JP2000269569A - Discharge excitation gas laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate degradation of stability in a beam direction caused by an unstable resonator by dividing gas discharge into a plurality of bands, by providing a recess to opposite surfaces of a pair of electrodes an providing an optical path of a laser resonator along the divided band-like discharges. SOLUTION: An electrode 1 and an electrode 2 are held by defining an electrode interval by an insulator 9, a space between the electrode 1 and the electrode 2 is filled with laser gas of proper composition and pressure, each of the electrodes 1, 2 makes cooling liquid circulate through a cooling liquid hole 10 for enough cooling, and heat of gas generated by discharge is effectively emitted. Three recess 8 are formed in each of the electrodes 1, 2, discharge 7 is divided into four as four band-like discharges 7, and the cooling liquid hole 10 as an optical path is formed along the band-like discharges 7. An optical path which is the cooling liquid hole 10 moves a position parallel in an opposite direction by a mirror 3 for reflection.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge-excited gas laser device.

[0002]

2. Description of the Related Art In recent years, a slab-type laser has been studied as a method for making a high-power laser compact. This is because a slab structure having a large surface area facilitates heat radiation, which is a problem of a high-power laser. As for a gas laser, a slab-type carbon dioxide laser (CO ₂ laser) has been studied. (DR Hall and HJ Baker, SPIE, Vol. 2502
(1995) p12) Discharge-excited gas lasers such as CO ₂ lasers have a slab-shaped discharge part, that is, tens or more times the width and length of the discharge to promote diffusion cooling of heat in the thickness direction. And improve efficiency. Two electrodes are opposed to each other in the thickness direction of the discharge (the distance between the electrodes is the discharge thickness), the metal electrode with high thermal conductivity is cooled by a refrigerant, and heat is efficiently discharged from the discharge gas in contact with the metal electrode. And solves the problem of heat dissipation. In order to realize stable and efficient discharge at a narrow electrode interval, a high frequency (10 MHz to 3.4 GHz) is used.
z) is used.

[0003] These technologies make gas circulation mechanisms unnecessary for cooling purposes, and enable a medium-power (500 W) CO ₂ laser device to seal off gas. (Kurt
(Bondelie, Laser Focus World, Aug (1996) p95) However, in the above-mentioned technology, the cross-sectional shape of the discharge is slender, and the width is several tens of times larger than the thickness. It is significantly different from conventional CO ₂ lasers.

That is, in the discharge thickness direction, a laser beam is propagated in a waveguide mode by an optical waveguide having two electrodes facing each other as a reflection surface, and the laser beam is propagated in the discharge width direction (in-plane direction of the electrode). Employs an irregular laser resonator that propagates a laser beam in a free space propagation mode. (John Tulip, Japanese Patent Publication No. 7-70708) (P
E Jackson, HJ Baker, DR Hall, Appl.Phys.Lett.5
4, (1989) p1950) In such a propagation mode, since the width direction of the discharge is wide, the mode in the width direction of the laser beam is easily deteriorated. For this reason, an unstable resonator capable of obtaining high mode quality in the width direction of the resonator is employed.

[0005]

As described in the above prior art, the slab-type discharge excitation laser employs an unstable resonator in the width direction of discharge (in-plane direction of the electrode). The unstable resonator includes a positive branch resonator and a negative branch resonator, and has different characteristics. The positive branch has a relatively uniform light intensity distribution inside the cavity, but has the problem that the pointing stability of the laser beam is several tens times worse than that of a normal cavity (WF Krupke, W RSooy, IEEE
J. Quantum Electron, QE-5 (1969) p575).

The negative branch has good beam directional stability, but has a very large focal point of light intensity inside the resonator, and when a high-power laser is realized, the discharge at the internal focal point becomes unstable. There are issues. (DR Hall and HJ Ba
ker, SPIE, Vol. 2502 (1995) p12) As described above, the unstable resonator for improving the laser mode quality has problems such as deterioration of beam direction stability and discharge instability due to internal focus.

An object of the present invention is to propose a method for solving the problems of deterioration of beam direction stability and unstable discharge due to internal focus due to such an unstable resonator, and an object of the present invention is to provide a stable laser.

[0008]

Means for Solving the Problems A gas discharge is excited by applying a high frequency voltage between a pair of opposed electrodes, and a gas discharge is divided into a plurality of strips by providing a concave portion on the opposed surface of the electrodes. The problem is solved by adopting a stable resonator that provides an optical path of a laser resonator along the strip discharge.

