JPH03155684A - Gas laser device - Google Patents

Abstract

PURPOSE:To obtain a gas laser device which is less sensitive to the tilt of a reflecting mirror, easy to control the tilt of the reflecting mirror and stable in performance by forming a laser resonator on a recessed part and a projected part respectively in terms of one dimension belonging to a longer dimension in a cross section of a discharge space, and constituting an unstable resonator of a negative branch. CONSTITUTION:This resonator is an unstable resonator of a negative branch comprising a combination of mirrors 50 and 51 in terms of one dimension belonging to a longer dimension in a cross section of a discharge space or in the direction of A. In terms of one dimension of a shorter one or in the direction of B, it serves as an optical waveguide resonator. Furthermore, the unstable resonator of negative branch is designed to deviate a laser light axis from the central axis of the discharge space in order to take out a laser beam from one end 671 of a longer dimension of the cross section of the discharge space. The construction of this unstable resonator of negative branch produces a focus point within the resonator wherein the light does not come into focus in one point only but along a line, and thereby prevents the occurrence of any problems induced by the concentration of light and exerts the maximum advantage enjoyed by the unstable reflector of negative branch which is less sensitive to the tilt of the reflecting mirror and improves the stability of the resonator.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a gas laser device in which a discharge space in which laser gas is excited is in the shape of a flat slab, and particularly relates to a gas laser device in which the stability of the laser resonator is improved. This is related to the improvement of

[Prior Art] FIG. 6 is a schematic sectional view of a conventional gas laser device disclosed in Japanese Patent Application Laid-Open No. 83-192285, and FIG. 7 is a schematic plan view showing the configuration of a resonator of this laser device. . In the figure, (11) is a 7214Hz high frequency generator, (21)
is a power matching circuit, (22) is a high frequency cable, (23)
are insulated feedthroughs (71), (72) are electrodes, (
73) and (74) are the surfaces of the electrodes polished to optically reflective surfaces. (75) is the discharge gap, (7B), (77
) is an electrode (71).

(72) is a spacer that insulates the electrodes (71), (72) and the spacer (76), (78) is a U-shaped base.
(77) is mounted on the base (78), the U-shaped base (78) being closed by a lid (79);
Ceramic insulator (80) connects M (79) and electrode (71)
). In addition, the laser resonator is the seventh
As shown in the figure, it is composed of a total reflection mirror (52) with a concave spherical surface and a total reflection mirror (53) with a convex spherical surface.

In the conventional gas laser device configured as described above, the high frequency generated by the high frequency generator (11) passes through the power matching device (21), the cable (22), and the electrodes (71), ( 72) is applied between. Electrode (7
The discharge gap (75) between 1) and (72) is filled with laser gas, and the laser gas is excited to discharge by the high frequency applied between ff1i (71) and <72).

In this way, the excited laser gas is present in the laser resonator constituted by the reflecting mirrors (52) and 53), so that laser oscillation is performed. At this time, the electrode (71)
, (72) is set to 21111, and the electrodes (71), (
The distance between the edge of 72) and the edge of convex mirror (53) is 2 +
By setting it to n, a square beam of approximately 2 dragons on one side can be obtained. This beam becomes a Gaussian circular beam (8) at a certain distance from the laser resonator.

[Problems to be Solved by the Invention] In the conventional gas laser device as described above, the laser resonator is a so-called positive branch unstable type resonator, which is a combination of a concave mirror and a convex mirror. This poses a problem in that it is difficult to ensure the stability of the resonator, as it is difficult to adjust the inclination of the reflecting mirror, and the adjustment is easily lost due to deformation due to temperature.

The present invention was made to solve these problems, and aims to provide a gas laser device that is insensitive to the inclination of the reflecting mirror, allows easy adjustment of the inclination of the reflecting mirror, and has good stability.

