JPH08274402A - Slab laser oscillator - Google Patents

Abstract

PURPOSE: To set a beam spreading angle in a width direction within an allowable angle of wavelength conversion by arranging a conversing optical system to converge a laser beam inside a resonator in the direction parallel to a short side of a rectangle whose cross section is vertical to the direction of laser beam projection and arranging nonlinear optical crystal in the converging part thereof. CONSTITUTION: A laser beam 6 is reflected by a dichroic mirror 3 and passes through a λ/2 wavelength plate 7, and converged in a thickness direction only by a cylindrical lens 8. A nonlinear optical crystal 5 is arranged in a linear converging part composed of a tubular concave mirror 2. Since the laser beam 6 is thin, the convergence angle by the cylindrical lens 8 becomes small enough when compared to an allowable angle in a thickness direction of phase matching in wavelength conversion. Furthermore, since the beam is not converged in a width direction but made parallel, the beam spreading angle is small and set within an allowable angle of a width direction of phase matching in wavelength conversion.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a slab laser oscillator in a solid-state laser.

[0002]

2. Description of the Related Art Generally, in a solid-state laser called a slab laser, a slab-shaped solid-state laser medium (hereinafter referred to as a slab) 11 is used as a laser medium, such as the slab laser oscillator 200 shown in FIG. Usually, the cross section of the slab 11 perpendicular to the direction in which the laser light 14 is emitted from the slab 11 (hereinafter referred to as the laser light direction) is a rectangle, and the length of the short side of this rectangle is the thickness and the length of the long side. Sa is called the width, the direction of the short side is called the thickness direction, and the direction of the long side is called the width direction. Note that reference numerals 12 and 13 in FIG. 2 are a total reflection mirror and an output mirror that form a resonator. Also,
Regarding slab laser, for example, Optronics, 1
1988, No. 6, pages 94-98.

Further, as in the general solid-state laser oscillator 200 shown in FIG. 3, arranging the nonlinear optical crystal 15 inside the resonator of the laser to perform wavelength conversion is called internal wavelength conversion, and laser oscillation is performed. The fundamental wave to be used is confined inside the resonator, and only the second harmonic laser light 13 generated by the wavelength conversion is taken out of the resonator, and the second harmonic can be efficiently obtained. . Also,
It is known that by condensing the laser light inside the resonator onto the non-linear optical crystal 18 by the condensing lens 19 or the like, the intensity of the laser light in the non-linear optical crystal 18 becomes high, so that the wavelength conversion efficiency becomes high. ing. Incidentally, FIG. 3 shows the rod 15
2 shows a configuration of internal wavelength conversion in a normal solid-state laser oscillator using a solid laser medium having a circular shape. Here, 16 is an output mirror having a high transmittance only for the second harmonic. Regarding internal wavelength conversion, see J. Op.
t.Soc.Am.B / Vol. 4, No. 7, 1987, pages 1066 to 1071.

[0004]

In the slab laser, if the ratio of the width to the thickness is increased, the thermal breakdown threshold value of the slab can be increased, which is advantageous for increasing the output of the laser. However, when the width of the slab becomes large, the long side of the rectangle (that is, the beam width) of the beam cross section of the oscillating laser light becomes long. As a result, as shown in FIG. 4, when the internal wavelength conversion is performed by the conventional slab laser 400, the converging angle θ of the laser light when condensing the laser light on the nonlinear optical crystal 20 becomes large, and the wavelength The allowable angle in the converted phase matching condition may be exceeded, and the wavelength conversion efficiency may decrease.

An object of the present invention is to provide a slab laser that can efficiently perform internal wavelength conversion even if a slab having a long width, which is advantageous for high output, is used.

[0006]

In order to achieve the above object, the present invention provides a cylindrical lens for condensing laser light inside the resonator in the resonator of the slab laser oscillator in the thickness direction of the slab. A condensing optical system that condenses light in only one direction, such as a cylindrical concave mirror, and a non-linear optical crystal is arranged in the condensing portion of the laser light condensed by the condensing optical system.

Further, in order to prevent the size of the available nonlinear optical crystal from increasing, a laser which is a fundamental wave such as a wave plate or an optical rotator oscillated between the slab and the nonlinear optical crystal inside the resonator. An optical element that rotates the polarization direction of light is arranged.

[0008]

Since the thickness of the slab is smaller than the width, it is easy to reduce the converging angle within the allowable wavelength conversion angle when converging in the thickness direction. Also, in the width direction of the slab, it is easy to make the beam divergence angle in the width direction within the allowable angle for wavelength conversion by making the parallel beam incident on the nonlinear optical crystal without condensing the laser light. You can However, in the slab laser, since the beam quality in the thickness direction of the oscillated laser light is generally higher than the beam quality in the width direction, the beam can be focused sufficiently strongly even if it is focused only in the thickness direction.

