JPH0856027A - Optical resonator of laser equipment - Google Patents

Abstract

PURPOSE:To enable obtaining large output laser light of high quality by a method wherein a shield wall which shields laser light and absorbs or scatters it is arranged in the outer peripheral part of a feedback reflecting mirror, a main reflecting mirror is a total reflection mirror, and the feedback reflecting mirror is partly transmitting mirror. CONSTITUTION:In an unstable resonator 18 which is a chemical pumping oxygen iodine laser, a main reflecting mirror 20 and a feedback reflecting mirror 21 having a diameter smaller than the main reflecting mirror 20 are separately arranged along an optical axis 22 so as to interpose laser medium 19 between the mirrors. A tube-shaped shield wall 24 constituting a water-cooled jacket is arranged in the outer peripheral part of the feedback reflecting mirror 21. The shield wall 24 is constituted to absorb the diffracted light of laser light 26 or scatter it, by forming a black colored covering film on the surface 25 facing to a resonance cavity. The main reflecting mirror 20 totally reflects the laser light. The feedback reflecting mirror 21 partly transmits the laser light, and the laser light reflectivity of the feedback reflecting mirror is set to be 90-99%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser device having an unstable resonator.

[0002]

2. Description of the Related Art A typical example of a conventional stable resonator is shown in FIG. In this stable resonator 1, a total reflection mirror 3 and a partial transmission mirror 4 are arranged with a laser medium 2 in between.
The laser light 5 is confined within the reflectors 3, 4 and part of the laser light 5 is extracted through the partial transmission mirror 4 as indicated by reference numeral 6.

A partial transmission mirror 4 is provided outside the stable resonator 1.
The intensity distribution of the near-field laser light 6 in the vicinity of is shown in Fig. 11 (1).
11B, the converged beam shape of the laser beam 6 on the surface of the workpiece is the far-field image shown in FIG. 11B, which is also a basic Gaussian beam.

In the stable resonator 1 shown in FIGS. 10 and 11, the beam intensity of the laser beam 6 has a Gaussian distribution and has the same shape in both the near field and the far field, and the energy loss is small. Excellent in terms.
However, in order to increase the output, the laser medium 2
When is increased, the higher-order Gaussian mode is displayed in the near field.
(3), and similarly in the far field as shown in FIG. 11 (4), in which case the condensing property of the laser beam 6 is poor, the spot diameter becomes large, and the energy density decreases. Therefore, this stable resonator does not include higher-order modes,
A high-quality beam including only the fundamental beam has a problem that it can be obtained only at a low output.

Another prior art is an unstable resonator 8 shown in FIG. 12, which has a main reflection mirror 10 with a laser medium 9 interposed therebetween.
And the feedback mirror 11 are arranged, and the laser light 1
The beam 2 is not confined in the reflecting mirrors 10 and 11, and the beam light 13 that is outside the feedback reflecting mirror 11 is extracted. The reflecting mirrors 10 and 11 have a confocal point 14, for example. An example of an unstable resonator is, for example, Japanese Patent Laid-Open No.
There is 1-234087.

A near-field image of the beam intensity of the laser light 13 from the unstable resonator 8 is as shown in FIG. 13A, and the cross section perpendicular to the optical axis is a donut-shaped beam. As shown in FIG. 13B, the far-field pattern has a loss component 16 in addition to the center lobe 15 and is a Bessel beam.

In such an unstable resonator shown in FIGS. 12 and 13, as described above, FIG.
The donut-shaped beam shown in (1) becomes the Bessel beam shown in FIG. 13 (2) in the far field, and only the center lobe 15 can be used for processing the workpiece, and therefore the unstable resonance is generated. However, there is a problem that energy loss is large. However, the mode of the laser light is a single mode of only the light passing through the confocal point 14, and there is an advantage that a high quality beam can be obtained. Moreover, even if the output is improved by enlarging the laser medium 9, the divergence angle of the extracted laser light can be reduced. Therefore, high-quality single-mode laser light can be obtained with a large output.

In this unstable resonator, when iodine that is chemically excited by excited oxygen is used as the laser medium 9, the gain of the iodine, that is, the small signal gain coefficient is about 3 to 5% / M. Since it is low, it is necessary to reduce the enlargement factor M in order to maintain the oscillation, which causes an important problem that the energy concentrated in the center lobe 15 is reduced. As shown in FIG. 12, when the inner diameter of the donut-shaped beam of the laser light 13 is D1 and the outer diameter is D2, the expansion ratio M is represented by M = D2 / D1.

