JP5062733B2 - Solid state laser equipment - Google Patents

Description

  The present invention relates to a solid-state laser device that obtains a high average output by liquid nitrogen cooling.

In a solid-state laser device, when trying to obtain a high average output, the maximum output is limited by a phenomenon that the laser medium is distorted by heat, a so-called thermal lens effect.
In a solid-state laser device using a sapphire crystal such as titanium sapphire as a laser medium, as shown in Patent Document 1 and Non-Patent Document 1, by cooling the laser crystal at an extremely low temperature, the thermal lens effect is reduced, It is known to configure to obtain a higher average output.

In the prior art, the most effective cooling method is to immerse the laser medium directly in liquid nitrogen. Even when the laser medium is fixed to a copper holder or the like, the metal portion is made as thin as possible, Liquid nitrogen has been configured to reach the vicinity of the laser medium by means such as drilling holes. This is because the metal portion has thermal resistance, and is designed based on the idea that the value should be as small as possible.
This concept was effective for an apparatus having a heat generation amount of several watts.
JP 2005-210037 A J. et al. Yang and B.J. Walker, Optics Letters Vol. 26, p453 (2001).

However, in a high-power laser device that generates more than 100 W, the conventional technology requires cooling to 140K or lower. However, there has been a problem that sufficient cooling cannot be obtained in a high-power laser device having a calorific value exceeding 100 W.
In the conventional high-power laser device, the reason why sufficient cooling could not be obtained was analyzed. According to this, in the conventional high-power laser apparatus, the area where the liquid nitrogen is in contact with the laser medium or the metal part holding the laser medium is limited and does not satisfy the sufficient cooling condition. It became clear that the gas which vaporized in the part which contact | connects the metal part which hold | maintains it, formed the heat insulation layer, and inhibited cooling.

  In view of the above problems, an object of the present invention is to provide sufficient cooling in a high-power laser device.

The present invention employs the following solutions in order to achieve the above object.
The solid-state laser device of the present invention holds a laser medium in a highly thermally conductive metal having a sufficiently large volume compared to the laser medium, for example, a solid laser medium having a volume 10 times or more that of the solid-state laser medium. The heat conductive metal is configured to come into contact with a cooling medium, for example, liquid nitrogen over a large area. As a configuration having a large area, a flat plate shape, a wedge shape in cross section composed of opposing tapered surfaces, or the like is adopted. This configuration prevents cooling from being inhibited by vaporized nitrogen.

Specifically, it is as follows.
(1) A solid-state laser device is a solid-state laser device that cools a heat dissipating metal body provided with a solid-state laser medium by a cooling medium,
A solid laser medium is provided on a heat dissipation metal block of the heat dissipation metal body, and a heat dissipation metal protrusion of the heat dissipation metal body is protruded into the cooling medium.
(2) The solid-state laser device according to (1) is characterized in that the heat-dissipating metal protrusion is formed so that a cooling medium that naturally convects along the surface of the heat-dissipating metal protrusion does not form a vortex. And
(3) In the solid-state laser device according to (1) or (2), the cooling medium that naturally convects the heat-dissipating metal protrusion along the surface of the heat-dissipating metal protrusion does not form a vortex. A groove is formed.
(4) The solid-state laser device according to any one of (1) to (3), wherein the heat radiating metal protrusion is formed into an arbitrary curved surface in a direction from the side continuous to the heat radiating metal block toward the free end. It is characterized by doing.
(5) The solid-state laser device described in the above (4) is characterized in that the curved surface is formed into an arc surface or a parabolic surface in a direction from the side continuous with the metal block for heat dissipation toward the free end.
(6) The laser device according to the above (1) is provided with a protrusion in the vertical direction at the contact portion between the highly heat conductive metal to which the solid laser medium is fixed and the liquid nitrogen, and the cooling capacity is improved by the natural convection of the liquid nitrogen. It is characterized by being enhanced.
(7) In the laser device according to (6), the high heat conductive metal has a concave portion that accommodates a solid laser medium, and is divided and formed including the concave portion. The solid-state laser medium is pressed against the solid-state laser medium so that the solid-state laser medium is accommodated in the recess in a close contact state.
(8) The laser device according to (6) or (7) is characterized in that a soft metal such as indium or a heat conductive compound is filled between the solid laser medium and the good heat conductive metal.
(9) The laser device according to any one of (6) to (8), wherein the laser device includes a liquid nitrogen injection channel and an evaporation gas exhaust channel.

  In the solid-state laser device of the present invention, the solid-state laser medium is provided on the heat-dissipating metal block of the heat-dissipating metal body, and the heat-dissipating metal protrusions of the heat-dissipating metal body are projected into the cooling medium. The heat dissipation area of the metal protrusion can be increased, the area of the heat dissipation metal block that conducts heat to the heat dissipation metal protrusion can be increased, and the solid laser medium can be used to release heat generated by the solid laser medium. It can be provided on the metal heat-dissipating metal block, and the cooling metal portion can be enlarged to obtain a high cooling effect that has been impossible in the past.

  Embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view of the solid-state laser device of the present invention.
The solid-state laser device 1 in FIG. 1 includes a solid-state laser medium 2, a heat-dissipating metal body 5 for dissipating heat generated by the solid-state laser medium 2 into a fluid, and a heat-dissipating metal body 5 for depriving heat. It consists of a cooling medium, for example, liquid nitrogen 9 and a pipe 8 for guiding the liquid nitrogen 9.
The heat dissipating metal body 5 includes a heat dissipating metal block 3 and a heat dissipating metal protrusion 4.
The pipe 8 includes an injection pipe 6 and a cooling / exhaust pipe 7.
The cooling / exhaust pipe 7 is opened at the lower end surface, and the injection pipe 6 is connected to the side surface connected to the lower end surface. The connection position of the cooling / exhaust pipe 7 and the injection pipe 6 is most preferably a side surface connected to the lower end surface of the cooling / exhaust pipe 7 in order to make the flow path along the heat radiating metal projection 4 longer. If it is in a position where the flow path along the heat radiating metal projection 4 can be formed, it can be used without any problem.

On the lower end surface of the cooling / exhaust pipe 7, the surface provided with the heat radiating metal projection 4 of the heat radiating metal block 3 is connected in a sealed state. As a result, the heat-dissipating metal projection 4 is inserted and arranged inside the cooling / exhaust pipe 7 containing the liquid nitrogen 9.
The solid laser medium 2 refers to a crystal for a laser light emitting element such as titanium sapphire.
The heat radiating metal body 5 includes a heat radiating metal block 3 and a heat radiating metal protrusion 4. The heat radiating metal block 3 is a combination of divided blocks divided along a diagonal line, and a concave portion for fixing the solid laser medium is formed at the combined joint.

The heat dissipating metal block 3 may be of any material, shape and structure that can efficiently conduct the heat generated by the solid laser medium 1 to the heat dissipating metal protrusion 4. The shape may be any shape such as a square, rectangle, circle, sector, or ellipse, and may be any structure such as a cube, a rectangular parallelepiped, a sphere, or a polyhedron when viewed three-dimensionally. The material of the heat dissipating metal block 3 is preferably copper or a copper alloy in terms of thermal conductivity and price. The metal block 3 is a highly heat conductive metal having a volume 10 times or more that of the solid laser medium.
In order to increase the cooling efficiency, the heat radiating metal protrusion 4 may have any shape that has a wide contact area with liquid nitrogen and does not generate vortices, such as a flat plate shape, a cross-sectional wedge shape having an opposing tapered surface, and the like. Is preferred. It is preferable that the connecting portion between the heat-dissipating metal projection 4 and the heat-dissipating metal block portion 3 is formed on a (circular) arc surface, a parabolic surface, or the like so that fluid vortices are not generated.
Increasing the contact area with liquid nitrogen means increasing the cooling area, and making it a shape that does not generate vortices causes the evaporated gas to become vortices and stay on the surface of the protrusions, exhibiting a heat insulation structure, cooling action The purpose is to prevent the deterioration.

  Good heat conduction is required from the laser medium 2 to the copper block 3, and the copper block may be divided diagonally and pressed with bolts so that no voids are generated, or there is a possibility that minute voids are generated. In some cases, a soft metal such as indium or a heat conductive compound is filled. The copper block has a protrusion 4 in the liquid nitrogen 3 in the vertical direction. The liquid nitrogen in contact with the protrusions 4 is heated and partially vaporized, but the bubbles rise due to buoyancy. Therefore, the liquid nitrogen performs a convection motion as shown by an arrow A in FIG.

  The thermal conductivity k of copper is 420 W / mK at −100 ° C., and the temperature difference generated when the heat power of P [W] is conducted through a copper block having a cross-sectional area S [square m] length L [m]. ΔT is expressed by the following equation.

As can be seen from the above formula, when the outer shape of the copper block is increased, the cross-sectional area increases with the square of the outer dimension, whereas the length is proportional to the outer dimension, resulting in the temperature of liquid nitrogen and the laser medium. The difference can be reduced.
On the other hand, the nucleate boiling heat transfer from the copper surface to the liquid nitrogen that determines the cooling capacity can be expected to be about 20 W / cm 2 in the case of a clean surface under atmospheric pressure. However, since the temperature difference between liquid nitrogen and copper does not exceed 20K at this time, it is possible to keep the temperature of the laser medium below the required 140K by sufficiently increasing the surface area of copper in contact with liquid nitrogen. Become. (The boiling point of liquid nitrogen at atmospheric pressure is approximately 77K).

