JPH0468582A - Device for elongating the pulse width of pulse laser - Google Patents

Abstract

PURPOSE:To optionally elongate pulse width by adding a subresonator comprising a small number of optical elements to a laser oscillator comprising a laser tube, a main resonator full reflecting mirror, and a main resonator output mirror, and changing the position of the arrangement of the full reflecting mirror of the subresonator. CONSTITUTION:The light generated in a laser tube 1 is resonated first in a main reflector total reflecting mirror 2 and a main reflector output mirror 3, and then becomes a laser beam and goes out of the main resonator output mirror 3. Some of this laser beam is reflected at the subresonator output mirror 4 inclined 45 deg. to the incidence direction, and the residual laser beam permeates the subresonator output mirror 4, and is turned back at a subresonstor total reflecting mirror 5, and passes the laser tube 1 again, and is turned back at a main resonator total reflecting mirror 2, and is amplified in the laser tube 1, and then it is reflected again from the subresonator output mirror 4. The laser beams obtained from the subresonator output mirror 4 overlap one after another, being shifted by the time required for this repeat.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a device for stretching the pulse width of a pulsed laser. Specifically, the present invention relates to a device that generates a laser pulse with a long time width by extending the time width of a laser pulse generated in a main resonator using a sub-resonator optical system.

(Prior Art) Conventionally, laser light with a long pulse width has been used in the following methods.

(1) Narrowing of the dye laser light oscillation spectrum Here, a dye laser is a laser that oscillates by dissolving a highly chromogenic organic dye in a solvent such as alcohol and optically exciting it with another pump laser. It is about. When the pump laser used for this optical excitation is a continuous wave laser, it is called an open (continuous oscillator) dye laser, and when it is a pulsed laser, it is called a pulse dye laser. Pulsed dye laser light is
One of its characteristics is high wavelength accuracy, and generally, the spectral width, which is a value representing wavelength accuracy, is a value proportional to the reciprocal of the pulse width of the pump laser. Therefore, by extending the pulse width of the pump laser, it becomes possible to obtain dye laser light with a narrower spectral width.

Examples of uses of such dye laser light with a narrow oscillation spectrum include highly accurate spectroscopic analysis, isotope separation, and the like.

(2) Pulsed laser using optical fiber - When pulsed laser light with a high peak power is propagated within an optical fiber, destruction by the laser light occurs at the entrance surface of the optical fiber or inside the fiber. . This is because the peak value of the pulsed laser beam instantly melts glass, which is the material of the fiber, thermally. This peak value is the value obtained by dividing the laser light output per pulse by its pulse width, so the longer the pulse width, the lower the peak value. Therefore, when using a pulsed laser light in a fiber, stretching the pulse width makes it difficult for the fiber to be damaged.

The use of optical fines in the propagation of pulsed laser light simplifies the handling of the laser, which greatly helps improve medical devices and laser processing equipment.

Therefore, in the conventional technology, a method of stretching the pulse width using a plurality of multiple reflection mirrors or a method of stretching the pulse width by controlling the discharge for laser oscillation is used. ing. however,
In methods using multiple multi-reflection mirrors, etc., (11) it is difficult to adjust the equipment used due to the large number of mirrors, (2) the propagation distance of the laser beam is long, so the optical path may change due to external forces such as vibrations. (3) The equipment used requires a large space; (4)
) There are problems such as the cost of the equipment used.

In addition, in the method of extending the pulse width by discharge control, (1) the equipment used is costly, (2) the discharge control section must be modified, and (3) the configuration of the equipment used is complicated. There is a problem.

(Problems to be Solved by the Invention) An object of the present invention is to provide an apparatus for extending the pulse width of a pulsed laser, which eliminates the above-mentioned problems.

(Means for solving the problem) As a result of intensive research to achieve this promise, the inventor of the present application has found that by using a small number of optical elements in the sub-resonator, the sub-resonator can be made simple and compact. The inventors came up with the idea that it is possible to change the pulse width by changing the position of the total reflection mirror, and came up with an apparatus for stretching the pulse width of the pulsed laser of the present invention.

