JPH118428A - Solid-state laser oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid-state laser oscillator which can improve beam quality in a laser width direction, and can exhibit good output efficiency. SOLUTION: A laser oscillator includes a condenser having an excition lamp and a laser element 15, and two sets of resonator mirrors 13 and 14 disposed at both ends of the condenser in its central axis direction for reciprocating and extracting a laser beam passed through the laser element 15 therebetween. The one resonator mirror 13 of the two mirrors 13 and 14 has a returning mirror 19 and a total reflecting mirror 20 positioned at both sides of a central axis line B of the condenser to be vertical thereto, respectively. The other resonator mirror 14 has an output mirror 22 and a returning mirror 21 positioned at the both sides of the central axis line B to be vertical thereto, respectively. That is, the reflecting mirrors 19 and 21 of the resonator mirrors 13 and 14 are positioned confronting each other at the both sides of the central axis line B of a light collector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid-state laser oscillator suitable for use when a slab type laser element is provided as a laser element (laser medium).

[0002]

2. Description of the Related Art In general, this type of solid-state laser oscillator is
A slab-type laser element is used as a laser element because it has an advantage of maintaining high beam quality with a low beam divergence angle even at a high average output of several hundred W to kW class.

This causes a temperature difference in the center axis direction (laser thickness direction) of the laser element. However, by forming a zigzag optical path in a vertical section including the center axis of the laser element, refraction caused by the temperature difference occurs. It is based on the principle that optical distortion such as a difference in index and birefringence does not adversely affect the beam, and high beam quality can be obtained.

On the other hand, in the direction perpendicular to the center axis of the laser element (laser width direction), a temperature difference does not occur in principle, but a temperature difference actually occurs due to non-uniformity of excitation and cooling. The lens effect due to the difference and the birefringence due to the stress distortion occur.

For this reason, in a basic resonator in which a laser element and a resonator mirror are arranged on a straight line (hereinafter, referred to as a “linear resonator”), it is possible to obtain high beam quality in the laser width direction. could not.

Therefore, in order to improve the beam quality in the laser width direction to the same level as that in the laser thickness direction, as shown in FIG. 4, the resonator component is formed in a V-shape in a longitudinal section including the center axis of the laser element. A resonator to be arranged (hereinafter, referred to as “V-type resonator”) is employed.

In FIG. 1, a solid-state laser oscillator denoted by reference numeral 1 comprises a condenser (only a laser element is shown) 2 and an output mirror 3.
, A total reflection mirror 4 and a folding mirror 5. The fixed laser oscillator 1 has two optical paths 6 and 7 reciprocating in the concentrator 2.
Are formed.

[0008] In such a solid-state laser oscillator,
Since each part in the width direction of the laser beam passes through the center part and the periphery of the laser element alternately, the effects of non-uniformity such as excitation, refractive index, and birefringence of the center part and the periphery that occur in the laser width direction Is corrected, and the beam quality in the laser width direction is improved.

[0009]

However, in this type of solid-state laser oscillator, the effect of correcting the non-uniformity in the laser width direction is limited only in a partial area near the output mirror 3 and the total reflection mirror 4. Thus, there is a problem that the entire optical path is insufficient and the beam quality in the entire laser width direction cannot be improved.

Further, in the conventional solid-state laser oscillator, since there is a portion in the laser element near the turning mirror 5 where the beam does not transmit, a linear resonator having the same overall length that allows the beam to pass through almost the entire area of the laser element. There is also a problem that the efficiency is reduced (about 10 to 20%) as compared with (the optical path length is twice as long in the V-type resonator).

The present invention has been made in view of such circumstances, and has as its object to provide a solid-state laser oscillator that can improve the beam quality in the entire laser width direction and obtain good output efficiency. I do.

In order to achieve the above object, a solid-state laser oscillator according to claim 1 of the present invention is provided with a condenser having an excitation lamp and a laser element, and disposed on both sides in the center axis direction of the condenser. And two sets of resonator mirrors for reciprocating laser light transmitted through the laser element and extracting a laser output, and one set of these two sets of resonator mirrors is the center of the collector. It consists of a reflecting mirror and a total reflection mirror respectively located on both sides in the direction perpendicular to the axis, and the other set of resonator mirrors consists of an output mirror and a folding mirror respectively located on both sides in the direction perpendicular to the central axis of the condenser. Each of the folding mirrors of the resonator mirror is configured to face each other on each side in the direction perpendicular to the central axis of the light collector. Accordingly, two linear optical paths equally divided in a direction perpendicular to the central axis of the laser element and an inclined optical path connecting these two linear optical paths are formed.

