JPH10303480A - Solid laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain laser output which has a small divergent angle and excellent convergence without being affected by output change, by installing solid laser medium between a rear mirror of a convex mirror and an output mirror of a plane mirror. SOLUTION: In a solid laser oscillator 1, a solid laser medium 7 having a length of L3 is arranged between a rear mirror 3 constituted of a convex mirror whose radius of curvature is R1 and an output mirror 5 constituted of a plane mirror. Both of the end surfaces of the solid laser medium 7 are constituted as convex surfaces having suitable radiuses of curvature. The distance L1 between the rear mirror 3 constituted of the convex mirror and the center of the laser medium 7 is set longer than the distance L2 between the output mirror 5 and the center of the laser medium 7. The rear mirror 3 constituted of the convex mirror acts to extend the fundamental mode radius, and forms a Galilean telescope. As a result, the thermal lens effect of the solid laser medium is reduced, and output dependency can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a solid-state laser oscillator.

[0002]

2. Description of the Related Art A high-power solid-state laser oscillator is required to increase the power density at a processing point. In order to meet this demand, in a solid-state laser oscillator, it is necessary to impinge a laser beam with improved light-collecting performance or beam quality on a small-diameter optical fiber. Usually, in a solid-state laser oscillator for extracting high output, a resonator is formed using a plane or a mirror close to a plane.

In a solid-state laser oscillator, a high-intensity xenon lamp or a krypton lamp is arranged, for example, around an Nd-YAG laser rod to excite the laser rod. In order to prevent the temperature of the laser rod from rising due to the excitation light, the outside of the laser rod is cooled by cooling water. As a result, a temperature gradient is generated between the inside and the outer peripheral portion of the laser rod, thereby causing a change in the refractive index between the central portion and the outer side of the laser rod, and the laser rod itself acts like a convex lens. Become like Such a phenomenon is generally called a thermal lens effect.

[0004]

The thermal lens effect is as follows.
Since it changes depending on the output of the laser resonator (or the power supplied to the excitation lamp), the laser beam diameter and the divergence angle of the laser beam change depending on the output.
Changes in laser beam diameter and laser beam divergence angle
When laser light is incident on a small-diameter optical fiber, the maximum incident angle is determined by the optical fiber, so a change in the beam diameter of the laser light on the incident lens directly leads to an increase in the condensing diameter and impairs the condensing ability. Will be.

[0005] In the solid-state laser oscillator in which the resonator is formed using the flat or nearly flat mirror as described above, it is difficult to improve the beam quality because the fundamental mode diameter cannot be increased. for that reason,
As means for improving beam quality, (a) use of a small diameter laser rod. (B) Increase the resonator length. (C) Insert an aperture into the resonator. (D) The resonator is composed of a concave mirror and a concave mirror, or a concave mirror and a convex mirror.
(E) Insert a telescope into the resonator. Various means are used.

[0006] In the various means for improving the beam quality described above, there is a problem that the laser output is reduced in the case of using the small diameter laser rod of (a). Also,
The method of (b) increasing the cavity length has a problem that the oscillation region of the laser is narrowed and the laser is not compact. In the method of (c) in which an aperture is inserted into the resonator, the efficiency is extremely reduced in a low power region, and the linearity of the laser output with respect to the input is lost, so that it is difficult to use. Further, in the method (d) or (e), there is a problem that a laser oscillation region becomes narrow. And, even if these various means (a) to (e) are used, the problem that the laser beam diameter or the divergence angle of the laser beam changes depending on the output has not been solved.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a solid-state laser oscillator which has a small laser output dependency and a small beam divergence angle and has a good light-collecting property. That is.

[0008]

According to a first aspect of the present invention, in the solid-state laser oscillator, a solid-state laser medium is provided between a rear mirror of a convex mirror and an output mirror of a plane mirror, and the rear mirror and the laser medium are provided. The point is that the distance to the center is longer than the distance between the output mirror and the center of the laser medium.

