JPH1022551A - Solid laser exciting module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise the absorption efficiency of exciting light and equalize the excitation distribution within a rod, by having a mean which radiates heat from each of N pieces of side faces of a transparent block to each of N pieces of heat sinks, and a means which radiates heat from each of N pieces of heat sinks to the outside of the device. SOLUTION: The heat generated in the solid laser rod 1 positioned at the rotational center of a transparent block passes the transparent block. The transparent block 6 is made of a medium high in heat conductivity, and also it is in axially symmetrical form. Next, the heat is radiated to the heat sinks 9 installed by heat contact means 11d at each side face through axially symmetrical side faces which have larger areas than that of the surface of the rod. Furthermore, the heat is radiated to outside of a module from the heat sink 9 by a heat pipe 10 low in heat resistance. Hereby, the heat generated in the rod is exhausted roughly axially symmetrically, and the temperature distribution axially symmetrical within the rod can be obtained. A solid laser exciting module low in heat resistance and small in temperature rise can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser pumping module for optically pumping a solid-state laser medium using a semiconductor laser, and more particularly to a solid-state laser suitable for a solid-state laser mounted on a flying object such as an artificial satellite or an aircraft. The present invention relates to a configuration of a laser excitation module.

[0002]

2. Description of the Related Art Solid-state lasers have the property of generating heat when excited by light. For this reason, in the conventional general solid-state laser device, while storing the laser rod in the case,
A cooling liquid was circulated in this case to cool the laser rod and exhaust heat. However, solid-state lasers with such a cooling method have low reliability due to the problem of the service life of the pump for circulating the cooling liquid and the necessity of sealing pipes, etc. Therefore, it was not suitable for mounting on a flying object such as an artificial satellite or an aircraft. For this reason, a method of exhausting heat from a laser rod instead of a coolant has been studied. However, it has not yet been realized that a solid-state laser mounted on an artificial satellite satisfies all of the requirements such as high efficiency, high average output, high beam quality, and compactness.

[0003] FIG. 7 is a schematic diagram of N. Sims et.al.
-Pumped, c-axis Nd: YLF Laser ", in technical dige
This is a cross-sectional view of the configuration of the conventional solid-state laser pumping module shown in st of Advanced Solid-State Lasers '93, p41, 1993. This is the most commonly used module configuration. In the figure, 1 is a solid-state laser rod, 2 is a semiconductor laser for excitation, and 3 is a metal heat sink.

In FIG. 1, excitation light emitted from an excitation semiconductor laser 2 is reflected by a contact surface of a metal heat sink 3 with the solid-state laser rod 1 and reciprocates in the solid-state laser rod 1, during which the solid-state laser rod 1 Is absorbed by. Excitation light that has not been absorbed returns to the excitation semiconductor laser 2 and is scattered outside the module. Part of the absorbed pump light generates heat in the solid-state laser rod 1. This heat is radiated from the metal heat sink 3 to the housing supporting the entire solid-state laser excitation module by heat conduction.

In a solid-state laser pumping module having such a configuration, a semiconductor laser 2 for pumping is generally provided on a side surface of a solid-state laser rod 1 having a diameter of about 3 mm to 5 mm.
And a metal heat sink 3 for exhausting heat from the solid-state laser rod 1 must be installed together. Therefore, the metal heat sink 3
Contact area of the solid laser rod 1 with the side surface becomes smaller,
When excitation with high average power (high repetition) is performed to have a high thermal resistance value, the temperature of the solid-state laser rod 1 becomes extremely high, which may lead to destruction. Therefore, the repetition rate of the laser is a low value of about 10 Hz at most. In addition, the cooling is performed from three directions of the rod. In this case, the temperature distribution in the cross section of the solid-state laser rod 1 is such that the temperature in the portion in contact with the metal heat sink 3 is low, and The temperature has an asymmetrical temperature distribution that increases. Such non-uniform temperature distribution in the solid-state laser rod 1 causes physical and optical distortions in the solid-state laser rod 1 itself, thereby deteriorating laser efficiency.

[0006] As another excitation module which does not circulate a coolant, SDJackson et.al.
ng of solid nonfocusing pump-light collectors used
fordiode-pumped Nd: YAG lasers ", Appl.Opt.Vol34, N
o12.p2022 1995. FIG. 8 is a cross-sectional view showing the structure of the second conventional example. In the figure, reference numeral 4 denotes a prism having an anti-reflection film provided on the incident surface of the semiconductor laser 2 for excitation with respect to the excitation light, and reference numeral 5 denotes an adhesive for bringing the solid-state laser rod 1 and the prism 4 into thermal contact.

