JPH0666490B2 - Laser equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laser device, and more particularly, to a high-power laser device for improving laser beam quality and measuring the laser power. Is.

[Prior Art] FIG. 7 shows, for example, the Laser Handbook 1
979. North-Holland Publishing Campaney) is a cross-sectional view showing an example of a conventional laser device having an unstable resonator. In the figure, (1) is a total reflection type collimating mirror consisting of a concave mirror, (2) is a collimating mirror (1)
It is a total reflection type magnifying mirror composed of a convex mirror arranged so as to face each other, and both mirrors (1) and (2) constitute a so-called unstable resonator. (3) is a laser medium, which is a gas medium excited by discharge or the like in the case of a gas laser such as a CO ₂ laser, and a glass medium excited by a flash lamp or the like in the case of a solid-state laser such as a YAG laser.
(4) is a wind mirror, (5) is a non-reflective coating film provided on the surface of the wind mirror (4), (6) is a box covering the surroundings, (7) is a collimating mirror (1) and a magnifying mirror. (2) a laser beam generated in the optical resonator constituted by
Reference numeral (8) is a laser beam taken out from the periphery of the magnifying mirror (2).

Next, the operation of the laser device configured as described above will be described.

The mirrors (1) and (2) form a so-called unstable resonator, and the laser beam (7) reflected and expanded by the expanding mirror (2) is amplified by the laser medium (3) and collimated mirror. It is collimated into a parallel beam by (1), reflected on the magnifying mirror (2) and the peripheral part of the magnifying mirror (2), and further becomes a ring-shaped laser beam (8) from the wind mirror (4) to the box ( It is taken out of 6). Since the extracted ring-shaped laser beam (8) can be obtained in almost the same phase, it becomes a medium-high beam by condensing it with a lens (not shown), etc., so that cutting and fusing of iron plates etc. can be performed efficiently. You can

The degree of focusing is determined by the ratio of the inner diameter and the outer shape of the extracted laser beam (8) [M value (Magnification f
acter)], the beam having a larger M value, that is, the beam taken out in a more centered manner is better focused. However, since the oscillation efficiency remarkably deteriorates when the M value is increased, the upper limit of the M value that is industrially used is about 2.

[Problems to be Solved by the Invention] According to the conventional laser device configured as described above, if the M value is increased in order to improve the condensing characteristics, the oscillation efficiency deteriorates. For this reason, there is a problem that the M value cannot be practically raised to infinity at which the maximum focusing performance can be obtained. Further, since the wind mirror (4) is unevenly heated by the ring-shaped laser beam (8), non-uniform internal stress is generated in the wind mirror (4), and the laser beam passing through the wind mirror (4) There was a problem that the phase distribution of (8) was destroyed and the light collection performance was deteriorated.

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

[Means for Solving the Problems] The present invention has been made to achieve the above object,
It has an unstable resonator consisting of a magnifying mirror with partial transparency and a collimating mirror that reflects the laser beam reflected and magnified by the magnifying mirror to the magnifying mirror and the periphery of the magnifying mirror. A semi-transmissive phase compensating mirror that cancels the phase difference between the laser beam that has passed through the magnifying mirror and the laser beam that has passed through the peripheral part of the magnifying mirror is provided outside the laser A laser device provided with a laser power sensor for measuring the output of a beam.

[Operation] The semi-transmissive phase compensation mirror eliminates the phase difference between the laser beams passing through the magnifying mirror and the peripheral portion of the magnifying mirror to create a laser beam having a uniform phase.
A part of the laser beam power is guided to the laser power sensor to measure the laser output.

Embodiment of the Invention FIG. 1 is a sectional view showing an embodiment of the present invention. The same or corresponding parts as those in FIG. 7 are designated by the same reference numerals and the description thereof will be omitted. In the figure, (4a) is a convex mirror that also functions as a wind mirror and is arranged so as to face the collimator mirror (1). Reference numeral (2a) is a partial reflection film (for example, Znse thin film) having partial reflectivity provided in the central portion on the inner surface side of the convex mirror (4a), and serves as a magnifying mirror. (5a) is a convex mirror (4a)
Is a non-reflective coating film (for example, PbF ₂ thin film) provided on the peripheral portion and the outer surface side of the partial reflection film (2a). Reference numeral (9) is a semi-transmissive phase compensating mirror, which is provided with a protruding step (10) at the center of the incident side surface of the laser beam (8a). (1
1) is a semi-transmissive partially reflective coating film provided on the outer peripheral portion of the step (10) of the phase difference compensation mirror (9), and (5b) is a non-reflective coating film provided on the other surface. Reference numeral (13) is a laser power sensor which measures the power of the laser beam (12) which has passed through the phase compensation mirror (9).

