JPH0426177A - Solid-state laser oscillation apparatus - Google Patents

Abstract

PURPOSE:To detect whether the thermal lens action of a solid-state laser medium is generated and to prevent the directivity of a laser beam from being lowered by a method wherein the thermal lens degree of the solid-state laser medium is detected and the light-path length of an optical resonator is controlled by this detection signal. CONSTITUTION:When the optical pumping operation of a solid-state laser medium 7 is repeated, the temperature in the central part of the medium becomes higher than the temperature at an outer circumferential part. As a result, the focal distance of the solid-state laser medium 7 is changed by a thermal lens action due to a thermal strain. At this time, a laser beam L1 is transmitted through the solid-state laser medium 7 and is condensed by using a condensing lens 19. Its spot size is detected by using an image sensor 20. The detected image size is input to a converter 21; and a change in the focal distance of the solid-state laser medium 7 is computed on the basis of a calibration value. The computed value is input to a drive control device 22; tables 4, 5 are driven by it via driving sources 15, 17; and the interval D between one pair of correction lenses 12, 13 is controlled. Thereby, the thermal lens action of the solid- state laser medium 7 is compensated for and a low-order transverse-mode oscillation whose directivity is excellent can be realized.

Description

[Detailed Description of the Invention] [Purpose of the Invention] (Industrial Application Field) The present invention relates to a solid-state laser oscillation device, and particularly relates to a solid-state laser oscillation device that can maintain a small spread angle of emitted laser light. .

(Prior Art) For example, a solid-state laser oscillation device such as a Nd:YAG laser includes an optical resonator formed by a plurality of resonator mirrors. A rod-shaped laser medium is placed in the optical path within this optical resonator. This laser medium is optically excited by an excitation means such as an excitation lamp. Thereby, the laser light emitted from the laser medium is amplified and oscillated by the optical resonator.

The laser medium is usually water-cooled to prevent it from being damaged by the heat of the excitation means. As a result, the center of the rod-shaped laser medium becomes hotter than the periphery, causing thermal distortion and exhibiting a thermal lens (convex lens) effect.

As a result, for example, in a strongly excited state, the divergence angle of laser light increases, resulting in poor light focusing.

In order to solve these problems, research is being carried out on slab-type solid-state laser devices. The slab-type solid-state laser device is
As is well known, instead of a rod-shaped laser medium, a slab material is used in which the upper and lower surfaces are parallel and the light incident from the input and output end faces takes a zigzag reflected optical path between the parallel surfaces.

However, slab-type solid-state laser devices are difficult to put into practical use not only because of their complicated structure but also because precision polishing of slab-shaped crystals is difficult.

(Problem to be Solved by the Invention) As described above, in the conventional solid-state laser device using a rod-shaped laser medium, the spread angle of the laser beam increases due to the thermal lens effect of the laser medium, and the directivity decreases. There was something that happened.

This invention was made based on the above circumstances, and its purpose is to detect the occurrence of a thermal lens effect in the solid-state laser medium and to reduce the directivity of the laser beam. An object of the present invention is to provide a solid-state laser oscillation device that prevents this.

[Structure of the Invention] (Means and Effects for Solving the Problems) In order to solve the above problems, the present invention provides an optical resonator in which an optical path is formed by a plurality of resonator mirrors, and a Excitation means for optically exciting the provided solid-state laser medium;
a detection means for detecting the degree of thermal lensing of the solid-state laser medium that is generated when the solid-state laser medium is optically excited by the excitation means; The invention is characterized by comprising a control means for controlling.

According to such a configuration, when a thermal lens effect occurs in the solid-state laser medium and the degree of the thermal lens effect is detected by the detection means, the optical path length of the optical resonator is controlled accordingly. Light directionality can be maintained in an optimal state.

(Example) An embodiment of the present invention will be described below with reference to the drawings.

The solid-state laser oscillation device shown in FIG. 1 includes a ring-shaped optical resonator 1. The solid-state laser oscillation device shown in FIG. This optical resonator 1 is inclined at an angle of 45 degrees and forms a rectangular optical path 3 by first to fourth resonator mirrors 2a to 2d arranged with their reflective surfaces facing each other. First to third resonator mirrors 2a
2C is a high reflection mirror, and the fourth resonator mirror 2d is a low reflection mirror having a lower reflectance than the first to third resonator mirrors 2a to 2c. The first and second resonator mirrors 2a and 2b are connected to the first table 4.
the third and fourth resonator mirrors 2c, 2 provided above;
d is provided on the second table 5.