[Means for Solving the Problems] In the gas laser device according to the present invention, the discharge space is formed in the shape of a flat slab with different vertical and horizontal dimensions in a cross section perpendicular to the laser optical axis direction, and both ends of the discharge space are A laser resonator mirror is arranged at each of the two sides, and the laser resonator mirror is formed into a concave surface and a concave surface, respectively, for the longer one dimension in the cross section of the discharge space, thereby forming an unstable negative branch resonator. The laser beam is taken out from one end of the longer dimension in the cross section of the discharge space.

[Operation] In this invention, an unstable resonator with a negative branch is constructed in one dimension of the longer dimension in the cross section of the discharge space, so although there is a focal point within the resonator, the light is concentrated at only one point. Compared to the case where a normal cylindrical axially symmetrical resonator is used as a negative branch, the concentration ratio of light is greatly reduced, and problems due to light concentration such as optical damage may occur. The feature of being insensitive to the tilt of the reflector of the unstable resonator is fully utilized.

[Example] Fig. 1(a) is a perspective view showing a resonator in an embodiment of the present invention, and Fig. 1(b) is an outline of the unstable resonator side of the resonator shown in Fig. 1(a). FIG. 1(e) is a side view schematically showing the leading waveguide resonator side of the resonator shown in FIG. 1(a).

In Figure 1 (a), (b) and (c), (50
) is a total reflection mirror and is a concave mirror. (51) is an exit total reflection mirror, which is a concave mirror. (67) is the discharge space,
This space corresponds to the discharge gap (75) surrounded by the surfaces of the electrodes (71) and (72) in FIG. 5. This discharge space (B7) is formed in the shape of a flat slab in which the vertical and horizontal dimensions (A and B) of the cross section perpendicular to the laser optical axis direction are different, and dimension B is the dimension of the optical waveguide with respect to the laser wavelength. It's Toshide. Note that the illustration of the discharge space (87) is simplified and only the outline is shown.

The resonator configured as described above is a negative branch unstable resonator combining mirrors (50) and (51) in the longer one dimension in the cross section of the discharge space, that is, in the A direction shown in the figure. As for the shorter one dimension in the cross section of the discharge space, that is, for the direction B shown in the figure, it is a leading waveguide resonator.

Furthermore, in the negative branch unstable resonator, the laser optical axis is shifted from the central axis of the discharge space in order to extract the laser beam (8) only from one end (071) where the cross-sectional dimension of the discharge space is longer. . That is, mirrors (50) and (5
At least one of 1) is arranged at an angle with respect to the central axis of the discharge space. Further, the mirror (51) is provided with a laser beam extraction section (511). In this embodiment, the laser beam extraction section (511) is a mirror (51
) is cut out to form a linear aperture.

In the figure, PLO indicates the laser light intensity distribution taken out from the mirror (51), and RT indicates the distribution of the laser light intensity taken out from the mirror (51).
50) and R3 is the radius of curvature of the mirror (51). Further, a and b indicate the effective length of the mirror.

Next, the sensitivity of the unstable resonator to mechanical fluctuations, that is, mirror tilt (hereinafter referred to as misalignment) will be explained.

FIG. 2 is an explanatory diagram for explaining the misalignment sensitivity of the positive branch unstable type resonator, and FIG. 3 is an explanatory diagram for explaining the misalignment sensitivity of the negative branch unstable type resonator.

In Figures 2 and 3, (1) and (2) are mirrors, and in Figure 2, mirror (52) and mirror (5) in Figure 7 are shown.
3), and FIG. 3 shows the mirror (50) and mirror (51) of FIG. 1. e is the center of curvature of the mirror (2), f is the original center of curvature of the mirror (1), g is the center of curvature of the displaced mirror (1), h is the focal point, and θ is the center of curvature of the mirror (1).
) is the deviation angle of the optical axis, and φ is the deviation angle of the optical axis. The optical axis C is a line connecting the centers of curvature, that is, a line perpendicular to both mirror surfaces, and changes from ef to eg when the mirror (1) is shifted, that is, when the mirror (1) is tilted. d indicates a shifted optical axis.