The laser power sensor (13) is not particularly limited and, for example, as shown in FIG. 2, an integrating sphere having an input port (16) and an output port (17) disclosed in JP-A-60-52072. You may use what was comprised from (15) and the detector (18) which measures the power of the laser beam output from the output port (17) of this integrating sphere (15).

In such a power sensor (13), the input port (1
The laser beam (12) incident from (6) becomes a large number of diffusely reflected laser beams on the inner surface of the integrating sphere (15) and is uniformly diffused, and the laser beam is uniformly dimmed in proportion to the incident laser beam (12). Beam exits the output port (17) and the detector (18)
Measured by Therefore, this makes it possible to measure the laser power of the laser beam (8a) emitted from the laser oscillator.

The power sensor (13) may be provided with a plurality of different time constants, for example, a short time constant for pulse waveform measurement, and a long time constant for average output measurement. The two types of power sensors described above can also be used to measure the laser beam power.

The operation of the present invention configured as described above will be described below. The partially reflecting film (2a) of the collimating mirror (1) and the convex mirror (4a) constitutes a so-called unstable resonator,
The laser beam (7) reflected and expanded by the partially reflecting film (2a) of the convex mirror (4a) is amplified by the laser medium (3) and collimated into a parallel beam by the collimating mirror (1), and the convex mirror (4a ) To the outside of the box (6)
Taken out as (8a). This laser beam (8a) passes through the partial reflection film (2a) (7a) Anti-reflection coating film (5a)
And a portion (7b) that passes through the laser beam (7b), the phases of which are corrected by the phase compensating mirror (9) to be reflected as a laser beam (8b) having an in-phase dome shape and taken out to the outside. Since this laser beam (8b) is in the middle, the M value defined by the conventional unstable resonator corresponds to infinity.

On the other hand, the laser beam (12) that passed through the phase compensation mirror (9)
Enters the laser power sensor (13) and the laser beam (8a)
Laser power is measured.

Although the convex mirror (4a) is used as the magnifying mirror in this embodiment, a concave mirror may be used as long as it has a function as the magnifying mirror.

3 (a) and 3 (b) are patterns when the laser beam generated by the unstable resonator according to the conventional example (FIG. 7) and the embodiment of the present invention (FIG. 1) is focused by a lens, respectively. In the characteristic diagram schematically showing the shape, the horizontal axis represents the distance from the optical axis, and the vertical axis represents the beam intensity.

In these experiments, the reflectance of the reflecting film (2a) was 50%, and the ratio of the diameter of the partially reflecting film (2a) to the outer shape of the beam was 1.5 (that is, M = 1.5, the magnifying mirror (2) of the conventional unstable resonator has a partial transmittance of 50% to form the unstable resonator of the present invention).
Further, the curvatures of both surfaces of the convex mirror (4a) were the same (the thickness was constant) so that the laser beam (7) was a parallel beam even after passing through the convex mirror (4a).

Comparing the light collecting performances shown in FIGS. 3 (a) and 3 (b), the light collecting performance according to the present invention (FIG. 3 (b)) has a high central intensity,
Moreover, it can be seen that a laser beam concentrated on the optical axis can be obtained.

Next, the operation of the phase compensation mirror (9) will be described. The laser beams (7a) and (7b) pass through the portions of the convex mirror (4a) provided with the two types of coating films (2a) and (5a), respectively, and are taken out of the box (6). In this case, the phase change given to the passing laser beam (8a) differs depending on the type of the coating film (5a). Therefore, the phase compensation mirror (9)
Without it, the equiphase laser beam (7) generated inside is taken out as a laser beam having a spatial phase distribution.

