JPH10125982A - Laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a solid-state laser slab elliptical in cross section to be corrected on a thermal lens effect. SOLUTION: One or more concave lenses 15 which corrects the refraction of light caused by a lens effect are arranged between the reflection-side edge face 11a of a solid-state laser slab 11 and a reflecting mirror 13 and/or between the output edge face 11b of the laser slab 11 and an output mirror 14, wherein the curved surface of the concave lens 15 is specified by the circumferences of columns which cross each other at right angles. The solid-state laser slab 11 can be corrected for deflection caused by a thermal lens effect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a laser oscillator using a substantially plate-shaped solid laser slab having high pumping efficiency.

[0002]

FIG. 12 shows Nd-Y in the first prior art.
It is the schematic which shows an AG rod type solid-state laser oscillator. In this laser oscillator, excitation lamps 2a and 2b are arranged on both sides of a cylindrical rod 1 as a laser medium.

[0003] In the rod type as in the first prior art, since the rod 1 has a small cross-sectional area, the pumping efficiency is low and the improvement of the output is limited, so that the plate shape as shown in FIG. There is also a method of using the Nd-YAG medium (hereinafter, referred to as “solid-state laser slab”) 4 to increase the excitation area as compared with the case of using a rod (second prior art). In the second prior art, pumping lamps 2a and 2b are arranged on both sides of a substantially flat solid-state laser slab 4, and light is oscillated while reciprocating light between a not-shown reflecting mirror and an output mirror to generate an excited laser. Light is being output from the output mirror.

[0004]

However, Nd-YA
Since the G-type laser device has a low thermal conductivity, if the pulse operation is repeated fast, the temperature distribution inside the laser media 1 and 4 becomes non-uniform, and accordingly, the refractive index changes,
As shown in FIG. 14, the thermal lens effect is generated as if the end faces of the laser media 1 and 4 were convex. Then, the laser beam emitted toward the reflecting mirror 5 or the output mirror 6 loses the parallelism as expected, and hence the output mirror 6
However, there arises a problem that the light efficiency at the time of entering into an external optical fiber (not shown) through the optical fiber is reduced or the incidence becomes difficult.

When the laser medium 1 is rod-shaped as in the first prior art, the effect of the thermal lens effect accompanying the change in the refractive index of the laser medium 1 is corrected as shown in FIG. There is also a method in which a concave mirror is used as the reflecting mirror 5 (Japanese Patent Laid-Open No. 6-152018: No. 3).
Prior art). In this case, the thermal lens effect of the laser medium 1 appears concentrically. Therefore, the concave surface of the end face of the reflecting mirror 5 may be formed in a substantially spherical shape as shown in FIG.

However, in the case of the solid-state laser slab 4 having a high pumping efficiency as in the second prior art, the divergence angle differs between the width direction and the thickness direction of the crystal of the solid-state laser slab 4 because the reciprocating light has a width. Therefore, accurate correction cannot be performed with the substantially spherical reflecting mirror 5 as in the third related art. Further, a solid-state laser slab having an elliptical cross section as shown in FIG. 16 has recently been proposed as a laser medium for the purpose of preventing cracks or the like at the corners of the solid-state laser slab. In the laser slab, the thermal lens effect could not be corrected as long as the existing reflecting mirror 5 as shown in FIG. 15 was used.

An object of the present invention is to provide a laser oscillator capable of correcting a thermal lens effect for a solid-state laser slab, particularly a solid-state laser slab having an elliptical cross section as shown in FIG.

[0008]

Means for Solving the Problems In order to solve the above problems,
The present invention provides a plate-shaped solid laser slab having a substantially oval cross section, an excitation lamp for irradiating the solid laser slab with excitation light, a reflecting mirror arranged near a reflection-side end face of the solid laser slab, An output mirror disposed near an output side end face of the solid-state laser slab, wherein the solid-state laser slab is used as a laser oscillator that excites laser light by reciprocally oscillating light between the reflection mirror and the output mirror. Correcting the refraction of light due to the thermal lens effect of the solid-state laser slab to at least one of between the reflection-side end surface and the reflection mirror and between the output-side end surface of the solid-state laser slab and the output mirror. A correction means is provided.

