The outer shape of the plate has an arbitrary shape such as a circular disk or a polygon.

  Further, since the thin plate type laser medium is used as a mirror for laser oscillation or amplification, if the laser medium moves, the optical axis of the incident laser beam is shifted and the output of the individual laser device is reduced. As a result, the optical axis of the emitted laser beam is shifted. Therefore, it is necessary to firmly fix the laser medium so that the laser medium does not move.

  On the other hand, a heat sink is bonded to the reflecting surface in order to exhaust heat generated in the excited thin plate-like laser medium. For this joining, a thermosetting adhesive or solder is used. If the thermal expansion amount of the laser medium and the heat sink is different during heating by joining, distortion or breakage due to stress occurs during cooling. Therefore, in order to suppress this distortion, a method of joining a heat sink having a linear expansion coefficient substantially the same as the linear expansion coefficient of the laser medium is generally used.

  However, in the thin plate type laser medium, a thermal resistance is generated by the dielectric total reflection film and the bonding agent between the laser medium serving as a heating element and the heat sink, so when excitation light is incident and heat is generated in the laser medium ( During operation, a difference occurs between the temperature of the laser medium and the heat sink temperature due to the thermal resistance from the laser medium to the heat sink. Due to this temperature difference, even when the linear expansion coefficient of the laser medium and the heat sink is the same, the amount of expansion due to heat differs, and the heat sink applies stress to the laser medium.

  As a bonding method for reducing this distortion, there is a method using an adhesive (see, for example, Patent Document 1). This adhesive comprises a stretchable fabric in which thermal conductive fibers are entangled with each other, and a thermosetting resin impregnated in this stretchable fabric. In particular, in order to reduce the stress of the adhesive, As the thermosetting resin, it is desirable to include a component having a glass transition temperature of room temperature or lower. In the thermosetting resin, since the outside temperature that is usually used is room temperature, the temperature of the adhesive is higher than the glass transition temperature. The thermosetting resin is in a semi-solid state below the glass transition temperature, and the thermal expansion difference generated at the time of bonding is absorbed by the thermosetting resin and the stretchable fabric to join the bonded product. Relieve stress and reduce strain.

JP 2005-232207 A

  However, in the conventional thin plate type solid state laser device, the heat sink material is selected so that the linear expansion coefficients of the laser medium and the heat sink are almost the same. There is a problem in that the amount of expansion due to heat differs and distortion occurs in the laser medium.

  Also, in a thin plate type solid state laser device using a conventional adhesive, since the temperature of the adhesive after curing is higher than the glass transition temperature of the thermosetting resin, the thin plate cannot be completely fixed and excited. There is a problem that the thin plate moves due to a temperature rise due to heat generated in the room and a temperature change due to a change in the outside air temperature.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to fix the laser medium so that it does not move, and to reduce distortion during laser operation. Is what you get.

  A solid-state laser device according to the present invention includes a thin plate-like laser medium that absorbs excitation light and generates gain, a cooling unit that exhausts heat of the laser medium to the outside, and the laser medium and the cooling unit are joined. A linear expansion coefficient in the bonding surface of the laser medium, a linear expansion coefficient of the cooling means η, a curing temperature of the bonding agent Ts, and the laser medium. When the operating temperature of Td is expressed as Td and the operating temperature of the cooling means is expressed as Th, there is a relationship of Ts ≧ Td ≧ Th and a relationship of α (Ts−Td) ≈η (Ts−Th). .

  The solid-state laser device according to the present invention has an effect that the laser medium can be fixed so as not to move, and distortion during laser operation can be reduced.

Embodiment 1 FIG.
A solid-state laser device according to Embodiment 1 of the present invention will be described with reference to FIGS. 1 is a cross-sectional view showing a configuration of a solid-state laser apparatus according to Embodiment 1 of the present invention. In the following, in each figure, the same reference numerals indicate the same or corresponding parts.