Here, the light emitted from the semiconductor laser 2 for excitation emits the excitation light perpendicular to the hypotenuse of the right-angled isosceles triangle of the prism 4. The excitation light directly or after total reflection on the inner surface of the prism 4 is incident on the solid-state laser rod 1 installed near the apex of a right-angled isosceles triangle. After propagating through the rod up to twice, it is released out of the hypotenuse. The heat generated in the solid-state laser rod 1 is conducted to the prism 4 through the adhesive 5 in contact with the periphery of the solid-state laser rod 1,
Heat is transferred or radiated from two sides of a right angle of the equilateral triangle.

In this conventional example, since the heat can be exhausted from the entire side surface of the solid-state laser rod 1, there is a problem that the temperature of the rod rises because the heat radiation area is small as in the above-mentioned conventional example. However, there are problems such as a low efficiency of incidence of the excitation light on the solid-state laser rod 1 and a problem of poor symmetry of the excitation distribution. The laser efficiency is reduced due to the low absorption efficiency of the excitation light, and the non-uniform excitation distribution lowers the energy extraction from the laser rod with the axisymmetric laser beam. Further, the generated heat distribution in the solid-state laser rod 1 due to the non-uniformity of the excitation distribution and the non-uniformity of the exhaust heat are made non-uniform, with the temperature distribution in the rod shifted from the axial symmetry. For this reason, thermal optical distortion (thermal aberration) occurs, further deteriorating the efficiency of the laser. Further, an adhesive 5 is used between the solid-state laser rod 1 and the prism 4. However, during operation at a high average power, the temperature of the laser rod 1 and the prism 4 increases, and the material (for example, Nd is used as the solid-state laser rod 1 in this conventional example). : BK7 glass or sapphire is used as the prism 4), but there is a problem that stress may be generated in the adhesive 5 due to a difference in thermal expansion coefficient and the adhesive 5 may be broken.

[0009]

As described above, the conventional solid-state laser pumping module has the following problems. In the first conventional example: (1) Since the heat-dissipating area of the solid-state laser rod 1 is small, the heat-dissipating efficiency is poor, the temperature of the rod tends to rise, and the operation at a high excitation average power cannot be performed. (2) The excitation distribution in the rod is likely to be non-uniform, and the efficiency at the time of high output is likely to deteriorate. (3) Non-uniformity of the temperature distribution in the rod deviating from the axial symmetry is likely to occur, and the efficiency at the time of high output is likely to deteriorate. There were issues such as.

In the second conventional example, (1) the excitation light absorption efficiency is poor and the efficiency is low. (2) The distribution of the excitation light in the solid-state laser rod is non-uniform, and the extraction efficiency from the laser medium is low. (3) The unevenness of the excitation distribution and the asymmetry of the exhaust heat are also taken into account, so that the temperature distribution in the rod tends to be uneven, and the efficiency is degraded by the operation at the high average excitation power. (4) Since an adhesive is used as a means for installing the solid-state laser rod in the prism, the reliability is low. There were issues such as.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has been made to improve the efficiency of absorption of excitation light, the uniformity of excitation distribution within a rod, the uniformity of temperature distribution within a rod, and the improvement of exhaust heat efficiency. It is an object of the present invention to provide a solid-state laser pumping module with improved reliability.

[0012]

According to a first aspect of the present invention, there is provided a solid-state laser excitation module, comprising: a transparent block having a substantially regular N prism; a rod insertion hole provided substantially coaxially with a rotationally symmetric axis of the transparent block; A solid-state laser rod, N excitation semiconductor lasers, holding means for inserting and holding the solid-state laser rod in the rod insertion hole, and excitation light emitted from the N excitation semiconductor lasers in the transparent block. Input means for inputting the excitation light, reflecting means for reflecting the excitation light incident on the transparent block, N heat sinks, and exhaust from each of the N side surfaces of the transparent block to each of the N heat sinks. A first heat discharging means for heating;
Second heat exhaust means for exhausting heat from each of the individual heat sinks to the outside of the apparatus.

A solid-state laser excitation module according to a second aspect of the present invention includes a transparent block having a substantially N prism having a shape of N = 2M + 1 (M is a natural number).