Here, the correcting means is a concave lens, and the curved surface of the concave lens is orthogonal to the peripheral surface of the first cylinder centered on the cross-sectional minor axis of the solid-state laser slab and to the sectional minor axis. It is defined by the peripheral surface of the second cylinder having a radius smaller than the radius of the first cylinder with the orthogonal axis as the central axis.

Alternatively, the correction means may include a first columnar concave lens having a first cylindrical curved surface formed around the short-axis of the solid-state laser slab as a central axis, and an orthogonal axis perpendicular to the short-axis of the cross-section. A second columnar concave lens having a second cylindrical curved surface formed as an axis is superposed and arranged in the path of light.

Alternatively, a first cylindrical curved surface centered on a short-axis cross-section of the solid-state laser slab is formed on one of the reflection-side end surface and the output-side end surface of the solid-state laser slab. A columnar concave lens is directly formed, and a second cylindrical curved surface having a central axis perpendicular to the sectional short axis is formed on the other of the reflection side end surface and the output side end surface of the solid-state laser slab. Alternatively, the second columnar concave lens may be directly formed.

Alternatively, a concave lens for correcting light refraction due to a thermal lens effect of the solid-state laser slab is formed on at least one of the reflection-side end surface and the output-side end surface of the solid-state laser slab, and the curved surface of the concave lens is A peripheral surface of a first cylinder centered on a cross-section minor axis of the solid-state laser slab, and a second cylinder having a radius smaller than the radius of the first cylinder centered on an orthogonal axis orthogonal to the cross-section minor axis; Is defined by the peripheral surface.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment FIG. 1 is a perspective view showing a laser oscillator according to a first embodiment of the present invention, FIG. 2 is a side view thereof, and FIG.
Is a plan view of the same. In these drawings, the emission end face and the reflection end face of the solid-state laser slab 11 as a laser medium are depicted as planes perpendicular to the upper and lower surfaces for convenience of explanation, but actually have a Brewster angle. Needless to say, a sloped surface may be used.

As shown in FIGS. 1 to 3, this laser oscillator comprises:
A plate-shaped solid laser slab 11 as a laser medium composed of an Nd-YAG crystal, having an elliptical cross section, an excitation lamp 12 arranged near flat upper and lower surfaces of the solid laser slab 11, and a solid laser slab 11; Existing flat reflecting mirror 1 arranged near one end surface (reflection side end surface) 11a
3 and the other end surface (output side end surface) 1 of the solid-state laser slab 11
In addition to the configuration provided with the existing flat output mirror 14 disposed near 1b, a concave lens 15 interposed between the reflection side end face 11a and the reflection mirror 13 is further provided.

Here, the concave lens 15 is made of a transparent glass or a transparent industrial plastic or the like, and its curved surface has a Z axis (first axis) as a vertical axis and a central axis as shown in FIG. This is defined by the peripheral surface of the first cylinder 21 and the peripheral surface of the second cylinder 22 centered on the Y axis (second axis) orthogonal to the Z axis. The radius (first radius) R1 of the first cylinder 21 is a radius of curvature that cancels out the refraction angle in plan view as shown in FIG.
The second radius (second radius) R2 is a radius of curvature that cancels out the refraction angle in side view as shown in FIG. Then, in the solid-state laser slab 11, R2 is set to be smaller than R1 due to the relationship between the refraction angle in plan view and the refraction angle in side view. Thereby, the concave lens 1
5 is formed so that the focal length in a plan view and the focal length in a side view are formed differently, so that the refraction due to the thermal lens effect can be corrected in both the vertical and horizontal directions of the solid-state laser slab 11 having an elliptical cross section. Become.

