JPH01128580A - Slab shaped solid state laser oscillator - Google Patents

Abstract

PURPOSE:To take out excellent laser luminous flux, whose expansion is less, by adjusting an interval between a convex lens and a concave lens, thereby controlling the expansion of the laser luminous flux, which is outputted from the side of a partial reflecting body in a laser resonating reflection system. CONSTITUTION:A convex lens 30 and a concave lens 40 are arranged between a partial reflecting body 21 and one end surface 11 of a laser medium with an interval l being provided. The convex lens 30 is arranged on the side of the end surface 11. The diverging laser luminous fluxes from both edge parts of the laser medium are corrected so as to obtain the parallel luminous fluxes. At this time, the correcting actions of both lenses can be intensified so as to expand the interval l. For example, when the output level of the laser luminous flux LB is small and therefore the diverging property and converging property of the laser luminous flux, which is outputted from the laser medium 10, are weak as a whole, both edge parts of the laser luminous flux LB can be corrected into the parallel luminous flux by adjusting the interval l into a small value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a slab-type solid-state laser oscillation device in which a flat rod-shaped solid body called a slab-type containing a laser active substance is used as a laser medium.

[Conventional technology]

(As is known, solid-state lasers are generally optically pumped, but the excitation light given to the laser medium from the excitation light source contains a large amount of wavelength components that are not effective for laser oscillation.
Such non-useful light components usually end up turning into heat within the laser medium, which can destroy the laser medium if its temperature rises above an acceptable limit, so In order to obtain as high a laser beam as possible from a large laser medium, it is necessary to cool the laser medium, and for this reason solid-state lasers for large outputs are usually liquid cooled. Although such cooling lowers the average temperature of the laser medium, temperature non-uniformity or temperature gradients inevitably occur inside the laser medium, and thermal distortion occurs within the laser medium accordingly. Since the temperature gradient is generated from the surface of the medium, the temperature gradient described above always decreases from the center of the laser medium toward the surface, and as a result, a compressive force due to thermal strain is applied to the center of the laser medium. Tension will act on the surface.

When thermal strain exists in the laser medium, the phase of the laser beam changes depending on the degree of thermal strain. When looking at the cross section of a half laser beam, the polarity of the thermal strain changes between the center and the surface. Since the sizes differ as described above, the wavefront of the laser beam does not match the cross section of the laser beam and is disturbed. When the laser medium is a normal Rondo with a circular cross section, the propagation direction of the laser beam is parallel to the Rondo axis, but the phase of the laser beam is shifted according to the radius from the central axis of the Rondo. Of course, in terms of laser oscillation including the laser resonant system, it is desirable that the phases of the laser beams are all aligned within the cross section of the laser beam, but if the above-mentioned degree of phase shift in the radial direction of the laser beam becomes significant, laser oscillation will fail. It stops.

Solid-state lasers using rod-shaped laser media are not suitable for high-output applications because the diameter of the laser medium becomes large (it becomes difficult to provide sufficient cooling and the phase shift in the radial direction of the laser beam becomes significant). Since the slab-type solid-state laser which is the subject of the present invention can solve this problem, its structure will be explained with reference to FIG.

As can be seen from FIGS. 4(a) and 4(b), the slab-shaped laser medium 10 has the shape of a flat bar with a rectangular cross section.
Both end faces 11 and 12 are obliquely shaped as shown in l.
7 has been completed. The laser resonant reflection system is a partial reflector 20
and a reflector 22, and the laser beam LL enters and exits the laser medium from a direction parallel to the axis of the laser medium 10.
Since the end faces 11 and 12 are oblique, the light travels in the shape of a broken line inside the laser medium 10 as shown in the figure while being totally reflected by the upper and lower side surfaces in the figure. Inside this laser medium, there is even a slight phase shift of the laser beam due to thermal strain in the y direction, which is the thickness direction shown in the same figure (al), but the laser beam L
Since L travels in a broken line as described above, it passes through places with various thermal distortions, so the phase shift of the laser beam is averaged out for the entire laser medium, and the phase of the laser beam in the y direction is changed. It will come together well. Furthermore, since the slab-shaped laser medium 10 has a flat rectangular cross section, it is essentially more advantageous in terms of cooling than the rod-shaped laser medium with a circular cross section, and this cooling is mainly achieved by the total reflection surface for the laser beam mentioned above. It is done from some upper and lower sides. Therefore, the temperature gradient in the y direction of the laser medium IO is originally small, and the accompanying phase shift of the laser beam is averaged out as described above, so the phase in the laser beam of the slab solid-state laser is almost completely adjusted in the y direction. It can be arranged.