The first resonator mirror 2a and the second resonator mirror 2b
A photodiode 6 that passes light only in the direction of the arrow is provided between the second resonator mirror 2b and the third resonator mirror 2c. A laser medium 7 is arranged with its axis aligned with the optical path 3.

A pair of excitation lamps 8, such as a DC arc lamp or a flash lamp, as excitation means are arranged in parallel on the sides of the solid-state laser medium 7. Therefore, when the solid-state laser medium 7 is optically excited by the excitation lamp 8 and laser light is generated, the laser light moves along the optical path 3 in the optical resonator 1 in the direction regulated by the photodiode 6. It progresses and is amplified. When the laser beam reaches a predetermined intensity, the first to third resonator mirrors 2
4th resonator mirror ~2d with lower reflectance than 8~2c
It is designed to oscillate from.

The solid-state laser medium 7 and excitation lens 8 are held in a cooling jacket 9. Cooling water is circulated through this cooling jacket 9 as shown by the arrow, thereby cooling the solid laser medium 7. When the solid-state laser medium 7 is repeatedly optically excited by the excitation lamp 8 while being cooled by cooling water, the temperature at the center becomes higher than that at the radial periphery, so the thermal distortion caused by the temperature difference causes a thermal lens (convex lens) effect. shows. The first optical path 3
An aperture 11 is arranged between the resonator mirror 2a and the fourth resonator mirror 2d. When the laser light passes through this aperture 11, components with large divergence angles included in the laser light are removed. Further, a first correction lens 12 fixed to the first table 4 is provided on one side of the aperture 11, and a second correction lens 13 fixed to the second table 5 is provided on the other side. It is provided so that its optical center coincides with the center of the optical path 3. The distance between the pair of correction lenses 12 and 13 is set to be the same.

The first table 4 is provided with a first feed mechanism 14 consisting of a feed screw or the like. This first feeding mechanism 1
4 is driven by a first drive source 15. Thereby, the first table 4 has a solid state laser medium 7 indicated by an arrow X.
It is designed to be driven along the axial direction. The second table 5 is also provided with a second feed mechanism 16, which also includes a feed screw or the like. This second feeding mechanism 1
6 is driven by a second drive source 17. As a result, the second table 5 is driven along the axial direction of the solid-state laser medium 7 as indicated by the arrow X, similar to the first table 4 described above.

A probe laser 18 that outputs a small output laser beam is arranged outside the third resonator mirror 2C. Laser light L1 output from this probe laser 18
passes through the third resonator mirror 2c, enters the solid-state laser medium 7 from one end surface, and exits from the other end surface. The laser light emitted from the other end face of the solid-state laser medium 7 passes through the second resonator mirror 2b and enters the condenser lens 19 having a focal length f. The laser beam L1 focused by this condensing lens 19 is transmitted to an image sensor 20 disposed at a distance of approximately twice the focal length 2f from this condensing lens 19.
incident on . The spot size of the laser beam Ll incident on the image sensor 20 varies depending on the degree of thermal lens action of the solid laser medium 7, since the laser beam passes through the solid laser medium 7. That is, when a thermal lens effect occurs in the solid-state laser medium 7, the spot size formed on the detection surface 20a of the image sensor 20 changes. Therefore, the focal length of the solid-state laser medium 7, which changes due to the thermal lens action, can be detected from the sporatra size detected by the image sensor 20.

A detection signal from the image sensor 20 is input to a converter 21. A calibration value of the focal length of the solid-state laser medium 7 corresponding to the spot size detected by the image sensor 20 is input into the converter 21 in advance. When the spot size of the laser beam L1 detected by the image sensor 20 is input to the converter 21, this spot size is compared with the above-mentioned calibration value, and the focal length changed by the thermal lens action of the solid laser medium 7 is calculated. It has become sought after. A signal of the focal length of the solid-state laser medium 7 determined by the converter 21 is input to a drive control device 22 . This drive control device 22 operates the first drive source 15 and the second drive source 17 in response to the signal from the converter 21 to drive the first table 4 and the second table 5. . As a result, the distance between the first correction lens 12 and the second correction lens 13 provided on the table 4.5 is controlled, and the spread angle of the laser beam changes due to the thermal lens action of the solid laser medium 7. It is designed to prevent

Next, the operation of oscillating laser light from the solid-state laser oscillation device having the above configuration will be explained. First, probe laser 1
8 is activated to output laser light, and while cooling water is being circulated through the cooling jacket 9, electric energy is supplied to the pair of excitation lamps 8 to optically excite the solid laser medium 7.

