JP2000261070A - Slab type solid-state laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve oscillation efficiency of a slab type solid-state laser by improving the excitation lamps of the laser and their peripheral structures, and causing a solid-state laser medium to efficiently absorb the energy of exciting light. SOLUTION: In a slab type solid-state laser, in which straight tube type excitation lamps 4, reflectors 5, and glass partition plates 3 for forming a coolant flowing passage are arranged on both sides of a slab type solid-state laser medium 1 and cooling water 6 is made to flow through the passage, the lamps 4 are formed into square cross sections, having flat surfaces on the laser medium 1 side and faced opposite to each other on both sides of the coolant flowing passage formed between the glass partition plates 3 and having a uniform width of about 0.5-1 mm, so as to suppress the energy loss of exciting light by reducing the absorbed and damped rates of the light transmitted through the solid- state laser medium by the cooling water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a slab type solid-state laser device for an Nd: YAG laser or the like.

[0002]

2. Description of the Related Art First, FIG. 4 shows a configuration of a conventional example of a slab type solid-state laser device. In the figure, 1 is a slab type solid laser medium, 2 is a heat insulating material superimposed on both upper and lower (width direction) end surfaces of the solid laser medium 1, and 3 is a left and right (thickness) thereof along the longitudinal direction of the solid laser medium 1. Direction) Flat glass partition plates disposed on both sides (for example, a Pyrex glass plate having a function of separating ultraviolet light harmful to the solid-state laser medium and a coolant passage), and 4 is a glass partition plate 3 A straight-tube-type excitation lamp (flash lamp such as Kr, Xe) having a circular cross section disposed so as to face the solid-state laser medium 1 at a distance, a reflector 5 having an elliptical cross-section having an internal reflecting surface, and a solid-state laser medium 6 The cooling water (pure water) flows through the refrigerant flow path partitioned between the glass partition plate 1 and the glass partition plate 2, and around the excitation lamp 4 surrounded by the glass partition plate 3 and the reflector 5.

The laser oscillation operation of the slab type solid-state laser device having such a configuration is well known, and the excitation light emitted from the excitation lamp 4 passes through the cooling water 6 surrounding the lamp and the glass partition plate 3 to form a glass partition. When passing through the plate 3, an ultraviolet region of 300 nm or less is cut and reaches the solid-state laser medium 1. Here, the solid-state laser medium 1 is Nd: Y
In the case of an AG crystal, the energy of the excitation light in each wavelength band is absorbed at an absorption rate as shown in FIG. 5 and contributes to laser oscillation. Further, light in a low absorption wavelength band slightly deviated from a wavelength having a high absorption rate (absorption wavelength) is partially absorbed by the solid-state laser medium 1, and the rest is transmitted through the laser medium and reflected by the reflector 5 on the opposite side. Thereafter, the light enters the solid-state laser medium 1 again and is absorbed by the solid-state laser medium 1 while repeating absorption and transmission. Although not shown, a laser resonator composed of a pair of a total reflection mirror and an output mirror (half mirror) is arranged on the optical axis before and after the solid-state laser medium 1 in FIG. The laser light oscillated in the resonator passes through the output mirror and is extracted as a laser output.

[0004]

However, the oscillation efficiency (laser output / excitation lamp input) of the slab type solid-state laser device is at most about 4% at present and the energy conversion efficiency is low. How to increase the oscillation efficiency is an important issue imposed on the development of a laser device.

That is, according to the study by the inventors,
The conversion efficiency of the light energy with respect to the input of the excitation lamp 4 (in the case of the Xe lamp) is 57% or more, whereas the conventional laser device absorbs the light emitted from the excitation lamp 4 into the solid-state laser medium 1. Is at most 10% moderate and very inefficient. The reason is as follows. That is, (1) The concentration of Nd ³⁺ ion, which is an active medium for absorbing light, is limited from the viewpoint of the growth of YAG crystals. For this reason, even if the thickness of the solid-state laser medium 1 is increased to increase the total amount of Nd ³⁺ ions, even if the thickness of the laser medium increases, the thermal stress increases rapidly even with the same heating value, so that the thickness increases. Also have limitations.

(2) As described above, most of the light in the low absorption wavelength band shown in FIG. 4 passes through the solid-state laser medium 1 and is reflected by the reflector 5 on the opposite side. The light is incident and repeats absorption and transmission. However, in this process, light having a low absorption wavelength is absorbed by the laser medium because there is attenuation due to the reflectance of the reflector 5 and the light absorption of the cooling water 6. The ratio is lower. In other words, taking an alumina reflector as an example, its light reflectance is 98%,
The loss from a single reflection is only 2%. on the other hand,
When light passes through the cooling water (pure water) 6, the absorptivity absorbed by the laser water is about 1% /
mm. However, as described above, the rate at which light having a low absorption wavelength is repeatedly reflected and reflected by the cooling water while traveling back and forth through the laser medium increases, so that the energy loss becomes a value that cannot be ignored. .