The solid-state laser oscillator according to claim 2 is
In a solid-state laser oscillator, a rear mirror of a convex mirror,
Provide a solid-state laser medium between the concave mirror and the output mirror,
The distance between the rear mirror and the center of the laser medium is longer than the distance between the output mirror and the center of the laser medium.

[0010] The solid-state laser oscillator according to claim 3 is
3. The solid-state laser oscillator according to claim 1, wherein a radius of curvature of the rear mirror is from 0.3 m to 2.
The point is that the distance is within a range of 0 m.

[0011] The solid-state laser oscillator according to claim 4 is
The solid-state laser oscillator according to claim 2, wherein the output mirror is a concave mirror having a radius of curvature of 1.0 m to ∞ (= plane mirror).

Therefore, according to the first, second, third or fourth aspect of the present invention, the rear mirror and the solid-state laser medium constitute a Galilean telescope optical system, and the solid-state laser medium The effect of reducing the thermal lens effect can be obtained, and a laser output with a small divergence angle and good condensing properties can be obtained. Further, the stable operation region of the oscillator is widened.

[0013] The solid-state laser oscillator according to claim 5 is
The solid-state laser oscillator according to claim 1, wherein both end surfaces of the solid-state laser medium are formed as convex surfaces.

Therefore, by forming both end surfaces of the solid-state laser medium as convex surfaces, it is possible to suppress an increase in the threshold value of laser oscillation in addition to the effects of the invention according to claims 1 to 4.

A solid-state laser oscillator according to claim 6 is
In a solid-state laser oscillator, a concave mirror rear mirror,
A solid laser medium is provided between the plane mirror and the output mirror,
The gist is that a distance between the rear mirror and the center of the laser medium is set longer than a distance between the output mirror and the center of the laser medium.

According to a seventh aspect of the present invention, in the solid-state laser oscillator, a solid-state laser medium is provided between a rear mirror of the concave mirror and an output mirror of the concave mirror, and a distance between the rear mirror and the center of the laser medium. Is longer than the distance between the output mirror and the center of the laser medium, and the radius of curvature of the rear mirror is smaller than the radius of curvature of the output mirror.

The solid-state laser oscillator according to claim 8 is
8. The solid-state laser oscillator according to claim 6, wherein a radius of curvature of the rear mirror is from 0.2 m to 0.1 mm.
The point is that the distance is within a range of 4 m.

A solid-state laser oscillator according to claim 9 is
9. The solid-state laser oscillator according to claim 6, wherein said output mirror has a radius of curvature of 1.0.
The gist is that the concave mirror has a radius of curvature ranging from m to ∞ (= plane mirror).

Therefore, according to the sixth, seventh, eighth or ninth aspect of the invention, the rear mirror and the solid-state laser medium constitute a Kepler-type telescope optical system, and the solid-state laser medium The effect of reducing the thermal lens effect can be obtained, and a laser output with a small divergence angle and good condensing properties can be obtained. Further, the stable operation region of the oscillator is widened.

A solid-state laser oscillator according to a tenth aspect is the solid-state laser oscillator according to the sixth, seventh, eighth or ninth aspect, wherein both end surfaces of the solid-state laser medium are formed as convex surfaces. The gist is that.

Therefore, by forming both end surfaces of the solid-state laser medium as convex surfaces, in addition to the functions of the invention according to claim 6, 7, 8 or 9, the increase in the threshold value of laser oscillation can be suppressed. Can be.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of a solid-state laser oscillator according to the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a solid-state laser oscillator (resonator). In FIG. 1, device components other than the optical system such as a light source for exciting the laser medium and a cooling device for the laser medium are omitted.

The solid-state laser oscillator 1 shown in FIG.
Includes a rear mirror 3 curvature radius is convex mirror of R _1,
In which a plane mirror (radius of curvature ∞) formed by arranging the solid-state laser medium 7 of length L ₃ between the output mirror 5 composed of. Both end faces of the solid laser medium 7 is formed on the convex surface having an appropriate radius of curvature R _2. Further, in the laser oscillator 1 having the above configuration, the rear mirror 3 made of a convex mirror is used.
The distance L ₁ from the laser medium 7 to the center of the laser medium 7 is longer than the distance L ₂ from the output mirror 5 to the center of the laser medium 7.

