JPH0644648B2 - Laser equipment - Google Patents

Description

The present invention relates to a laser device, and more particularly to improving the quality of a laser beam thereof.

[Prior Art] FIG. 8 shows, for example, Laser Handbook 19
79 North-Holland Publishing Campany) is a cross-sectional configuration diagram showing a laser device having a conventional unstable resonator described in (79 North-Holland Publishing Campany). In the figure, (1) is a collimating mirror which is a concave mirror, (2) is a magnifying mirror which is a convex mirror which is arranged to face this collimating mirror, and both mirrors (1) and (2) form a total reflection mirror. (3) is a laser medium, for example, a gas laser such as a CO ₂ laser is used as an example, a gas medium excited by discharge or the like, and a solid laser such as a YAG laser is used as a glass, which is excited by a flash lamp or the like. It is a medium. (4) is a wind mirror, (5) is a non-reflective coating film applied on the surface of the wind mirror, (6) is a box covering the surroundings, (7) is light composed of mirrors (1) and (2) A laser beam generated in the resonator, (8) is a laser beam taken out from the periphery of the magnifying mirror.

Next, the operation will be described.

The mirrors (1) and (2) form a so-called unstable resonator.The laser beam reflected and expanded by the magnifying mirror (2) is amplified by the laser medium (3) and collimated by the collimating mirror (1). The beam is collimated, reflected on the magnifying mirror (2) and the peripheral portion of the mirror, and taken out from the wind mirror (4) as a ring-shaped beam. Since the ring-shaped laser beam (8) to be extracted is obtained in almost the same phase, it becomes a medium-high beam by being condensed by a lens or the like, and cutting and welding of an iron plate or the like can be efficiently performed.

Also, the degree of focusing depends on the ratio of the inner diameter and the outer diameter of the extracted ring-shaped beam (M value (Magnification facter)). To be done. However, when the M value is increased, the oscillation efficiency is remarkably deteriorated, and therefore, the upper limit of the M value which is industrially actually used is about 2.

[Problems to be Solved by the Invention] Since the conventional laser device is configured as described above,
If the M value is increased in order to improve the light condensing characteristics, the oscillation efficiency is deteriorated, so that there is a problem that the M value cannot be practically raised to infinity where the maximum light condensing performance can be obtained. Further, since the wind mirror (4) is non-uniformly heated by the ring-shaped laser beam, non-uniform internal stress is generated and the phase distribution of the passing laser beam is destroyed,
There was a problem that the light collecting performance was deteriorated.

The present invention has been made to solve the above problems, and facilitates a laser device capable of extracting a high-quality laser beam with an M value close to infinity without lowering the oscillation efficiency. The purpose is to get.

[Means for Solving the Problems] In the laser device according to the present invention, the magnifying mirror is composed of a concave or convex mirror, and a partially reflective film is formed in the center of the surface facing the collimating mirror and a non-reflective coating film is provided in the periphery thereof. The thickness of the partial reflection film is adjusted so that the laser beam passing through the central portion of the concave or convex mirror and the peripheral portion thereof is phased.

[Operation] The magnifying mirror according to the present invention allows a part of the laser beam to pass therethrough, thereby extracting the beam shape from the conventional ring-shaped laser beam. Further, the partially reflected film having the thickness adjusted adjusts the phase of the confined laser beam.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional configuration diagram showing a laser device according to an embodiment of the present invention. In the figure, (40) is a convex mirror that also serves as a wind mirror, and an antireflection coating film is provided on the outside thereof.
(5) is applied, a partial reflection film (20) is applied to the center of the inner surface facing the collimating mirror (1), and a non-reflective coating film (5) is applied to the surrounding area to further increase the thickness. A coating film (22) for adjustment is provided on the partial reflection film (20).

Next, the operation will be described.

Partial reflection film (2) of collimator mirror (1) and convex mirror (40)
The (0) part constitutes a so-called unstable resonator, and the convex mirror
Laser beam reflected and expanded by the partial reflection film (20) of (40)
(7) is amplified by the laser medium (3) and collimated into a parallel beam by the collimating mirror (1),
It is taken out as a laser beam (8) from the convex mirror (40) to the outside. This laser beam (8) is composed of a part that passes through the partial reflection film (20) and the coating film (22) and a part that passes through the non-reflection coating film (5).
Since the portion that passes through (20) has partial transparency, the laser beam is a hollow, and the M value defined by the conventional unstable resonator corresponds to infinity.

FIGS. 2 (a) and 2 (b) are characteristic diagrams schematically showing the pattern shapes when the laser beam generated by the unstable resonator according to the embodiment of the present invention and the unstable resonator according to the present invention are focused by the lens, respectively. The horizontal axis is the distance from the optical axis, and the vertical axis is the beam intensity.
In this experiment, the reflectance of the partial reflection film (20) was 50%, and the ratio of the diameter of the partial reflection film (20) to the outer diameter of the beam was set to 1.5 in order to make the oscillation characteristics of the two substantially the same. (That is, the unstable mirror of the present invention is obtained by making the magnifying mirror (2) of the conventional unstable resonator of M = 1.5 have a partial transmittance of 50%). Are the same (the thickness is constant), and the laser beam (8) is a parallel beam even after passing through the convex mirror (40). Comparing the light-collecting performances shown in FIGS. 2 (a) and 2 (b), according to the present invention (see FIG.
(b)), it can be seen that a laser beam with high central intensity and concentrated on the optical axis can be obtained.