  In FIG. 1, a solid-state laser device according to the first embodiment includes a thin plate-like laser medium 1 that absorbs excitation light and generates a gain, and a heat sink (cooling means) that exhausts heat from the laser medium 1 to the outside. 3 and a bonding agent 2 for bonding the laser medium 1 and the heat sink 3 are provided.

  As the laser medium 1, a general solid laser medium can be used. For example, Nd; YAG, Yb; YAG, or the like is used. Although not shown in the figure, an “antireflection film” is applied with one side of the wide plate-like surface of the laser medium 1 as the incident surface, and almost all of the incident laser light is transmitted and opposite to the incident surface of the laser medium 1. The wide surface is provided with a “total reflection film” as a reflection surface, and reflects almost all of the laser light incident from the incident surface. The antireflection film uses a laminate of dielectric thin films, and the total reflection film uses a laminate of dielectric thin films or vapor deposition of a metal film.

  The bonding agent 2 can be realized by metal solder or an adhesive.

  Next, the operation of the solid-state laser device according to the first embodiment will be described with reference to the drawings. FIG. 2 is a diagram for explaining a situation in which distortion occurs in the laser medium of the solid-state laser device according to Embodiment 1 of the present invention.

  The temperature (curing temperature) at the time of bonding with the bonding agent 2 is Ts, the temperature of the laser medium 1 when the excitation light is incident and heat is generated in the laser medium 1 (at the time of operation), Td, and the temperature of the heat sink 3 at the time of operation. Is Th, normal temperature is T0, and Ts ≧ Td ≧ Th. Further, the linear expansion coefficient of the laser medium 1 is α, and the linear expansion coefficient of the heat sink 3 is η, which has the relationship of the following formula (1).

  α (Ts−Td) ≈η (Ts−Th) Equation (1)

  The bonding temperature Ts is equal to the melting point of the metal solder when the bonding agent 2 is metal solder. Further, when the bonding agent 2 is an adhesive, even if the bonding is performed at a temperature higher than the glass transition temperature Tg of the adhesive, the adhesive is in a semi-solid state at Tg or higher, so the temperature at which the laser medium 1 is fixed is Tg. Therefore, when an adhesive is used as the bonding agent 2, the bonding temperature Ts is equal to the glass transition temperature Tg regardless of the curing temperature.

  Here, the situation where distortion occurs in the laser medium 1 will be described with reference to FIG. As shown in FIG. 2A, at the bonding temperature Ts, the laser medium 1 and the heat sink 3 do not apply stress to each other, and no distortion occurs.

  As shown in FIG. 2B, when the laser medium 1 and the heat sink 3 are cooled from the bonding temperature Ts to the room temperature T0, the laser medium 1 has a ratio α (Ts) based on the size at the bonding temperature Ts. -T0) changes in magnitude. On the other hand, the heat sink 3 changes in the magnitude of the ratio η (Ts−T0). Since the amount of change between the laser medium 1 and the heat sink 3 is different except for the case of Ts = Td or Ts = T0 from the relationship of the expression (1), stress is generated in the laser medium 1 by the heat sink 3 due to cooling. To do. At this time, since α ≧ η, a tensile stress is generated in the laser medium 1.

  On the other hand, as shown in FIG. 2C, during operation, the laser medium 1 has a ratio α (Ts−Td) and the heat sink 3 has a ratio η (Ts−Th) with reference to the size at the temperature Ts at the time of bonding. A change in the size of occurs. Therefore, since the change amount of the laser medium 1 and the heat sink 3 is constant with respect to the temperature Ts at the time of bonding from the relationship of the expression (1), no stress is generated in the laser medium 1.

  The laser medium 1 only needs to be free from distortion due to stress when the solid-state laser device is operating, and there is no problem even if distortion due to stress occurs during cooling as long as the laser medium 1 does not break down. Therefore, if configured as described above, it is possible to configure a thin plate type solid-state laser device that does not generate distortion when the solid-state laser device is in operation and is capable of high-brightness and high-efficiency laser output.