In the laser oscillator having such a configuration, first, the excitation lamp 12 is caused to emit light, and this light is applied to the upper and lower surfaces of the solid-state laser slab 11. Solid laser slab 11
The light that has entered the inside enters an oscillation state by reciprocating between the reflecting mirror 13 and the output mirror 14, and is emitted forward from the output mirror 14.

Here, the material of the laser medium is Nd-Y
When using a material with low thermal conductivity such as AG,
When the pulse operation is repeated fast, the temperature distribution inside the solid-state laser slab 11 becomes non-uniform, and the temperature at the center of the solid-state laser slab 11 becomes higher than the surrounding temperature. As a result, as shown in FIG. It is as if the reflection-side end face 11a of the solid-state laser slab 11 had a convex lens shape. Then, the laser beam emitted toward the reflecting mirror 13 loses the parallelism as expected. In particular, when a solid-state laser slab 11 having an elliptical cross section is used for the purpose of high output and high durability as in this embodiment, refraction of light in a side view as shown in FIG. Since the angle and the refraction angle in a plan view as shown in FIG. 3 are different, the divergence angle differs in the width direction and the thickness direction of the crystal of the solid-state laser slab 11, so that light draws a complicated path. Become.

However, the radius of curvature (first radius) R1 in plan view and the radius of curvature (second radius) R2 in side view are different between the reflecting end face 11a of the solid-state laser slab 11 and the reflecting mirror 13. Since the concave lens 15 set in advance is installed, the thermal lens effect in the solid-state laser slab 11 having an elliptical cross section can be corrected in any direction. Therefore, the oscillation efficiency can be improved, and the laser output can be increased.

In order to correct the thermal lens effect,
As shown in FIG. 4, the first column 21 having the Z axis as the axis center
It is only necessary to consider the radius R1 of the second lens 22 and the second radius R2 of the second cylinder 22 centered on the Y-axis direction.
It is only necessary to perform extremely easy work during the design and molding of 5. In particular, there is an advantage that it is possible to correct the thermal lens effect in both the width direction and the thickness direction of the solid-state laser slab by using only one lens.

Second Embodiment FIG. 5 is a view showing a part of a laser oscillator according to a second embodiment of the present invention. In FIG. 5, the same reference numerals are given to elements having the same functions as those of the first embodiment. As shown in FIG. 5, the laser oscillator according to the present embodiment includes a solid-state laser slab 11 having a reflection-side end face 1.
As a means for correcting the thermal lens effect in 1a, a first columnar concave lens 15a for canceling the refraction angle in plan view
And the second columnar concave lens 15b for canceling the refraction angle in a side view, and the reflection-side end surface 11 of the solid-state laser slab 11.
a and the reflecting mirror 13.

Here, the curved surface of the first columnar concave lens 15a is defined by the peripheral surface of the first cylinder 21 having the Z axis (first axis) as a vertical axis as a center axis. The radius (first radius) R1 of the cylinder 21 is a radius of curvature that cancels out the refraction angle in plan view as shown in FIG. Further, the curved surface of the second columnar concave lens 15b is defined by the peripheral surface of the second cylinder 22 having the Y axis (second axis) orthogonal to the Z axis as the center axis. The radius (second radius) R2 is a radius of curvature that cancels out the refraction angle in side view as shown in FIG. In FIG. 5, the first columnar concave lens 15a is arranged near the reflecting mirror 13 and the second columnar concave lens 15b is connected to the solid-state laser slab 1.
1, the first columnar concave lens 15a is disposed near the reflection side end surface 11a of the solid-state laser slab 11, and the second columnar concave lens 15a is disposed near the first columnar concave lens 15a.
b may be arranged near the reflecting mirror 13.

The other configuration is the same as that of the first embodiment, and the description is omitted.

In the laser oscillator having such a configuration, first, an excitation lamp (not shown) is caused to emit light, and this light is applied to both upper and lower surfaces of the solid-state laser slab 11. The light that has entered the solid-state laser slab 11 reciprocates between the reflection mirror 13 and an output mirror (not shown) to be in an oscillation state, and is emitted forward from the output mirror.