[0007] In particular, in the conventional structure shown in FIG. 4, the flat glass partition plate 3 including the circumference of the tubular excitation lamp 4 is included.
Since the space between the reflector 5 and the reflector 5 is completely filled with the cooling water 6, as described above, the distance through which the cooling water 6 passes through the path of the reflection and reciprocation of light between the opposite reflector 5. And the rate at which light is absorbed and attenuated by the cooling water increases accordingly.

In this respect, if the refrigerant passage partitioned between the excitation lamp 4 and the glass partition plate 3 can be set to a very small gap in the entire area, the distance for transmitting light through the cooling water is also shortened. Is reduced, and the oscillation efficiency of the laser device is improved.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide a slab-type solid-state laser device whose structure is improved so that a high oscillation efficiency can be obtained by efficiently absorbing excitation light energy in a solid-state laser medium. To provide.

[0010]

To achieve the above object, according to the present invention, a slab type solid-state laser device is constructed as follows.

According to the first aspect of the present invention, a straight tube-type excitation lamp, a reflector, and a glass partition plate forming a coolant flow path are arranged opposite to a slab type solid laser medium, and cooling water is supplied therein. In the slab-type solid-state laser device to be flowed, at least the surface of the excitation lamp tube facing the solid-state laser medium has a flat tube shape, and a gap serving as a coolant flow path is separated from the glass partition plate. (Claim 1). Specifically, it is configured in the following manner.

(A) The tube shape of the excitation lamp is square in section (claim 2). (b) The tube shape of the excitation lamp is a cross-sectional shape in which the outer peripheral surface excluding the surface facing the solid-state laser medium has a curved surface (claim 3). (c) Further, a reflection surface functioning as a reflector is formed on a part or the entire surface of the tube of the excitation lamp except for a surface region directly facing the solid-state laser medium (claim 4).

According to a second aspect of the present invention, there is provided a slab type solid-state laser device in which an excitation lamp is disposed to face a slab type solid-state laser medium, and cooling water is caused to flow therein. A glass block (for example, an ultraviolet light absorbing glass block) having a flat surface facing the solid-state laser medium, and a gap serving as a coolant flow path between the flat surface of the glass block and the solid-state laser medium. (Refer to claim 5), and a reflection surface functioning as a reflector is formed on a part of or a whole surface area except a surface area directly facing the solid-state laser medium (claim 6).

According to each of the above constructions, since the end face of the excitation lamp facing the solid-state laser medium or the glass block surrounding the excitation lamp is a flat surface, the refrigerant passage defined between the solid-state laser medium and the solid-state laser medium. Can be set to the minimum width required for cooling in the entire area, for example, a narrow gap of about 0.5 to 1 mm. As a result, as described above, the distance through which the light having a low absorption wavelength permeates the cooling water on the path reciprocating between the solid-state laser medium and the reflector becomes shorter, and the attenuation ratio due to absorption into the cooling water decreases accordingly. The excitation energy can be efficiently absorbed by the solid-state laser medium.

According to the study by the inventors, the lasing efficiency of the laser (laser output / excitation lamp input) is 5 to 7 by setting the gap of the refrigerant passage to about 0.5 to 1 mm.
%.

Further, in addition to the above configuration, a part of the outer peripheral surface area excluding the excitation lamp or a surface area of the glass block directly facing the solid-state laser medium (which becomes a transmission window for excitation light),
Or forming a reflective surface that functions as a reflector by applying gold plating or the like on the entire surface, so that the light from the excitation lamp is reflected on the reflective surface just before passing through the refrigerant flow path defined on the back side thereof Since the laser beam is directed toward the solid-state laser medium from the flat surface area on which no plating is applied, the attenuation ratio due to absorption into the cooling water is correspondingly reduced, and the oscillation efficiency is further improved.

Further, in a configuration in which the excitation lamp is surrounded by a glass block made of ultraviolet light absorbing glass or the like, the glass block serves as a refrigerant flow path partition member for the solid-state laser medium instead of a glass partition plate in a conventional laser device. Fulfill. Moreover, by opening a round hole in the glass block and inserting a circular tube-shaped excitation lamp therein, the coolant flow path between the excitation lamp and the glass block can be set to a narrow gap with a uniform width. The attenuation ratio when light passes through the cooling water is suppressed to a low level.

[0018]

FIG. 1 is a block diagram showing an embodiment of the present invention.
A description will be given based on each embodiment shown in FIGS. In each of the illustrated embodiments, the same members corresponding to those in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted.