According to a third aspect of the present invention, there is provided a solid-state laser pumping module including a solid-state laser rod using Y ₃ Al ₅ O ₁₂ (YAG) as a host material and a transparent block using sapphire as a material. is there.

According to a fourth aspect of the present invention, there is provided a solid-state laser excitation module, wherein Y ₃ Al ₅ O ₁₂ (YAG), YLiF ₄ (YL
F), a solid laser rod using LiCaAlF ₆ (LiCAF) and LiSrAlF ₆ (LiSAF), and a transparent block using MgF ₂ as a material.

According to a fifth aspect of the present invention, there is provided a solid-state laser excitation module including a transparent block having N side surfaces as ground rough surfaces.

According to a sixth aspect of the present invention, there is provided a solid-state laser excitation module including a solid-state laser rod whose side surface is a ground rough surface.

According to a seventh aspect of the present invention, in the solid-state laser pumping module, the position of each of the N ridge lines of the transparent block is perpendicular to a plane including each ridge line and the N-fold rotationally symmetric central axis of the transparent block. Are provided, and the input means is configured to set the optical axis to be substantially perpendicular to the incident slit surface from each of the N excitation light incident slit surfaces so that each of the N excitation semiconductor lasers has an optical axis. The excitation light is input.

According to an eighth aspect of the present invention, there is provided a solid-state laser excitation module including a reflecting means which is a thin metal film provided on each of the side surfaces of the transparent block.

A ninth aspect of the present invention is a solid-state laser pumping module, wherein the thin film of the metal is made of copper.

According to a tenth aspect of the present invention, there is provided a solid-state laser pumping module including a reflecting means which is a ceramic plate provided on each of the N side surfaces of the transparent block.

In the solid-state laser pumping module according to the eleventh aspect of the present invention, the N heat sinks are provided on the N side surfaces of the transparent block as thin films of indium or gold as the first heat discharging means. It is provided.

According to a twelfth aspect of the present invention, in the solid-state laser pumping module, a metal is deposited on each of the N side surfaces of the transparent block as the first heat discharging means, and each of the N heat sinks is formed of indium. , Gold and a solder material.

According to a thirteenth aspect of the present invention, in the solid-state laser pumping module, as each of the second heat-dissipating means, a heat-dissipating hole is formed in each of the heat sinks, and a condensing unit is provided outside the device. The evaporator of the heat pipe is inserted.

According to a fourteenth aspect of the present invention, in the solid-state laser pumping module, the N heat sinks are provided on each of the N heat sinks.
Each of the semiconductor lasers for excitation is provided.

According to a fifteenth aspect of the present invention, in the solid-state laser excitation module, each of the N heat sinks is thermally connected by a heat conducting ring.

In the solid-state laser pumping module according to the present invention, the length of the solid-state laser rod is substantially equal to N.
The one that is longer than the height of the transparent block of the prism and is filled with liquid between the solid laser rod and the rod insertion hole, and the liquid is sealed between both end surfaces of the transparent block and the side surface of the solid laser. It is.

In the solid state laser pumping module according to the seventeenth aspect of the present invention, the liquid is a silicon oil whose refractive index is set to be smaller than the refractive index of the solid laser rod and larger than the refractive index of the transparent block. is there.

In the solid-state laser pumping module according to the invention, the liquid has a refractive index smaller than that of the solid-state laser rod and larger than that of the transparent block. It is an aqueous solution.

A solid-state laser excitation module according to a nineteenth aspect of the present invention uses silicone rubber as a means for sealing the liquid.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a configuration diagram of a non-liquid-cooled excitation module according to an embodiment of the present invention. In the figure, 1 is a solid-state laser rod, 2 is a semiconductor laser for excitation, 6 is a transparent block, 7 is excitation light reflection means, 8 is rod thermal contact means, 9
Is a metal heat sink, 10 is a heat pipe, 11 is a thermal contact means, 12 is a rod holding means, and 13 is a heat conducting ring.

FIG. 1 shows a cross section perpendicular to the laser optical axis through which the laser light actually passes. This is because a solid-state laser that performs pumping from the side direction with the pumping semiconductor laser 2 only needs to expand the pumping semiconductor laser 2 in the longitudinal direction according to the required output. It is. For this reason, the description assumes the same shape in the longitudinal direction unless otherwise specified. For example, a circle in a cross section is actually a cylinder, and a polygon is actually a polygon.