Next, the apparatus of the present invention will be specifically explained using FIG.

The device for stretching the pulse width of a pulsed laser according to the present invention includes:
It consists of a laser oscillator, a main resonator, and a sub-resonator optical system. The light generated in the laser tube 1 first resonates within the main resonator total reflection mirror 2 and the main resonator output mirror 3, and then becomes a laser beam and is emitted from the main resonator output mirror 3.

A part of this laser light is reflected by the sub-resonator output mirror 4 tilted at 45 degrees with respect to the incident direction, and the remaining laser light is transmitted through the sub-resonator output mirror 4, and is reflected by the sub-resonator total reflection mirror 5. It is turned back and passes through the leather tube 1 again.
The main cavity is reflected by the total reflection mirror 2, and the laser tube 1
After being amplified by the sub-resonator output mirror 4, it is reflected again from the sub-resonator output mirror 4.

The laser beams obtained from the sub-resonator output mirror 4 overlap one after another with a time lag required for this repetition. This is shown in FIG. That is, FIG. 2 shows the process of stretching the pulse width, and in the figure, (a) and (b)
), fcl indicate laser light reflected by the sub-resonator output mirror 4 in FIG. In other words, the time required for repetition is the interval between these laser pulses, which is twice the interval between the main cavity total reflection mirror 2 and the sub cavity total reflection mirror 5 in Fig. 1, divided by the speed of light. corresponds to

Therefore, by changing the arrangement position of the sub-resonator total reflection mirror 5, it is possible to arbitrarily extend the pulse width.

Furthermore, in order to reduce the reflection loss at the sub-resonator output mirror 4, it is possible to utilize polarization of the laser beam. In this case, the sub-resonator output mirror 4 in FIG. 1 is replaced with a polarizing cube 7, and a wavelength plate 6 and a 45-degree retardation plate 8 are arranged on both sides of the cube. As a result, the polarization directions of the laser light before and after the polarizing cube 7 differ by 90 degrees, so that the laser light can be reflected only in the direction of the broken line arrow, and reflection loss can be reduced. By this method,
Since the laser light whose pulse width has been extended is polarized in one direction, it becomes a higher quality laser beam.

(Example) The experimental configuration of the example is shown in FIG. 3. Laser tube 1
A copper vapor laser was used as the laser. Further, as the main resonator total reflection mirror 2 and the main resonator output mirror 3, unstable resonators with a magnification of 5 times were used. Let the distance from the main resonator total reflection mirror 2 to the sub-resonator total reflection mirror 5 be L,
The pulse width of the laser beam emitted from the sub-resonator output mirror 3 was measured at each end. As a result, for the laser pulse width of 21 ns obtained with the main oscillator, L =
At 2.55 m, the pulse width of 40 ns (half width) is
= 3.3 m, 42 ns (half width) was obtained.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram of the apparatus of the present invention. An oscillator optical system is used as a main resonator, and a sub-resonator optical system is used to extract a portion of the laser light obtained from the main resonator and return the remaining laser light to the oscillator. FIG. 2 shows the process of stretching the pulse width. (a), (b), and (c) in the figure show laser light reflected by the sub-resonator mirror in FIG. 1. FIG. 3 is a schematic diagram of an experiment and a diagram showing the measurement results of the stretched pulse width.

Claims (1)

[Claims] 1) A sub-resonator output mirror and a sub-resonator total reflection mirror are added as a sub-resonator optical system to a laser oscillator consisting of a laser tube, a main-resonator total-reflection mirror, and a main-resonator output mirror. A device that extends the pulse width of a pulsed laser composed of 2) The device for extending the pulse width of the pulsed laser according to item 1, which uses a polarizing cube instead of the sub-resonator output mirror, and arranges a wavelength plate and a 45-degree retardation plate on both sides of the polarizing cube.