Further, by disposing an optical element for rotating the polarization direction of the laser light, which is the fundamental wave oscillating, such as a wave plate or a rotator inside the resonator between the slab and the nonlinear optical crystal, nonlinear optical The phase matching condition can be satisfied without rotating the crystal around the laser beam direction as the central axis.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory diagram of a slab laser oscillator 100 which is an embodiment of the present invention. Slab laser oscillator 1
In the resonator No. 00, the total reflection mirror 1, the cylindrical concave mirror 2, and the dichroic mirror 3 constitute the resonator. Inside the resonator, a slab 4 made of a YAG crystal and a nonlinear optical crystal 5 made of a KTP crystal are arranged, and in this embodiment, the slab 4 is continuously excited. However, an arc lamp, a semiconductor laser, or the like can be used as the excitation light source. As a result, the fundamental wave laser beam 6 oscillates as a continuous wave. The laser light 6 reflects off the dichroic mirror 3,
After passing through the λ / 2 wave plate 7, the cylindrical lens 8 condenses the laser light only in the thickness direction, and the nonlinear optical crystal 5 is arranged in the linear condensing portion formed by the cylindrical concave mirror 2. . Since the thickness of the laser beam 6 is small, the converging angle when condensed by the cylindrical lens 8 is sufficiently smaller than the allowable angle in the thickness direction of phase matching in wavelength conversion. Further, since the beam is not focused in the width direction and is a parallel beam, the beam divergence angle is small, and is smaller than the allowable angle in the width direction of phase matching in wavelength conversion. Therefore, since the laser light is within the allowable angle for phase matching in both the thickness direction and the width direction, the wavelength is efficiently converted and the second-order harmonic green laser light 9 is generated and transmitted through the dichroic mirror 3. And is taken out of the resonator.

[0012] Generally, in a slab laser, the beam quality in the thickness direction is high. Therefore, if the laser light is focused in the thickness direction, it can be focused strongly. As a result, the laser light intensity can be sufficiently increased in the nonlinear optical crystal 5. More strictly speaking, if the width of the slab is longer than the thickness (however, in a normal slab laser, the width is longer than the thickness), the beam quality in the width direction becomes worse than the beam quality in the thickness direction. , The light collecting performance in the width direction is deteriorated. On the other hand, in the present invention, since the light is condensed in the thickness direction having a short length, not only the light can be strongly condensed, but even if a slab having a wider width is used to increase the output, the collection performance is deteriorated. There is no.

The polarization direction of the laser light 6 oscillated from the slab 4 is parallel to the thickness direction of the slab 4.
However, in this embodiment, the polarization direction of the laser light that can be phase-matched by the nonlinear optical crystal 5 is angularly separated from the thickness direction. Therefore, by passing the fundamental wave, which is the laser light 6, through the λ / 2 wavelength plate 7, the polarization direction can be rotated, so that the nonlinear optical crystal 5 can be phase-matched. As a result, it is not necessary to rotate the nonlinear optical crystal 5 itself about the propagation direction of the laser light for phase matching, and the nonlinear optical crystal 5 having a long shape only in the width direction in which the laser light is not condensed is obtained. Can be used. That is, in the conventional method of performing phase matching by rotating the non-linear optical crystal itself, the size of the non-linear optical crystal needs to be longer than its beam width regardless of the direction of the incident laser light. Met. According to the present invention, since the size of the nonlinear optical crystal 5 can be reduced in the thickness direction, the cooling effect in the case of cooling from the upper and lower two surfaces perpendicular to the thickness direction is enhanced.

[0014]

According to the present invention, the internal wavelength conversion can be efficiently performed even when the laser output is increased by using the slab having a long width, and particularly the second harmonic of the continuous wave can be efficiently generated. It became so.

Further, since the phase matching condition can be satisfied without rotating the nonlinear optical crystal about the propagation direction of the laser light as the central axis, it is possible to use the nonlinear optical crystal having a small size in the thickness direction.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a slab laser oscillator of the present invention.

FIG. 2 is an explanatory view of a general slab laser.

FIG. 3 is an explanatory diagram of internal wavelength conversion in a general solid-state laser oscillator.

FIG. 4 is an explanatory diagram of internal wavelength conversion in a conventional slab laser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Total reflection mirror, 2 ... Cylindrical concave mirror, 3 ... Dichroic mirror, 4 ... Slab, 5 ... Nonlinear optical crystal, 6,9 ... Laser light, 7 ... λ / 2 wavelength plate, 8 ... Cylindrical lens,
100 ... Slab laser oscillator.

Claims (2)

[Claims] 1. Inside a resonator of a laser oscillator using a slab-shaped solid-state laser medium, in the direction of the short side of a rectangle having a cross section perpendicular to the laser light emission direction in the slab-shaped solid-state laser medium, A condensing optical system, such as a cylindrical lens or a cylindrical concave mirror, for condensing only one direction is arranged so as to condense the laser light inside the resonator, and a condensing unit for the laser light condensed by the condensing optical system. A slab laser oscillator in which a non-linear optical crystal is arranged in the. 2. An optical element, such as a wave plate or an optical rotator, for rotating the polarization direction of the oscillated laser light is arranged between the slab-shaped solid-state laser medium and the nonlinear optical crystal inside the resonator. Item 2. The slab laser oscillator according to Item 1.