JPH11163452A - Solid-state laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve beam quality, the intensity distribution of output light, and stability and to prevent a slab seal material from deteriorating, by providing a temperature distribution adjustment heating means for adjusting temperature distribution of a slab crystal near an edge part. SOLUTION: As a temperature distribution adjustment heating means, soft heat-conductive materials 6 and 7 are so provided as to be adhesive to a crystal side surface, at an edge part of a slab crystal 1 outside a sealing material 5. Furthermore, flat plate-like heaters 8 and 9 for heating the slab crystal 1 through them are pasted to the heat-conductive materials 6 and 7. The heaters 8 and 9 change the temperature distribution at an edge part of the slab crystal 1, changing optical distortion at an edge part which is a cause for deterioration quality in conventional technologies, for even effect on beam. Thus, beam quality, beam intensity distribution, and output stability of a slab laser oscillator can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser device such as a slab laser concentrator having an input / output portion for inputting / outputting a beam from an edge portion of a wedge-shaped slab crystal.

[0002]

2. Description of the Related Art A slab type solid-state laser oscillator has several hundreds.
Even with a high average power of W to kW class, a high beam quality with a low divergence angle is maintained, so that a laser beam having high beam luminance can be generated.
This is achieved by using a zigzag optical path that propagates through the crystal while repeating total reflection on the side surface of the slab crystal in the slab thickness direction, thereby producing a refractive index difference resulting from the temperature distribution,
This is based on the principle of a slab-type solid-state laser oscillator that cancels out the influence of optical distortion such as birefringence on a beam and obtains high beam quality.

However, in the case of an ideally infinite slab crystal, the above principle is followed. In practice, however, it is necessary to refract light at the entrance / exit surface of the slab in order to form a zigzag optical path. Generally, the edge portion of a slab crystal has a wedge-shaped shape with a sharp tip.

FIG. 3 is a cross-sectional view showing, as an example of the prior art, a cross section of an input / output portion of a slab laser concentrator and an isotherm in a slab crystal. In this slab laser concentrator, a slab crystal 1 has a flat plate shape and a rectangular cross section, and a lamp 2 as a light source for excitation is arranged so that excitation and cooling can be performed uniformly from a side surface including a long side thereof. Cooling water 4 flows at high speed between glass plates 3 arranged parallel to the slab crystal 1. Further, on the side surface including the short side, a heat insulating material is adhered to the slab crystal 1, and escape of heat from this surface is blocked. In such a structure, the temperature distribution in the crystal is uniform in the long side direction (slab width direction) of the cross section and in the short side direction (slab thickness direction).
Only occurs as a gradient that decreases from the center toward both sides. The optical distortion generated by the temperature distribution in the thickness direction of the slab is compensated for its influence on the beam by a zigzag optical path that repeats total reflection on both side surfaces including the long side.

A slab sealing material 5 is provided near the edge of the slab crystal 1 to prevent the cooling water 4 from flowing out. The slab crystal 1 outside the sealing material 5 has a zigzag shape. In order to refract incident light to form an optical path, for example, the incident light is cut into an acute angle shape that becomes Brewster. Also, this portion is a portion that normally comes into contact with air.

[0006]

In the slab crystal as shown in FIG. 3, the portion inside the sealing material 5 where excitation and cooling are performed is formed with an isotherm parallel to the side surface of the slab. Beam 20 transmitted through slab crystal 1
Of the beam uniformly pass through the high-temperature section 24 and the low-temperature section, and the above-described principle makes uniform the influence of optical distortion on each section of the beam.

However, as shown in FIG. 3, the outer edge portion of the sealing material 5 is formed by the relationship between the heat conduction from the inside of the slab, the wedge shape of the edge, and the escape of heat to the atmosphere near the edge. , The isotherm 21 in the crystal is disturbed. When the beam 20 passes through the edge portion, the beam 20 passes through greatly different temperature regions on both sides of the beam. Therefore, since the influence of the optical distortion on each part of the beam 20 is different, the wavefront may be disturbed, the emitted beam may spread, or a partially strong part may be generated due to interference or the like.

Further, for example, “Solid-St” written by W. Koechner
ate Laser Enginnering '' (Springer-Verlag) 7.3 Sl
As shown in ab and Disc Geometries, the edges are sharp and the crystals expand due to thermal expansion. That is, in the slab crystal 1 cut to the Brewster angle for the purpose of suppressing the reflection loss at the entrance / exit surface,
Since the tip has an acute angle, the edge portion is deformed and bent by thermal expansion inside the slab. In FIG. 3, the shape 22 of the original slab crystal 1 and the shape 2 of the slab crystal 1 in the excited state are shown.
3 is qualitatively indicated. As a result of this deformation of the slab crystal, the direction of the emitted laser light is shifted, and the laser light reciprocating in the resonator becomes a loss at the end face of the slab crystal, and the loss of the slab seal material due to stray light resulting in the loss. Also, this causes a problem of a change in the optimum oscillation state with respect to a change in the excitation input, that is, an adjustment deviation.