In this way, slab-type solid-state lasers are much more advantageous than rod-type solid-state lasers in terms of the phase shift of the laser beam caused by thermal strain within the laser medium, so even if the solid-state laser is made to have high output, the phase shift of the laser beam There is almost no possibility that oscillation will stop due to misalignment, and the laser output can be increased to the limit where the laser medium will be destroyed by internal thermal distortion.

[Problem that the invention seeks to solve]

However, even in slab-type solid-state lasers, there remains the problem of phase shift of laser light due to thermal distortion in the width direction of the laser medium, that is, in the X direction shown in the fourth report. Although this phase shift of the laser beam in the X direction is not serious enough to stop the laser oscillation, it causes the problem that the laser beam emitted from the laser medium 10 tends to spread in the X direction, as shown in the same publication). arise. For this reason, both the partial reflector 20 and the total reflector 22 of the laser resonant reflection system have concave reflecting surfaces as shown in the figure, so that the diverging laser beam incident from the laser medium 10 is convergent and sent back. will be done. However, with this alone, the output laser beam LB taken out from the partial reflector 20 to the right in the figure becomes divergent as shown in the figure.Of course, even if the laser beam is slightly divergent, it is converted into a parallel beam by the lens. Alternatively, it is possible to condense the light at a predetermined focal point, but in practice it is not possible to convert it into a completely parallel light beam,
It is not always easy to completely focus light into a small focal range.

For this reason, if precision is required, the outside portion of the laser beam in the direction of incidence may be canted and only the central portion may be used, but this naturally reduces the utilization efficiency of the laser beam.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems and provide a slab-type solid-state laser oscillation device that can extract a high-quality laser beam with little spread of the beam.

[Means for solving problems]

This object is achieved according to the invention by providing a laser medium which is a flat bar-like slab-shaped solid containing a laser-active substance and which receives excitation light from the side and carries out the laser action under cooled conditions;
A slab-type solid-state laser oscillator is equipped with a laser resonant reflection system consisting of a partial reflector for the laser beam disposed on one side of both longitudinal end faces of the laser medium and a total reflector disposed on the other side. A convex lens body and a concave lens body are provided between the medium and the partial reflector and each formed into a columnar shape with the axis in the thickness direction of the laser medium,
This is achieved by adjusting the mutual spacing between the convex lens body and the concave lens body to control the spread of the output laser beam extracted from the partial reflector side of the laser resonant reflection system.

[Effect]

The convex lens body and concave lens body mentioned in the above configuration are of course for correcting the laser beam into a parallel beam, but
Since the cause of deviation of the laser beam from the parallel beam is the temperature gradient in the width direction of the laser medium, each lens body is formed into a columnar shape with its axis in the thickness direction perpendicular to the width direction.
Next, if the purpose is simply to correct the laser beam into a parallel beam, it is not necessarily necessary to combine two types of lens bodies in this way, and it is also possible to use only a convex lens body, but laser beams based on thermal distortion Since the manner in which the light beam deviates from the parallel light beam is somewhat complex and its degree varies depending on the output value of the solid-state laser, in the present invention two types of lens bodies are combined and the mutual spacing between them is adjustable. Hereinafter, the deviation of the laser beam from the parallel beam will be explained with reference to FIGS. 2 and 3.

FIG. 2 shows a cross section of the laser medium 10, and within this cross section there is excitation light E mainly applied from the upper and lower sides of the figure.
Almost --like heat generation is caused by L. Cooling for this is mainly done from these upper and lower sides,
Since cooling is also effected from the left and right sides of the figure, a heat flow 1 (F) also exists in the X direction, which is the width direction of the laser medium as shown in the figure.
Therefore, a temperature gradient in the X direction occurs. Based on this temperature gradient, compressive force is generated at the center 10c of the laser medium 10 in the figure, and tension is generated at both edges 10e. The direction or positive/negative sign differs between the parts, and as a result, the laser beam passing through the central part becomes convergent, while the laser beam passing through both edges becomes divergent. Figure 3 shows this situation, where the horizontal axis of the figure shows the position variable X in the width direction, and the vertical axis shows the position variable The reciprocal 1/f of the focal path 111f when viewed as a lens is taken. The width of the laser medium 10 is indicated by W in the figure. When the output value of the laser beam is large, the reciprocal 1/f of this focal length becomes as shown by curve A in the figure, and as shown in the figure, the value of the focal length is positive in the range of X that corresponds to the central portion 10c of the laser medium. The laser medium exerts a convex lens effect on the laser beam passing through this range, making it convergent. On the other hand, X that hits both edges 10e of the laser medium
In the large range of values of , the focal length has a liability, and the laser medium in this range exerts a temperature lens effect on the laser beam, making it divergent. When the laser medium 10 has a rectangular cross section that is quite elongated in the width direction as shown in FIG. Although the focal length is constant, the focal length of the thermal lens effect of the -ship edge 10e strongly depends on the value of X.