FIG. 1 shows a first embodiment of the present invention.
1 shows an embodiment corresponding to FIG. In this embodiment, a straight tube-type excitation lamp 4 disposed on both sides of a solid-state laser medium 1 via glass partition plates 3 has a tube (quartz glass tube) whose outer peripheral surface is flat as shown in the figure. And a flat surface thereof is disposed so as to face the solid-state laser medium 1 and the glass partition plate 3 in parallel. The coolant passage width d defined between the glass partition plate 3 and the outer peripheral surface of the excitation lamp 4 and between the excitation lamp 4 and the reflector 5 surrounding the excitation lamp 4 is necessary for cooling to about 0.5 to 1 mm. The minimum gap is set, and the cooling lamp is cooled by flowing cooling water through this gap. In the illustrated embodiment, two pump lamps 4 are arranged on one side of the solid-state laser medium 1, but the present invention is not limited to this, and one pump lamp 4 may be used. Further, the excitation lamp may be arranged on only one side of the solid-state laser medium 1.

According to this configuration, the pumping light transmitted through the solid-state laser medium 1 is reflected by the reflector 5 on the opposite side, and passes through the cooling water 6 in the coolant flow path on the optical path until returning to the solid-state laser medium 1 again. The distance is at most about 4 mm (four times the aforementioned gap width d). Here, the light absorptivity when light having a wavelength of 700 to 900 nm passes through cooling water (pure water) is about 1% /
mm, the rate of absorption by the cooling water in the reciprocating optical path can be suppressed to only about 4 to 5%. Therefore, even if the attenuation ratio of the reflector 5 is set to 2%, the energy attenuation ratio in the light reciprocating path is less than 7%.

According to a calculation made by the inventor based on this, when the solid-state laser medium 1 is a Nd: YAG crystal, the laser device having the conventional configuration shown in FIG.
Although only about 20% of the excitation light energy of 00 to 900 nm can be used, and its laser oscillation efficiency is at most 4%, according to the configuration of the present invention, the wavelength of 700 to 9
It has been confirmed that the laser oscillation efficiency can be improved to 5 to 7% by increasing the utilization of the 00 nm excitation light to 50% or more.

[Embodiment 2] FIG. 2 shows a third embodiment of the present invention.
1 shows an application example corresponding to FIG. In this embodiment, the tube shape of the excitation lamp 4 is
And the outer peripheral surface excluding the opposing surface is formed into a curved surface (an elliptical surface, a paraboloid, or another irregular surface). Then, as described in the first embodiment, the flat surface of the excitation lamp 4 is disposed so as to face the solid laser medium 1 and the glass partition plate 3 in parallel with each other. Reflector 5 surrounding the periphery of
A coolant passage having a width of about 0.5 to 1 mm is defined between them, and the cooling water 6 flows through the passage. Further, in this embodiment, a reflecting surface 4a plated with gold or the like is formed on the outer peripheral surface area of the tube of the excitation lamp 4 excluding the surface area directly facing the solid-state laser medium 1. The reflecting surface 4a may be provided on a part of the outer peripheral surface, and when the flat surface of the excitation lamp 4 is larger than the width of the solid-state laser medium 1, a surface directly facing the solid-state laser medium. Gold plating may be applied to the upper and lower ends of the flat surface while leaving the area.

According to such a configuration, light emitted backward from the excitation lamp 4 (the side opposite to the solid-state laser medium 1) passes through the cooling water flowing between the outer peripheral surface of the excitation lamp 4 and the reflector 5. The light is reflected by the reflection surface 4a before this, and then propagates toward the solid-state laser medium 1. Also, the solid-state laser medium 1 emitted from the excitation lamp 4 located on the opposite side
Most of the light that has passed through is reflected by the reflection surface 4a in the same manner as described above, and returns to the solid-state laser medium 1 again. As a result, the attenuation ratio of the pump light absorbed by the cooling water in the reciprocating path is further reduced as compared with the first embodiment, and the oscillation efficiency of the laser device is further improved.

[Embodiment 3] FIG. 3 shows a third embodiment of the present invention.
1 shows an embodiment corresponding to FIG. In this embodiment, an excitation lamp (circular tube lamp) 4 is surrounded by a glass block 7, for example, a glass block made of ultraviolet light absorbing glass such as Pyrex glass, and is incorporated in a laser device. Here, the glass block 7 has a flat surface on the surface facing the solid-state laser medium 1 and a cross-sectional shape having a curved outer peripheral surface excluding the flat surface, similar to the cross-sectional shape of the excitation lamp 4 in the above-described embodiment. A lamp insertion hole having an inside diameter slightly larger than the lamp diameter for inserting the excitation lamp 4 is opened in the layer along the longitudinal direction thereof,
Further, a reflection surface 7a plated with gold or the like is formed on an outer peripheral surface area of the glass block 7 excluding a flat surface area directly facing the solid-state laser medium 1. Although one excitation lamp 4 is inserted into the glass block 7 in the illustrated example, two excitation lamps 4 can be accommodated by opening two lamp insertion holes in the glass block 7. .