When the solid-state laser medium 7 is optically excited, laser light is generated. This laser light travels along an optical path 3 within the optical resonator 1 along a travel direction regulated by a photodiode 6 and is amplified. When the laser beam is amplified to a predetermined intensity, oscillation is output from the fourth resonator mirror 2d, which has the lowest reflectance among the four resonator mirrors forming the optical resonator 1.

When the solid-state laser medium 7 is repeatedly optically excited, the temperature at the center of the solid-state laser medium 7 becomes higher than the temperature at the outer periphery, so that the solid-state laser medium 7 exhibits a thermal lens effect due to thermal distortion. As a result, the focal length of the solid laser medium 7 changes.

In other words, the focal length of the solid laser medium 7 becomes shorter than when the thermal lens effect is small. When the focal length of the solid laser medium 7 changes, this is detected by the image sensor 20. In other words, the laser beam L1 output from the probe laser 18 is passed through the solid-state laser medium 7 and condensed by the condensing lens 19, and the spot size is detected by the image sensor 20, so the spot size A change in the spot size due to a change in the focal length of the solid-state laser medium 7 is detected from . The spot size detected by the image sensor 20 is input to a converter 21 . This converter 21 calculates a change in the focal length of the solid laser medium 7 based on the calibration value.

The value calculated by the converter 21 is transmitted to the drive control device 22.
is input. Thereby, the drive control device 22
The first table 4 and the second table 5 are driven via a drive source 15 and a second drive source 17 to control the distance between the pair of correction lenses 12 and 13. In other words, depending on the degree of the thermal lens action of the solid laser medium 7, the first correction lens 12 and the second correction lens 13 are controlled to be driven closer to each other than twice their focal length. Ru.

Then, the thermal lens effect of the solid-state laser medium 7 is compensated, and low-order transverse mode oscillation with excellent directivity becomes possible. In other words, laser light with a small divergence angle can be oscillated from the fourth resonator mirror 2d.

This invention is not limited to the one embodiment described above, but can be modified in various ways within the scope of its gist. For example, although a rectangular ring-shaped optical resonator is used in the above embodiment, a triangular ring-shaped optical resonator composed of three resonator mirrors may be used, or a ring-shaped optical resonator may be used. Instead, it may be an optical resonator in which two resonator mirrors are arranged in parallel and facing each other.

Further, in the above embodiment, an aperture disposed between the second resonator mirror and the fourth resonator mirror and a first
, the second correction lens is not necessarily necessary, and even without them, the distance between the pair of resonator mirrors provided on the first table and the pair of resonator mirrors provided on the second table, In other words, by controlling the optical path length according to the degree of convex lens action of the solid-state laser medium, it is possible to control the spread angle of the oscillated laser light.

[Effects of the Invention] As described above, in the present invention, the degree of thermal lensing of the solid-state laser medium is detected, and the optical path length of the optical resonator is controlled based on the detected signal.

Therefore, even if a thermal lens effect occurs in the solid-state laser medium, the divergence angle of the laser light is prevented from increasing, so that the light focusing performance does not deteriorate.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a solid-state laser oscillation device showing one embodiment of the present invention. 1... Optical resonator, 2a to 2d... Resonator mirror 3.
... optical path, 7 ... solid laser medium, 8 ... excitation lamp (excitation means), 19 ... condensing lens (detection means),
20... Image sensor (detection means) 1... Converter (detection means) 2... Drive control device (control means)

Claims (1)

[Claims] an optical resonator having an optical path formed by a plurality of resonator mirrors; an excitation means for optically exciting a solid-state laser medium provided in the optical path of the optical resonator; and the solid-state laser medium is optically excited by the excitation means. and a control means for controlling the optical path length of the optical resonator in accordance with the degree of thermal lensing detected by the detecting means. Solid-state laser oscillation device.