JP2003258345A - High output laser light generator using slab-type laser medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the economic efficiency of a generator. <P>SOLUTION: A beam expander (BE) 2 radiating a spot laser beam having a circular cross section, which is emitted from a laser beam main oscillator 1, to a first slab-type amplifier 3 has a function of only enlarging the laser beam in one direction in the width direction of a laser medium arranged in the slab-type amplifier 3. A polarized beam splitter (PBS) 6 totally reflects a high output laser beam 7 in the width direction of the laser medium, which is emitted from the slab-type amplifier 3 in the opposite direction, to the outside of the generator. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser beam generator for obtaining a high output by using a slab type laser medium for amplifying a laser beam, and more particularly to a laser beam generator for improving the output and The present invention relates to a laser light generator that can be expected to improve economy and reliability. 2. Description of the Related Art First, a slab type laser medium 10 used in a slab type amplifier for generating a high output laser light will be considered with reference to FIGS. The illustrated slab type laser medium 10
Is a generally adopted shape, and is an optically transparent crystal of a plate-like body having a thickness direction on the Y axis and a width direction on the X axis with respect to the length direction as the Z axis. . That is, the laser medium 10 has a rectangular cross section (X direction) obtained by cutting perpendicular to the propagation direction of laser light (Z axis direction).
Two planes parallel to the XZ plane in the thickness direction (Y axis direction) and the thickness direction (Y axis direction)
Two end faces in the width direction parallel to the plane are referred to as side faces 14. Further, the laser medium 10 has light entrance / exit surfaces 11 and 12 that are planes parallel to the X-axis at both end surfaces in the length direction (Z-axis direction) that is the propagation direction of the amplified laser light. I have. The illustrated light entrance / exit surfaces 11 and 12 are further inclined with respect to the Z axis, that is, inclined with respect to the excitation surface 13. Accordingly, as shown in FIG. 3, when a laser beam 21 parallel to the Z axis is incident on the light entrance / exit surface 11 oblique to the Z axis, the incident internal laser beam 22 is Two parallel XZs that are refracted in the thickness direction (Y-axis direction) and perpendicular to the Y-axis direction due to the light refractive index of 10
A zigzag optical path for total reflection is formed with the plane excitation surface 13 as an internal total reflection surface, and the laser light 23 is emitted from the light entrance / exit surface 12 in parallel with the Z axis. The laser light traveling inside the laser medium 10 reciprocates to increase its amplification. When the light entrance / exit surfaces 11 and 12 are perpendicular to the Z-axis, the laser beam 21 is inclined from the light entrance / exit surface 11 with respect to the Z-axis so that the internal laser light 22 forms a similar zigzag optical path. And travel from the light entrance / exit surface 12 to Z
The laser beam 23 can be emitted at an angle to the axis. In this structure, the excitation plane (XZ plane) 13
A temperature gradient is generated in the Y-axis direction inside the laser medium 10 by absorbing the excitation light supplied through the
Since the zigzag optical path is also formed parallel to the YZ plane, it has an excellent characteristic that the above-described thermo-optic effect is compensated. Furthermore, by increasing the dimension in the width direction (X-axis direction), the cooling surface area of the excitation surface 13 forming the total internal reflection surface, which is the XZ plane, is increased. Can accept. Therefore, this structure is suitable for obtaining high output. [0006] Some slab-type laser media have an input / output surface perpendicular to the Z axis, that is, perpendicular to the excitation surface. In this case, the laser light is totally reflected on the excitation surface by obliquely entering and exiting the incident / exit surface, and forms a zigzag optical path inside the laser medium as described above. The effect can be exhibited. Conventionally, a laser beam generating device converts a laser beam emitted by a laser beam main oscillator 1 into an optical path of a laser beam generating optical system composed of elements such as a lens, an aperture, a mirror, a polarizer, and a half-wave plate. , And is formed into a spot light having a desired circular cross section as P-polarized light, and is emitted to a polarization beam splitter (PBS) 6a as shown in FIG. Since this laser light is P-polarized light, it passes through the PBS 6a and enters the beam expander (BE) 2a. BE2a is a slab type laser medium 10 having the above-described cross-sectional dimension of the circular cross-section beam.
