JPH01140784A - Laser device - Google Patents

Abstract

PURPOSE:To output a laser beam of high quality without decreasing an oscillation efficiency by forming a nonreflection coating film on the periphery surrounding opposite faces and a center, so regulating the thickness of the film as to equalize in phase laser beams which pass the center and the periphery. CONSTITUTION:A convex mirror 4 which is also used as a window mirror is coated at the center of opposite face to a collimator mirror 1 with a partial reflection coating film 20, at the periphery surrounding the opposite faces and the center with a nonreflection coating film 5 and further with a thickness regulating nonreflection coating film 22. That is, the mirror 1 and the film 20 construct an unstable type resonator, a laser beam 7 reflected and enlarged by the film 20 of the mirror 4 is amplified by a laser medium 3, collimated by the mirror 1 to a parallel beam, and output as a laser beam 8 externally from the mirror 4. Thus, a laser beam having good condensing characteristic of solid state is obtained without sacrificing its emitting efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to improvements in beam quality in laser devices, particularly in high-output laser devices.

[Conventional technology]

Figure 8 shows, for example, the Laser Handbook (LBsetHan).
dbook 19γ9. Nnrth-Ho1l
A laser device with a conventional unstable resonator described in
FIG. In the figure, 11) is a frimating mirror made of a concave mirror, [2] is a magnifying mirror made of a convex mirror placed opposite to this collimating mirror, and 91 and 1121 are total reflection mirrors. (3) is a laser medium, and in the case of a gas laser such as a CO2 laser, it is a gas medium excited by an electric discharge, and in the case of a solid laser such as a YAG laser, it is a glass medium excited by a flash lamp, etc. 4) is a wind mirror, (
5) is the anti-reflection coating film applied on the wind mirror surface, (6) is the box that covers the surrounding area, and (7) is the mirror +11.
(A laser beam generated within an optical resonator constituted by 21.

(8) is a laser beam taken out from the periphery of the magnifying mirror.

Next, the operation will be explained. The mirror +ll, t2) constitutes a so-called unstable resonator, and the magnifying mirror (
2) The laser beam reflected and expanded by the laser medium (
3) and is amplified by collimating mirror 11)
collimated into a parallel beam by a magnifying mirror 12)
The beam is then reflected onto the periphery of the mirror and taken out as a ring-shaped beam to the outside through the wind mirror (4). Since the extracted ring-shaped laser beam (8) is obtained with almost the same phase, it becomes a medium-height beam by condensing it with a lens or the like, and can efficiently cut, weld, etc. iron plates.

The degree of condensation is determined by the ratio of the inner diameter and outer diameter of the ring-shaped beam (M value).
factor) ) can-$J, the larger the M value,
In other words, the beam extracted from the center is well focused. But M 11i? thick (as this will significantly deteriorate oscillation efficiency,
The upper limit of the value is about 2.

[Problem that the invention seeks to solve]

Conventional laser equipment is configured as described above, so
In order to improve the light-gathering characteristics, increase the M value (this will deteriorate the oscillation efficiency, so in practice, it is recommended to increase the M value to near infinity (where the best light-gathering performance can be obtained), otherwise there will be problems. Furthermore, since the wind mirror (4) is unevenly heated by the ring-shaped laser beam, uneven internal stress is generated.

There were problems such as disrupting the phase distribution of the passing laser beam and deteriorating the focusing performance.

This invention was made to solve the above-mentioned problems, and it is an object to easily obtain a laser device that can extract a high-quality laser beam with a VcM value close to infinity without causing a decrease in oscillation efficiency. With the goal.

[Means for solving problems]

The laser device according to the present invention is configured such that the magnifying mirror is a concave or convex mirror with a partially reflective coating film applied to the central part of the surface facing the collimating mirror, and a non-reflective coating film is applied to the peripheral part surrounding the central part of the facing surface. The thickness of this anti-reflection coating film is adjusted so that the laser beams passing through the central portion and the peripheral portion have the same phase.

[Effect]

The magnifying mirror of the present invention allows a portion of the laser beam to pass through, thereby extracting the beam shape from the conventional ring shape to a peg-shaped laser beam. Furthermore, the laser beam in the hollow shape is made to have the same phase by a non-reflection coating film whose thickness is adjusted.