[0009]

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a laser device having an unstable resonator capable of obtaining a high-quality laser light with a large output by using a low gain laser medium. Is.

[0010]

SUMMARY OF THE INVENTION The present invention provides a laser device in which an unstable resonator is constructed by disposing a main reflecting mirror and a feedback reflecting mirror smaller than the main reflecting mirror with a laser medium interposed therebetween. On the outer circumference of the mirror,
An optical resonator of a laser device characterized in that a blocking wall for blocking and absorbing or scattering laser light is arranged, a main reflecting mirror totally reflects, and a feedback reflecting mirror is partially transmissive. Further, the present invention is characterized in that the feedback reflecting mirror changes its reflectance as it moves away from the optical axis of the laser light in the radial direction. The present invention also provides
In a laser device that forms an unstable resonator in which a main reflecting mirror and a feedback reflecting mirror smaller than the main reflecting mirror are arranged with a laser medium in between, a laser beam is blocked on the outer peripheral portion of the feedback reflecting mirror, An optical resonator of a laser device, characterized in that an absorbing or scattering blocking wall is arranged, the main reflecting mirror is partially transmissive and the feedback reflecting mirror is total internal reflection. Further, the present invention is characterized in that the reflectance of the main reflecting mirror changes as it moves away from the optical axis of the laser light in the radial direction. The present invention also provides
The reflectance is 90 to 99%. Further, the present invention is characterized in that the cross-sectional area of the diffracted light that is absorbed or scattered by the blocking wall is 5% or less of the cross-sectional area of the laser light in the resonator that is perpendicular to the optical axis. The unstable resonator may be arranged in either positive branch or negative branch.

[0011]

According to the present invention, a blocking wall is provided on the outer peripheral portion of the feedback reflecting mirror in the unstable resonator of the laser device, and at least one of diffracted light is absorbed or scattered by the blocking wall. It prevents the diffracted light from returning into the resonant cavity between the main reflector and the feedback mirror, thus generating only a plane wave perpendicular to the optical axis in the resonant cavity, which is a plane wave perpendicular to the optical axis. The phase-matched wave of the laser light in the inside is taken out through the feedback reflecting mirror or the main reflecting mirror which is partially transmissive, and a solid laser beam is obtained. As a result, even in a low gain laser medium, for example, an iodine laser, it is possible to produce a single-mode, high-quality laser beam having a good converging property.
Further, it is possible to enlarge the laser medium and obtain a large output.

Further in accordance with the invention, the reflectivity of the partially transmissive feedback or main reflector is arranged to change as it moves away from the optical axis of the laser light radially outward, for example, It is possible to produce a laser beam having a desired intensity distribution such as a basic Gaussian beam by providing the reflectance with a super Gaussian distribution around the optical axis. The cross section perpendicular to the axis of the laser light may be circular, but may be other shapes, such as a rectangle such as a square.

In accordance with the invention, the reflectivity of the partially transmissive feedback or main reflector is, for example, 9
By selecting 0 to 99% and setting such a relatively low reflectance, it is possible to maintain the laser oscillation by the laser medium having a low gain.

Further, according to the present invention, the sectional area of the diffracted light absorbed or scattered by the blocking wall is 5% or less of the sectional area of the laser light in the resonator perpendicular to the optical axis, and the unstable resonance is achieved. It is possible to suppress the loss inside the vessel as low as possible.

[0015]

1 is a sectional view showing an unstable resonator 18 of a laser device according to an embodiment of the present invention. This unstable resonator 18 is a chemically excited oxygen iodine laser (ChemicalOxyg).
en Iodine Laser), a main reflecting mirror 20 and a feedback reflecting mirror 21 having a diameter smaller than that of the main reflecting mirror 20 are arranged with an interval between them along the optical axis 22 with the laser medium 19 interposed therebetween. To be done. The laser medium 19 is iodine that is chemically excited by excited oxygen. The two reflectors 20, 21 have a confocal point 23.