The above-described nonuniformity of the optical distortion at the edge portion and the beam shift due to the deformation of the crystal have caused the following problems.

The first problem is that the beam divergence exiting the slab becomes large due to insufficient compensation of the thermal lens effect due to the irregular refractive index gradient occurring at the edge of the slab crystal. The beam quality of the slab laser oscillator deteriorates.

The second problem is that the intensity distribution of the output light is locally concentrated due to interference caused by repeated wavefront disturbance and total reflection of the laser light passing through the edge portion.

The third problem is the misalignment and the deterioration of output stability caused by the displacement of the beam with respect to the change of the excitation input to the slab crystal.

A fourth problem is deterioration of the slab seal material which occurs when stray light and scattered light appearing when emitted from the slab crystal are reflected by the resonator mirror and return to the slab crystal again.

The present invention has been made to solve the above-mentioned problems of the prior art, and is a solid-state laser device which is excellent in beam quality, intensity distribution and stability of output light, deterioration prevention of a slab seal material, and the like. The purpose is to provide.

[0015]

SUMMARY OF THE INVENTION The present invention is directed to a solid-state laser device having a slab laser concentrator for inputting and / or emitting a beam from an edge portion of a slab crystal. A solid-state laser device having a temperature distribution adjusting heating means for adjustment.

In the present invention, a heating means for adjusting the temperature distribution is provided to adjust the temperature distribution in the vicinity of the edge of the slab crystal, so that the optical distortion or deformation of the edge caused by the beam passing through the edge is obtained. Can be improved, and the above problems can be solved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below.

FIG. 1 is a sectional view showing a cross section of an input / output portion of a slab laser concentrator and an isotherm in a slab crystal as an example of a solid-state laser device of the present invention. FIG. FIG. 4 is a perspective view showing an edge portion of the slab crystal as viewed from the input / output side of the slab laser concentrator. In the apparatus shown in this figure, a zigzag optical path is formed in a part where a beam enters and exits in a condenser using the zigzag slab type laser crystal 1. Although FIG. 1 shows only the vicinity of one edge of the light collector, the same shape and isotherm 21 are formed symmetrically near the opposite edge.

In the apparatus shown in FIG. 1, similarly to the conventional example shown in FIG. 3, the slab crystal 1 has a flat plate shape and a rectangular cross section, so that the slab crystal 1 can be uniformly excited and cooled from a side surface including its long side. A lamp 2 serving as a light source for excitation is arranged, and a cooling water 4 flows at a high speed between glass plates 3 arranged in parallel with the slab crystal 1. Further, on the side surface including the short side, a heat insulating material is adhered to the slab crystal 1, and escape of heat from this surface is blocked.

A slab sealing material 5 is provided near the edge of the slab crystal 1 to prevent the cooling water 4 from flowing out. The slab crystal 1 outside the sealing material 5 has a zigzag shape. In order to refract incident light to form an optical path, for example, the incident light is cut into an acute angle shape that becomes Brewster. Also, this portion is a portion that normally comes into contact with air.

In the apparatus shown in FIG. 1, a structure different from the conventional example shown in FIG. 3 is used as a heating means for adjusting a temperature distribution so that the edge of the slab crystal 1 outside the sealing material 5 is brought into close contact with the crystal side surface. Are provided with soft heat transfer materials 6 and 7, and flat heaters 8 and 9 for heating the slab crystal 1 through the heat transfer materials 6 and 7 are provided with heat transfer materials 6 and 7, respectively.
That is attached to the These heaters 8, 9
Changes the temperature distribution occurring at the edge portion of the slab crystal 1, changes the optical distortion at the edge portion, which caused beam quality deterioration in the prior art, and makes the effect of the beam uniform. The beam quality, beam intensity distribution and output stability of the oscillator can be improved.

In order to optimize the temperature distribution in the edge portion, instead of mounting a resonator and adjusting the laser oscillation state, a high excitation light is used by using a visible laser beam such as a He-Ne laser beam as a probe beam. Slab crystal 1 in the state
It is preferable that the heating amounts of the heaters 8 and 9 arranged on both sides of the slab crystal are independently adjusted while observing the pattern of the emitted light so that a good pattern can be obtained. Conventionally, as the excitation energy is increased when such probe light is transmitted, the pattern of the emitted light has a larger divergence angle in the slab thickness direction and interference fringes have appeared, but the temperature distribution at the slab edge is improved. This can alleviate this phenomenon.

FIG. 1 qualitatively shows a state in which the heating from both sides of the edge of the slab crystal 1 reduces the temperature difference between the slab crystal 1 and the high-temperature portion 24 and changes the isotherm 21. In such a state, both sides of the beam passing through the edge portion pass through a portion having a smaller temperature difference than in the related art. In addition, since the entire edge portion is heated even when the edge portion is deformed, bending of the tip due to thermal expansion is small. FIG. 1 qualitatively shows the shape 22 of the original slab crystal 1 and the shape 23 of the slab crystal 1 in the excited state. This result is obtained by optimizing the heating amounts of the heaters at both ends of the slab crystal, and the problem of the influence on the beam as described above is solved.