According to a second aspect of the present invention, in the solid-state laser oscillator according to the first aspect, each of the folding mirrors is inclined toward the condenser. Therefore, an inclined optical path is formed between the two resonator mirrors at right angles to the two mirrors.

According to a third aspect of the present invention, there is provided the first or second aspect.
In the solid-state laser oscillator described above, the reflecting surface of the folding mirror is constituted by a reflecting surface formed by any one of a spherical surface and a cylindrical surface. Therefore, the spread of the laser beam reflected by each folding mirror is corrected.

According to a fourth aspect of the present invention, in the solid-state laser oscillator according to the first, second, or third aspect, the reflecting surface of the total reflection mirror is formed from a reflecting surface formed by any one of a spherical surface and a cylindrical surface. There is a configuration. Therefore, the spread of the laser beam reflected by the total reflection mirror is corrected.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described with reference to the drawings. FIGS. 1A and 1B are optical path diagrams showing a solid-state laser oscillator according to a first embodiment of the present invention, and FIG. 2 is a perspective view showing a condenser of the solid-state laser oscillator according to the first embodiment of the present invention. FIG. In the figure,
The solid-state laser oscillator (Z type) indicated by reference numeral 11
2 and two sets of resonator mirrors 13 and 14.

The condenser 12 includes a laser element 15, an excitation lamp 16, a glass plate 17, and a heat insulating material 18. The laser element 15 is made of a slab crystal, and is disposed at the center of the light collector 12 in the central axis direction (laser thickness direction). This laser element 15 is cooled by circulating water.

The excitation lamps 16 are arranged on both sides of the laser element 15 in the laser thickness direction as shown in FIG. The glass plate 17 is provided between the laser element 15 and the excitation lamp 16. The heat insulating material 18 is attached to the side of the laser element 15 in the laser width direction. Thereby, the temperature distribution in the laser width direction is made uniform.

The resonator mirror 13 includes a folding mirror 19 and a total reflection mirror 20, and is arranged on one side of the light collector 12 in the central axis direction (laser thickness direction). On the other hand, resonator mirror 1
Reference numeral 4 denotes a folding mirror 21 and an output mirror 22, which are arranged on the other side of the light collector 12 in the central axis direction.

Each of the mirrors 19,
By inclining toward the light collector 12, 20 is positioned at a position facing each other on each side in a direction perpendicular to the central axis B of the light collector 12.

Thus, between the two sets of resonator mirrors 13 and 14, two linear optical paths 23 and 24 equally divided in a direction perpendicular to the central axis B of the laser element 15 and these two linear optical paths 23 and 24 are formed. A combined inclined optical path 25 is formed. That is, zigzag optical paths 23 to 25 in which the laser beam travels while repeating total reflection are formed between the two sets of resonator mirrors 13 and 14 in the longitudinal section including the central axis B of the condenser 12. Then, a laser beam transmitted through the laser element 15 is reciprocated to extract a laser output.

As the folding mirrors 19 and 21 and the total reflection mirror 20, a reflection mirror whose reflection surface is subjected to a concave polishing treatment such as a spherical surface or a cylindrical surface is used. Thereby, the spread of the laser beam reflected on each reflection surface is corrected, and the laser beam passes through the optical path in the laser element 15 as parallel light.

The trajectory of a laser beam and the effect of a laser element in an excited state in the solid-state laser oscillator configured as described above will be described. In the linear optical path 23, the beam part passing through the central part of the laser element 15 and the beam part passing through the peripheral part are respectively the linear optical path 2
In No. 4, the laser beam passes through the central portion and the peripheral portion of the laser element 15 in reverse.

For this reason, the influence of optical distortion such as birefringence due to the refractive index difference and stress distortion received from the laser element 15 having a non-uniform temperature distribution in the width direction indicated by the arrow in FIG. 2 is corrected. Similarly, the difference in gain between the central part and the peripheral part of the laser element 15 is averaged.

Further, since the inclined optical path 25 is formed so as to be inclined in the laser element 15, the laser beam is transmitted uniformly in the laser width direction, and the optical distortion and the gain of the folding mirrors 19 and 21 are also reduced. The difference is corrected.

The correction of the refractive index difference obtained in this manner has the effect of reducing the spread angle of the laser beam emitted from the output mirror 22 in the laser width direction, and is defined by the product of the width of the beam waist and the spread angle. Beam quality is improved. In this case, in a configuration having the same overall length as that of the V-type resonator, the resonator length becomes 1.5 times and the diffraction loss of a higher-order spatial mode becomes large. A laser beam having many next spatial mode components is obtained.

