JPH05167146A - Solid-state laser equipment - Google Patents

Abstract

PURPOSE:To obtain a solid-state laser element in which a one-dimensional laser beam of high output and high quality can be generated by holding a diver gent angle constant without using an expensive slab type solid state element. CONSTITUTION:Two sets of slab type solid elements 1, 11 are provided in series on an optical path of a laser resonator, the element 1 is excited by a light source 2, sound wave generating elements 9 are mounted on both side surfaces along an optical path of the element 11 to drive the element 9, and a sound wave output of the element 9 is regulated in response to the value of a power to be applied to the source 2.

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to quality stabilization of a one-dimensional laser beam generated from a solid-state laser device, particularly a slab-type solid-state laser device.

[0002]

2. Description of the Related Art FIG. 8 is a sectional view showing a conventional slab-type solid-state laser device described, for example, in Laser Handbook (Ohmsha, 1982). b) is a cross-sectional view from the side; _In the figure, 1 is a solid-state element, for example a YAG laser, a slab _- like crystal made of Y3 _{- xNdxAl5O12} ; 4 is a total reflection mirror; 5 is an output mirror opposite to the total reflection mirror 4; is a laser beam extracted out of the laser resonator by the output mirror 5 .

[0003] Next, the operation will be described. A solid-state device 1 is excited by direct light from a light source 2 turned on by a power source 3 to form a laser medium. At this time, since the solid-state element 1 is cooled from its width direction, it has a parabolic temperature gradient in its thickness direction. A laser beam 7 confined in a laser resonator consisting of a total reflection mirror 4 and an output mirror 5 passes through the solid-state element 1 multiple times in the thickness direction where a temperature gradient occurs each time the mirrors 4 and 5 are reciprocated. It is amplified while being repeatedly reflected, and when it reaches a certain value or more, part of it is taken out as a laser beam 8 outside the laser resonator through the output mirror 5 .

[0004] Due to the secondary temperature distribution occurring in the thickness direction of the solid-state element 1 , a secondary refractive index distribution is generated in the solid-state element 1 . Accordingly, a convex one-dimensional thermal lens is generated in the thickness direction of the solid-state element 1, and the phase of the laser beam 7 passing through the solid-state element 1 is changed by this thermal lens.
In general, conventional slab-type solid-state lasers are designed to repeat total reflection multiple times in the thickness direction when the laser beam 7 passes through the solid-state element 1. Therefore, the laser beam 7 that has passed through the solid-state element 1 passes Front and rear are not affected by phase change due to the thermal lens.

[0005]

The conventional slab-type solid-state laser device is constructed as described above. to prevent
_ing is done. In order to generate a laser beam 8 of good quality, it is desirable to increase the number of times of total reflection in the solid-state element 1. In line with this, optical polishing of the reflecting surface and _coating technology adapted to changes in the angle of total reflection are required. It is very expensive in terms of cost due to the difficulty of coating and the increase in the number of _coating locations. Further, even if the laser beam 7 is designed to repeat total reflection in the solid-state element 1, there actually exists a very small reflection loss. was worse than that of the solid-state laser device.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and it is an object of the present invention to generate a high-power laser beam with a constant divergence angle without using an expensive slab-type solid-state device. It is an object of the present invention to obtain a slab-type solid-state laser device capable of

[0007]

A solid-state laser device according to the present invention has two sets of slab-type solid-state elements arranged in series on the optical path of a laser resonator, and one of the slab-type solid-state elements is excited by a light source, A sound wave generating element is attached to both sides of the other slab-type solid-state element facing each other along the optical path, the sound wave generating element is driven, and sound wave output is generated from the sound wave generating element according to the value of the power input to the light source. is adjusted.

Another solid-state laser device according to the present invention is configured such that a part of a slab-type solid-state element placed on an optical path of a laser resonator is excited by a light source, and another part of the slab-type solid-state element is excited. 2, sound wave generating elements are attached to both surfaces facing each other along the optical path, the sound wave generating elements are driven, and the sound wave output emitted from the sound wave generating elements is adjusted according to the value of the power input to the light source. is.

[0009]

In the solid-state laser device constructed as described above, the influence of a thermal lens generated when a solid-state element is excited by a light source is not canceled by a zigzag optical path, but is provided in series on the optical path of the laser resonator. Two sets of slab-type solid-state elements or one slab-type solid-state element is divided into two parts. This is compensated by adjusting the frequency and output of the sound wave generated by the sound wave generating element attached to the mold solid-state element. As a result, an extremely stable laser beam with a constant divergence angle can be extracted even when the power applied to the light source, ie, the laser output, is changed.