The solid-state laser medium 7 includes:
YAG (Y ₃ Al ₅ O ₁₂ : Nd ^{3 +} ), YLF (LiY
F ₄ : Nd ^{3 +} ), alexandrite (BeAl ₂ O)
₄ : Cr ^{3 +} ), ruby (Al ₂ O ₃ : Cr ^{3 +} ), C
A rod material of a laser medium such as TH: YAG can be used. In the laser oscillator 1, the distance L ₁ , the distance L _{2, the} curvature of the rear mirror 3, and the like are appropriately set so that the laser oscillator 1 enters a region where the laser oscillator 1 can oscillate stably.

In the laser oscillator 1, when the solid-state laser medium 7 is excited by an excitation light source (not shown), a temperature gradient between the center and the surface of the solid-state laser medium 7 is high at the center and low at the surface. As a result, the refractive index between the central part and the surface side changes, and the solid-state laser medium 7 has the function of a convex lens due to the so-called thermal lens effect. The degree of the thermal lens effect varies depending on the type of the laser medium.

In the laser oscillator 1 having the above-described configuration, the rear mirror 3 composed of the convex mirror has a Galilean type with the solid laser medium 7 having the function of expanding the fundamental mode diameter and having the function of a convex lens due to the thermal lens effect. Is formed to reduce the thermal lens effect of the solid-state laser medium, and it is possible to obtain a laser output with little output dependency and a small divergence angle and a good condensing property. In addition, the stable operation area of the laser oscillator is widened.

Further, the laser oscillator 1 having the above-described configuration is used.
In this case, the threshold value of the laser oscillation tends to be relatively high. However, in order to cope with this tendency, both ends of the solid-state laser medium 7 are provided with convex surfaces having an appropriate radius of curvature R ₂ , so that Can be reduced.

FIG. 2 shows a second embodiment of the solid-state laser oscillator (resonator) according to the present invention. In FIG. 2, as in FIG. 1, device components other than the optical system, such as a light source for exciting the solid-state laser medium and a cooling device for the laser medium, are omitted. The same solid laser medium as that used in the first embodiment can be used.

Laser Oscillator 10 of Second Embodiment
It is rear mirror 11 which curvature radius is a convex mirror of R ₃
When, in which the radius of curvature is disposed a solid-state laser medium 15 of a length L ₆ between the output mirror 13 consisting of a concave mirror of R _4. In FIG. 2, device parts other than the optical system such as a light source for exciting the laser medium and a cooling device for the laser medium are omitted. Also in this laser oscillator 10, the rear mirror 1 made of a convex mirror is used.
The distance L ₄ between the laser medium 1 and the center of the laser medium 15 is longer than the distance L ₅ between the output mirror 13 and the center of the laser medium 15. In the laser oscillator 10,
The distance L ₄ , the distance L _{5, the} curvature of the rear mirror 11, and the like are appropriately set so that the laser oscillator 10 enters a region where the laser can stably oscillate.

In the laser oscillator 10 having the above configuration,
The rear mirror 11 composed of the convex mirror has a function of enlarging the fundamental mode diameter and forms a Galilean telescope with the solid laser medium 15 having the function of a convex lens due to a thermal lens effect. The effect of reducing the thermal lens effect is obtained, and a laser output with a small output angle, a small divergence angle, and a good condensing property can be obtained. Further, the stable operation area of the laser oscillator 10 is also widened.

FIG. 3 shows a third embodiment of the solid-state laser oscillator (resonator) according to the present invention. In FIG. 3, as in FIG. 1, device components other than the optical system, such as a light source for exciting the solid-state laser medium and a cooling device for the laser medium, are omitted. The same solid laser medium as that used in the first embodiment can be used.