The temperature distribution in the laser element 15 changes depending on the excitation conditions when the energy applied to the lamp is increased or decreased. In this case as well, the difference in refractive index is corrected, so that the deviation of the adjustment of the resonator is suppressed. High output stability can be obtained.

Further, the correction of the influence of birefringence due to the stress distortion is performed by adjusting the linearly polarized laser beam to the linear optical path 2.
Since the total reflection is repeated in the zigzag optical path including the optical paths 3 and 24 and the inclined optical path 25, there is an effect of suppressing output loss when depolarized by birefringence.

In addition, when the output efficiency is prioritized over the normal beam quality, the maximum output can be obtained by using a linear resonator in which the output mirror 22 and the total reflection mirror 20 are arranged on a straight line. Since the energy is extracted from the entire laser element 15 in the type resonator, an output equivalent to that in the case of the linear resonator can be obtained.

When the same condenser is used for each of the Z-type resonator (Z), the linear resonator (L), and the V-type resonator (V) in this embodiment, the oscillator performance is compared. The result is as shown in FIGS.

FIG. 3A shows the change in the laser output with respect to the lamp input, and FIG. 3B shows the beam quality in the laser width direction with respect to the lamp input. In this case, the M2 value is used as the beam quality, and the smaller the M2 value is, the higher the beam quality is, and is “1” in the TEM00 mode.

With a linear resonator, the maximum output can be obtained, but the beam quality in the laser width direction deteriorates. In the V-type resonator, the beam quality in the laser width direction is greatly improved, but the maximum output is lower than that of the linear resonator. Z
In the type resonator, the beam quality in the laser width direction is improved as compared with the V-type resonator, and the maximum output equivalent to that of the linear type resonator is obtained.

[0033]

As described above, according to the present invention, one of the two sets of resonator mirrors has a reflecting mirror and a total reflection which are located on both sides in the direction perpendicular to the central axis of the condenser. And the other set of resonator mirrors comprises an output mirror and a folding mirror located on both sides in the direction perpendicular to the central axis of the collector. Each of the mirrors of the resonator mirror is connected to the central axis of the collector. Are formed so as to oppose each other at right angles in the direction perpendicular to the central axis of the laser element, so that two linear optical paths equally divided in a direction perpendicular to the central axis of the laser element and an inclined optical path connecting these two linear optical paths are formed.

Accordingly, the non-uniformity in the laser width direction is sufficiently corrected over the entire optical path, so that the beam quality in the laser width direction can be improved.

Further, since the laser beam is transmitted through the entire area of the laser element, the energy stored in the laser element can be efficiently taken out, and good output efficiency can be obtained.

[Brief description of the drawings]

FIGS. 1A and 1B are optical path diagrams showing a solid-state laser oscillator according to a first embodiment of the present invention.

FIG. 2 is a perspective view showing a condenser of the solid-state laser oscillator according to the first embodiment of the present invention.

FIGS. 3A and 3B are diagrams showing a change in laser output with respect to a lamp input and a beam quality in a laser width direction with respect to a lamp input.

FIG. 4 is an optical path diagram showing a conventional solid-state laser oscillator.

[Explanation of symbols]

 Reference Signs List 11 solid-state laser oscillator 12 concentrator 13, 14 resonator mirror 15 laser element 19 folding mirror 20 total reflection mirror 21 folding mirror 22 output mirror B center axis

Claims (4)

[Claims] 1. A condenser having an excitation lamp and a laser element, and arranged on both sides in the central axis direction of the condenser to reciprocate laser light transmitted through the laser element to extract a laser output. And two sets of resonator mirrors, one of the two sets of resonator mirrors being composed of a folding mirror and a total reflection mirror located on both sides in the direction perpendicular to the central axis of the light collector. The other set of resonator mirrors comprises an output mirror and a return mirror located on both sides in the direction perpendicular to the central axis of the light collector. A solid-state laser oscillator characterized by being opposed to each other at right angles. 2. The laser processing apparatus according to claim 1, wherein each of the folding mirrors is inclined toward the light collector. 3. The solid-state laser oscillator according to claim 1, wherein the reflecting surface of the folding mirror comprises a reflecting surface formed of one of a spherical surface and a cylindrical surface. 4. The solid-state laser oscillator according to claim 1, wherein said reflecting surface of said total reflection mirror comprises a reflecting surface formed by any one of a spherical surface and a cylindrical surface.