Curve B shows the case where the output value of the laser beam is small, and the general trend is the same as curve A, but the focal length is longer in all meters, so the tendency of the convergence and divergence of the laser beam is It will be weaker than in the case of high output.

As mentioned above, the laser beam contains a mixture of convergent and divergent beams, and the degree of convergence and divergence also changes depending on the output value of the laser beam, so a simple lens body alone can correct the beam into a parallel beam. Therefore, in the present invention, as described above, a convex lens body and a concave lens body are combined, and the distance between both lens bodies is adjusted according to the output level of the laser beam, and the laser beam is increased by the total of both lens bodies. to make it possible to correct the beam into a nearly parallel beam. In order to correct this parallel light flux, it is ideally desirable to make the cross-sectional shapes of both lens bodies different from that of a normal lens. Although it is theoretically desirable to have the same cross-sectional shape as a normal lens, experimental results show that there is not much difference in practice even if the cross-sectional shapes of both lens bodies are made to be the same shape as a normal lens.On the other hand, the output level of the laser beam changes. Since the divergence and convergence of the laser beam and the convergence of the laser beam vary considerably accordingly, in the present invention, by adjusting the mutual distance between the convex lens body and the concave lens body, it is possible to always correct the beam to a parallel beam. When correcting the divergent light beams from both edges of the laser medium to make them parallel so as not to cause divergence as a whole, the mutual spacing should be increased when the output level of the laser beam is high.

When the output level is low, the mutual spacing can be adjusted to be small. By adjusting the mutual spacing, the overall divergence and convergence of the laser beam can be easily controlled, and it can be made into a nearly parallel beam. Very useful for correction.

As described above, with the above configuration of the present invention, it is possible to correct a laser beam having a mixture of diverging and converging properties into a practically perfectly parallel beam and then extract it from the solid-state laser device, thereby solving the above-mentioned problem. resolved.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to FIG.

Fig. 1 f8) shows the width direction X and longitudinal direction 2 of the laser medium 10.
As in the conventional case, a partial reflector 21 is disposed on one end face 11 side of this laser medium 10, and a full reflector 22 is disposed on the other end face 12 side. A laser resonant reflection system is configured by the re-reflector.

However, since the partial reflector 21 receives the laser beam corrected to be a parallel beam unlike the conventional one, its reflecting surface is formed into a flat plate shape. This partial reflector 21 and 7 and the medium 1
0, a convex lens body 30 and a concave lens body 40 according to the present invention are arranged with a distance l between them, with the convex lens body 30 facing the end face 11 in this embodiment.

As can be seen from Figure 3), each of these lens bodies is a columnar body that is straight in the thickness direction y of the laser medium 10 and has a curved surface in the width direction X of the laser medium. In this embodiment, the cross sections of these lens bodies 30 and 40 shown in the figure Tal have the same shapes as a normal convex lens and a concave lens, respectively.

As described above, a convergent laser beam LBc is emitted from the center of the end surface 11 of the laser medium 10, and a diverging laser beam LBe is emitted from both edges.
Each focal length of 0.40 is, for example, a divergent laser beam LB.
The beam e is selected so as to be made parallel to the beam and incident on the partial reflector 21. As a result, the diverging laser beam LBe incident on both edges of the convex lens body 30 becomes a slightly convergent laser beam LBe, and is converged into the concave lens body 4.
The concave lens body 40, which receives the light beams on both sides thereof, aligns the beams into almost completely parallel beams and passes them to the partial reflector 21. On the other hand, the weakly convergent light beams incident on the central part of the convex lens body 30 from the laser medium 1O The convergent laser beam LBc is converted into a convergent laser beam by the convex lens body 30, and is turned into a convergent laser beam by the concave lens body 4.
0, the concave lens body 40 turns the laser beam into a nearly parallel but convergent laser beam, which is reflected by the partial reflector 2.
Enter 1.