Laser Oscillator 20 of Third Embodiment
It is rear mirror 21 which curvature radius is a concave mirror for R ₅
When, those formed by arranging the solid-state laser medium 25 of a length L ₉ between the output mirror 23 consisting of a plane mirror (radius of curvature ∞). Both end surfaces of the solid-state laser medium 25 are formed as convex surfaces having an appropriate curvature half R ₆ . Further, a distance L between the rear mirror 21 and the center of the laser medium 25 is determined.
₇ is provided longer than the distance L ₈ between the output mirror 23 and the center of the laser medium 25. In addition, laser oscillator 2
At 0, the distance L ₇ , the distance L ₈ and the rear mirror 21
Is appropriately set so that the laser oscillator 20 enters a region where the laser oscillator 20 can stably oscillate.

In the laser oscillator 20 having the above structure,
Rear mirror 21 composed of a concave mirror and solid-state laser medium 2
5, a Kepler-type telescope is formed, which serves to reduce the thermal lens effect of the solid-state laser medium 25, and can provide a laser output with a small output dependence and a small divergence angle and a good condensing property. . Further, the stable operation region of the laser oscillator 20 is also widened.

FIG. 4 shows a fourth embodiment of the solid-state laser oscillator (resonator) according to the present invention. In FIG. 4, as in FIG. 1, device components other than the optical system such as a light source for exciting the solid-state laser medium and a cooling device for the laser medium are omitted. The same solid laser medium as that used in the first embodiment can be used.

Laser Oscillator 30 of Fourth Embodiment
Is rear mirror 31 radius of curvature is made of a concave mirror R ₇
When, in which the radius of curvature is disposed a solid-state laser medium 35 of a length L ₁₂ between the output mirror 33 of the concave mirror of R _8. The rear mirror 31 and the distance L ₁₀ to the center of the laser medium 35, is provided longer than the distance L ₁₁ to the center of the output mirror 33 and the laser medium 35. In addition,
In the laser oscillator 30, the distance L _10, such as the curvature of the distance L ₁₁ and the rear mirror 31 is set appropriately to enter the region can oscillate laser oscillator 30 is stable.

In the laser oscillator 30 having the above configuration,
Rear mirror 31 composed of a concave mirror and solid-state laser medium 3
5, a Kepler-type telescope is formed, which acts to reduce the thermal lens effect of the solid-state laser medium 35, and can provide a laser output with little output dependence and a small divergence angle and good condensing properties. . Further, the stable operation area of the laser oscillator 30 is also widened.

[0037]

EXAMPLE A first example corresponding to the first embodiment will be described below. This solid-state laser oscillator 1 includes a rear mirror 3 having a convex mirror with a radius of curvature R ₁ = 600 mm at a position 500 mm from the main plane of the laser medium 7 on the rear mirror side, and a mirror 2 having a radius of curvature R ₁ = 600 mm from the main plane on the output mirror side of the laser medium 7.
An output mirror 5 composed of a plane mirror (having a radius of curvature of ∞) was arranged at a position of 00 mm. The laser medium 7 used was YAG (Y ₃ Al ₅ O ₁₂ : 8 mm in diameter and L ₃ = 152 mm).
Nd ^{3 +} ) rods with a radius of curvature R ₂ = 3 on both end surfaces.
m convex surface processing.

The stable laser oscillation region of the laser oscillator 1 having the above configuration is 3.5 kW to 10 kW, and the maximum output is 35 kW.
It was 0W. In the entire laser oscillation region, the change in the diameter of the emitted beam was 0.2 mm or less, and the divergence angle of the beam was 2.2 mrad or less. When the laser beam was condensed by a convex lens having a focal length of 20 mm, the condensing diameter (spot diameter) was 100 μm or less, and the laser beam could enter the optical fiber having a core diameter of 200 μm without loss. The change in the focal position in the entire laser oscillation region was 50 μm or less.

When the radius of curvature R _{1 of the} rear mirror is less than 0.3 m, the laser operating range is less than 5 kW, which is not practical. Further, if the radius of curvature R ₁ exceeds 2.0m, since the focused diameter may exceed the 200 [mu] m, making it impossible to entering the optical fiber core diameter 200 [mu] m.