[0010]

Examples Example 1. FIG. 1 is a block diagram of a solid-state laser device showing an embodiment of the present invention, where (a) is a cross-sectional view from the top and (b) is a cross-sectional view from the side. In the figure, 1
.about.8 are exactly the same as the above conventional device. Reference numeral 9 denotes a sound wave generating element provided in the solid-state laser device of the present invention, 10 denotes a driving device for driving the sound wave generating element 9, and 11 denotes a slab-type solid state element. The sound wave generating element 9 is adjusted in the crystal of the slab type solid element 11 so as to generate a standing wave sound wave in the thickness direction. Frequency and output can be set arbitrarily. In this embodiment, the driving device 10 is adjusted so that the relationship D/Λ=1 holds between the thickness D of the slab-type solid-state element 11 and the wavelength Λ of the sound wave.

In the solid-state laser device constructed as described above, the slab-type solid-state element 1 is excited by direct light from the light source 2 turned on by the power source 3 to form a laser medium. On the other hand, the laser beam 7 confined in the laser resonator consisting of the total reflection mirror 4 and the output mirror 5 is amplified by the slab-type solid-state element 1 each time it reciprocates between the mirrors 4 and 5, and is amplified by a certain value or more. Then, part of it is taken out as a laser beam 8 outside the laser resonator through the output mirror 5 .

A method of compensating for solid-state thermal lensing by acoustic waves will now be described in detail. 2(a) and 2(b) respectively show the states of the laser resonator before and after laser oscillation of the solid-state laser device in the above embodiment of the present invention.
As shown in FIG. 2A, no thermal lens occurs in the slab-type solid-state element 1 before laser oscillation, and the laser resonator maintains the state of being composed of the total reflection mirror 4 and the output mirror 5. FIG. When the light source 2 is turned on, the slab-type solid-state element 1 is excited, and laser oscillation starts, the slab-type solid-state element 1 is related to the one-dimensional laser output in its thickness direction, as shown in FIG. 2(b). It becomes a thermal lens with a focal length f _t . Conventionally, a zigzag optical path was adopted to prevent the state change of the laser resonator caused by the thermal lensing of the slab-type solid-state element 1, but in the present invention, the focal length f _t of the thermal lens of the slab-type solid-state element 1 is , is compensated by generating a one-dimensional lens with a focal length of _-ft on the slab-type solid-state element 11 using sound waves, so that a zigzag optical path is not required and a stable state of the laser resonator is always maintained. be able to.

When a standing sound wave as shown in FIG. 3(a) is applied in the thickness direction of the slab-type solid-state element 11 using the sound wave generating element 9 and the driving device 10, the slab becomes as shown in FIG. 3(b). A one-dimensional refractive index distribution is generated in the thickness direction of the mold solid element 11 due to the density of the sound waves. The phase distribution of the laser beam passing through the slab-type solid-state element 11 having this refractive index distribution changes as shown in FIG. . Since this phase distribution changes when the sound wave output is changed, the focal length f A lens with a focal length -f _t exactly opposite sign of _t can be generated in the slab solid state element 11 .

The focal length f _t of the thermal lens generated in the slab-type solid state element 1 varies depending on the laser output. The thermal lens can be compensated, and the state of the laser cavity can remain unchanged before and after lasing.

FIG. 5 shows the measurement results of the input power dependency of the divergence angle when an experiment was conducted using the solid-state laser device of the above embodiment. From the results of FIG. 5, it can be seen that by using the present invention, the divergence angle exhibits a constant value with respect to changes in the applied power, that is, changes in the laser output.

An advantage of the present invention is that the thermal lens in the thickness direction of the slab-type solid-state element is compensated for using sound waves, so the time required for compensation is extremely short and the time response is excellent. That is. Therefore, even in laser processing that is performed while changing the laser output, for example, the condensed beam diameter can be kept constant, so that the laser processing can be performed very stably. Furthermore, since there is no need for optical polishing or _coating of the laser beam totally reflected within the slab-type solid-state element, the cost can be very low.

Example 2. In the first embodiment, the sound wave generating element 9 is arranged so as to generate a concave lens on the slab type solid element 11 .
is adjusted, the sound wave generating element 9 may be adjusted so that the slab-type solid element 11 becomes a convex lens.

FIGS. 6(a) and 6(b) show the state of the resonator before and after laser oscillation in the above embodiment. In FIG. 6(a), although no thermal lens exists in the slab-type solid-state element 1 before laser oscillation, a one-dimensional standing acoustic wave is applied to the slab-type solid-state element 11 in its thickness direction in advance. The slab-type solid-state element 11 is made to be a convex lens with a focal length f. Therefore, in the cavity state before laser oscillation, a one-dimensional convex lens having a focal length f exists in the laser cavity. When laser oscillation starts,
As shown in FIG. 6(b), a thermal lens with a one-dimensional focal length f _t is generated in the slab solid state element 1 in its thickness direction. By adjusting the focal length f _a of the convex lens that occurs at 1/f so that 1/f=1/f _t +1/f _a holds, the state of the resonator can be kept unchanged before and after laser oscillation.