On the outer circumference of the feedback reflecting mirror 21,
A tubular blocking wall 24 forming a water cooling jacket is provided, and the feedback reflecting mirror 21 is provided by this blocking wall 24.
Is supported. Cooling water is supplied into the blocking wall 24.
The blocking wall 24 is made of metal such as iron,
The surface 25 facing the resonance cavity is formed with a black coating to absorb the diffracted light of the laser light 26, or has a structure in which the surface is made into fine irregularities to scatter the diffracted light. The return of diffracted light into the cavity is prevented. The surface 25 of the blocking wall 24 may be formed with a black film and formed into fine irregularities so as to simultaneously absorb and scatter the diffracted light of the laser light. The blocking wall 24 blocks the laser light from the resonance cavity to the outside (to the right in FIG. 1).

In this embodiment, the main reflecting mirror 20 totally reflects the laser light 20. The feedback reflector 21 is partially transmissive. The reflectance of the laser beam of the feedback reflecting mirror 21 is, for example, about 70 to 99.9%, preferably 90 to 99%, which is selected to be a low value, whereby iodine as a low gain laser medium is selected. This makes it possible to maintain laser oscillation. In this way, the laser beam denoted by reference numeral 27 is extracted to the outside, and the work can be processed.

Of the sectional area S1 of the laser light 26 in the resonator perpendicular to the optical axis 22, the sectional area S2 of the diffracted light absorbed or scattered by the blocking wall 24 is as low as possible, for example, 5
% Or less, for example, about 1%, thereby reducing the internal loss of the resonator and enabling highly efficient output extraction.

The reflectivity of the feedback reflecting mirror 21 is made uniform so that the laser beam 2 emitted to the outside can be obtained.
The intensity distribution of the near-field image of No. 7 has a diameter D as shown in FIG.
The intensity distribution has a constant value in the cross section perpendicular to the axis having 11. The cross section of the laser beam 27 perpendicular to the axis is circular as shown in FIG.

As another embodiment, the feedback mirror 21 and the blocking wall 2 are arranged so that the laser beam 27 having a rectangular cross section such as a square shown in FIG.
4 may be configured.

Laser light 27 in the unstable resonator 18
The far-field pattern of the laser beam is as shown in FIG. 4, and the laser power included in the center lobe 28 is the laser beam 2
This is about 80% of the total transmission power of No. 7.

FIG. 5 is a sectional view showing an unstable resonator 18a of a laser device according to another embodiment of the present invention. This embodiment is similar to the previous embodiment, and corresponding parts bear the same reference numerals. Notably, in this embodiment, the main reflector 20a is partially transmissive of the laser light 26 and the feedback reflector 21a is configured to totally reflect. Laser light 29 is extracted to the outside of the resonance cavity (left side of FIG. 5) through the main reflecting mirror 20a. The cross section of the laser beam 29 perpendicular to the axis may be circular as shown in FIG. 6 (1), or may be rectangular such as square as shown in FIG. 6 (2). The shape may be. Other configurations are the same as those in the above-mentioned embodiment.

FIG. 7 is a sectional view of still another embodiment of the present invention. This embodiment is also similar to the embodiment shown in FIGS. 1 to 4 above, but it should be noted that in this embodiment, the light transmissive feedback reflector 21 is shown in FIG.
As shown in, the surface of the resonance cavity side is coated with the film 31 having different reflectances in the radial direction. The feedback reflecting mirror 21 is made of quartz glass. The film has a multi-layered structure of dielectric films such as Ge and SiO ₂ , and the reflectivity thereof has a super Gaussian distribution. It becomes higher and the reflectance is the lowest near the optical axis 22.

As a result, a near-field image of the beam intensity of the beam light 27 transmitted through the feedback reflecting mirror 21 is shown in FIG.
As shown in (1), the intensity distribution of the laser light 27 becomes a basic Gaussian beam. Also the laser light 2
A far-field image with a beam intensity of 7 becomes a basic Gaussian beam as shown in FIG. 9 (2). In this way, a Gaussian beam can be obtained similarly to the stable resonator described above, and in the present invention, since it is an unstable resonator, it can be made into a single beam with high light quality. Therefore, the converging property of the beam light 27 can be improved, and the work material can be processed by the laser light having a high energy density.

As still another embodiment of the present invention, in the structure shown in FIGS. 5 and 6, the surface of the main reflecting mirror 20a, which is partially transmissive of laser light, facing the resonance cavity is formed in the same manner as in FIG. A coating having a Gaussian reflectance may be formed.

As another embodiment of the present invention, the reflectance of the laser light may have a distribution other than a Gaussian distribution.