The role of the transparent block 6 in the configuration of FIG. 1 is that the excitation light is confined in the block by the excitation light reflection means 7 on the side surface, and the excitation light is passed through the solid-state laser rod 1 by a plurality of times. To improve the absorption efficiency by improving the absorption efficiency, to make the excitation distribution uniform, and to efficiently transmit the heat generated in the solid-state laser rod 1 to the metal heat sink 9 so as not to form an uneven temperature distribution in the block. That is.

In order to enhance the confinement of the excitation light in the transparent block 6 and increase the absorption efficiency of the excitation light in the solid-state laser rod 1, first, the area of the inner surface of the side surface portion having the excitation light reflection means 7 is excited. It is necessary to reduce the area of the inlet, which is one of the escape paths of light. Further, it is necessary to reduce the loss at the time of reflection by the excitation light reflecting means 7. On the other hand, in order to make the excitation distribution uniform, it is effective that the excitation light is incident on the solid-state laser rod 1 in a rotationally symmetric manner.

First, considering the symmetrical excitation, the transparent block 6 is made up of the solid-state laser rod 1 arranged in the transparent block 6.
The shape is rotationally symmetrical about three times or more about the rod axis of rotation. A regular polygonal prism or a cylinder is selected as such a shape. Next, the excitation light introduction port is also arranged at a rotationally symmetric position of three or more times with the rod axis being rotationally symmetric. In the case of a regular polygonal prism, such an arrangement is a side or a ridge position.In order to make the area of the introduced light as small as possible, the excitation light introduction port is provided at the ridge position, and the side is reflected by the excitation light. Means 7 was adopted. As a specific regular polygonal shape, as shown in FIG.
Since the excitation light incident toward the laser beam easily leaks from the opposed inlet after passing through the solid-state laser rod 1,
N + 1 (N is a natural number) regular polygonal prism and the number of inlets is 2N
+1 (N is a natural number) is desirable. FIG. 3 shows excitation light in the transparent block 6 when the same triangular prism as in FIG. 1 is used, which is the simplest shape. In this shape, the excitation light that has once passed through the solid-state laser rod 1 is reflected by the excitation light reflection means 7 and is again reflected toward the excitation light inlet. That is, the excitation light along the excitation optical axis passes through the solid-state laser rod 2 twice and then leaks out of the transparent block 6 through the excitation light inlet. This is shown in FIG.
In this case, the excitation light along the excitation light axis passes through the solid-state laser rod 1 only once, so that a higher absorption efficiency is provided. Further, if the length of the pumping light inlet is D, and the distance between the pumping light inlets facing each other in FIG. 2 and the distance between the pumping light inlet and the pumping light reflecting means 7 in FIG. The angle θ in which the light incident from the light introduction port looks into the opening (ie, the length of the excitation light introduction port) is about half that in FIG. 2 than in FIG. Considering that the excitation light emitted from the semiconductor laser 2 for excitation at an angle equal to or larger than θ is confined in the transparent block 6, FIG. 3 in which θ is small is more effective for confinement of the excitation light by the transparent block 6. I understand.

The restrictions on the material of the transparent block 6 are that the thermal conductivity is high and the refractive index is lower than that of the solid-state laser rod 1. The first condition is, of course, to carry the heat generated by the rod. The second condition will be briefly described with reference to FIG. Here, the state of refraction of the excitation light in the solid-state laser rod 1 when the rod thermal contact means 8 is substantially equal to the refractive index of the transparent block 6 is qualitatively shown. The excitation light that has entered the side surface of the solid-state laser rod 1 has a refractive index nr of the solid-state laser rod 1 outside the refractive index n.
If it is larger than b (shown by a solid line in the figure), all the light enters the rod up to an incident angle of 90 degrees. On the other hand, when the refractive index nr is smaller than the outer refractive index nb (indicated by a dashed line in the figure), when the incident angle is equal to or more than SIN ^-1 (nb / nr), the light does not enter the rod due to total reflection. That is, since the refractive index of the transparent block 6 is lower than that of the solid-state laser rod 1, the efficiency of incidence of the excitation light on the rod can be increased. In FIG. 4, the refractive index of the rod thermal contact means 8 is assumed to be substantially equal to the refractive index of the transparent block 6, but this can be neglected if the thickness of the rod thermal contact means 8 hardly changes with respect to the rod. (The incident angle from the transparent block 6 to the rod thermal contact means 8 is
It almost coincides with the incident angle from the rod thermal contact means 8 to the solid-state laser rod 1. As a material of such a transparent block 6 having a high thermal conductivity and a refractive index smaller than that of the laser rod 1, for example, Y ₃ Al ₅ O ₁₂ (YAG) having a high refractive index as a host material for determining the refractive index of the solid-state laser rod. ) (1.82),
Sapphire (refractive index 1.76, thermal conductivity 28W / m
K) and MgF ₂ (refractive index: 1.37) are used as host materials such as YLiF ₄ (YLF) (refractive index: 1.47) and LiCaAlF ₆ (Li
When CAF) and LiSrAlF ₆ (LiSAF) are used, MgF ₂ (refractive index 1.
37, a thermal conductivity of 21 W / mK) is a desirable material selection.

The solid-state laser rod 1 is, as described above,
It is located at the rotationally symmetric center of the transparent block 6. For installation, a hole slightly larger than the solid-state laser rod 1 is made in the center of rotation of the transparent block 6 by drilling and polishing, and the solid-state laser rod 1 is inserted here. The solid-state laser rod 1 is made longer than the transparent block 6 in consideration of operability at the time of assembly and ease of fixing. (The length of the rod is longer than the height of the prism or cylinder.)

Since it is necessary to conduct the heat generated in the solid-state laser rod 1 to the transparent block 6, it is necessary to fill the rod thermal contact means 8 between the solid-state laser rod 1 and the transparent block 6. When the solid-state laser rod 1 is not in the rod shape but in the slab shape, a manufacturing method such as an optical contact can be used. Therefore, the rod thermal contact means 8 does not need to be filled with anything. Become. Of course, the rod thermal contact means 8 needs to be transparent to the excitation light. Further, it is not desired that the solid laser rod 1 is stressed by the thermal contact means 8. On the other hand, an epoxy-based adhesive or the like satisfies these conditions, but may be broken during operation due to a difference in the coefficient of thermal expansion between the solid-state laser rod 1 and the transparent block 6, so reliability is increased. Further, once the solid-state laser rod 1 is installed, replacement or the like does not remain. For this reason, in this embodiment, a liquid medium is used as the rod thermal contact means 8. On the other hand, as described in the refractive index of the material of the transparent block 6, the refractive index of the rod thermal contact means 8 is lower than the refractive index of the solid laser rod and higher than that of the transparent block 6 so that the excitation light enters the solid laser rod 1. Increases efficiency. When a material that can adjust the refractive index and does not solidify when used at a low temperature is selected, for example, the transparent block 6 is made of MgF ₂ (refractive index: 1.37), and the laser rod 1 is made of YAG. (Refractive index 1.82), YLF (refractive index 1.4)
7), LiSAF (refractive index 1.4), LiCAF (refractive index 1.3)
In the case of 9), a silicone oil (a commercially available product, which can be adjusted at 1.38 to 1.53, which is a refractive index matching agent often used for optical fiber communication) and the like can be mentioned.
In addition, while utilizing the high thermal conductivity, an aqueous solution of ethylene glycol whose concentration has been adjusted, which is often used in a circulating cooling type solid-state laser used in the field, is used. 9
By adjusting the refractive index at 0%, the refractive index becomes 1.37 to 1.4.
2 can be adjusted).

A hole formed in the side surface of the solid-state laser rod 1 and the center of rotation of the transparent block 6 serves as an interface when excitation light enters the solid-state laser rod 1. Also here, when considering the uniformity of the excitation distribution formed in the solid-state laser rod 1, it is effective to reduce the directivity of the excitation light as much as possible. For this purpose, it is desirable that the side wall of the solid-state laser rod and the outer wall of the hole formed in the center of rotation of the transparent block 6 be made rough to provide diffuse transmission. The surface roughness of the ground rough depends on the refractive index of the rod thermal contact means 8, but is several times to 10 times the wavelength of the excitation light (the larger the difference in refractive index, the higher the surface roughness is the higher the diffusivity). Several μm to 10
It is good to set it to μm. There are both mechanical polishing and chemical treatment in order to obtain the ground rough, but chemical treatment is preferable because cracking and the like can be suppressed.