At the time of assembling into a laser device, the glass partition plate 3 employed in each of the above-described embodiments and the conventional example shown in FIG. To the solid-state laser medium 1
The coolant flows through the outer peripheral area of the glass block 7 including the gap between the glass block 7 and the gap between the lamp insertion hole of the glass block 7 and the excitation lamp 4 as a coolant flow path, and the solid-state laser medium 1, The excitation lamp 4 is cooled.

According to this configuration, even if the excitation lamp 4 is a tube-shaped lamp, the width of each refrigerant flow path crossing the reciprocating optical path of the excitation light is set to, for example, a narrow gap of about 0.5 to 1 mm. Accordingly, the same effect as in the above-described embodiment can be obtained. In addition, by forming the reflecting surface 7a on the outer peripheral surface of the glass block 7 except for the flat surface area directly facing the solid-state laser medium 1, the reflecting surface formed on the outer peripheral surface of the excitation lamp 4 in the second embodiment described above. An effect similar to that of 4a is obtained.

In the slab type solid-state laser device of the Nd: YAG crystal, the thermal lens effect due to the temperature distribution in the crystal is substantially suppressed by making the laser beam zigzag in the slab type laser medium. Thus, even if the present invention absorbs more excitation light and increases the amount of heat generated, the quality of the laser beam does not deteriorate.

[0028]

As described above, according to the structure of the present invention, the coolant flow path defined inside the laser device, particularly in the area around the excitation lamp, and in the area facing the solid-state laser medium. By setting the path width to a uniform narrow gap, the rate of attenuation of light absorbed when passing through the cooling water can be reduced, and the lamp excitation light can be efficiently absorbed by the solid-state laser medium. Compared with that, the laser oscillation efficiency can be improved to about 2 to 5 to 7%.

An excitation lamp according to claim 4 or 6,
Further, a further effect can be expected by forming a reflecting surface on the peripheral surface of the glass block surrounding the excitation lamp and having the reflector function itself.

[Brief description of the drawings]

FIG. 1 is a configuration sectional view of a slab type solid-state laser device according to a first embodiment of the present invention;

FIG. 2 is a configuration sectional view of a slab type solid-state laser device according to a second embodiment of the present invention;

FIG. 3 is a configuration sectional view of a slab-type solid-state laser device according to a third embodiment of the present invention;

FIG. 4 is a cross-sectional view of a configuration of a conventional slab type solid-state laser.

FIG. 5 is a characteristic diagram showing a relationship between a wavelength of light and an absorptivity for an Nd: YAG crystal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid-state laser medium 3 Glass partition plate 4 Excitation lamp 4a Reflection surface 5 Reflector 6 Cooling water 7 Glass block

Claims (6)

[Claims] 1. A slab type in which a straight tube-type excitation lamp, a reflector, and a glass partition plate forming a coolant flow path are arranged opposite to a slab type solid laser medium, and cooling water flows through the inside thereof. In the solid-state laser device, the tube of the excitation lamp has at least a surface facing the solid-state laser medium in a flat tube shape, and is arranged close to the glass partition plate with a gap serving as a coolant flow path therebetween. A slab-type solid-state laser device characterized by the above-mentioned. 2. The solid-state laser device according to claim 1,
A slab-type solid-state laser device, wherein the tube shape of the excitation lamp is rectangular in cross section. 3. The solid-state laser device according to claim 1,
A slab-type solid-state laser device, wherein the tube shape of the excitation lamp is a cross-sectional shape in which the outer peripheral surface excluding the surface facing the solid-state laser medium has a curved surface. 4. A solid-state laser device according to claim 1, wherein a part of the peripheral surface of the tube of the excitation lamp except for a surface directly facing the solid-state laser medium or a reflector is provided on the entire surface. A slab-type solid-state laser device having a reflection surface functioning as a slab. 5. A slab-type solid-state laser device in which a straight-tube-type excitation lamp is disposed opposite to a slab-type solid-state laser medium, and cooling water is flowed therein. A slab-type solid-state laser, wherein the opposing surface is surrounded by a glass block having a flat surface, and the flat surface of the glass block is disposed to face the solid-state laser medium with a gap serving as a refrigerant flow path therebetween. apparatus. 6. The solid-state laser device according to claim 5,
A slab-type solid-state laser device, wherein a reflection surface functioning as a reflector is formed on a part or the entire surface of a glass block excluding a surface area directly facing the solid-state laser medium.