[0027]

As described above, according to the present invention, a blocking wall is provided at the outer peripheral portion of the feedback reflector in the unstable resonator to absorb or scatter the diffracted light, and either the feedback reflector or the main reflector is provided. Since one is partially transmissive and the laser light is extracted, the plane wave arranged by the unstable resonator of the present case can be obtained as a solid beam. Therefore, even when a low gain laser medium such as iodine is used, it is possible to obtain a high-quality laser beam having a single mode and good converging property.
It becomes possible to obtain a large output by enlarging the laser medium.

Further, according to the present invention, the reflectance of the laser light of the feedback mirror or the main reflector which is partially transmissive is made to increase as it goes away from the optical axis of the laser light in the radial direction. Therefore, it is possible to easily obtain a laser beam such as a Gaussian beam.

Further, according to the present invention, the reflectance is 90%.
˜99%, which makes it possible to maintain laser oscillation when a low gain laser medium is used.

Further, according to the present invention, the diffracted light absorbed or scattered by the blocking wall is set to 5% or less, the internal loss of the unstable resonator of the present invention is set to a small value, and high power output can be taken out.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an unstable resonator 18 of a laser device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a near-field image of the beam intensity of a laser beam 27 of the embodiment shown in FIG.

FIG. 3 is a laser beam 2 extracted from an unstable resonator 18.
FIG.

FIG. 4 is a diagram showing a far-field image of the beam intensity of a laser beam 27 in the embodiment shown in FIGS.

FIG. 5 is a sectional view of an unstable resonator 18a of a laser device according to another embodiment of the present invention.

FIG. 6 is an unstable resonator 18a of the embodiment shown in FIG.
It is sectional drawing which shows the cross section orthogonal to the axis of the laser beam 29 taken out from.

FIG. 7 is a sectional view of an unstable resonator 18 of a laser device according to still another embodiment of the present invention.

FIG. 8 is an enlarged cross-sectional view of the feedback reflecting mirror 21 in the embodiment shown in FIG.

9 is a diagram showing a near-field image and a far-field image of the beam intensity of the laser beam 27 in the examples shown in FIGS. 7 and 8, respectively.

FIG. 10 is a cross-sectional view of a prior art stable resonator 1.

11 is a diagram showing a near-field image and a far-field image of the beam intensity of the stable resonator shown in FIG.

FIG. 12 is a cross-sectional view of another prior art unstable resonator 8.

13 is a diagram showing a near-field image and a far-field image of the beam intensity of the unstable resonator 8 shown in FIG.

[Explanation of reference symbols] 18,18a Unstable resonator 19 Laser medium 20,20a Main reflecting mirror 21,21a Feedback reflecting mirror 22 Optical axis 23 Confocal 24 Blocking wall 25 Surface on resonance cavity side 27,29 Extracted laser light 31 film

Claims (6)

[Claims] 1. A laser device comprising an unstable resonator in which a main reflecting mirror and a feedback reflecting mirror smaller than the main reflecting mirror are arranged with a laser medium interposed therebetween, and a laser beam is provided on an outer peripheral portion of the feedback reflecting mirror. An optical resonator of a laser device, characterized in that a blocking wall for blocking and absorbing or disposing is arranged, a main reflecting mirror is totally reflecting, and a feedback reflecting mirror is partially transmissive. 2. The optical resonator of a laser device according to claim 1, wherein the feedback reflecting mirror changes its reflectance as it goes away from the optical axis of the laser beam in the radial direction. 3. A laser device comprising a main reflection mirror and a feedback reflection mirror smaller than the main reflection mirror with a laser medium interposed therebetween to form an unstable resonator, wherein a laser beam is provided on an outer peripheral portion of the feedback reflection mirror. An optical resonator of a laser device, characterized in that a blocking wall for blocking or absorbing is arranged, a main reflecting mirror is partially transmissive, and a feedback reflecting mirror is total internal reflection. 4. The optical resonator of a laser device according to claim 3, wherein the reflectance of the main reflecting mirror changes as it moves away from the optical axis of the laser light in the radial direction. 5. The optical resonator of a laser device according to claim 2, wherein the reflectance is 90 to 99%. 6. The cross-sectional area of the diffracted light absorbed or scattered by the blocking wall is 5% or less of the cross-sectional area of the laser light in the resonator perpendicular to the optical axis.
An optical resonator of a laser device according to claim 1.