The heating temperature of the heaters 8 and 9 may be set by adjusting the temperature distribution at the edge of the slab crystal using an observation device such as a thermoviewer.

The heat transfer members 6 and 7 are preferably made of a soft material having good thermal conductivity, little distortion given to the crystal at the time of bonding and not deteriorated by laser light, for example, a metal such as indium.

Since the internal temperature of the slab crystal is usually 100 to 150 ° C., the heaters 8 and 9 are preferably surface heating elements such as ceramic heaters capable of heating within this temperature range.

The heat transfer materials 6, 7 and the heaters 8, 9 have a width equal to or larger than the crystal length in the slab width direction, so that the slab width direction can be uniformly heated. An electric wire 12 for flowing a current from the heaters 8 and 9 is wired outside the collector.
It is connected to the driving power supply. The heaters 8 and 9 are arranged on both side surfaces of the slab, and each heater can independently adjust the heating amount. In addition, in order to stabilize the vicinity of the slab edge at a predetermined temperature even when heat is generated by absorbing laser scattered light such as a part holding a crystal near the slab edge or a change in the temperature of the atmosphere, a signal of the temperature measuring element is used. It is desirable to adjust the current flowing through the heater by inputting it to the temperature controller instead of the power supply.

Further, in the example shown in FIG. 1, the position of the sealing material 5 is slightly inside the slab entrance / exit surface and is inside, so that the long heat transfer material 7 and the heater 9 are short on both sides of the slab crystal 1. Two types of heat transfer material 6 and heater 8 are arranged,
When a sealing material is arranged very close to the slab entrance / exit surface, the same effect can be obtained by using only the long heat transfer material 7 and the heater 9.

[0029]

According to the present invention described above, by adding a temperature distribution adjusting heating means for adjusting the turbulence of the temperature distribution at the edge portion, it is possible to reduce the optical distortion given to the passing beam and to reduce the heat distortion. The deformation of the edge portion due to the expansion can be suppressed, and as a result, various characteristics in the thickness direction of the slab forming the zigzag optical path can be improved as described below.

First, the influence of the thermal optical distortion of the laser medium, which is a characteristic of the slab type solid-state laser oscillator, on the beam is low, and the optical distortion is also exerted on the edge portion of the slab crystal which has not been fully utilized. Can be improved, and a laser beam with good beam quality at a low beam divergence angle can be obtained.

Second, it is possible to reduce the local concentration of the intensity distribution of the output light caused by the disturbance and interference of the wavefront of the laser light passing through the edge portion.

Third, the displacement of the beam caused by the change of the excitation input to the slab crystal is suppressed to reduce the adjustment deviation,
The output stability of the oscillator can be improved.

Fourth, stray light and scattered light appearing when emitted from the slab crystal are returned by the resonator mirror, and are prevented from being deteriorated by irradiating the slab seal material, thereby improving the reliability of leakage of cooling water. .

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a cross section of an input / output portion of a slab laser concentrator and an isotherm in a slab crystal as an example of a solid-state laser device of the present invention.

FIG. 2 is a perspective view showing an edge portion of a slab crystal as viewed from an input / output side of the slab laser concentrator of FIG. 1;

FIG. 3 is a cross-sectional view showing, as an example of the prior art, a cross section of an input / output portion of a slab laser concentrator and an isotherm in a slab crystal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Slab crystal 2 Excitation lamp 3 Glass plate 4 Cooling water 5 Slab seal material 6,7 Heat transfer material 8,9 Heater 12 Heater wire 20 Laser beam 21 Isothermal line in slab crystal 22 of slab crystal when not excited Shape 23 Shape of slab crystal when excited 24 High temperature part in slab crystal

Claims (6)

[Claims] 1. A solid-state laser device having a slab laser concentrator for entering and / or emitting a beam from an edge portion of a slab crystal, for adjusting a temperature distribution for adjusting a temperature distribution near an edge portion of the slab crystal. A solid-state laser device having heating means. 2. A slab seal member for preventing cooling water from flowing out of the slab crystal is provided near an edge of the slab crystal, and a heating means for adjusting a temperature distribution includes an edge of the slab crystal outside the seal member. 2. The solid-state laser device according to claim 1, wherein the device is a means for adjusting a temperature distribution of the portion. 3. The heating means for adjusting a temperature distribution comprises a soft heat transfer material which is in close contact with a slab crystal surface outside the seal material, and a heater which heats the slab crystal via the heat transfer material. The solid-state laser device as described in the above. 4. The solid-state laser device according to claim 3, wherein the heat transfer material is made of indium. 5. The solid-state laser device according to claim 3, wherein the heater is a ceramic heater. 6. The solid-state laser device according to claim 1, wherein an edge portion of the slab crystal has a wedge shape.