Here, the laser beam emitted from the reflection-side end face 11a of the solid-state laser slab 11 toward the reflecting mirror 13 loses the parallelism due to the thermal lens effect. A first columnar concave lens 15a having a curvature in plan view and a second columnar concave lens 15b having a curvature in side view are provided between , And the refraction angle in side view can be canceled by the second columnar concave lens 15b. That is, the thermal lens effect in the solid-state laser slab 11 having an elliptical cross section can be corrected in any direction, so that the oscillation efficiency can be improved and the laser output can be increased.

As for the curvature of the first cylindrical concave lens 15a, it is sufficient to consider only the first radius R1 of the first cylinder 21 centered on the Z axis, and the curvature of the second cylindrical concave lens 15b. As regards the above, there is an advantage that it is only necessary to consider the second radius R2 of the second cylinder 22 centered on the Y-axis direction, so that it is only necessary to perform an extremely easy operation when designing and molding the concave lens 15. .

Third Embodiment FIG. 6 is a view showing a part of a laser oscillator according to a third embodiment of the present invention. In FIG. 6, elements having the same functions as those of the above embodiments are denoted by the same reference numerals. As shown in FIG. 6, in the laser oscillator of this embodiment, the concave lens 15 has two opposite surfaces, each of which is a first concave surface 31 and a second concave surface 3.
2 is formed in a columnar curved surface shape.
The concave surface 31 has a cylindrical shape whose center is the Z axis.
The second concave curved surface 32 functions as a first columnar concave lens 15a having a curvature in a plan view by being defined by the peripheral surface of the first cylindrical lens 22. By being defined by the peripheral surface, it functions as a second columnar concave lens 15b having a curvature in a side view. That is, in this embodiment, the first columnar concave lens 15a and the second columnar concave lens 15b are integrally formed to constitute the concave lens 15.

The use of the concave lens 15 has the same effect as the above embodiments. In particular, similarly to the first embodiment, only one lens is used, and the width and thickness of the solid-state laser slab are changed. The thermal lens effect can be corrected in any direction of the vertical direction.

Fourth Embodiment FIG. 7 is a diagram showing a part of a laser oscillator according to a fourth embodiment of the present invention. In FIG. 7, the same reference numerals are given to elements having the same functions as those of the above-described embodiments. In each of the above embodiments, the concave lenses 15a, 15b (15) are configured separately from the solid-state laser slab 11, but in this embodiment,
As shown in FIG. 7, the reflection-side end face 11a of the solid-state laser slab 11 is formed.
By forming the shape of the output side end surface 11b as a columnar curved surface, the concave lenses 15a, 15b
1 are integrally formed. Here, similarly to the second embodiment, the curved surface of the first columnar concave lens 15a formed on one end surface is, as shown in FIG. 7A, a first column having the Z axis (vertical axis) as a central axis. The curved surface of the second columnar concave lens 15b formed on the other end face is defined by the peripheral surface of Y and is orthogonal to the Z axis as shown in FIG.
It is defined by the peripheral surface of the second cylinder 22 having the axis as the central axis.

It is needless to say that the thermal lens effect can be corrected in both the width direction and the thickness direction of the solid-state laser slab 11 by this configuration.

{Modification} In the fourth embodiment, the concave lenses 15a, 15a
Although each of the lenses 5b is formed, a concave lens 15 similar to that of the first embodiment may be integrally formed only on one end face as shown in FIG. FIG. 8A shows the solid-state laser slab 1
1 (B) is a side view of the same. With such a configuration, the same effect as in the fourth embodiment can be obtained.