, And is formed into an elliptical shape such that the shape after the enlargement is substantially inscribed in the cross section of the slab, and is emitted toward the slab amplifier 3 as incident laser light. The laser light is amplified while traveling in a zigzag optical path inside the slab type amplifier 3, but is not sufficiently amplified in a single pass. Therefore, the excitation energy stored in the laser medium cannot be sufficiently extracted,
As shown in FIG. 4, the laser light emitted in the same direction as the incident laser light is returned to the entrance side of the slab type amplifier 3 by using a mirror, and is again incident on the slab type amplifier 3 with a small angle of inclination. Multiplex amplification is realized. Normally, another slab-type amplifier is inserted into the return circuit to form a multiplex amplification to further increase the amplification. In the block configuration shown in FIG. 4, a Faraday rotator (FR) 4 of an optical element and a phase conjugate mirror (P
CM) 5, and a laser light reflecting optical system optical path for reflecting the laser light emitted from the slab type amplifier 3 and making the P-polarized light enter the slab type amplifier 3 as S-polarized laser light. Next, the FR4 and PCM5 will be described. As described above, a multi-stage configuration in which a plurality of stages are stacked as necessary is employed in the laser light amplifier and the optical path around it. However, as a result, the total optical path length becomes long, and the alignment of the optical axis tends to be out of order. In addition, even in the case of the slab type, in the multi-stage amplification, the thermal lens effect that occurs in the X-axis direction is accumulated and cannot be ignored. In order to solve such a problem, a phase conjugate mirror (PCM) 5 that generates a phase conjugate wave of the laser light is provided at a turning point of the amplification. Since the phase conjugate wave is a time-reversed wave, the laser light reflected from the PCM 5 travels in the direction of the incident wavefront in a faithful manner, so that when returning to the incident point, the same wavefront as the incident wave is used in principle. Will have. The difference is that the strength has increased several thousand times. However, in this state, only the upstream laser light main oscillator 1 is destroyed and cannot be taken out as an output. Therefore, an optical element acting on the polarized light, for example, the illustrated Faraday rotator (FR) 4 is inserted before the PCM 5. Faraday rotator (FR) 4
Makes the emitted laser light, which was linear P-polarized light at the time of incidence when reflected from the PCM 5 again, become S-polarized light rotated 90 degrees from its polarization plane. The S-polarized emitted laser light is totally reflected by the PBS 6a, and can be extracted as an output. The outgoing laser light having a high output through the plurality of slab-type amplifiers has S-polarized light orthogonal to the polarization direction of the incident laser light, which is P-polarized light. The light is emitted to the BE 2a. The BE 2a returns the received laser light having a substantially elliptical shape in the width direction of the received slab type laser medium to a spot light having the same circular cross section and central axis as the laser light before amplification, and the PBS 6a is used as the high output laser light 7a. The light is emitted toward. The PBS 6a totally reflects the received high-power laser light 7a and outputs it outside the apparatus. In the above-described laser light generating apparatus, the beam expander (BE) expands the incident laser light having a circular cross section in one direction in the width direction of the laser medium, and in the opposite direction. The high-power output laser light having an elliptical shape in the width direction of the laser medium is compressed back into a spot light having the same circular cross section and central axis as the incident laser light before amplification. However, in this system, the optical element is likely to be damaged by the laser beam during actual operation. For example, the BE is a one-way expander for the outward laser light, but acts as a one-way compressor on the return path for the output laser light amplified to high output. Therefore, on the entrance side of the BE, that is, on the exit side for the return laser beam,
The laser energy density per unit area becomes very large. As a result, the inside of the BE member or the antireflection coating film is easily damaged. In addition, a polarizing beam splitter (PB
S) is formed from an optical film having an advanced multilayer structure in order to increase the ratio of reflection / transmission by S / P polarized light. Therefore, PBS is easily damaged by laser light. Also,
It is no exaggeration to say that the strength of these optical films limits the output performance of the entire device as a laser. An object of the present invention is to provide a reliable and economical laser light generator by avoiding an increase in the cost of a beam expander (BE) and a polarizing beam splitter (PBS). A laser light generating apparatus according to the present invention obtains a high output by using a slab type laser medium for amplifying laser light, and receives laser light from a laser light main oscillator. Beam expander (BE) that expands the laser beam in the width direction of the slab-type laser medium and emits the laser beam is arranged in front of a polarizing beam splitter (PBS) that totally reflects the high-power output laser light and outputs the laser light to the outside of the apparatus. I have. For this reason, the polarizing beam splitter (PBS) totally reflects the high-power laser light emitted from the slab-type laser medium and having an elliptical shape in the width direction of the slab-type laser medium and outputs it to the outside. On the other hand, the beam expander (BE)
E, the function can be limited to only the function of expanding the weak laser light received from the laser light main oscillator in one direction in the width direction of the slab-type laser medium, and making the shape of the weak laser light substantially inscribed in the cross section of the slab. Therefore, the BE and the PBS in the configuration of the conventional apparatus are used.
The function of the BE can be reduced by changing the connection position of the BE. In addition, since the beam area to the PBS can be made large, the proof stress on the laser beam can be reduced. That is, economical efficiency can be improved without substantially changing the configuration of the entire apparatus. Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an embodiment of block connection according to the present invention. The illustrated laser light generator includes a laser light main oscillator 1, a beam expander (BE) 2, a slab type amplifier 3, a Faraday rotator (FR) 4, and a phase conjugate mirror (PC).