A second embodiment corresponding to the second embodiment will be described below. The solid-state laser oscillator 10 is 500 m from the main plane of the laser medium 15 on the rear mirror side.
The rear mirror 11 composed of a convex mirror having a radius of curvature R ₃ = 1000 mm at a position of m and a radius of curvature R ₄ = 4 at a position of 200 mm from a main plane of the laser medium 15 on the output mirror side.
An output mirror 13 composed of a 000 mm concave mirror was arranged. The laser medium 15 used has a diameter of 8 mm and L ₆ =
It is a 152 mm YAG (Y ₃ Al ₅ O ₁₂ : Nd ^{3 +} ) rod, and both end faces are planes perpendicular to the optical axis.

The stable laser oscillation range of the laser oscillator 1 having the above configuration is 2.5 kW to 10 kW, and the maximum output is 35 kW.
It was 0W. In the entire laser oscillation region, the change in the diameter of the emitted beam was 0.2 mm or less, and the divergence angle of the beam was 2.8 mrad or less. When the laser beam was condensed by a convex lens having a focal length of 23 mm, the condensing diameter (spot diameter) was 110 μm or less, and the laser beam could be incident on an optical fiber having a core diameter of 200 μm without loss. The change in the focal position in the entire laser oscillation region was 50 μm or less.

The radius of curvature R _{4 of the} output mirror is 1
If it is less than m, the beam divergence angle exceeds 5 mrad, which is not desirable.

A third embodiment corresponding to the third embodiment will be described below. The solid-state laser oscillator 20 includes a rear mirror 21 having a concave mirror with a radius of curvature R ₅ = 300 mm at a position 700 mm from the main plane of the laser medium 25 on the rear mirror side, and a position 200 mm from the main plane of the laser medium 25 on the output mirror side. An output mirror 23 made of a plane mirror (having a radius of curvature of ∞) is disposed on the output mirror 23. The laser medium 25 used was YAG (Y) having a diameter of 8 mm and L ₉ = 152 mm.
₃ Al ₅ O ₁₂ : Nd ^{3 +} ) rods, both ends of which have a convex surface with a radius of curvature R ₆ = 1 m.

The stable laser oscillation range of the laser oscillator 20 having the above configuration is 3.5 kW to 10 kW, and the maximum output is 3 kW.
It was 50W. Also, in the entire laser oscillation region,
The change in the diameter of the output beam was 0.2 mm or less, and the divergence angle of the beam was 2.2 mrad or less. When the laser beam was condensed by a convex lens having a focal length of 20 mm, the condensing diameter (spot diameter) was 100 μm or less, and the laser beam could enter the optical fiber having a core diameter of 200 μm without loss. The change in the focal position in the entire laser oscillation region was 50 μm or less.

When the radius of curvature R _{5 of the} rear mirror is less than 0.2 m, the laser operating range is less than 5 kW, which is not practical. Further, if the radius of curvature R ₅ exceeds 0.4m, since the condensing diameter exceeds 200 [mu] m, making it impossible to incidence on the optical fiber.

A fourth example corresponding to the fourth embodiment will be described below. The solid-state laser oscillator 30 moves the rear mirror 31 composed of a concave mirror having a radius of curvature R ₇ = 300 mm at a position 700 mm from the main plane on the rear mirror side of the laser medium 35 at a position 200 mm from the main plane on the output mirror side of the laser medium 35. Radius of curvature R ₈ = 1,500 m
An output mirror 33 composed of a m concave mirror is arranged. The laser medium 35 used was 8 mm in diameter and L ₁₂ = 152 mm.
YAG (Y ₃ Al ₅ O ₁₂ : Nd ^{3 +} ) rod, both end faces of which are planes perpendicular to the optical axis.

The stable laser oscillation range of the laser oscillator 30 having the above configuration is 3 kW to 10 kW, and the maximum output is 350 kW.
W. In the entire laser oscillation region, the change in the diameter of the emitted beam was 0.2 mm or less, and the divergence angle of the beam was 3.5 mrad or less. When the laser beam is focused by a convex lens having a focal length of 25 mm, the focused diameter (spot diameter) is 100 μm or less, and the core diameter is 2 μm.
The light could be incident on the optical fiber of 00 μm without loss. The change in the focal position in the entire laser oscillation region was 50 μm or less.

