JPH0240222B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a surface-cooled/surface-excited solid-state laser device, such as a laser processing device for welding and drilling, and a laser annealing device used for semiconductor surface treatment. It is used for etc.

[Conventional technology]

In a typical conventional solid-state laser device, a cylindrical laser active medium and an excitation lamp are respectively arranged at the focal point of an ellipsoidal reflector, and the excitation light from the excitation lamp is reflected by the reflector to form the laser active medium. It has a structure that focuses light. This solid-state laser device has no problems when the laser light output is relatively low, but when it exceeds 1 J, a temperature difference occurs between the center of the laser active medium and its surface. this is,
A temperature gradient occurs from the surface of the laser active medium toward the center, and when looking at the cylindrical cross section of the laser active medium, the refractive index distribution becomes non-uniform in the radial direction, and the phenomenon of lens effect due to heat causes the laser beam to become laser active. Due to condensation in the medium or birefringence due to heat,
Disturbs the transverse mode (TEM mode) of the laser beam,
This caused the output to become unstable. Furthermore, if the temperature difference becomes large, the laser active medium will be destroyed due to thermal strain.

In order to solve these problems, surface-cooled, surface-excited (slab) solid-state laser devices have been proposed.

As shown in the front view of FIG. 1 and the vertical sectional view of FIG. Cooling passages 8 and 9 are formed by separating partition plates 4 and 5 made of a magnetic substance from the surface (upper and lower surfaces) of the laser active medium 1 and fixing them to reflectors 6 and 7. The surface (upper and lower surfaces) of the laser active medium 1 is directly excited (pumped) by excitation lamps 12 and 13 as well as by reflectors 6 and 7.
Since the excitation lamps 12 and 13 side surfaces form a parabolic curve and the excitation lamps 12 and 13 are arranged at the focal point, the excitation lamps 12 and 13 are indirectly excited by the reflected light from the reflectors 6 and 7. . As a result, the incident laser beam 10 enters from one end surface of the laser active medium 1, undergoes multiple reflections on the upper and lower surfaces parallel to each other, and the emitted light 11 is amplified and output from the other end surface.

Next, the temperature distribution and refractive index distribution of the laser active medium 1 of such a surface-cooled/surface-pumped solid-state laser device will be explained with reference to FIG. First, the temperature distribution T(X) in the thickness direction of the medium 1, that is, in the It is indicated by.

T (X) = (b ^{2 -} of
To is To=b ² Q/2K.

As shown in Fig. 2, the laser beam is repeatedly reflected on the surface (upper and lower surfaces) of the medium 1 and passes through a zigzag optical path, and at that time, it passes through the low-temperature parts of the cooled surface (upper and lower surfaces of +b and -b). Since the light travels alternately between the central high-temperature portion and the center, the light propagates through the medium 1 with an averaged temperature distribution.

Next, the refractive index distribution n(x) in the X direction of the medium 1 depending on the temperature is expressed by the following equation (2), and its curve diagram is shown in FIG. 3c.

n(x)=no−(dn/dT)Qx ₂ /2K …(2) Also, regarding the refractive index, the laser beam is transmitted to the high refractive index portion of the surface of the medium 1 (the upper and lower surfaces of +b and −b). Since the light travels through the central low refractive index portion repeatedly, it propagates through the medium 1 with an averaged refractive index distribution state.

As a result, in such a surface-cooled/surface-pumped solid-state laser device, thermal distortion of the laser light is removed in the X direction by multiple reflections of the laser light on the cooled surface of the medium 1, and lens effects and complex It has the advantage of not causing refraction phenomena.

However, the excitation light distribution due to the direct excitation light from the excitation lamps 12 and 13 and the reflected excitation light from the reflectors 6 and 7 is not uniform in the width direction (y direction) of the medium 1. That is, as shown in FIG. 4, the parabolic curved surface of the reflector 6 is, for example,
It has a curve of y ² = 40X, the distance OM from the center O of the lamp 12 to the center M of the parabolic curved surface is 10 mm, the distance OP to the point P on the surface of the medium 1 is 20 mm, and the reflector 6
If the reflectance of is 80%, then point P on the surface of medium 1
The relative light amount ratio between (O) and any point Q(y) is
The actual measurement result is shown by the curve α in FIG. According to this curve α, point Q (15) 15 mm away from point P
In this case, the relative light amount ratio drops to 46%. This means that a temperature distribution occurs in the width direction (y direction) of the medium 1, and along with this temperature distribution, a refractive index distribution in the same direction also occurs.