The partial reflector 21 transmits a part of these laser beams received from the concave lens body 40 and outputs a laser beam LB that is generally aligned as a parallel beam as a whole, and reflects the remaining part to pass through the concave lens body 40 and the convex lens body 30. Both edges of this reflected laser beam are returned to the laser medium 10 as a laser beam having convergence comparable to the divergence when first emitted from the laser medium. On the other hand, the central part of the reflected laser beam is returned to the laser medium as a laser beam with a slightly stronger divergence than the convergence when it was initially emitted from the laser medium. In this embodiment, the partial reflector 21
As mentioned above, the laser beam LB output from the convex lens body 30 to the right side of the figure cannot theoretically be aligned into a perfectly parallel beam at both the center and both edges at the same time.
and the concave lens body 40, the light flux is almost perfectly parallel in practice, and the parallel light flux is controlled by, for example, the concave lens body 4.
It can be controlled by finely adjusting the position of 0 as shown by arrow M in the figure.

The output level of the laser beam LB is controlled by controlling the amount of excitation light EL applied to the laser medium 10, but when the amount of excitation light applied to the laser medium changes, the amount of heat generated inside the laser medium and therefore the thermal distortion changes. Therefore, the degree of divergence and convergence of the laser beam emitted from the laser medium also changes, and in the present invention, the amount of correction corresponding to this is controlled by adjusting the mutual distance l between the lens bodies 30 and 40. can do. When correcting the diverging laser beams from both edges of the laser medium so as to align them into parallel beams, the correction effect of both lens bodies can be strengthened by increasing the mutual distance l, so for example, the laser beam LB When the output level of the laser beam LB is small and the divergence and convergence of the laser beam emitted from the laser medium 10 are weak overall, the two edges of the laser beam LB can be made parallel by adjusting the mutual distance l to a small value. The luminous flux can be corrected.

The partial reflector 21, which receives the laser beam that has been made almost parallel by the lenses 30 and 40, is formed into a flat plate shape as described above, but the other total reflector 22 is formed to reflect the laser medium 10. Since the other end face 12 receives a diverging laser beam as a whole, it is formed as a concave mirror as in the conventional case, and converts the reflected laser beam into a convergent beam and sends substantially all of it back to the laser medium IO.

FIG. 1 (bl is a side view including the thickness direction y and longitudinal direction 2 of the laser medium, and for reference, a closed container 1 housing a laser medium 10 and an excitation light source 2 incorporated therein)
is schematically shown. The laser medium 10 is inserted into the closed container 1 from an opening 1a formed on both end surfaces thereof to the oblique end surface 1.
1.12 is inserted to the outside, and the opening 1a
The space between the two is kept liquid-tight by a suitable means such as a seal. The excitation light source 2 is a high-intensity xenon lamp, for example, and is installed as a pair inside the closed container 1, for example, on the upper and lower sides of the laser medium 10, and emits excitation light EL to the laser medium 10 mainly through its upper and lower sides. give it. The entire inner surface of the closed container 1 is finished with a mirror surface, and the excitation light EL from the excitation light source 2
is reflected by this mirror surface and all of it ends up in the laser medium 1.
given to 0. The closed vessel l is further provided with a pair of inlets and outlets 1b for a cooling medium CM, and as the coolant CM, for example, pure water is passed through these inlets and outlets 1b into the closed vessel l, and the laser medium 10 and the excitation Cool the light source 2.

The slab-type solid-state laser shown in FIG. The laser resonant reflection system consisting of the reflector 22 performs a high-output laser oscillation action under the resonant condition.As mentioned above, the laser light travels along the polygonal line in the laser medium 10, so as shown in the figure (false). There is almost no tendency for the laser beam to spread in the thickness direction y of the laser medium, and the laser beam as a whole has a tendency to spread in the width direction X of the laser medium. The entire beam is aligned into a nearly parallel beam and then output from the solid-state laser.

When starting up a solid-state laser or changing its output level, the degree of divergence and convergence of the laser beam emitted from the laser medium changes based on temperature changes in the laser medium, but it is necessary to adjust the mutual distance l between both lens bodies. By doing so, the parallel luminous flux property of the output laser beam can be maintained. In addition, if you want to control the divergence or convergence of the laser beam due to the convenience of the user of the output laser beam, you can easily achieve the desired characteristics by finely adjusting the position of one of both lens bodies as shown by arrow M. Can be matched.

In addition to the embodiments described above, the present invention can be implemented in various ways. For example, in the embodiments, the convex lens body is disposed on the laser medium side, but as can be easily understood, the convex lens body and Even if the positions of the concave lens bodies are interchanged, the same effect of correcting the divergence and convergence of the laser beam can be obtained. However, if the main objective is to align the diverging laser beams from both edges of the laser medium into a parallel beam, it is slightly more advantageous to arrange the convex lens body on the laser medium side as in the first embodiment. . In addition, the cross-sectional shapes of both lens bodies were the same as those of ordinary columnar convex lenses and concave lenses in the example, but for example, the convex lens body had its center portion flat, and the concave lens body had its both edges flat. Theoretically, it is possible to make the correction effect of the divergence and convergence of the laser beam more complete. Forming a portion of each lens body into a flat surface in this manner can be easily done by processing the convex portions of ordinary columnar lenses.