As for holding the solid laser rod 1 and sealing the liquid used for the rod thermal contact means 8, it is pressed by the end face of the transparent block 6 as shown in FIG. Generally, there is an O-ring seal as an application for sealing a liquid. However, when an O-ring is used, processing and mechanical parts for fixing the O-ring to the transparent block 6 and the outside thereof are required, and the configuration tends to be complicated. For this reason, here, a method was adopted in which the side surface of the rod and the end surface portion of the transparent block were bonded with silicone rubber which hardened into a rubber state. Such silicone rubber is generally called RTV rubber, which reacts with moisture in the air and has a rubber-like effect. It is often used as a sealant, and its elasticity does not deteriorate even at a low temperature of about -50 ° C. There is. This elasticity can relieve the stress on the rubber part due to the difference in the coefficient of thermal expansion between the solid-state laser rod 1 and the transparent block 6, thereby avoiding the problem of breakage that is a problem with commonly used epoxy adhesives. it can. In general, if there is an adhesive or the like that generates outgas near the end face of the solid-state laser rod 1, the end face of the solid laser rod 1 may be burned by laser light to cause damage, but the outgas is very small and used in a vacuum specification. We have a track record in satellite-borne products.

As described above, it is effective to select the excitation light reflecting means 7 set on the side surface of the transparent block 6 as high as possible in reflectance. In consideration of excitation light confinement due to multiple reflections in the transparent block 6, the incident angle of the excitation light incident on the excitation light reflecting means 7 varies. For this reason, it is desired that the excitation light reflecting means 7 has a high reflectance regardless of the incident angle. FIG. 6 shows a wavelength of 800 nm which is an excitation wavelength of the solid-state laser.
4 shows the calculation results of the incident angle dependence of the reflectance of a typical metal material in FIG. Accordingly, it is effective to coat the side surface of the transparent block 6 with gold, silver, copper, or the like having a high reflectivity near 800 nm, which is the excitation wavelength of the solid-state laser at the full incident angle, with a high reflectivity. However, of course, in the case of silver or copper, it is necessary to provide a protective film for preventing oxidation after coating. On the other hand, when simultaneously considering the uniformity of the excitation distribution, it is effective for the excitation light reflecting means 7 to obtain diffuse reflection that makes the direction of the optical axis of the excitation light propagate randomly. In this case, a method of vapor-depositing metal using the side surface of the transparent block 6 as a ground rough surface is effective. The preferred surface roughness at which the diffusion effect can be obtained is about several times to ten times the wavelength, and about several μm to 10 μm. In addition to this, as a method for obtaining diffuse reflection, it is also effective to apply or adhere a diffusive material to the side surface of the transparent block 6. Examples of the diffusible material include various ceramic materials, BaSO ₄ powder, and highly reflective resin (for example, trade name: Spectralon: Lab Sphare).

Further, in the case of pumping from the side, if the solid-state laser rod 1 has a high absorption coefficient for the pumping light wavelength, a strong pumping distribution may be generated on the rod side. As a countermeasure in this case, it is also effective to lower the absorption coefficient to lower the absorption coefficient when the excitation light passes through the rod once. In order to lower the absorption coefficient, the active ion concentration of the solid-state laser rod 1 is reduced, the oscillation wavelength width of the semiconductor laser 2 for excitation is widened, and the oscillation wavelength of the semiconductor laser 2 for excitation is shifted from the absorption peak wavelength. Are effective.

Next, another important point of the present invention, that is, exhaust heat will be described. In order to obtain an axially symmetric temperature distribution in the solid-state laser rod 1, it is necessary to radiate heat symmetrically from the side surface of the solid-state laser rod 1. In addition, even if the amount of heat generated in the solid-state laser rod 1 due to the operation at a high average power increases, the temperature in the solid-state laser rod 1 does not increase so much, so it is effective to reduce the thermal resistance of the heat-dissipating path. In the present embodiment, heat generated by the solid-state laser rod 1 at the center of rotation of the transparent block 4 passes through the transparent block 4. The transparent block 6 is made of a medium having high thermal conductivity and has an axially symmetric shape. Next, heat is exhausted to the heat sink 9 provided by the thermal contact means 11 on each side surface through axially symmetric side surfaces having an area larger than the surface area of the rod. As the thermal contact means 11, a method of sandwiching a thin soft metal thin film such as In or gold, a thin soft metal thin film such as In or gold, a metal coating on the transparent block 6, and a metal such as In or gold, or a solder A method of fusing an alloy such as Furthermore, from the heat sink 9,
The heat is discharged to the outside of the module by the heat pipe 10 having a low thermal resistance. It is desirable to fill the space between the heat pipe 10 and the metal heat sink 9 with a silicon paste having a high thermal conductivity or to silver braze the heat pipe 10 directly to the metal heat sink 9. (In the case of a satellite, etc., the heat is ultimately exhausted to space through a heat panel, etc.) In this configuration, the heat generated by the rod is hardly generated because the exhaust heat path itself is arranged axisymmetrically Heat is axisymmetrically discharged, and an axisymmetric temperature distribution is obtained in the rod. Furthermore, by increasing the area of the surface through which the heat flow flows as the distance from the axis increases, the solid laser rod 1 is excited with low thermal resistance, that is, with high average power, and the temperature rise of the solid laser rod 1 is small even when the amount of generated heat increases. A solid state laser pumping module can be obtained.