[0009]

According to the present invention, a high frequency (10 MHz to 3.4 GHz) voltage is applied between opposing electrodes. In order to obtain an effective gas cooling effect, the width and length of the electrode are set to be several times or more larger than the electrode interval (1 mm to 10 mm). That is, the discharge space has a slab shape.

A discharge gas having a predetermined composition is filled between the electrodes at a predetermined pressure. (For example, CO ₂ in CO ₂ laser,
The gas condition is a mixed gas of N ₂ and He at several tens to several hundred Torr. ) Since the impedance of discharge changes according to the electrode shape, frequency, gas condition, input power amount, etc., the power supply must have a discharge impedance matching function. Can supply.

In the prior art, the discharge is made uniform between the electrodes, but in the present invention, the discharge is divided into a plurality of strips. If a concave portion is formed on the opposing electrode surface at a depth of 10% or more of the electrode interval, the electric field in this portion is weakened and discharge is suppressed. When a band-shaped concave portion is formed on the electrode by utilizing this effect, the discharge is divided into a band. A plurality of strip-shaped discharges can be obtained by the plurality of strip-shaped concave portions. By adjusting the length direction of the plurality of strip-shaped discharges to the length direction of the electrodes, the discharges can be effectively divided in the width direction of the electrodes.

The width of the discharge thus divided becomes narrower than the width of the electrode (same as the width of the slab shape), and if the optical path of the laser resonator is provided along the width, the width of the optical path also becomes narrower. . When a stable resonator is configured for such a narrow optical path, a resonator that performs laser oscillation close to a good single mode without producing multiple laser beam modes can be produced. (If the electrode spacing is small, the direction orthogonal to the electrode surface is the same as the conventional waveguide mode, but the direction in the electrode surface is free space mode because there is no reflective surface.) As is well known, the mode is Is a singular condition is the Fresnel number N of the resonator
_F must be about 1 or less. N _F is 2a the width of the light path
Where L is the resonator length and λ is the wavelength, and is given by the following equation.

[0013]

(Equation 1)

In order to provide an optical path along a plurality of strip-shaped divided discharges, it is desirable to form a folded optical resonator comprising a plurality of mirrors. In particular, a reflecting mirror combining two perpendicular mirrors has an opposite optical path. It is suitable for a mirror that provides an optical path along a plurality of divided discharges for moving in parallel to the direction. Further, the stable resonator can be easily constituted by a combination of a spherical total reflection mirror and a semi-transmission mirror as an output mirror, and an optical path along a discharge can be set in combination with the above-mentioned folding mirror.

The specific method described above will be described later in detail as Embodiment 1. By employing the structure of the present invention, a laser beam having a good mode can be obtained.
Also, as is well known, the directional stability (pointing stability) of the laser beam from the stable resonator
Is good, and a condition in which no focus is formed inside the resonator can be set, so that discharge instability due to the focus does not occur. As described above, in the configuration of the present invention, the conventional problem of stability can be solved and a stable and good laser beam can be obtained.

(Embodiment 1) FIG. 1 is a diagram showing a configuration of a first embodiment of the present invention. FIG. 1 (a) is a plan view, and FIG.
It is sectional drawing of -A '. FIG. 2 is a perspective view of the portion shown in FIG. 1B, and FIG. 3 is a perspective view of the optical portion shown in FIG.

1, 2 and 3, 1 and 2 are electrodes, 3 is a mirror, 4 is a total reflection mirror, 5 is an output mirror, 6 is a laser output, 7 is a discharge, 8 is a concave portion of the electrode, 9 Is an insulator, 10
Is an optical path.

In this embodiment, the basic configuration of the present invention will be described. There is a discharge region below the electrode 1 in FIG. 1 (a), and an optical system is constituted by a mirror 3, a total reflection mirror 4 and an output mirror 5,
Laser output 6 is emitted from output mirror 5. Fig. 1 (b) shows A-
A high-frequency voltage is applied to the electrode 1 from the power supply 3 in the cross section of A ′.