  For example, Yb: YAG (α≈7.7 ppm) is used as the laser medium 1, an adhesive having a glass transition temperature Tg = 90 ° C. is used as the bonding agent 2, and the operating temperature Td = 60 ° C. and Th = 40 ° C. Then, if AlN (aluminum nitride) having a linear expansion coefficient of 4.5 ppm is used for the heat sink 3, the formula (1) is substantially satisfied.

  Further, when metal solder having a melting point of 250 ° C. is used as the bonding agent 2, Ts = 250 ° C., and CuW (Cu 85%, W 15%) having a linear expansion coefficient of 7.2 ppm in the heat sink 3 under the above operating conditions. Is almost satisfied with the expression (1).

  Note that the linear expansion coefficient η of the heat sink 3 does not have to strictly satisfy the expression (1), and it is sufficient that the stress is reduced to such an extent that the laser medium 1 and the heat sink 3 are not distorted. In addition, by selecting an appropriate commercially available adhesive, or by adjusting the components of the adhesive, the glass transition temperature Tg of the adhesive can be adjusted, and a combination that substantially satisfies Equation (1) should be selected. Is easy.

  When an adhesive is used for the bonding agent 2, generally the bonding temperature can be lowered, and the generated stress is reduced not only during operation but also during cooling after bonding. In the present embodiment, it is particularly effective when an adhesive is used as the bonding agent 2, and the effect is greater as the bonding temperature and the operating temperature are closer. When an adhesive is used for the bonding agent 2, if the temperature of the adhesive becomes higher than the glass transition temperature Tg, the adhesive becomes semi-solid and the laser medium 1 may move during operation. Therefore, it is desirable that the glass transition temperature Tg is equal to or higher than the operating temperature Td of the laser medium 1. On the other hand, since the stress generated during cooling increases as the bonding temperature Ts increases, it is desirable that Ts be low. Accordingly, if the bonding agent 2 having a bonding temperature Ts equal to or slightly higher than Td is selected, a thin plate type laser medium with a small distortion can be formed during operation and during cooling. .

  When an anisotropic material having a different coefficient of thermal expansion in the axial direction is used for the laser medium 1, it is desirable to select a material having the same anisotropy as the heat sink material. At this time, the linear expansion coefficients β and γ (β <γ) of the laser medium 1 are provided in the plane bonded to the heat sink 3, and the linear expansion coefficients ε and ρ (ε <ρ) of the heat sink 3. Suppose that

here,
β (Ts−Td) ≈ε (Ts−Th)
γ (Ts−Td) ≈ρ (Ts−Th) Equation (2)
If the operating temperature Th of the heat sink 3 and the heat sink material are selected so as to have the following relationship, a thin plate type solid-state laser device with less distortion during operation can be configured even for an anisotropic laser medium. it can.

Embodiment 2. FIG.
A solid-state laser device according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 3 is a perspective view showing a configuration of a solid-state laser apparatus according to Embodiment 2 of the present invention.

  When an anisotropic material having a different coefficient of thermal expansion in the axial direction is used for the laser medium 1, it is desirable to select a material having the same anisotropy as the heat sink material, but the thermal conductivity suitable for the heat sink 3 is high. There are few materials having anisotropy, and it is difficult to select a heat sink material suitable for the laser medium 1 having anisotropy.

  In the second embodiment, a configuration of a thin plate type solid-state laser device that uses an anisotropic laser medium 1A and an isotropic heat sink material and has a small distortion during operation is disclosed.

  In FIG. 3, the solid-state laser device according to the second embodiment has a thin plate-like laser medium 1A having anisotropy in thermal expansion coefficient and generating a gain by absorbing excitation light, and the heat of the laser medium 1A. A heat sink (cooling means) 3 for exhausting heat to the outside and a bonding agent 2 for bonding the laser medium 1 and the heat sink 3 are provided.