In the second embodiment, the configuration is not limited to the configuration shown in FIG. 5. For example, as shown in FIG. 9, the curved surfaces of a pair of columnar concave lenses 15a and 15b are arranged so as to face in mutually opposite directions. Although not shown, or not shown, the first columnar concave lens 15a is arranged not only on one end face of the solid-state laser slab 11 but on one end face of the solid-state laser slab 11, The columnar concave lens 15b may be arranged on the other side of the solid-state laser slab 11.

Further, in the first embodiment, the concave lens 15 is provided only between the reflecting end face 11a of the solid-state laser slab 11 and the reflecting mirror 13. However, as shown in FIGS. 10 and 11, the reflecting end face 11a is provided. And the output side end face 1
The concave lens 15 may be provided between the output mirror 14 and the output mirror 14. Alternatively, the reflection-side end face 1 of the solid-state laser slab 11
Nothing is provided between the output side end surface 1a and the reflector 13.
The concave lens 15 may be provided only between the output mirror 14 and the output mirror 14. Furthermore, as a modification of the second embodiment, a first columnar concave lens 15a and a second columnar concave lens 15b
To the output side end face 11b of the solid-state laser slab 11 and the output mirror 1
Of course, it may be arranged only between the reflection side and the reflection side and the output side.

[0033]

When a solid-state laser slab having a laser medium having an elliptical cross section is used for the purpose of improving the pumping efficiency,
Although the divergence angle differs in the width direction and the thickness direction of the crystal of the solid-state laser slab, according to the first aspect of the present invention, the divergence angle is located near at least one of the reflection-side end face and the output-side end face of the solid-state laser slab. The curved surface of the concave lens having a radius smaller than the radius of the first cylinder with the peripheral surface of the first cylinder centered on the cross-section minor axis of the solid-state laser slab and the orthogonal axis orthogonal to the cross-section minor axis as the center axis. It is defined by the peripheral surface of the second cylinder, and can provide a concave lens effect having a different focal length in each direction. By using one lens, the solid laser slab can be formed in any of the width direction and the thickness direction. It is also possible to correct the thermal lens effect in the direction of.

According to the second aspect of the present invention, the first cylindrical concave lens having the first cylindrical curved surface centered on the minor axis of the cross section of the solid-state laser slab is formed in the width direction of the solid-state laser slab. Of the solid laser slab in the thickness direction of the solid-state laser slab by the second columnar concave lens in which the second cylindrical curved surface is formed with the perpendicular axis perpendicular to the cross-section minor axis as the center axis. Can be corrected. In this case, the design and molding of each columnar lens can derive an accurate curvature only by separately considering the thermal lens effect in the width direction and thickness direction of the solid-state laser slab, and improve the efficiency of design and molding. Can be achieved.

Further, according to the third and fourth aspects of the present invention, the thermal lens effect can be obtained in both the width direction and the thickness direction of the solid-state laser slab simply by forming a curved surface on the end face of the solid-state laser slab. There is an effect that correction can be easily performed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a laser oscillator according to a first embodiment of the present invention.

FIG. 2 is a side view showing the laser oscillator according to the first embodiment of the present invention.

FIG. 3 is a plan view showing a laser oscillator according to the first embodiment of the present invention.

FIG. 4 is a perspective view showing the radius of curvature of the laser oscillator concave lens according to the first embodiment of the present invention.

FIG. 5 is a perspective view showing a part of a laser oscillator according to a second embodiment of the present invention.

FIG. 6 is a perspective view showing a concave lens according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a solid-state laser slab according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a solid-state laser slab according to a modification of the present invention.

FIG. 9 is a perspective view showing a part of a laser oscillator according to a modified example of the invention.

FIG. 10 is a side view showing a laser oscillator according to a modification of the present invention.

FIG. 11 is a plan view showing a laser oscillator according to a modification of the present invention.

FIG. 12 is a perspective view showing a part of a laser oscillator according to the first prior art.

FIG. 13 is a perspective view showing a part of a laser oscillator according to a second conventional technique.

FIG. 14 is a principle diagram for explaining a thermal lens effect of a laser medium.

FIG. 15 is a perspective view showing a rod-type laser medium and a concave reflecting mirror.