〔Example〕

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

FIG. 1 is a cross-sectional side view showing a laser device according to an embodiment of the present invention. In FIG. 1, (4) is a convex mirror that also serves as a wind mirror, and the central part of the surface facing the collimating mirror +1) is partially reflective coated. A non-reflective coating film (5) and a non-reflective coating film for thickness adjustment are applied to the peripheral portion surrounding the central portion of the facing surface.

Next, the operation will be explained.

The partially reflective film ridges of the collimating mirror (1) and the convex mirror (4) constitute a so-called unstable resonator.

The laser beam (7) reflected and expanded by the partial reflecting mirror (a) of the convex mirror (4) is amplified by the laser medium (3), and is collimated into a parallel beam by the collimating mirror 11)K. The laser beam (
8). This laser beam (8) is made up of a part that passes through the partially reflective film (to), a part that passes through the non-reflective coating film (5) and Ω, and the part that passes through the partially reflective film (c!). The part that passes through 1r is partially transparent.

The laser beam (8) is hollow, defined by a conventional unstable resonator, and has an fcM value of infinity.

FIGS. 2(a) and 2(kl) are characteristic diagrams schematically showing pattern shapes when a laser beam generated in an unstable resonator according to a conventional method and an embodiment of the present invention are focused by a lens, respectively. , the horizontal axis is the distance from the optical axis.

The vertical axis is the beam intensity.

In this experiment, in order to make the oscillation characteristics of the two almost the same, the reflectance of one reflective film (2) was set to 50%, and the ratio between the diameter of the reflective film (2) and the beam outer diameter was set to 1.5. (i.e.

Magnifying mirror of conventional unstable resonator with M=1.5 (2)
The unstable resonator of the present invention was obtained by giving 50% partial transparency to the resonator. ) Also, the curvatures on both sides of the convex mirror (4) were the same and the thickness was constant), so that the laser beam (8) remained a parallel beam even after passing through the convex mirror (4). Figure 2 (a), (1
) Comparing the respective light focusing performances indicated by 1, it can be seen that the laser beam according to the present invention (FIG. 2(b)) has a high central intensity (and a laser beam concentrated on the optical axis).

Next, the design of the magnifying mirror according to the present invention will be explained.

The thickness of the above non-reflective coating film■ is the above partial reflective coating■
It is determined such that the phase difference between the laser beam passing through the anti-reflection coating film (5) 122 is small, and the laser beam completely passes through the non-reflection coating film (5) 122.

Figure 3 shows the relationship between the diameter of the point at which the axial intensity is 1/e2 times the focal point (spot diameter), the ratio of the laser power contained within that diameter to the total (power concentration), and the phase difference. This is a characteristic diagram showing the laser beam generated in the resonator by wave calculation,
This is based on the results of calculating the intensity distribution at the focal point using this information.

It can be determined that the smaller the spot diameter and the higher the power concentration, the better the light collection performance.

For example, if the phase difference is canceled within about 45 degrees from 01, the power concentration and spot diameter are almost the same, but
It can be seen that when a phase difference of 100° or more occurs, the spot diameter deteriorates significantly and the light collection performance deteriorates.

The relationship between this phase difference and the thickness of the coating film is shown in FIG. In this example, PbF2 is placed around the Zn8e substrate.
(refractive index 1.55) for 1.7 am to form an anti-reflection coating film +5+ 1Fr: and P in the center.
l) In the case where a partially reflective coating film (■) with a reflectance of 50% is formed by applying F2 to a thickness of 2.1 μm, the coating film @ (Zn8e) is replaced with a non-reflective coating film (
5) What is the transmittance of the laser beam passing through the coating film (5) (curve HC) and the phase difference (curve iD) between the two laser beams passing through the center and outer periphery, depending on how many μm is coated on the coating film (5)? It shows that.

To obtain the characteristics shown in Figures 4 to 2 (bl), the thickness of the coating film must be approximately 6.5 μm to achieve transmittance of 50%, phase difference within 45°, and 100% transmittance. Recognize.