  The bonding agent 2 and the heat sink 3 have the same configuration as that shown in FIG. 1, and have the same functions as the bonding agent 2 and the heat sink 3 shown in FIG. 1 unless otherwise specified.

  Although not shown, the laser medium 1A is provided with an antireflection film with one side of the wide plate-like surface of the laser medium 1A as an incident surface, transmits almost all of the incident laser light, and enters the incident surface of the laser medium 1A. The wide surface opposite to the surface is provided with a total reflection film as a reflection surface, and reflects almost all of the laser light incident from the incident surface.

  The laser medium 1 </ b> A has linear expansion coefficients β and γ that differ depending on directions in the plane bonded to the heat sink 3, and has a relationship of β <γ. The temperature at the time of bonding by the bonding agent 2 is Ts, the temperature of the laser medium 1A when the excitation light is incident and heat is generated in the laser medium 1A (at the time of operation) is Td, and the temperature of the heat sink 3 at the time of operation is Th. Ts> Td> Th. The linear expansion coefficient η of the heat sink 3 has the relationship of the following formula (3).

  {(Β + n · γ) / (1 + n)} (Ts−Td) ≈η (Ts−Th) Equation (3)

  Here, n is a ratio between the compressive stress limit and the tensile stress limit of the laser medium 1A (n = | compressive stress limit / tensile stress limit |). In the crystal or glass material used as the laser medium 1A, the compressive stress limit is larger than the tensile stress limit, and the ratio is generally about three times (n≈3).

  The stress applied to the laser medium 1A by the heat sink 3 is proportional to the difference in expansion coefficient (= product of linear expansion coefficient and temperature difference) between the heat sink 3 and the laser medium 1A, and the stress in the β direction in FIG. 3 is β (Ts− Td) −η (Ts−Th), and the stress in the γ direction in FIG. 3 is substantially proportional to γ (Ts−Td) −η (Ts−Th). Here, since η has the relationship of Equation (3), a compressive stress is generated in the β direction and a tensile stress is generated in the γ direction from the relationship of Ts> Td> Th. Stress / tensile stress in the γ direction | = n. Therefore, if the actual stress does not exceed the fracture limit stress, the ratio between the fracture limit stress and the actual stress is approximately equal in each direction, so that the same margin from the fracture limit can be realized.

  If comprised in this way, the thin plate type solid-state laser apparatus with a small distortion at the time of operation | movement can be comprised using the laser medium 1A which has anisotropy, and an isotropic heat sink material.

  For example, Nd: GdVO4 (β≈4.4 ppm, γ≈11.4 ppm) is used as the laser medium 1A, an adhesive having a glass transition temperature Tg≈80 ° C. is used as the bonding agent 2, and an operating temperature Td = 60 ° C. Assuming that Th = 40 ° C., if AlN (aluminum nitride) having a linear expansion coefficient of 4.5 ppm is used for the heat sink 3, the expression (3) is substantially satisfied.

  Further, when metal solder having a melting point of 250 ° C. is used as the bonding agent 2, Ts = 250 ° C., and CuW (Cu 80%, W 20%) having a linear expansion coefficient of 8.3 ppm in the heat sink 3 under the above operating conditions. Is almost satisfied with the expression (3).

  Note that the linear expansion coefficient η of the heat sink 3 does not have to strictly satisfy the expression (3), and may be in a range in which each axial stress has a margin with respect to the fracture limit stress. In addition, by selecting an appropriate commercially available adhesive, or by adjusting the components of the adhesive, the glass transition temperature Tg of the adhesive can be adjusted, and a combination that substantially satisfies Equation (3) should be selected. Is easy.