FIG. 16 is a diagram showing a laser oscillator of a proposal example.

[Explanation of symbols]

 Reference Signs List 11 solid-state laser slab 11a reflection-side end face 11b output-side end face 12 excitation lamp 13 reflection mirror 14 output mirror 15 concave lens 15a first columnar concave lens 15b second columnar concave lens 21 first cylinder 22 second cylinder

Claims (4)

[Claims] 1. A solid-state laser slab having a substantially elliptical cross section, an excitation lamp for irradiating the solid-state laser slab with excitation light, and a reflecting mirror arranged near a reflection-side end face of the solid-state laser slab; An output mirror disposed near an output side end face of the solid-state laser slab, wherein the laser oscillator excites laser light by reciprocating oscillation of light between the reflection mirror and the output mirror; At least one of the position between the reflection-side end surface of the slab and the reflection mirror and the position between the output-side end surface of the solid-state laser slab and the output mirror corrects light refraction due to the thermal lens effect of the solid-state laser slab. The concave surface further includes a curved surface of the concave lens, and the curved surface of the concave lens has a peripheral surface of the first cylinder whose center axis is a short-axis section of the solid-state laser slab, and a center axis that is orthogonal to the short-axis section. Serial first second radius smaller than the radius of the cylinder of the laser oscillator, characterized in that it is defined by the peripheral surface of the cylinder. 2. A solid-state laser slab having a substantially elliptical cross section, an excitation lamp for irradiating the solid-state laser slab with excitation light, and a reflecting mirror arranged near a reflection-side end face of the solid-state laser slab; An output mirror disposed near an output side end face of the solid-state laser slab, wherein the laser oscillator excites laser light by reciprocating oscillation of light between the reflection mirror and the output mirror; At least one of the position between the reflection-side end surface of the slab and the reflection mirror and the position between the output-side end surface of the solid-state laser slab and the output mirror corrects light refraction due to the thermal lens effect of the solid-state laser slab. And a first columnar concave lens having a first cylindrical curved surface formed around the short-axis of the cross section of the solid-state laser slab as a central axis, and a cross-section perpendicular to the short-axis of the cross-section. Laser oscillator and a second columnar concave second cylindrical curved surface centered axis orthogonal axes is formed is characterized by comprising superimposed disposed in the path of light. 3. A solid-state laser slab having a substantially elliptical cross section, an excitation lamp for irradiating the solid-state laser slab with excitation light, and a reflecting mirror arranged near a reflection-side end face of the solid-state laser slab. An output mirror disposed near an output side end face of the solid-state laser slab, wherein the laser oscillator excites laser light by reciprocating oscillation of light between the reflection mirror and the output mirror; A first columnar concave lens in which a first cylindrical curved surface having a central short axis of a cross section of the solid-state laser slab is formed on one of the reflection-side end surface and the output-side end surface of the slab; On the other of the reflection-side end face and the output-side end face of the laser slab, a second columnar concave lens having a second cylindrical curved surface formed around a perpendicular axis perpendicular to the sectional short axis was formed. thing Laser oscillator according to features. 4. A solid-state laser slab having a substantially elliptical cross section, an excitation lamp for irradiating the solid-state laser slab with excitation light, and a reflecting mirror arranged near a reflection-side end face of the solid-state laser slab. An output mirror disposed near an output side end face of the solid-state laser slab, wherein the laser oscillator excites laser light by reciprocating oscillation of light between the reflection mirror and the output mirror; At least one of the reflection-side end surface and the output-side end surface of the slab is formed with a concave lens that corrects refraction of light due to a thermal lens effect of the solid-state laser slab, and the curved surface of the concave lens is a short-axis cross section of the solid-state laser slab. And the peripheral surface of the second cylinder having a radius smaller than the radius of the first cylinder with the orthogonal axis perpendicular to the cross-sectional minor axis as the central axis. Laser oscillator characterized in that it is a constant.