Even if the solid-state laser device of the above embodiment is used,
Since the divergence angle shows a constant value independent of input power and the condensed beam diameter can be kept constant, extremely stable laser processing can be realized.

Example 3. In Example 1, two sets of slab-type solid-state elements were used, one for excitation and the other for thermal lens compensation. A slab solid state element 12 may be used to compensate for thermal lensing.

Again, a single slab solid state element 12
is functionally divided into thermal lens compensation,
It is possible to perform operations similar to those of the first and second embodiments, and therefore very stable laser processing can be performed.

[0022]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, two sets of slab-type solid-state devices are provided in series on the optical path of a laser resonator,
One of the slab-type solid-state elements is excited by a light source, and the other slab-type solid-state element is provided with sound wave generating elements on both sides facing each other along the optical path, and the sound wave generating elements are driven to input electric power to the light source. Since the sound wave output emitted from the sound wave generating element is adjusted according to the value of , the thermal lens generated when one slab-type solid state element is excited by the light source is attached to the other slab-type solid state element. Since it can be compensated by adjusting the frequency and output of the sound wave generated by the sound wave generating element, even if the input power to the light source, that is, the laser output, is changed, a very stable laser beam with a constant divergence angle can be extracted. be able to. In addition, since the thermal lens is compensated using sound waves, the time required for compensation is extremely short, and there is an advantage that time responsiveness is excellent. Therefore, even in laser processing that is performed while changing the laser output, for example, the focused beam diameter can always be kept constant.
It can be done very stably. In addition, since there is no need for optical polishing or _coating of the laser beam totally reflected within the slab-type solid-state element _, it can be manufactured at a very low cost.

A part of the slab-type solid-state element placed on the optical path of the laser resonator is excited by the light source, and the other part of the slab-type solid-state element is irradiated with acoustic waves on both sides facing each other along the optical path. Even if a sound wave generating element is attached, the sound wave generating element is driven, and the sound wave output emitted from the sound wave generating element is adjusted according to the value of the power input to the light source, the same effect as that of the solid-state laser device can be obtained. be done.

[Brief description of the drawing]

FIG. 1 is a configuration diagram of a solid-state laser device showing Embodiment 1 of the present invention;

FIG. 2 is an explanatory diagram for explaining the operation of the solid-state laser device according to Example 1 of the present invention;

3A and 3B are explanatory diagrams for explaining the principle of lens generation by sound waves in Embodiment 1 of the present invention; FIG.

FIG. 4 is a distribution diagram showing a phase distribution immediately after a laser beam passes through a lens generated by sound waves in Example 1 of the present invention;

FIG. 5 is a characteristic diagram showing divergence angles of laser beams generated according to Example 1 of the present invention;

6A and 6B are explanatory diagrams for explaining the operation of the solid-state laser device according to the second embodiment of the present invention; FIG.

FIG. 7 is a configuration diagram of a solid-state laser device showing Example 3 of the present invention;

FIG. 8 is a configuration diagram of a conventional solid-state laser device;

[Description of symbols]

1 Solid state element 2 light source 4 total reflection mirror 5 output mirror 7 laser beam 8 laser beam 9 sound wave generating element 10 drive 11 solid state elements 12 solid state elements

continuation of the front page (72) Inventor Masanori Seguchi 8-1-1 Tsukaguchi Honcho, Amagasaki City Mitsubishi Electric Central Research Institute Co., Ltd. (72) Inventor Suguru Yamamoto 8-1-1 Tsukaguchi Honcho, Amagasaki City Mitsubishi Electric Central Research Institute Co., Ltd.

Claims (2)

[Claims] 1. A laser resonator comprising an output mirror and a total reflection mirror, first and second slab-type solid-state elements placed in series on an optical path of said laser resonator, and pumping the first slab-type solid-state element. a light source, a second slab-type solid state element, sound wave generating elements mounted on opposite sides along the optical path;
and means for driving the sound wave generating element and adjusting the sound wave output emitted from the sound wave generating element in accordance with the value of the electric power applied to the light source. 2. A laser resonator comprising an output mirror and a total reflection mirror, a slab-type solid-state element placed on an optical path of said laser resonator, a light source for exciting a part of said slab-type solid-state element, and said slab-type solid state. In another part of the element, the sound wave generating element is attached to both sides of the slab solid state element facing each other along the optical path, and the sound wave generating element is driven, depending on the value of the power input to the light source. A solid-state laser device comprising means for adjusting a sound wave output emitted from the sound wave generating element.