FIG. 2 is a perspective view of FIG.
And the electrode 2 are held by an insulator 9 at a fixed electrode interval. The space between the electrodes 1 and 2 is filled with a laser gas at an appropriate composition and pressure. For example, in an example of a carbon dioxide gas laser, a mixed gas of CO ₂ : N ₂ : He = 1: 1: 3 and the pressure is several tens Torr. The electrodes 1 and 2 circulate the cooling liquid through the cooling liquid hole 10 to sufficiently cool and efficiently discharge the heat of the gas due to the discharge.

A recess 8 is formed in the electrodes 1 and 2 in a strip shape.
The electric field in this portion is weakened to suppress discharge. As a result, the discharge 7 is formed in a band shape as shown in FIG. Here, the band shape refers to a state in which the discharge 7 has a narrow width and a long length, and in FIG. 2 in a perspective view, the discharge 7 is long in the depth direction.

In this embodiment, the recess 8 has three electrodes 1 and 2 respectively.
The discharge 7 is formed into four, and is divided into four parts to form four strip-shaped discharges 7.
It has become. The longitudinal direction of the band of the discharge 7 corresponds to the electrode 1.
And 2 are formed in a strip shape so as to face in the longitudinal direction. As shown in FIG. 1, an optical path 10 is formed along a strip-shaped discharge 7. This optical path is formed by the mirror 3.

FIG. 3 shows a perspective view of the optical system.
Is reflected by the mirror 3 by translating the position in the opposite direction. The mirror 3 is constituted by a set of two mirrors forming a right angle, and the optical path 10 is folded back by one set. The total reflection mirror 4 and the output mirror 5 constitute a resonator with the mirror 3. For example, a stable resonator can be formed by making the total reflection mirror 4 a spherical mirror and the output mirror 5 a semi-transmissive mirror.

The output mirror 5 may be a spherical mirror, and an optimum stable resonator can be set by appropriately selecting the radius of curvature of the total reflection mirror 4 and the radius of curvature of the output mirror 5 according to the shape and size of the device. Width of the optical path 10 is matched to the width of the discharge 7, also can be set to an optimum value Fresnel number N _F of the aforementioned by setting the width of the discharge 7 appropriately, also thereby selecting the single-mode It becomes possible.

With the above basic configuration, it is possible to obtain a stable and good beam laser output 6 as described above. However, in the beam thickness direction of the laser output 6 (vertical direction in the perspective view of FIG. 3), the waveguide mode propagates through the waveguide by electrode surface reflection composed of the electrodes 1 and 2 of FIG. The waveguide mode is determined by setting the interval. The selection of the waveguide mode is the same as that of the conventional device.

Although the discharge 7 is divided into four parts in this embodiment, the number of divisions can be selected as required. In any case, it is desirable to make the discharge 7 and the optical path 10 coincide. Although the concave portion 8 is provided in both the electrode 1 and the electrode 2 in this embodiment, the discharge 7 can be divided by only one side of the electrode.

In this embodiment, the distance between the electrode 1 and the electrode 2 is small, and the propagation of the waveguide mode by the reflection on the electrode surface occurs. However, when the interval is wide, the propagation mode becomes a free space mode, but there is no difference in the effect of the present invention.

(Embodiment 2) Hereinafter, a second embodiment of the present invention will be described with reference to FIG. Fig. 4 (a)
FIG. 4A is a partial view of the left part of FIG. 1A, and FIG.
13 is a cross-sectional view taken along the line BB ′ of FIG. FIG. 4 (b) shows the second
FIG. 13 is a configuration diagram in which an optical waveguide 11 which is a feature of the second embodiment is added, and is a basic configuration diagram of the second embodiment. FIG. 4D is FIG.
It is sectional drawing of the CC 'part of (b).

In FIG. 4, 1 is an electrode, 3 is a mirror, 1
0 is an optical path and 11 is an optical waveguide. (The same parts as those in the first embodiment are denoted by the same reference numerals.) FIG. 4A shows the first embodiment, and FIG. 4C shows an optical path 10 in a sectional view, and FIG. When the distance between the electrode 1 and the electrode 2 is small (for example, about 3 mm or less by a carbon dioxide laser), the light propagates in a waveguide mode in which the electrode 1 and the electrode 2 are used as reflection surfaces. The propagated laser light is reflected by the mirror 3 to change the optical path, but propagates in space between the electrodes 1 and 2 and the mirror 3. When the light in the propagation mode propagates in space, it is reflected and returns to the waveguide mode between the electrodes 1 and 2 again, causing a loss due to diffraction.
(JJ Degnan, DR Hall, IEEE J. Quantum Electronic
s, Vol. QE-9, (1973) p901) This loss increases when the distance between the electrodes 1 and 2 is small and when the distance between the mirror 3 and the electrodes 1 and 2 is large. The quantitative evaluation formula for the loss is in the above document,
If the loss is not negligible in the resonator, it is necessary to add the optical waveguide 11 of this embodiment.