The sensitivity M to misalignment of an unstable resonator is
IEEE JOURNAL OF QUANT
UMELECTRONIC8, DEOEMBER198
9, P. 579), below (1)
~(3) Expression.

φ M− (1) θ 22, where m is the magnification ratio and can be considered as the curvature ratio of the mirror in a confocal resonator.

2 R1 and R2 are the radii of curvature of mirrors (1) and (2), and since convex curvature and concave curvature are distinguished by the sign, equation (5) is negative.

This m is geometrically (optically) a ratio of the effective length of the mirror (a and b shown in FIGS. 1 and 7) limited by edges and apertures.

m-□ ・・・
(8) Note that the effective length of the mirror is limited by edges and apertures and is the portion of the mirror that is actually illuminated by light. (In the case of axial symmetry, it becomes the effective diameter.) That is, the magnification ratio is the ratio of the size of the beam before being expanded and the size of the beam after being expanded in the resonator.

In the example of the CO2 laser prototyped according to Fig. 1, the discharge space length is 400 mus, the cross-sectional dimension is 2 x 2 huw, and the magnification factor m is about 1.1 to achieve both an appropriate output coupling rate of 10% and symmetry of the emitted beam. It is designed to.

In this case, M:22, M:l:1.

Therefore, the misalignment sensitivity of the negative branch is 1/22 of the misalignment sensitivity of the positive branch.

That is, the deviation of the optical axis due to the tilting of the mirror is much smaller in the negative branch. Therefore, the deviation between the optical field created by the resonator and the active medium excited by the discharge is much smaller (and the stability of the resonator is improved).

In addition, in this invention, the magnification ratio m is on the unstable side (cross-sectional dimension A
), and the leading waveguide side (cross-sectional dimension B)
It has nothing to do with it.

By the way, an unstable negative branch resonator has a focal point within the resonator, and when used in a normal cylindrical axially symmetrical resonator, there is a point where light is concentrated within the resonator, causing problems such as optical damage. It is rarely used in general. In contrast, the present invention applies an unstable negative branch resonator to a conventional resonator that is not symmetrical about the cylindrical axis and constitutes a leading waveguide resonator in the shorter one dimension in the cross section of the discharge space. Therefore, although there is a focal point within the resonator, the light is concentrated not at one point but on a line (Fig. 1(b) and (C)
), the rate of light concentration is greatly reduced compared to when applied to a normal cylindrical axially symmetrical resonator, and problems due to light concentration such as optical damage do not occur, and the negative branch can be easily This makes it possible to take full advantage of the unstable reflector's insensitivity to tilt. In the above example, the fourth
As shown in the figure, in the positive branch, the mode is distorted from about 25 W due to the distortion of the mirror, and the output becomes saturated, but in the negative branch, more than 80 W was obtained.

Further, since the radius of curvature of the mirror is smaller in the negative branch, the curvature is larger and the curvature error with respect to the shape error is smaller. For the same shape error (accuracy), the error (accuracy) in the radius of curvature increases approximately to the square of the target radius of curvature, and the negative branch is also advantageous in terms of precision in mirror manufacturing. For example, in the example of the C02 laser mentioned above, a mirror with a diameter of about 30mm is used with a shape error of ±0.5μm, but in the case of a negative branch, the curvature of the unstable type is about 4
00, the error is ±0.5mm, but in the case of the positive branch, the curvature is approximately 90QO, resulting in an error of ±200mm, and in the positive branch, the deviation from the confocal position is large, and the magnification rate also deviates from the target, and the light control is not as designed. I did not go.

5(a) and 5(b) both show resonators in other embodiments of the present invention, and FIG.
) 6(c). Although not shown, the structure of the resonator of this embodiment viewed from an oblique direction is the same as that shown in FIG. 1(a). In this example, as shown in FIG. 5(a), the longer dimension is an unstable resonator with a negative branch, as in FIG. 1(b). The first dimension is not a guiding waveguide resonator, but a normal open-type resonator as shown in Figure 5(b), with a total reflection mirror (
The laser beam (8) is taken out from one end of the longer discharge space cross section of the exit total reflection mirror (52) and the exit total reflection mirror (53).