Considering an industrial manufacturing method, for example, znSe is 6.5μ
Although the surface is somewhat rough when m layers are stacked, the influence of the roughness on laser oscillation is small and can be ignored because the laser beam passing through the coating film does not contribute to resonance.

In the above embodiments, the non-reflective coating film (5) is a single film, but as shown in FIG.
52) may be.

Furthermore, one anti-reflection coating film may be composed of a plurality of films (220) (221) as shown in FIG.

In addition, the anti-reflection coating film (5) on the opposing surface of the collimating mirror is not provided (for example, PI).
F2) alone may be provided to equalize the phase.

Furthermore, the magnifying mirror is a concave mirror IAuf as shown in Figure 1.
It may also be configured using

〔Effect of the invention〕

As described above, according to the present invention, the magnifying mirror is constructed by applying a partially reflective coating film to the central part of the surface facing the collimating mirror of a concave or convex mirror, and the peripheral part surrounding the central part of the facing surface is blank. With reflective coating film,
The thickness of this anti-reflection coating film is adjusted so that each laser beam passing through the central part and the peripheral part has the same phase, so the laser beam has good focusing characteristics without sacrificing the efficiency of a single shot. Therefore, by using this laser beam, it is possible to perform high-speed, efficient, and highly accurate laser processing. In addition, since the laser beam heats the entire wind mirror, thermal stress is generated and the beam can be extracted stably for a long period of time.

Furthermore, since the thickness of the non-reflection coating film that does not contribute to resonance is adjusted to equalize the phase of the laser beam, there is the effect that laser oscillation can be maintained stably.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional side view showing a laser device according to an embodiment of the present invention, and FIG. 2 (al, (1)) is a characteristic diagram showing the focusing characteristics of a conventional laser device and a laser device according to an embodiment of the present invention, respectively. , FIG. 3 is a characteristic diagram showing the relationship between the spot diameter and power concentration at the focal point and the phase difference. FIG. 4 is a characteristic diagram showing the relationship between the film thickness of the anti-reflection coating film, phase difference, and transmittance, and FIGS. 5 and 6 are cross-sectional side views showing magnifying mirrors according to other embodiments of the present invention. FIG. 7 is a cross-sectional side view showing a laser device according to another embodiment of the present invention, and FIG. 8 is a cross-sectional side view showing a conventional laser device. 11) is a collimating mirror, (3) is a laser medium, (4
) is a convex mirror, +51 (s1X52) ■(220
)(221) is a non-reflective coating film, +71T8
+ is a laser beam, CXJ is a partial reflecting mirror, (4υ is a concave mirror. In the 3 figures, the same symbols indicate the same or equivalent parts. Convex other mu L 5 -Ij! ＃、Intangible Turtle Hutinff）(Zg
: Hizado na zo : li'/l-7t, lt'1lJL2z
, 祢 (1 piece in 2 pieces) Fig. 2 (α) (b) 01?0 Phase ((presentation Cαree) Fig. 4 Fig. 5 Fig. J Fig. 6 η 220.221: 4.ri, H- 1-t i>
``') 1%, Figure 7 fig Procedure amendment (self-initiated, Showa year, month, day 1, case description Patent application No. 1983-299369 2,
Name of the invention Laser device 3, person making the amendment S Column for detailed description of the invention in the specification to be amended. a Contents of the amendment (1) “The above membrane” on page 5, line 14 of the specification has been replaced with “agricultural
However, the above is corrected. (2) “Transmittance 50% 2 Phase difference 45” on page 3, line 2
J 'er phase difference 45'''. (3) "Emission efficiency" on page 10, line 11 is corrected to "oscillation efficiency."that's all

Claims (1)

[Claims] An unstable resonator is configured by a magnifying mirror and a collimating mirror arranged opposite to each other to extract a laser beam, and the magnifying mirror is a concave or convex mirror, and a partially reflective coating film is applied to the central part of the surface facing the collimating mirror. A non-reflection coating film is applied to a peripheral part surrounding the central part of the facing surface, and the thickness of the non-reflection coating film makes each laser beam passing through the central part and the peripheral part equal in phase. A laser device characterized by being adjusted to.