If each of the N excitation semiconductor lasers 2 is disposed on each of the N heat sinks 9, the N excitation semiconductor lasers can be simultaneously discharged with heat from the N side surfaces from the transparent block 6. 2 can be exhausted simultaneously. At this time,
Since there is no need to independently provide a heat exhaust path from the solid-state laser rod 1 and the semiconductor laser 2 for excitation, the apparatus can be simplified.

When heat is transferred from the heat sink 9 by the heat pipe 10, a difference in thermal resistance between a plurality of heat pipes to be used and a temperature difference on a heat-dissipating side are caused by a plurality of heat sinks installed on each side of the transparent block 6. When a temperature difference occurs between the transparent blocks 9 and heat enters and exits through the transparent block 6, a temperature distribution that is not axially symmetric may occur in the transparent block 6. Further, when the excitation semiconductor lasers 2 are installed on the respective heat sinks 9, the respective excitation semiconductor lasers 2
There is a possibility that a temperature distribution that is not axially symmetric may similarly occur in the transparent block 6 due to heat generation variation between the two. For this reason, the heat sinks 9 are connected to each other with good heat contact by the heat conducting ring 13. As a result, the temperature difference between the heat sinks 9 is smaller than that of the transparent block 6.
3 can be made uniform by the heat flow flowing through. As the heat conducting ring 13, a metal having high thermal conductivity such as copper or Al, or a metal mesh can be used. It is obvious that the same effect can be obtained even if each heat sink 9 is formed of an integral metal block.

[0046]

As described above, according to the present invention, high absorption efficiency can be obtained in the solid-state laser rod by confining the excitation light in the transparent block and passing the light through the solid-state laser rod a plurality of times. Further, since the excitation light propagating in the transparent block is rotationally symmetric N times with respect to the rod, the excitation distribution formed in the rod can be made uniform. Furthermore, N heat sinks are provided on the side of the transparent block having high thermal conductivity, and the heat is coaxially symmetrically viewed from the rod, so that the temperature distribution in the rod is coaxially symmetric and uniform, and the solid-state laser rod is provided. The efficiency of exhaust heat from the fuel can be increased. Furthermore, the gap between the solid-state laser rod and the transparent block is filled with liquid, and the gap between the end face of the transparent block and the side surface of the solid-state laser rod is sealed with a rubber-like medium. With good introduction, stress due to a difference in thermal expansion between the solid-state laser rod and the transparent block can be reduced, and reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration diagram of a solid-state laser excitation module according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing propagation of excitation light in a positive (2N) prism (N is a natural number) transparent block.

FIG. 3 is a diagram schematically showing propagation of excitation light in a positive (2N + 1) prism (N is a natural number) transparent block.

FIG. 4 is a diagram schematically showing propagation of excitation light due to a difference in the relationship between the refractive index of the transparent block and the solid-state laser rod.

FIG. 5 is a view showing holding means for holding a solid laser rod on a transparent block.

FIG. 6 shows the results of calculating the incident angle dependence of the reflectance of various types of metal with respect to excitation light having a wavelength of 800 nm.

FIG. 7 is a cross-sectional view illustrating a configuration method of a first conventional solid-state laser excitation module.

FIG. 8 is a cross-sectional view illustrating a configuration method of a second conventional solid-state laser excitation module.