In order to obtain a resonator with such a configuration, for the longer one dimension, as shown in FIG. The mirror is made into a concave surface with appropriate radii of curvature R, Tl pi . The other one dimension is to set the radius of curvature R, R of both mirrors so that the beam diameter is smaller than the shorter dimension B2 of the discharge space cross section without the light hitting the electrode surface, as shown in Figure 5(b). Make it a concave surface with an appropriate T2 P2. That is, the resonator mirror is a so-called toroidal mirror that has different curvatures in both the longer one dimension and the shorter one dimension in the cross section of the discharge space.

Even with this configuration, like the one in Figure 1, an unstable negative branch resonator is applied to a normal resonator that is not symmetrical about the cylindrical axis. However, since the light is concentrated on a line rather than a single point, the effect is similar to that shown in Figure 1.

In each of the above-mentioned embodiments, the present invention was applied to a gas laser device that generates a discharge using a high-frequency electric field and excites a laser gas.
A cross section perpendicular to the laser optical axis direction between a conductive wall that constitutes a part of a microwave circuit and a dielectric provided opposite to this conductive wall, as disclosed in Japanese Patent No. 86483. The same effect can be obtained even when applied to a gas laser device in which a space with different vertical and horizontal dimensions is formed, a laser gas is sealed in this space, and the laser gas is destroyed by discharge using a microwave electric field to generate plasma and excite the laser gas. is obtained.

In addition, the laser beam extraction portion (51) of the mirror (51)
1) forms a linear aperture, but there is no problem in using a circular mirror as long as it has a diameter sufficiently larger than the shorter dimension of the cross section of the discharge space.

[Effects of the Invention] As explained above, this invention constitutes an unstable resonator with a negative branch only in the longer one dimension in the cross section of the discharge space, so although there is a focal point within the resonator, the light The light is concentrated in a line rather than at one point, and there are no optical damage or other problems caused by the concentration of light, and the feature of being insensitive to the tilt of the reflector of the negative branch unstable resonator is maximized, and the resonator This has the effect of improving the stability of.

[Brief explanation of the drawing]

FIG. 1(a) is a perspective view showing a resonator according to an embodiment of the present invention, and FIG. 1(b) is a plan view showing an outline of the unstable resonator side of the resonator shown in FIG. 1(a). , FIG. 1<c> is a side view showing the outline of the leading wavepath resonator side of the resonator shown in FIG. 1(a), and FIG. 2 is an explanatory diagram illustrating the misalignment sensitivity of the positive branch unstable resonator , Fig. 3 is an explanatory diagram explaining the misalignment sensitivity of the negative branch unstable type resonator, Fig. 4 is a graph showing the characteristics of the CO2 laser resonator with the positive branch and negative branch unstable type resonators, and Fig. 5 (a ) is a plan view schematically showing the unstable resonator side of a resonator according to another embodiment of the present invention, FIG. 5(b) is a side view schematically showing the open resonator side of the resonator, and FIG. This figure is a schematic sectional view of a conventional gas laser device, and FIG. 7 is a schematic plan view showing the configuration of a resonator of the gas laser device shown in FIG. 6. In the figure, (50) and (52) are total reflection mirrors (
concave mirror), (51), and (53) are the exit total reflection mirrors (
concave mirror), (511), (531) are the laser beam extraction part, (67) is the discharge space, (8) is the laser beam, A, A2 are the longer dimensions in the cross section of the discharge space, B,
B2 is the shorter dimension in the cross section of the discharge space. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] In a gas laser device in which laser gas is excited by discharge, a discharge space in which laser gas is excited by discharge is formed in the shape of a flat slab with different vertical and horizontal dimensions in a cross section perpendicular to the laser optical axis direction, Laser resonator mirrors are arranged at both ends of this discharge space, and an unstable negative branch resonator is constructed for the one dimension with the longer dimension in the cross section of the discharge space. A gas laser device characterized in that a laser beam is extracted from one end.