JPH038591B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to improvements in laser oscillators, particularly those equipped with unstable resonators used in laser processing.

[Conventional technology]

The configuration of a conventional device of this type is shown in FIG.

In this figure, 1 is an oscillator housing, 2 is a laser excitation medium such as CO ₂ disposed inside the housing, and 3 and 4 are a concave mirror and a convex mirror placed between the laser excitation medium 2, and the unstable resonance occurs. Configure the vessel.

5 is a beam extraction mirror installed near the convex mirror 4 and between the convex mirror 4 and the laser excitation medium 2;
7 is a laser beam extracted by the beam extraction mirror 5, and 7 is a beam extraction window mounted on the oscillator housing 1.

Next, the operation will be explained.

Wavelength stimulated emission from CO ₂ laser excitation medium 2
The 10.6 μ light resonates in an unstable resonator consisting of a concave mirror 3 and a convex mirror 4, and is transmitted to a beam extracting mirror 5.
A ring-shaped laser beam 6 is taken out.
This laser beam 6 is extracted into the atmosphere through a beam extraction window 7. In the case of a CO ₂ laser with an oscillation wavelength of 10.6μ, the substrate of the beam extraction window 7 is ZnSe.
It is. The refractive index n of ZnSe depends on the temperature T.
Its value is dn/dT=4.8×10 ⁻⁵ /deg. ZnSe
The beam extraction window 7 consists of
Absorbs 0.3-1.0%. Furthermore, since the periphery of the beam extraction window 7 is cooled, the temperature at the center is high and the temperature at the periphery is low. And for this temperature distribution, ZnSe beam extraction window 7
acts like a convex lens.

The strength of this thermal lens effect is proportional to the power density of the laser beam 6 and changes with the oscillation time until a thermal equilibrium state is reached.

That is, the quality of the laser beam taken out into the atmosphere changes with the oscillation time.

[Problem that the invention seeks to solve]

Although the laser beam is ring-shaped, the ZnSe beam extraction window 7 does not act as a perfect spherical lens, so the higher the power density of the laser beam 6, the stronger the lens action becomes, and the quality of the laser beam extracted into the atmosphere deteriorates. There is a drawback.

On the other hand, in order to reduce the thermal lens effect of the ZnSe beam extraction window, it is difficult to increase the cross-sectional area of the laser excitation medium 2 from the standpoint of discharge excitation, and this also reduces the laser oscillation efficiency.

Furthermore, since the strength of the thermal lens effect changes with the oscillation time, there are drawbacks such as the inability to obtain stable beam quality as a laser oscillator.

The present invention has been made to eliminate these drawbacks, and aims to obtain a high-quality laser beam with less thermal lensing of the beam extraction window up to a high output range.

[Means for solving problems]

The laser oscillator according to the present invention is characterized in that an optical system for enlarging the laser beam extracted from the beam extraction mirror is disposed within the oscillator housing.

[Effect]

In this invention, the laser beam is expanded by an optical system disposed inside the oscillator housing, increasing its diameter, but since the power density is low, the thermal lens effect of the beam extraction window made of ZnSe is very small. Therefore, even if the oscillation output increases, a high quality laser beam can be stably extracted.

〔Example〕

An embodiment of the present invention shown in FIG. 1 will be described below.

This figure schematically shows a cross section of the device. In this figure, 8 is a plane mirror that transmits the laser beam 6 to a convex mirror 9, and 10 is a concave mirror placed opposite to the convex mirror 9, which is integrated with the plane mirror 8. It is organized into a structure. Further, the concave mirror 8 and the convex mirror 9 are arranged coaxially and confocal. Reference numeral 11 denotes a plane mirror provided opposite to the concave mirror 10, and is constructed integrally with the convex mirror 9.

The rest of the configuration is the same as the conventional configuration shown in FIG. 2, so a description thereof will be omitted.

In such a configuration, the light stimulated and emitted from the CO ₂ laser excitation medium 2 is transmitted through the concave mirror 3 and the convex mirror 4.
The laser beam 6 is resonated and amplified by an unstable resonator consisting of the following, and the laser beam 6 is extracted from the beam extraction mirror 5. This laser beam is transmitted from the plane mirror 8 to the convex mirror 9, and the laser beam reflected by the convex mirror 9 is transmitted to the concave mirror 10 while being expanded.

In this case, the optical axes of the convex mirror 9 and the concave mirror 10 coincide, and since the two mirrors are confocal, the laser beam 12 reflected by the concave mirror 10 becomes a parallel beam with a large beam diameter. By changing the radius of curvature of the convex mirror 9 and the concave mirror 10, the diameter of the laser beam 12 can be changed.

This expanded laser beam 12 is reflected by a plane mirror 11
is transmitted to the ZnSe beam extraction window 7 by
taken out into the atmosphere.

Since the diameter of the laser beam transmitted to the beam extraction window 7 is large and the power density is low, the thermal lens effect of the ZnSe beam extraction window 7 is small. Therefore, even if the oscillation output is high, a high quality laser beam can be stably extracted.

Note that in the above embodiments, the laser excitation medium is CO ₂
The case where the material of the beam extraction window is ZnSe is shown, but the material of the beam extraction window is
It may be KCl or GaAs.

Further, the same effect can be obtained even if the laser excitation medium is other than excimer laser.

〔Effect of the invention〕

Since the present invention is constructed as described above, it is possible to stably extract a high quality laser beam with little thermal lens effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an embodiment of the present invention, and FIG. 2 is a schematic sectional view showing the configuration of a conventional device. In the figure, 1 is the oscillator housing, 2 is the laser excitation medium,
3 and 10 are concave mirrors, 4 and 9 are convex mirrors, 5 is a beam extraction mirror, 8 and 11 are plane mirrors, 7 is a beam extraction window, and 6 and 12 are laser beams. In addition,
The same reference numerals indicate corresponding parts.

Claims (1)

[Claims] 1 A laser excitation medium housed in a housing, an optical system that resonates the light stimulated and emitted from the laser excitation medium and extracts it as a beam, a plane mirror that deflects the beam, a convex mirror that magnifies the deflected beam, and A concave mirror is arranged coaxially with the confocal confocal mirror and has an integral structure with the plane mirror, and the parallel beam from this concave mirror is deflected, and the parallel beam is deflected into a parallel beam with the convex mirror. 1. A laser oscillator comprising: a second flat mirror with a deflected beam; and a beam extraction window for extracting the deflected and enlarged beam.