[Explanation of symbols]

1 solid laser rod, 2 semiconductor laser for excitation, 3
Metal heat sink, 4 prism, 5 adhesive, 6 transparent block, 7 excitation light reflection means, 8 rod thermal contact means, 9 metal heat sink, 10 heat pipe, 11
Thermal contact means, 12 rod holding means, 13 heat conducting ring.

Claims (19)

[Claims] 1. A transparent block of a substantially regular N prism, a rod insertion hole provided substantially coaxially with a rotationally symmetric axis of the transparent block, a solid laser rod, N semiconductor lasers for excitation, and the rod insertion Holding means for inserting and holding the solid-state laser rod in the hole; input means for inputting excitation light emitted from the N excitation semiconductor lasers to the transparent block; and inputting the excitation light incident on the transparent block. Reflecting means for reflecting light, N heat sinks, first heat discharging means for discharging heat from each of the N side surfaces of the transparent block to each of the N heat sinks, and each of the N heat sinks And a second heat exhaust means for exhausting heat to the outside of the apparatus. 2. The transparent block has a shape of N = 2.
2. The solid-state laser pumping module according to claim 1, wherein the module is a substantially positive N prism of M + 1 (M is a natural number). 3. The solid-state laser rod according to claim 1, wherein Y ₃ Al ₅ O ₁₂ (YAG) is used as a host material, and sapphire is used as the material of the transparent block. Solid-state laser excitation module. 4. The solid-state laser rod according to claim 1, wherein Y ₃ Al ₅ O ₁₂ (YAG), YLiF ₄ (YLF), LiCaAlF ₆ (LiCAF), Li
2. The solid-state laser excitation module according to claim 1, wherein SrAlF ₆ (LiSAF) is used, and MgF ₂ is used as a material of the transparent block. 5. The solid-state laser excitation module according to claim 1, wherein the transparent block has N side surfaces formed as ground rough surfaces. 6. The solid-state laser excitation module according to claim 1, wherein the solid-state laser rod has a side surface formed as a ground rough surface. 7. An excitation light incidence slit surface is provided at each position of the N ridge lines of the transparent block at a position perpendicular to a plane including each ridge line and an N-fold rotationally symmetric central axis of the transparent block, The input means inputs the excitation light from each of the N excitation semiconductor lasers from each of the N excitation light entrance slit surfaces with the optical axis substantially perpendicular to the entrance slit surface. Item 2. A solid-state laser excitation module according to Item 1. 8. The solid-state laser pumping module according to claim 1, wherein said reflection means is a thin metal film provided on each of the side surfaces of said transparent block. 9. The solid-state laser excitation module according to claim 11, wherein said metal thin film is copper. 10. The solid-state laser excitation module according to claim 1, wherein said reflection means is a ceramic plate provided on each of N side surfaces of said transparent block. 11. The heat sink according to claim 1, wherein the N heat sinks are provided on each of the N side surfaces of the transparent block through a thin film of indium or gold. Solid state laser excitation module. 12. As the first heat discharging means, a metal is deposited on each of the N side surfaces of the transparent block, and each of the N heat sinks is fused with an alloy of indium, gold and a solder material. The solid-state laser excitation module according to claim 1, wherein: 13. As the second heat discharging means, a heat discharging hole is formed in each of the heat sinks, and an evaporating part of a heat pipe having a condensing part outside the apparatus is inserted into the heat discharging hole. The solid-state laser excitation module according to claim 1, wherein: 14. The solid-state laser pump module according to claim 1, wherein each of said N heat sinks is provided with each of said N pump semiconductor lasers. 15. The solid-state laser pumping module according to claim 1, wherein each of the N heat sinks is thermally connected by a heat conducting ring. 16. The length of the solid-state laser rod is longer than the height of the transparent block of the substantially regular N prism, and
2. The solid-state laser according to claim 1, wherein a liquid is filled between the solid-state laser rod and the rod insertion hole, and the liquid is sealed between both end surfaces of the transparent block and side surfaces of the solid-state laser. Excitation module. 17. The liquid according to claim 16, wherein the liquid is silicon oil whose refractive index is set smaller than the refractive index of the solid-state laser rod and larger than the refractive index of the transparent block. Solid-state laser excitation module. 18. The ethylene glycol aqueous solution whose refractive index is set to be smaller than the refractive index of the solid-state laser rod and larger than the refractive index of the transparent block. The solid-state laser excitation module as described in the above. 19. The solid-state laser excitation module according to claim 16, wherein silicone rubber is used as the means for sealing the liquid.