FIG. 4B shows a configuration in which an optical waveguide 11 is added. The cross-sectional view (d) illustrates the effect of the optical waveguide 11. The waveguide mode that has propagated between the electrodes 1 and 2 propagates through the optical waveguide 11 as it is, is reflected by the mirror 3, and returns from the optical waveguide 11 to the waveguide mode between the electrodes 1 and 2 again. In this configuration, the propagation mode rarely propagates in space, and no loss occurs.

It is desirable that the distance between the waveguides of the optical waveguide 11 is equal to the distance between the electrodes 1 and 2, and that the inner surface of the optical waveguide 11 needs to have a high light reflectance. When there is a possibility of a discharge between the electrodes 1 and 2 and the optical waveguide 11, the optical waveguide 11 needs to be formed of an insulator. It is also possible to reduce the number of parts by integrating the optical waveguide 11 and the mirror 3.

Although not explicitly shown in FIG. 4, if the same diffraction loss as described above occurs due to the distance between the total reflection mirror 4 or the output mirror 5 and the electrodes 1 and 2 in FIG. Providing the optical waveguide 11 is also effective in reducing the loss. As described above, according to the second embodiment, it is possible to prevent the loss accompanying the reflection of the waveguide mode.

[0032]

As described above, according to the present invention, a stable resonator can be formed from the conventional unstable resonator, and the beam direction stability is deteriorated due to the unstable resonator, and the discharge is unstable due to the internal focus. Can be solved, and the effect is great.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a first embodiment.

FIG. 2 is a perspective view of a portion shown in FIG.

FIG. 3 is a perspective view of the optical part of FIG.

FIG. 4 is a basic configuration diagram of a second embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electrode 2 electrode 3 mirror 4 total reflection mirror 5 output mirror 6 laser output 7 discharge 8 electrode recess 9 insulator 10 optical path 11 optical waveguide

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyoshi Yajima 3-10-1 Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa F-term in Matsushita Giken Co., Ltd. 5F071 AA05 CC04 CC10 JJ05

Claims (12)

[Claims] 1. A gas laser in which a high frequency voltage is applied between at least a pair of opposed electrodes to excite a gas by discharge, wherein the gas discharge is formed into a plurality of strips by providing a concave portion on the opposed surface of the electrodes. A discharge-excited gas laser device comprising a stable resonator which is divided and provides an optical path of a laser resonator along the band-shaped discharge. 2. The discharge-excited gas laser device according to claim 1, wherein the laser resonator is a folded resonator using a folded mirror. 3. The discharge-excited gas laser device according to claim 1, wherein a waveguide mode is formed in a direction orthogonal to the opposing electrode surface in an optical path, and a free space mode is formed in an electrode surface direction. 4. The discharge-excited gas laser device according to claim 2, wherein the folding mirror comprises a plurality of mirrors each including a pair of right-angled mirrors. 5. An optical waveguide is provided between a folding mirror and the opposing electrode.
The discharge-excited gas laser device as described in the above. 6. The discharge-excited gas laser device according to claim 1, wherein the length direction of the strip of the strip discharge coincides with the length direction of the electrode. 7. The discharge excitation laser device according to claim 1, wherein the laser gas is a carbon dioxide laser containing CO ₂ , N ₂ , and He gas. 8. The depth of the recess is one of the distance between the electrodes.
The discharge-excited gas laser device according to claim 1, wherein the value is 0% or more. 9. The discharge-excited gas laser device according to claim 1, wherein the stable resonator uses a spherical total reflection mirror and a semi-transmission mirror as an output mirror. 10. The discharge-excited gas laser device according to claim 1, wherein the width of the electrode is several times or more the interval between the electrodes. 11. The discharge-excited gas laser device according to claim 1, wherein the concave portion on the surface facing the electrode has a band shape. 12. The discharge-excited gas laser device according to claim 1, wherein the Fresnel number of the resonator is about 1 or less.