Next, the design of the magnifying mirror according to the present invention will be described. The thickness of the coating film (22) is the antireflection coating film (5), the partial reflection film (20) and the coating film (22).
The phase difference between the laser beams passing through is small, and the laser beam is partially reflected by the coating film (22) and the partial reflection film (20). Fig. 3 shows the diameter (spot diameter) at the point where 1 / e ² times the axial intensity at the focal point is reached.
3 is a characteristic diagram showing curves A and B showing the relationship between the phase difference and the ratio (power concentration degree) of the laser power included in the diameter to the whole. This curve returns to the result of calculating the intensity distribution at the condensing point using the laser beam generated in the resonator by wave calculation. It can be determined that the smaller the spot diameter and the larger the power concentration degree, the better the light converging performance.

For example, if the phase difference is canceled within 0 ° to 45 °, the power concentration and the spot diameter are almost the same,
It can be seen that particularly when a phase difference of 100 ° or more occurs, the spot diameter significantly deteriorates, and the condensing performance deteriorates.

The relationship between this phase difference and the film thickness of the coating film (22) is
Shown in the figure. This example shows PbF ₂ (refractive index 1.55) on a ZnSe substrate.
Is applied to form a non-reflective coating film (5) with a thickness of 1.7 μm, while PbF ₂ is applied on the ZnSe substrate to a thickness of 2.9 μm for 50%
If the thickness of the partial reflection film is further increased, the transmittance at the central portion (curve C) and the phase difference between the beams passing through the central portion and the peripheral portion (curve D) will be what. It shows that. From FIG. 4 to FIG. 2 (b), it is understood that the thickness of the coating film (22) is about 6 μm so that the transmittance is 50% and the phase difference is within 45 ° in order to obtain the characteristics shown in FIG. Considering an industrial manufacturing method, it is expensive to form such a thin thin film, but in this example of the invention, only the central portion is thickened, so that the area is small and the cost increase can be reduced. Further, since the partial reflection film (20) and the coating film (22) in the central portion are formed independently of the non-reflection coating film (5) in the peripheral portion, the degree of freedom in design is increased.

Although the partial reflection film (20) is a single film in the above embodiment, it may be composed of two or more layers as shown in FIG.

Further, the coating film (22) may be composed of a plurality of films as shown in FIG.

Further, the magnifying mirror may be a concave mirror (41) as shown in FIG.

[Effects of the Invention] As described above, according to the present invention, the magnifying mirror of the laser device is composed of a concave or convex mirror, a partial reflection film is formed in the center of the surface facing the collimating mirror, and a non-reflection coating film is formed in the periphery thereof. Since the thickness of the partial reflection film is adjusted so as to make the laser beam passing through the central portion of the concave or convex mirror and its peripheral portion equal phase, the condensing performance of the centered light can be reduced without sacrificing the oscillation efficiency. A good laser beam can be obtained, and since the laser beam heats the entire wind mirror, there is an effect that thermal stress hardly occurs and the beam can be stably taken out for a long period of time. Further, since the thick coating film is formed only on the central portion of the mirror, there is an effect that the phase equalization can be realized at low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram showing a laser device according to an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) show the focusing characteristics of a laser beam in a conventional laser device and an embodiment of the present invention, respectively. FIG. 3 is a characteristic diagram showing the relationship between the spot diameter at the converging point and the power concentration degree and the phase difference, and FIG. 4 is a relationship between the film thickness of the partially reflective film and the phase difference and the transmittance. FIG. 5 is a sectional view showing a magnifying mirror according to another embodiment of the present invention, and FIG. 7 is a sectional view showing a laser device according to another embodiment of the present invention. , And FIG. 8 are cross-sectional configuration diagrams showing a conventional laser device. In the figure, (1) is a collimating mirror, (3) is a laser medium, (40) is a convex mirror, (5) is a non-reflective coating film, (7)
(8) is a laser beam, (20) (201) (202) is a partially reflective film, (2
2) (221) and (222) are coating films, and (41) is a concave mirror. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In an unstable resonator comprising a magnifying mirror and a collimating mirror which are arranged so as to face each other to extract a laser beam, the magnifying mirror is a concave or convex mirror, and a central portion of a surface facing the collimating mirror. The partial reflection film is provided with a non-reflective coating film on its peripheral portion, and the thickness of the partial reflection film is adjusted so as to make the laser beam passing through the central portion of the concave or convex mirror and its peripheral portion equal phase. A laser device characterized by the above.