Therefore, in the conventional surface-cooled/surface-pumped solid-state laser device, the thickness direction (x
However, in the width direction (y direction), there was a drawback that temperature distribution and refractive index distribution occurred, similar to the cylindrical laser active medium. In order to keep the relative light amount ratio shown in FIG. 5 within 10% in practice, the medium 1
The total width of the laser beam had to be within 10 mm, which put a limit on the ability to increase the output of the laser beam.

[Problem that the invention seeks to solve]

The present invention has been made in order to eliminate the above-mentioned conventional drawbacks, and the present invention has been made to eliminate the above-mentioned drawbacks of the conventional laser active medium 1.
The purpose of the present invention is to provide a surface-cooled, surface-pumped solid-state laser device that significantly reduces temperature distribution and refractive index distribution not only in the thickness direction (x direction) but also in the width direction (y direction). .

[Means for solving problems]

In order to achieve such an object, in the surface-cooled/surface-pumped solid-state laser device according to the present invention, the excitation lamp has a flat surface facing the laser active medium, and a width of the laser active medium. It has a flat shape that spreads in the direction, and is characterized in that the upper surface of the laser active medium and the flat surface are arranged parallel to each other.

[Effect]

The basic operation of the surface cooling/surface excitation type of the present invention is the same as described above, but in particular, the excitation lamp has a flat surface facing the laser active medium, and the excitation lamp has a flat surface facing the laser active medium. It has a flat shape that spreads in the width direction, and by arranging the upper and lower surfaces of the laser active medium and the flat surface parallel to each other, the upper and lower surfaces of the laser active medium and the excitation opposite to the surfaces are arranged parallel to each other. Since the spacing from the flat surface of the lamp is substantially uniform across the width, the excitation light applied to the laser active medium has a uniform width distribution, and the temperature and refractive index distributions in the same direction are also uniform. It is becoming uniform.

〔Example〕

An embodiment of the surface _- cooled/surface- _pumped solid-state laser device according to the present invention is shown in FIG.
2 is a sectional view taken along the line X ₂ -X ₂ of FIG.

The laser active medium 1 is phosphate glass (LHG).
-8: Made by Hoya Glass Co., Ltd.) with a flat parallelogram cross-sectional shape (dimensions: 6 x 30) with both end faces inclined at an inclination angle of 45 degrees.
(thickness x width) mm), and in particular, the input/output surfaces, which are both end surfaces, and the upper and lower surfaces parallel to each other that perform multiple reflections are polished smooth to reduce loss. This medium 1
is fixed and supported by supports 2 and 3 on both sides thereof. The partition plates 4 and 5 are the excitation lamps 1
They are made of a material that transmits the excitation light of 8 and 19, such as quartz glass, and are placed parallel to each other at a distance of about 1 to 3 mm from the opposing surfaces of the medium 1 and the supports 2 and 3. Supports 14,
It is firmly supported by 15, 16, and 17. The excitation lamps 18 and 19 are made of quartz glass with a wall thickness of approximately 1 mm and dimensions of approximately 4 x 34 x 120 (thickness x width x length) mm.
The supports 20, 21, 22, 23 are arranged parallel to the upper and lower surfaces of the medium 1 and are spaced approximately 2 to 5 mm from the partition plates 4 and 5, with Xe gas sealed inside. It is supported by fixing its both sides to. And the reflector 24,
25 has a U-shaped cross section, and its internal bottom surface, that is, the surface facing the lamps 18 and 19, is parallel to the flat surfaces of the lamps 18 and 19 to increase the reflectance. , gold plating is applied, and is spaced from the opposing surfaces of the supports 20, 21, 22, 23 and the lamps 18, 19 by about 1 to 5 mm.

By separating the medium 1 and supports 2, 3 from the partition plates 4, 5 and supports 14, 15, 16, 17, the cooling passages 8, 9 are separated from the lamp 18 and supports 20, 21.
By separating the partition plate 4 and the reflector 24, the cooling passages 26 and 27 are separated from the lamp 19 and the support 2.
Cooling passages 28 and 29 are formed by spacing between 2 and 23 and the partition plate 5 and reflector 25, respectively,
These cooling passages 8, 9, 26, 27, 28, 29
Cooling water (pure water) is passed through the medium 1 and lamp 1.
8 and 19 are cooled.