  When an adhesive is used for the bonding agent 2, generally the bonding temperature can be lowered, and the generated stress is reduced not only during operation but also during cooling after bonding. In the present embodiment, it is particularly effective when an adhesive is used as the bonding agent 2, and the effect is greater as the bonding temperature and the operating temperature are closer. When an adhesive is used as the bonding agent 2, if the temperature of the adhesive becomes higher than the glass transition temperature Tg, the adhesive becomes semi-solid, and the laser medium 1A may move during operation. Therefore, it is desirable that the glass transition temperature Tg is equal to or higher than the operating temperature Td of the laser medium 1A. On the other hand, since the stress generated during cooling increases as the bonding temperature Ts increases, it is desirable that Ts be low. Therefore, if a bonding agent 2 having a bonding temperature Ts equal to or slightly higher than Td is selected, a thin plate type solid-state laser device having a small distortion in both operation and cooling can be configured. Can do.

It is sectional drawing which shows the structure of the solid-state laser apparatus concerning Embodiment 1 of this invention. It is a figure for demonstrating the condition where distortion generate | occur | produces in the laser medium of the solid-state laser apparatus concerning Embodiment 1 of this invention. It is a perspective view which shows the structure of the solid-state laser apparatus concerning Embodiment 2 of this invention.

Explanation of symbols

  1, 1A laser medium, 2 bonding agent, 3 heat sink.

Claims (6)

A thin plate-like laser medium that absorbs the excitation light and generates a gain;
Cooling means for exhausting heat of the laser medium to the outside;
A solid-state laser device comprising the laser medium and a bonding agent for bonding the cooling means,
Α is a linear expansion coefficient in the joining surface of the laser medium,
The linear expansion coefficient of the cooling means is η,
The curing temperature of the bonding agent is Ts,
The operating temperature of the laser medium is Td,
When the operating temperature of the cooling means is expressed as Th,
While having a relationship of Ts ≧ Td ≧ Th,
A solid-state laser device having a relationship of α (Ts−Td) ≈η (Ts−Th). A thin plate-like laser medium that absorbs the excitation light and generates a gain;
Cooling means for exhausting heat of the laser medium to the outside;
A solid-state laser device comprising the laser medium and a bonding agent for bonding the cooling means,
Two anisotropic linear expansion coefficients in the joining surface of the laser medium are β, γ (β <γ),
Two anisotropic linear expansion coefficients in the joint surface of the cooling means are ε, ρ (ε <ρ),
The curing temperature of the bonding agent is Ts,
The operating temperature of the laser medium is Td,
When the operating temperature of the cooling means is expressed as Th,
While having a relationship of Ts ≧ Td ≧ Th,
β (Ts−Td) ≈ε (Ts−Th),
A solid-state laser device having a relationship of γ (Ts−Td) ≈ρ (Ts−Th). A thin plate-like laser medium that absorbs the excitation light and generates a gain;
Cooling means for exhausting heat of the laser medium to the outside;
A solid-state laser device comprising the laser medium and a bonding agent for bonding the cooling means,
Two anisotropic linear expansion coefficients in the joining surface of the laser medium are β, γ (β <γ),
The ratio of the compressive stress limit and the tensile stress limit of the laser medium is n,
The linear expansion coefficient of the cooling means is η,
The curing temperature of the bonding agent is Ts,
The operating temperature of the laser medium is Td,
When the operating temperature of the cooling means is expressed as Th,
While having a relationship of Ts ≧ Td ≧ Th,
A solid-state laser device having a relationship of {(β + n · γ) / (1 + n)} (Ts−Td) ≈η (Ts−Th). The solid-state laser device according to claim 3, wherein a ratio n≈3 of a compressive stress limit and a tensile stress limit of the laser medium. The solid-state laser device according to any one of claims 1 to 4, wherein the bonding agent is an adhesive. 6. The solid-state laser device according to claim 1, wherein a curing temperature Ts of the bonding agent and an operating temperature Td of the laser medium are substantially equal.

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