JPH0476975A - Laser oscillator - Google Patents

Abstract

PURPOSE:To reduce the diffraction loss of an optical element for a resonator, to make a spatial distribution uniform and to increase a laser output by a method wherein a spatial filter which can transmit the image by an aperture forward and backward and which can form the image again is installed inside the resonator and a pinhole whose diameter can be adjusted is installed at the condensing position at its inside. CONSTITUTION:A pinhole 9 is arranged at the focus of convex lenses 7, 8. Thereby, a spatial filter 20 is constituted. The convex lenses 7, 8 can be moved slightly in their optical-axis direction. A tube 10 keeps the inside of the spatial filter vacuum. The image by an aperture 6 is transmitted by using the filter 20; it is returned by an output mirror 3; it is formed at a point B. In addition, it is transmitted by the filter 20; it is returned by a total reflection mirror 2; it is formed at a point A. The above operation is repeated and the image is transmitted. When the diameter of the pinhole 9 of the filter 20 is adjusted to an optimum value, only an essential spatial frequency component can be passed. Thereby, the spatial distribution of an output laser can be made uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser oscillator, and particularly to a laser oscillator using a fixed laser element as a laser medium.

[Conventional technology]

Conventionally, this type of laser oscillator uses a solid-state laser element 11 as a laser medium, as shown in FIG. 3, and a total reflection mirror 2.
By configuring a resonator with the output mirror 3 and adjusting the diameter of the aperture 14, the laser output and the spatial distribution of the laser were controlled.

[Problem to be solved by the invention]

In the conventional laser oscillator described above, the laser light inside the resonator undergoes diffraction loss due to the aperture of the resonator optical element constituting the laser oscillator, and the spatial distribution of the output laser light is
As shown in the figure, there are disadvantages in that the laser becomes non-uniform, resulting in a decrease in laser output, and the energy density at the center of the laser beam increases, which inevitably causes laser damage to the optical element.

Means for Solving Problem C8] The laser oscillator of the present invention includes a laser medium, an aperture for controlling the spatial distribution of the oscillated laser, and a pair of mirrors forming a resonator. and a spatial filter that performs reciprocating transfer within the resonator while repeating the process of forming an image in the resonator and re-forming a further image at the position of the image by the aperture. be done.

Further, in the laser oscillator of the present invention, the spatial filter has a configuration of a Kevlar type telescope with convex lenses having different focal lengths at both ends and movable in the direction of the central axis, and a diameter at the focusing position. It has a configuration with a pinhole that can be arbitrarily adjusted from the outside.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention.

The embodiment shown in FIG. 1 includes a YAG rod 1 as a laser medium, a total reflection mirror 2 and an output mirror 3 which are plane mirrors constituting a resonator, a polarizer 4, and a Pockels cell 5 for performing Q-switch operation. , aperture 6, and lens barrel 10
A convex lens 7 is disposed at both ends of the lens and is movable in the direction of the central axis.
and a convex lens 8 and a spatial filter 20 having a pinhole 9 disposed at the condensing position of the convex lens 7.8 and whose diameter can be arbitrarily closed off from the outside. This forms the structure of a Kevlar telescope.

Next, the operation of this embodiment will be explained.

The convex lens 7 has a focal length f1. The convex lens 8 has a focal length f2
The pinhole 9 is arranged at the focal point of the convex lenses 7 and 8, and these optical elements arranged in the lens barrel 10 constitute a spatial filter 20 as a whole. The lens barrel 10 is a lens barrel of a spatial filter having a Kevlar type telescope structure.
On the other hand, the convex lens 7 and the convex lens 8 are capable of slight movement in the optical axis direction, and the lens barrel 10 has a structure that maintains a vacuum inside the spatial filter depending on the laser beam intensity at the pinhole 9.

In the laser oscillator of this example, the optical elements are as follows (
They are arranged so as to satisfy each of formulas 1) to (3).

2L2 +d2=MD M2d 1...(
1) M = f2/f1
...(3) The above-mentioned Ll, L2, dt,
d2 and D are respectively shown in FIG. 1, Ll is between the total reflection mirror 2 and the aperture 6, L2 is between the output mirror 3 and point B, where the image of point A is formed by the aperture 6 by the spatial filter 20, dl is between point A and convex lens 7,
d2 is the distance between the convex lens 8 and point B, D is the distance between the convex lens 7.8, and Ll and L2 in equations (1) and (2> are the values corrected by the refractive index of the transmission optical element. ing.

Depending on the dimensions and arrangement of the optical elements, an image formed by the aperture 6 is transferred by the spatial filter 20, reflected by the output mirror 3, and imaged at point B. Next, the image formed at point B is similarly transferred by the spatial filter 20, reflected by the total reflection mirror 2, and imaged at the aperture 6 at point A. Image transfer is performed one after another by the filter 20. Further, by adjusting the diameter of the pinhole 9 of the spatial filter 20 to an optimal value, only necessary spatial frequency components can be passed through the pinhole 9.

In this way, the diffraction loss due to the aperture of the intracavity optical element is reduced, and the spatial distribution of the output laser is made uniform as shown in FIG.

〔Effect of the invention〕

As explained above, the present invention provides a spatial laser oscillator using a fixed laser element in which an aperture is arranged together with a resonator on the optical path, in which the image of the aperture can be sequentially transferred back and forth and re-imaged at the original aperture position. By installing the filter inside the resonator and providing a pinhole whose diameter can be arbitrarily adjusted at the focal point inside the spatial filter, the diffraction loss of the resonator optical element can be significantly reduced. This has the effect of making the spatial distribution uniform and increasing the laser output.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram showing the spatial distribution of laser output according to the embodiment of FIG. 1, FIG. 3 is a block diagram of a conventional laser oscillator, and FIG. FIG. 4 is a diagram showing the spatial distribution of the laser output of the laser oscillator of FIG. 3; 1... YAG rod, 2... Total reflection mirror, 3...
・Output mirror, 4... Polarizer, 5... Pockels cell, 6... Aperture, 7... Convex lens, 8...
Convex lens, 9... Pinhole, 10... Lens barrel, 11
... solid-state laser element, 12 ... total reflection mirror, 13
...Output mirror, 14...Aperture, 20...Spatial filter.

Claims (2)

[Claims] 1. In a laser oscillator comprising a laser medium, an aperture for controlling the spatial distribution of the oscillated laser, and a pair of mirrors forming a resonator, an image formed by the aperture is formed within the resonator, and further imaging is performed. A laser oscillator comprising: a spatial filter that repeatedly re-images the image at the position of the image formed by the aperture and performs reciprocating transfer within the resonator. 2. The spatial filter has a Keplerian telescope configuration with convex lenses having different focal lengths at both ends and movable in the direction of the central axis, and a pin whose diameter can be arbitrarily adjusted from the outside at the focusing position. 2. The laser oscillator according to claim 1, further comprising a hole.