The excitation light from the lamps 18 and 19 directly excites the upper and lower surfaces of the medium 1 through the partition plates 4 and 5, and
The upper and lower surfaces of the medium 1 are excited through the partition plates 4 and 5 by the excitation light reflected by the reflectors 24 and 25.
In this case, the lamps 18 and 19 have a flat surface facing the laser active medium, and have a flat shape extending in the width direction of the laser active medium, and have upper and lower surfaces of the laser active medium. Since the flat surfaces are arranged parallel to each other, the temperature distribution on the upper and lower surfaces of the medium 1 caused by the above-mentioned excitation light, especially in the width direction, is made almost uniform. This uniformity of temperature distribution is even more effective because in this example the surfaces of the lamps 18 and 19 are cooled as described above.

On the other hand, the temperature distribution in the thickness direction of the medium 1 is determined by multiple reflections of the laser beam on the upper and lower surfaces of the medium 1.
Similar to the conventional surface cooling/surface excitation type, it is made uniform. The solid-state laser device of this example is
The incident light 10 is incident perpendicularly to the incident surface of the medium 1,
It propagates while being amplified due to multiple reflections on the upper and lower surfaces and surface excitation on the upper and lower surfaces, and the output light 1 is emitted from the output surface.
1 is emitted. Note that a solid-state laser oscillation device is configured by arranging mirrors 30 and 31 perpendicular to the optical axis on each side of the incident light 10 and the output light 11.

The above-mentioned relative light quantity ratio in the width direction of the medium 1 according to this example is shown by the curve β in Fig. 5, and is only 80% at a total width of 30 mm (Q(15) in the figure), compared to 46% in the conventional case. It can be seen that the uniformity of temperature distribution has been significantly improved. In addition, the practical light intensity ratio
Regarding 10%, it can be seen that in this example, the total width is 20 mm, which is twice as wide as the conventional 10 mm. This is because the input energy of destruction due to the lens effect due to temperature difference, birefringence, or thermal strain is proportional to the square of the relative light intensity ratio (80%/46%) in the full width dimension. This means that it can be tolerated more than twice as much, and high output can be achieved.

In other embodiments of the invention, individual functional components may be modified. For example, the material of the laser active medium may be Nd:YAG, Nd:GGG, YLF, etc., or its shape may be a flat parallelogram cross-section with the incident angle at the Brieusta angle, so that the incident light and the outgoing light are parallel to each other. You may also do so. The gas sealed in the excitation lamp may be Kr, and the reflective surface of the reflector may be silver-plated with an anti-oxidation film or BaSo ₄ .
A film such as the above may be formed. Moreover, cooling gas may be used for cooling.

〔Effect of the invention〕

As described above, according to the present invention, the excitation lamp has a flat surface facing the laser active medium, and has a flat shape extending in the width direction of the laser active medium, and Since the upper and lower surfaces of the active medium and the flat surface are arranged parallel to each other, the surface of the laser active medium can be excited uniformly, and the temperature distribution in the width direction can be made uniform. Moreover, it has the advantage that it can tolerate three times as much input energy for destruction due to lens effect due to temperature difference, birefringence, or thermal strain as compared to the conventional method, and can realize a high-output laser device.

[Brief explanation of drawings]

Fig. 1 is a front view of a conventional surface-cooled/surface-pumped solid-state laser device, Fig. 2 is a vertical cross-sectional view of Fig. 1, and Fig. 3 is a temperature distribution and temperature distribution in the thickness direction of the laser active medium in the conventional device. Diagram showing refractive index distribution, 4th
The figure shows the pumping light reflected by the reflector of a conventional device, FIG. 5 is a curve diagram showing the relative light intensity ratio in the width direction of the laser active medium, and FIG. 6 is a surface-cooled/surface-pumped solid-state laser according to the present invention. An example of the device is shown, and figure a is a perspective view and figure b is a perspective view of figure a.
The X ₁ -X ₁ sectional view and the same figure c are the X ₂ -X ₂ sectional views of the same figure a. 1... Laser active medium, 4, 5... Partition plate, 18,
19...Excitation lamp, 24, 25...Reflector.

Claims (1)

[Scope of Claims] 1. A laser active medium having upper and lower surfaces parallel to each other that reflects the laser beam multiple times, and an excitation lamp and a reflector arranged separately from the upper and lower surfaces of the laser active medium, Surface cooling in which excitation light from an excitation lamp directly excites the upper and lower surfaces of the laser active medium, and the upper and lower surfaces of the laser active medium are excited by reflected light from the reflector to cool the upper and lower surfaces of the laser active medium. - In the surface-pumped solid-state laser device, the excitation lamp has a flat surface facing the laser active medium and a flat shape that extends in the width direction of the laser active medium. A surface-cooled/surface-excited solid-state laser device, characterized in that the upper and lower surfaces of the laser active medium and the flat surface are arranged parallel to each other.