M) 5, a polarization beam splitter (PBS) 6, and the above-described laser light generation optical system optical path and laser light reflection optical system optical path. The difference from the prior art is that the positions of the BE 2 and the PBS 6 on the traveling path of the laser beam are alternated. The laser light main oscillator 1 emits laser light linearly polarized in one direction. The laser light is applied to a straight line P via a lens, an aperture, a mirror, a polarizer, a half-wave plate, and the like.
The laser beam is incident on the BE 2 via an optical path of a laser beam generating optical system that forms a beam of polarized light and a desired circular cross section. The BE 2 beam-expands the P-polarized circular section beam in one direction in the width direction of the slab type laser medium constituting the slab type amplifier 3 as described above, and emits the beam to the slab type amplifier 3 via the PBS 6. BE with unidirectional beam expansion
May be an anamorphic prism pair (APP) combining two right-angle prisms or a combination of a cylindrical convex lens and a cylindrical concave lens, and any of them may be employed. However, in the combination of lenses, aberration of the lens is inevitable. The slab type amplifier 3 amplifies and emits the laser light transmitted through the PBS 6. The outgoing laser light shown here is amplified by another multi-stage slab type amplifier and returned. Here, the laser beam returning to the slab type amplifier 3 is tilted by a small angle at each of emission and incidence. The P-polarized laser light emitted from the return slab type amplifier 3 through the multi-stage configuration includes an FR 4 that converts P-polarized light into S-polarized light and a PCM 5 that is almost totally reflected, and includes a lens,
The reflected light becomes S-polarized light via a laser light reflecting optical system optical path composed of an aperture, a mirror, and the like, and returns to the slab type amplifier 3 through the same optical path. Therefore, the laser light which has been almost totally reflected, converted into an S-polarized beam and amplified again becomes a high-power laser light 7, and has an elliptical shape in the width direction of the slab type laser medium from the slab type amplifier 3. It is emitted in the opposite direction on the same optical axis as the incident light. The PBS 6 totally reflects the S-polarized high-power laser light 7 emitted from the slab type amplifier 3 and outputs it to the outside of the device. In the above description, the high-power output laser light having an elliptical shape in the width direction is directly output from the slab type laser medium of the slab type amplifier to the outside of the apparatus. By adding a beam expander that expands, it is easy to change to a spot light having a circular cross section of approximately the same diameter as the width of the laser medium. In this case, the beam expander is used only for the expansion, so that it is not damaged by the laser beam, and can be easily arranged. In the above description, appropriate conditions are described with reference to the drawings. However, the configurations and combinations such as the shapes and sizes and the mutual positions shown and described are mutually related with the environmental conditions, but are free as long as the functions described above are satisfied, and the present invention is limited to the above description. is not. As described above, according to the present invention, the beam expander (BE) that emits laser light to the first slab-type amplifier emits spot light having a circular cross section in the width direction of the laser medium. It has only a function of expanding in one direction, and outputs a high-output laser beam having an elliptical shape in the width direction of the laser medium emitted from the slab type amplifier in the opposite direction to a polarization beam splitter (PB).
S) is totally reflected toward the outside of the device. like this,
If necessary, the high-power output laser light having an elliptical shape in the width direction of the laser medium can be shaped into a spot light having a circular cross section by adding a BE that expands in one direction in the thickness direction. As a result, the non-reflective optical thin film of BE or the expensive optical thin film of PBS can be prevented from being damaged by light due to the intensity of the high-power output laser light, and the amplifier can be operated in a higher pumping state. Can be. That is, output performance is improved. Therefore, not only can the cost of the PBS and BE be increased, but also the reliability and performance can be improved, so that the economical efficiency of the device can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an embodiment of block connection according to the present invention. FIG. 2 is a perspective view showing one embodiment of a slab type laser medium. FIG. 3 is a diagram showing one form of a laser beam propagating inside a laser medium in FIG. 2; FIG. 4 is a diagram showing an example of a conventional block connection. [Description of Signs] 1 laser beam main oscillator 2 beam expander (BE) 3 slab type amplifier 4 Faraday rotator (FR) 5 phase conjugate mirror (PCM) 6 polarization beam splitter (PBS) 7 high-power laser beam

Claims (1)

Claims: 1. A laser light generator for obtaining high-power laser light by using a slab type laser medium for amplifying the laser light, wherein the laser light emitted from the laser light main oscillator is a P-polarized circular light. A laser light generating optical system optical path for forming a cross-sectional laser light;
A laser light reflection optical system optical path for reflecting the laser light transmitted through the slab type laser medium and for re-entering the slab type laser medium as P-polarized laser light as S-polarized laser light;
A beam expander that receives a P-polarized circular cross-section laser beam from the optical path of the laser light generating optical system and expands and emits the laser beam in the width direction of the slab type laser medium; and between the beam expander and the slab type laser medium. From the beam expander
The slab laser medium receives and transmits polarized light, transmits the slab laser medium, and transmits the slab laser medium.
A laser light generator comprising: a thin-film polarization beam splitter that totally reflects a polarized high-power laser beam and outputs the reflected laser beam toward an outside of the device.