Here, liquid nitrogen exhibits a cooling ability by evaporation, but smooth maintenance of liquid nitrogen is required to maintain this ability. In order to prevent the liquid injection from being hindered by the evaporated nitrogen gas, a liquid injection channel is provided separately from the exhaust gas exhaust channel, thereby enabling continuous operation of the laser apparatus.
In this way, the temperature difference generated between the liquid nitrogen and the laser medium is kept small, while the liquid nitrogen has a sufficiently large contact area compared to the cooling power and maintains a high cooling capacity by convection, Smooth liquid supply enables continuous operation. For this reason, a laser apparatus having a high average output, which has been impossible in the past, becomes possible.

FIG. 2 is a configuration diagram of Embodiment 2 of the solid-state laser apparatus of the present invention. Fig.2 (a) is CC sectional drawing of FIG.2 (b) which is a side view. FIG.2 (b) is a BB side view of Fig.2 (a). Here, the parts denoted by the same reference numerals as those in FIG. 1 in FIG. 2 use the description in FIG. 1, and the description thereof is omitted here.
As shown in the cross section of FIG. 2A, the cross-sectional shape of the heat radiating metal protrusion 4 is expanded. In other words, when viewed in cross-section, the heat radiating metal projection 4 has a wide side on the side connected to the heat radiating metal block 3 (upstream side of the flow path) and a width on the tip side of the heat radiating metal projection 4. In addition, a curved surface is formed so as to gently connect the both sides. The curved surface is preferably a gentle curved surface. As shown in FIG. 2B, the heat radiating metal projection 4 is provided with a plurality of grooves on both side surfaces along the flow path. The direction of the flow path is from the outlet of the injection pipe 6 toward the direction in which the evaporative gas exits.

Thus, since the heat radiating metal protrusion 4 is formed in a gentle curved surface, liquid nitrogen vortices are not generated, and the cooling effect is improved. Moreover, since the metal protrusion part 4 for heat dissipation provided the groove | channel along the flow path, a surface area increases and the cooling effect increases.
The copper block may use other metals or heat conductive materials as long as the temperature difference generated between the liquid nitrogen and the laser medium is within an allowable range, and the cooling medium is liquid helium instead of liquid nitrogen. Other liquefied gas or cooling liquid may be used.

  Until now, the titanium sapphire laser has not been used much for industrial use because of its small average output. However, according to the present invention, a high average output is possible and it can be applied to industrial uses such as processing. Moreover, it is applicable not only to a titanium sapphire laser but also to other industrial laser applications that require cryogenic cooling.

It is sectional drawing of the solid-state laser apparatus of this invention. It is a block diagram of Example 2 of the solid-state laser apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Solid state laser apparatus 2 Solid state laser medium 3 Heat radiation metal block part 4, 4a Heat radiation metal projection part 4b Groove part 5 Heat radiation metal body 6 Injection pipe 7 Cooling / exhaust pipe 8 Pipe 9 Liquid nitrogen A Convection direction

Claims (7)

A solid-state laser device for cooling a heat-dissipating metal body provided with a solid-state laser medium by liquid nitrogen,
The solid-state laser device further has a cooling pipe and an injection pipe ,
The heat dissipating metal body is made of a good heat conductive metal,
The cooling pipe is connected to the heat dissipating metal body in a sealed state at the opened lower end surface,
The injection pipe is connected to a side surface connected to the lower end surface of the cooling pipe,
The heat dissipating metal body has a protrusion in the vertical direction and protrudes into the cooling pipe,
The liquid nitrogen guided from the injection pipe is accommodated in the cooling pipe and contacts the heat radiating metal body,
The stored liquid nitrogen convects in the cooling pipe along the vertical projection by the buoyancy of the nitrogen gas which is heated and evaporated by the heat dissipation of the metal body for heat dissipation.
A solid-state laser device characterized by that. Before SL collision caused the groove in the vertical direction by the cross-sectional wedge shape consisting of flat or opposing tapered surface is formed,
The solid-state laser device according to claim 1. The pre SL collision force, a solid-state laser apparatus according to claim 1 or claim 2, characterized in that molded into any curved surface in a direction toward the free end from the protrusion base portion. The pre-Symbol curved, comments in the direction toward the free end of the projection base portion, or solid-state laser apparatus according to claim 3, wherein the shaping parabolic. The good heat conductive metal has a concave portion for accommodating a solid laser medium, and is divided and formed including the concave portion. The good heat conductive metal thus formed is in a state where the solid laser medium is in close contact with the concave portion. 5. The solid- state laser device according to claim 1 , wherein the solid-state laser device is press-contacted to the solid-state laser medium so as to be accommodated in the solid-state laser medium. Solid-state laser apparatus according to claim 5, wherein the wherein the filled soft metal or heat conductive compound such as indium between the good thermal conductivity metal and the solid body laser medium. 7. The solid state laser device according to claim 1, further comprising an evaporative gas exhaust channel.

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