〔Effect of the invention〕

As explained above, in the present invention, there is provided a laser medium which is a flat bar-shaped solid slab containing a laser active substance and which receives excitation light from the side and performs a laser action under cooled conditions; A slab-type solid-state laser oscillator is equipped with a laser resonant reflection system consisting of a partial reflector for a laser beam disposed on one side of the laser beam and a total reflector disposed on the other side. A convex lens body and a concave lens body each formed in a column shape with the thickness direction of the laser medium as an axis are provided between the convex lens body and the concave lens body, and by adjusting the mutual spacing between the convex lens body and the concave lens body, partial reflection of the laser resonant reflection system can be achieved. Since the spread of the output laser beam extracted from the body side can be controlled, the laser beam, which has a mixture of diverging and converging characteristics, emitted from the laser medium is corrected to an almost completely parallel beam by both lens bodies, and the solid-state 6 The nearly parallel laser beam extracted from the solid-state laser according to the present invention has a well-aligned laser beam phase in a cross section perpendicular to the beam axis, and has good coherence, and can be used with a lens. Despite its high output, it has excellent properties unique to laser beams, such as being able to focus within a very small range when condensed. Additionally, if the degree of divergence or convergence of the laser beam emitted from the laser medium changes, such as when starting up the solid-state laser or changing the output level, the mutual distance between both lens bodies can be adjusted as appropriate. By doing so, the output laser beam from the solid-state laser can be very easily aligned into almost completely parallel beams. Even when it is desired to control the divergence or convergence of the output laser beam to a desired degree depending on the user's convenience, the output laser beam can be easily adjusted to the desired characteristics by finely adjusting the mutual spacing between both lenses. Can be done. Furthermore, regarding the laser oscillation effect as a solid-state laser, the laser beam is corrected by both lens bodies according to the present invention so that the phase of the laser beam is well aligned within its cross section, and then reflected by a partial reflector and sent back to the laser medium. As a result, the laser resonant state including the laser resonant reflection system and laser medium can be made sharper than before, and as a result, an excellent laser beam with less variation in the oscillation wavelength is output despite the high output. can do.

Both the convex lens body and the concave lens body necessary for carrying out the present invention are columnar lens bodies that are easy to manufacture. According to the present invention, the above-mentioned effects can be obtained with a slight increase in cost, and the performance of the slab-type solid-state laser oscillation device can be improved compared to the conventional one. can be improved significantly.

[Brief explanation of the drawing]

Figures 1 to 3 relate to the present invention, with Figure 1 being a plan view and side view of an embodiment of the slab-type solid-state laser oscillation device according to the present invention, and Figure 2 explaining the thermal lens effect of the laser medium. FIG. 3 is a cross-sectional view of a laser medium for this purpose, and is a characteristic diagram showing the divergence and convergence of the laser beam based on the thermal lens effect. FIG. 4 is a side view and a plan view of a slab-type solid-state laser oscillation device according to the prior art. Light source, 10: Laser medium, 10c: Center portion in the width direction of the laser medium, 10e: Edge portion in the width direction of the laser medium, 11, 12: End surface of the laser medium, 2
0, 21: Partial reflector, 22: Full reflector, 30: Convex lens, 40:11! ! ] Lens body, Surrounding: Cooling medium, E
L: excitation light, f: focal length of laser beam, )IF: heat flow at the edge of the laser medium in the width direction, LB: laser beam extracted from the solid-state laser, LEc: convergent laser beam,
LBe: Divergent laser beam, LL: Laser light, 1: Mutual distance between convex lens body and concave lens body, M: Fine adjustment direction of lens body, W: Width of laser medium, X: Width direction of laser medium, y: The thickness direction of the laser medium is 2: the longitudinal direction of the laser medium.

Claims (1)

[Claims] 1) A laser medium that is a flat rod-shaped slab-shaped solid containing a laser active substance and receives excitation light from the side and performs a laser action under cooled conditions; a laser resonant reflection system consisting of a partial reflector for the laser beam and a total reflector disposed on the other side; A convex lens body and a concave lens body are formed, and by adjusting the mutual distance between the convex lens body and the concave lens body, the spread of the output laser beam extracted from the partial reflector side of the laser resonant reflection system can be controlled. A slab-type solid-state laser oscillation device characterized by: