JP5088623B2 - Laser resonator - Google Patents

Description

  The present invention relates to a laser resonator for improving hold-off performance.

  For example, Patent Documents 1 to 3 have already been proposed as high-efficiency laser resonators.

The “laser resonator” of Patent Document 1 aims to obtain laser light that has been wavelength-converted with high efficiency.
Therefore, as shown in FIG. 5, the laser resonator reflects the excitation medium 50 having a laser medium 50a and an excitation light source 50b for exciting the laser medium, and fundamental waves emitted from the excitation apparatus 50 in opposite directions. First and second reflecting mirrors 51 and 52, and third and fourth reflecting mirrors that return and reciprocate the fundamental waves reflected by the first and second reflecting mirrors 51 and 52 through the excitation device, respectively. 53, 54, between the first and third reflecting mirrors 51, 53 and between the second and fourth reflecting mirrors 52, 54, and converts a part of the fundamental wave to The first to fourth reflecting mirrors 51, 52, 53, and 54 reflect the fundamental wave and the first and the second nonlinear optical media 56 and 57 that emit converted waves having different wavelengths. Second nonlinear optical medium Those having a wavelength separating means for transmitting a converted wave emitted from 6,57.

An object of “Laser resonator and its assembling method” of Patent Document 2 is that a wavelength conversion element can be suitably arranged at a focal position of laser light.
Therefore, as shown in FIG. 6, this laser resonator emits laser light from a laser medium 64 and adds an image transfer optical system to a basic optical system that determines a reference point at the focal position of the laser light. 67. The image transfer optical system includes image transfer lens means for determining the image transfer projection point using the focal lengths f1 and f2 of the plurality of lenses 60 and 61 from the reference point of the laser beam. Is configured by arranging a wavelength conversion element 66 capable of changing the wavelength of the laser light.

The “laser oscillator” of Patent Document 3 is intended to output laser light having a desired pulse width.
Therefore, as shown in FIG. 7, this laser oscillator switches an optical resonator 76 composed of a pair of mirrors 73 and 74 provided with a laser medium 71 interposed therebetween, and a laser beam excited in the optical resonator 76. The Q switch 72 that is disposed in the optical resonator 76 and the light image at a predetermined position excited in the optical resonator 76 is transferred to a position separated by a predetermined distance to adjust the resonator length of the optical resonator 76. And an image transfer optical system 70.

JP 2000-216465 A, “Laser resonator” Japanese Patent Application Laid-Open No. 2005-45174, “Laser Resonator and its Assembly Method” JP 2005-72131 A, “Laser Oscillator”

FIG. 1 shows a conventional laser resonator using an AO-Q switch as a Q-switch. In this laser resonator 1, a laser medium 4 (for example, Nd: YAG) is disposed between a terminal mirror 2 and an output mirror 3, and a plurality (two in the figure) of AOs are disposed between the laser medium 4 and the output mirror 3. -The Q switch 5 is arranged.
That is, in this example, two AO-Q switches 5 are arranged in series as means for improving the laser oscillation ON / OFF (Hold-off) performance. In this figure, reference numeral 6 denotes an output laser, which is a pulse laser beam when a Q-switch is used.

  FIG. 2 is an operation explanatory diagram of the AO-Q switch 5. The AO-Q switch 5 is a Q switch that uses an acoustooptic effect. When the ultrasonic wave a is propagated to a medium (such as quartz) having an acoustooptic effect, the incident laser 7 is used as a kind of diffraction grating. Is diffracted and reflected at a certain angle (diffraction angle), and utilizes the characteristic of moving straight when the ultrasonic wave is stopped. The diffracted reflected light 8 is referred to as “first-order diffracted light”, and the straight traveling light 9 is referred to as “0th-order light”.

  The AO-Q switch 5 has a structure in which a piezo element or the like is attached to one side surface of a medium. That is, as a Q switch, a state where a voltage is applied to the piezo element to propagate the ultrasonic wave a and the incident laser is diffracted and reflected is OFF, and a state where the voltage application is stopped and the incident laser is caused to travel straight is ON.

FIG. 3 is an explanatory diagram showing the influence of the diffracted light 8 of the AO-Q switch 5 on the laser.
As described above, the AO-Q switch 5 performs Hold-off by diffracting the incident laser light 7 in a specific direction, but is in a transient state when the Laser starts oscillation after the Hold-off is turned off. Therefore, the diffracted light 8 remains, which affects laser oscillation. That is, the diffracted light 8 is on the plane 8a of the diffraction direction, and the diffraction direction is non-uniform, so that the laser light is affected non-uniformly, causing non-uniformity of the beam profile shape (intensity distribution).

  Therefore, as shown in FIG. 1, when a plurality of (two) AO-Q switches 5 are arranged in series, the diffracted light in a transient state when the laser starts oscillating with the hold-off of the AO-Q switch 5 turned off. There is a problem that the influence of the above becomes larger and the beam profile shape (intensity distribution) becomes too uneven.

The present invention has been developed to solve the above-described problems.
That is, the object of the present invention is to improve the performance of laser oscillation ON / OFF (Hold-off) by arranging a plurality of AO-Q switches in series, and in the transition period of AO-Q switch switching, An object of the present invention is to provide a laser resonator capable of making the beam profile of the generated laser light uniform.

According to the present invention, a laser oscillator that amplifies linearly polarized laser light,
One or more pairs of AO-Q switches disposed on the optical path of the laser beam and having diffraction directions alternately orthogonal;
There is provided a laser oscillator comprising: a polarization rotation element positioned between the pair of AO-Q switches and rotating a polarization plane by 90 °.

  According to the configuration of the present invention, in the case of a laser oscillator that amplifies linearly polarized laser light, one or a plurality of pairs of AO-Q switches have diffraction directions alternately orthogonal to each other, and a polarization plane is set between them. Since the polarization rotation element that rotates is provided, laser light can be incident on both Q switch elements with an optimum polarization direction by the polarization rotation element disposed between the Q switches. Thereby, diffraction occurs evenly in two orthogonal directions, and the beam profile shape (intensity distribution) can be made uniform in the two orthogonal directions.

  Therefore, a plurality of AO-Q switches can be arranged in series to improve the laser oscillation ON / OFF (Hold-off) performance, and the laser beam generated during the transition period of the AO-Q switch switching can be improved. The profile can be made uniform.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In each figure, common portions are denoted by the same reference numerals, and redundant description is omitted.

FIG. 4 is a diagram showing an embodiment of a laser resonator according to the present invention. In this figure, a laser resonator 10 of the present invention is a laser oscillator that amplifies linearly polarized laser light.
The laser resonator 10 includes a pair of AO-Q switches 12A and 12B, a polarization rotation element 14, a laser medium (not shown), and a pair of reflection mirrors. The pair of AO-Q switches 12A and 12B is one pair (two units) in this example, but may be a plurality of pairs.
Hereinafter, a case where the AO-Q switch is a pair will be described.

  The laser medium (not shown) is a solid laser medium such as Nd: YAG, and is excited by an excitation source (not shown) to emit laser light. This laser beam is preferably linearly polarized from the time of emission. However, circularly polarized light may be converted into linearly polarized light using a polarizing filter or the like.

  A pair of reflection mirrors (not shown) is composed of a total reflection mirror and a semi-reflection mirror, and is provided with a laser medium sandwiched between them in the axial direction. The light is amplified, and laser light is emitted to the outside through a semi-reflective mirror.

  In FIG. 4, a pair of AO-Q switches 12A and 12B are disposed on the optical path 11 of the laser beam and have diffraction directions b that are alternately orthogonal. Note that c is the optimum polarization direction of each Q switch, and is orthogonal to the diffraction direction b. X and Y indicate the polarization directions of linearly polarized light passing through each Q switch. The polarization directions X and Y coincide with the optimum polarization direction c of each Q switch.

  The polarization rotation element 14 is, for example, a half-wave plate, is positioned between the pair of AO-Q switches 12A and 12B, and rotates the polarization direction (polarization plane) of the linearly polarized light passing therethrough by 90 °. It has become.

With the configuration of the above-described embodiment, linearly polarized light in the polarization direction Y in the figure passes through the optimal AO-Q switch 12A in the same polarization direction c, and the polarization plane is rotated by 90 ° by the polarization rotation element 14 to be polarized. It becomes linearly polarized light in the direction X, and then the linearly polarized light in the polarization direction X passes through the optimum AO-Q switch 12B in the same polarization direction c.
Further, a laser beam (not shown) and a pair of reflecting mirrors reciprocate linearly polarized laser light between them, amplify the laser light by optical resonance, and emit the laser light to the outside through the semi-reflecting mirror.

  Therefore, the polarization rotation element 14 disposed between the pair of AO-Q switches 12A and 12B allows laser light to be incident on both Q switch elements in an optimum polarization direction, and two orthogonal directions X, Diffraction occurs evenly with respect to Y, and the beam profile shape (intensity distribution) can be made uniform in two orthogonal directions X and Y.

  As described above, according to the embodiment of the present invention, a plurality of AO-Q switches can be arranged in series to improve the performance of laser oscillation ON / OFF (Hold-off), and the AO-Q switch The beam profile of the generated laser light can be made uniform during the transition period of switching.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change variously in the range which does not deviate from the summary of this invention.

It is a conventional example of a laser resonator using an AO-Q switch. FIG. 6 is an operation explanatory diagram of the AO-Q switch 5. It is explanatory drawing which shows the influence on the laser by the diffracted light 8 of the AO-Q switch 5. FIG. 1 is an embodiment diagram of a laser resonator according to the present invention. FIG. 6 is a schematic diagram of a “laser resonator” in Patent Document 1. FIG. 10 is a schematic diagram of a “laser resonator” of Patent Document 2. FIG. 10 is a schematic diagram of a “laser oscillator” in Patent Document 3. FIG.

Explanation of symbols

10 laser resonator, 11 optical path of laser light,
12A, 12B AO-Q switch, 14 Polarization rotating element (1/2 wavelength plate)

Claims (1)

A laser oscillator that amplifies linearly polarized laser light,
One or more pairs of AO-Q switches disposed on the optical path of the laser beam and having diffraction directions alternately orthogonal;
A laser oscillator comprising: a polarization rotation element positioned between the pair of AO-Q switches and rotating a polarization plane by 90 °.

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