The radius of curvature R _{8 of the} output mirror is 1
If it is less than m, the beam divergence angle exceeds 5 mrad, which is not desirable.

[0049]

According to the first, second, third or fourth aspect of the present invention, it is possible to obtain a laser output having a small divergence angle and a good light-collecting property which is not affected by an output change. Further, the stable operation region of the oscillator is widened.

According to the invention of claim 5, according to claim 1,
In addition to the effects of the invention according to claim 4, it is possible to suppress an increase in the threshold value of laser oscillation.

According to the sixth, seventh, eighth or ninth aspect of the present invention, it is possible to obtain a laser output having a small divergence angle and a good condensing property which is not affected by a change in output. Further, the stable operation region of the oscillator is widened.

According to the tenth aspect, in addition to the effects of the sixth, seventh, eighth, and ninth aspects, a rise in the threshold value of laser oscillation can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a solid-state laser oscillator according to the present invention.

FIG. 2 is a diagram showing a second embodiment of the solid-state laser oscillator according to the present invention.

FIG. 3 is a diagram showing a third embodiment of the solid-state laser oscillator according to the present invention.

FIG. 4 is a diagram showing a fourth embodiment of the solid-state laser oscillator according to the present invention.

[Explanation of symbols]

1,10,20,30 solid-state laser oscillator 3,11,21,31 rear mirror 5,13,23,33 output mirror 7,15,25,35 solid-state laser medium L _1, L _4, and L _7, L ₁₀ rear mirror distance _{L 2, L 5, L 8} , L 11 distance to the center of the output mirror and the laser medium _{L 3, L 6, L 9} , L 12 solid length of the laser medium R ₂ to the center of the laser medium, R ₆ the radius of curvature R ₁ of the end surfaces of the laser medium, R ₃ convex mirror radius of curvature R _{4 of, R 5, R 7, R} 8 concave radius of curvature

Claims (10)

[Claims] In a solid state laser oscillator, a solid state laser medium is provided between a rear mirror of a convex mirror and an output mirror of a plane mirror, and a distance between the rear mirror and the center of the laser medium is equal to a distance between the output mirror and the center of the laser medium. A solid-state laser oscillator characterized by being longer than the distance. 2. In a solid-state laser oscillator, a solid-state laser medium is provided between a rear mirror of a convex mirror and an output mirror of a concave mirror, and a distance between the rear mirror and the center of the laser medium is equal to a distance between the output mirror and the center of the laser medium. A solid-state laser oscillator characterized by being longer than the distance. 3. The solid-state laser oscillator according to claim 1, wherein a radius of curvature of the rear mirror ranges from 0.3 m to 2.0 m. 4. The solid-state laser oscillator according to claim 2, wherein the output mirror is a concave mirror having a radius of curvature ranging from 1.0 m to ∞ (= plane mirror). 5. The solid-state laser oscillator according to claim 1, wherein both end surfaces of said solid-state laser medium are formed as convex surfaces. 6. A solid-state laser oscillator, wherein a solid-state laser medium is provided between a rear mirror of a concave mirror and an output mirror of a plane mirror, and a distance between the rear mirror and the center of the laser medium is set between the output mirror and the center of the laser medium. A solid-state laser oscillator provided longer than the distance. 7. A solid-state laser oscillator, wherein a solid-state laser medium is provided between a rear mirror of a concave mirror and an output mirror of the concave mirror, and a distance between the rear mirror and the center of the laser medium is between the output mirror and the center of the laser medium. A solid-state laser oscillator which is longer than the distance and has a radius of curvature of the rear mirror smaller than a radius of curvature of the output mirror. 8. The solid-state laser oscillator according to claim 6, wherein a radius of curvature of the rear mirror is in a range of 0.2 m to 0.4 m. 9. The output mirror according to claim 6, wherein the output mirror is a concave mirror having a radius of curvature ranging from 1.0 m to ∞ (= plane mirror). Solid state laser oscillator. 10. The solid-state laser oscillator according to claim 6, wherein both end surfaces of said solid-state laser medium are formed as convex surfaces.