FIG. 4 is a partial reflection film (2) on the inner surface of the convex mirror (4a) shown in FIG.
FIG. 6 is a diagram showing an example of calculation of light collection characteristics with respect to a difference between a phase given to a laser beam passing through a) and a phase given to a laser beam passing through an antireflection coating film (5a). Focusing characteristics include the diameter of the focused spot where the beam intensity when the laser beam is focused with a lens becomes 1 / e ² in the center, and what percentage of the total power is included in that diameter. Indicates the power concentration degree. The smaller the former is, the narrower the laser beam can be focused, and the larger the latter is, the more concentrated power can be concentrated in the narrowed range, and therefore the efficient processing can be performed, so that it can be determined that the condensing characteristic is good. It can be seen from FIG. 4 that the phase difference must be kept within about 45 ° in order to keep the focused spot diameter small and the power concentration high. However, it is often observed that the phase difference is 60 ° or more even when a mirror for CO ₂ laser is taken as an example. The phase compensation mirror (9) is configured to cancel this phase difference. In the example of FIG. 1, a step (10) is provided between the portions where the laser beams (7a) and (7b) pass, Each has a different thickness.

Now, for example, the phase given to the laser beam passing through the partial reflection film (2a) on the inner surface of the convex mirror (4a) is advanced by δ (degree) from the phase given to the laser beam passing through the antireflection coating film (5a). Suppose The step (10) (d) in the center of the phase compensation mirror (9) for correcting this is
When the incident angle of the laser beam (8a) to the phase compensation mirror (9) is 45 ° as in the embodiment of FIG. 1, the laser beam (8a)
If the wavelength λ is Can be obtained by

FIG. 5 is a sectional view showing another embodiment of the present invention. First
The figure shows a laser beam (12) passing through a phase compensation mirror (9)
Although the power of the laser beam is measured by the laser power sensor (13), the power of the laser beam (12) reflected by the phase compensation mirror (9a) is measured in this embodiment. In this case, the phase of the laser beam (8a) is compensated by the concave portion, that is, the step (10a) provided on the emission surface side of the phase compensation mirror (9a).

FIG. 6 is a sectional view showing still another embodiment of the present invention. In the embodiment of FIGS. 1 and 5, the phase compensation mirror
(9), the phase change on the surface of (9a) is shown to be realized by the steps (10), (10a), but in the present embodiment, the antireflection films (5c), (5d) having different configurations are shown. Is used. For example, taking a mirror for CO ₂ laser as an example, a non-reflective coating film can be realized by using PbF ₂ 1 layer or ZnSe, ThF ₄ 2 layer for the substrate (ZnSe). In this case, The phase difference due to passing through both films is 20 ° or more. What is essential is that the central portion and its surroundings are devised so that a phase difference is produced.

[Effects of the Invention] As is clear from the above description, according to the present invention, since the magnifying mirror of the unstable resonator is configured to have partial transparency, it is possible to collect the jamming without sacrificing the oscillation efficiency. A laser beam having good optical characteristics can be obtained. Therefore, by utilizing this laser beam, high-speed, efficient and highly accurate laser processing can be performed. Also, the laser beam heats the entire convex mirror and phase compensation mirror,
The thermal stress hardly occurs, the beam can be stably taken out for a long time, and the laser power can be accurately measured.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view showing an example of a power sensor used in the present invention, and FIG.
(a) and (b) are characteristic diagrams showing the pattern shapes of the laser beam according to the conventional example and the embodiment of the present invention, respectively. FIG. 4 is a diagram for explaining the necessity of phase compensation, and FIG. 6 is a sectional view showing another embodiment of the present invention, FIG. 6 is an enlarged view of a main part of another embodiment of the present invention, and FIG. 7 is a sectional view showing an example of a conventional laser device. (1) ... Collimating mirror, (2a) ... Partial reflection film, (3) ... Laser medium, (4a) ... Convex mirror, (5a), (5b), (5c), (5d) ... Antireflection coating film, ( 7), (7a), (7b), (8a), (8b), (12) ... laser beam, (9), (9a) ... phase compensation mirror, (10), (10a) ... partially reflective coating film , (13) ... Laser power sensor. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-199686 (JP, A) JP-A-64-20679 (JP, A) JP-A-62-185386 (JP, A)

Claims (1)

[Claims] 1. An anxiety comprising a magnifying mirror having partial transparency and a collimating mirror which is arranged to face the magnifying mirror and reflects a laser beam reflected and magnified by the magnifying mirror to the magnifying mirror and a peripheral portion of the magnifying mirror. A semi-transmissive resonator that has a fixed resonator and cancels the phase difference between the laser beam that has passed through the magnifying mirror and the laser beam that has passed through the peripheral portion of the magnifying mirror outside the laser beam emitting side of this unstable resonator. A laser device comprising a phase compensation mirror and a power sensor for measuring the laser power of a laser beam which has passed through or is reflected by the phase compensation mirror.