JPH0371683A - Gas laser device - Google Patents

Abstract

PURPOSE:To improve a resonator in stability as a whole by a method wherein reflecting surfaces most adapted to an unstable type resonator are made to work on the broad side of a discharge space in cross section to constitute an unstable resonator of negative branch, and reflecting surfaces most adapted to an optical waveguide resonator are made to work on the narrow side of the discharge space in cross section to constitute an optical waveguide resonator. CONSTITUTION:The reflecting surfaces possessed of a first curvature of mirrors 50 and 51 are combined to constitute an unstable type resonator of negative branch in a discharge space in the direction of one-dimensional A or a longer side of the discharge space in cross section, and the reflecting surfaces of a second curvature constitute an optical waveguide resonator in the direction of one-dimensional B or a shorter side of the discharge space in cross section. Therefore, there is a focal point in the resonator, but light rays 8 do not concentrate on a single point but on a line, so that the light rays 8 are decreased in concentration rate and problems such as optical damage and the like caused by the concentration of light can be prevented, and moreover a feature that an unstable type resonator of negative branch is insensitive to the inclination of reflecting mirrors is displayed to the utmost. By this setup, a gas laser device of excellent stability can be obtained.

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

The spacer (78) insulates the electrodes (71) and (72), and the spacer (78) is a U-shaped base.
, (77) is mounted on the base (78), the U-shaped base (78) is closed by M (79), the ceramic insulator (80) is connected to the lid (79〉) and the electrode (71). As shown in FIG. 6, the laser resonator is composed of a concave spherical total reflection mirror (52) and a convex spherical total reflection mirror (53).

In the conventional gas laser device configured as described above, the high frequency generated by the high frequency generator (tl) passes through the power matching device (21), the cable (22), and the electrodes (71), ( 72) is applied between. Electrode (7
A discharge gap (75) between electrodes (71) and (72) is filled with laser gas, and the laser gas is excited to discharge by the high frequency applied between electrodes (71) and (72). In this way, since the excited laser gas exists in the laser resonator composed of the reflecting mirrors (52) and (53),
Laser oscillation is performed. At this time, the electrode (71), (
72) A rectangular beam with a side of approximately 2 mm is obtained by setting the distance between the electrodes (71) and (72) and the edge of the convex mirror (53) to 2 mm.

This beam becomes a Gaussian circular beam 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 slug in which the vertical and horizontal dimensions of the cross section perpendicular to the laser optical axis direction are different. Laser resonator mirrors are disposed at both ends, and at least one of the mirrors is an asymmetric concave mirror having a reflecting surface with a first curvature in one direction and a reflecting surface with a second curvature in a direction perpendicular to this, For one dimension with the longer dimension in the cross section of the discharge space, a reflecting surface of the first curvature acts to constitute an unstable negative branch resonator, and in the one dimension with the shorter dimension in the cross section of the discharge space.
Regarding the dimension, an optical waveguide resonator is constructed by using a reflecting surface having a second curvature, and a laser beam is extracted from one end of the longer dimension in the cross section of the discharge space.

[Function] In the present invention, for the longer one dimension in the discharge space cross section, a reflecting surface of the first curvature is used to configure a negative branch unstable resonator, and the dimension in the discharge space cross section is changed. Regarding the shorter one dimension, the optical waveguide resonator is constructed by using a reflecting surface with the second curvature, so although there is a focal point within the resonator, the light is concentrated in a line rather than at a single 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 do not occur, and the unstable negative branch resonator reflects The feature of being insensitive to the tilt of the mirror is maximized.

Furthermore, a high quality beam mode can also be obtained on the optical waveguide resonator side.

[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(C) is a side view schematically showing the optical waveguide resonator side of the resonator shown in FIG. 1(a).

In Figure 1 (a), (b) and (e), (50
) is a total reflection mirror. This total reflection mirror (50) is an asymmetric concave mirror having a reflecting surface with a first curvature that is optimal for an unstable resonator and a reflecting surface that has a second curvature that is optimal for an optical waveguide resonator, and in this embodiment is a toroidal mirror. It's a mirror. (5
1> is an exit total reflection mirror. This exit reflection mirror (
51) is also an asymmetrical concave mirror having a reflecting surface with a first curvature and a reflecting surface with a second curvature similar to the mirror (50>), and is a cylindrical mirror in this embodiment. and the second curvature are curvatures in directions perpendicular to each other. In addition, a concave mirror having reflective surfaces having the first curvature and the second curvature as described above will be referred to as an asymmetric concave mirror in this specification.

(BT) is the discharge space and is the electrode (71) in FIG.

This is a space corresponding to the discharge gap (75) surrounded by the surface of (72). 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. In addition, the discharge space (67
) is simplified and only the outline is shown. A mirror (50) for this discharge space (B7).

(51) is arranged so that the reflective surfaces of the first curvature face each other so as to expand the light one-dimensionally in the A direction when viewed from the plan view shown in FIG. 1(a). As shown in FIG. 1(b), when viewed from a direction perpendicular to FIG. 1(a), the reflective surfaces of the second curvature are arranged to face each other.

The resonator configured as described above is constructed by combining the reflecting surfaces of the mirrors (50) and (51) with the first curvature for the longer one dimension in the cross section of the discharge space, that is, for the direction A shown in the figure. In the shorter one dimension in the cross section of the discharge space, that is, in the direction B shown in the figure, it becomes an optical waveguide resonator with a reflective surface of the second curvature. There is.

By the way, when the mirrors (50) and (51) are spherical concave mirrors with a curvature suitable for an unstable resonator, the optical waveguide resonator side does not have a curvature suitable for an optical waveguide resonator. , the higher-order mode of the optical waveguide may be excited and a strong side lobe may occur, and it is difficult to become the so-called lowest-order single mode, whereas this resonator
In the B direction, the curvature is changed to make the curvature in which the lowest-order single mode among the optical waveguide modes is efficiently excited in one dimension of the shorter dimension in the cross section of the discharge space, so that the higher-order optical waveguide modes are excited. Laser oscillation can be performed in a high-quality circular mode that is difficult to detect.

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 (871) with a longer cross-sectional dimension of the discharge space. . 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 beam extraction section (511).

In this embodiment, the laser beam extracting portion (511) is formed by cutting out a portion of the mirror (51) to form a linear noa verture.

In the above embodiment, a toroidal mirror is used for the mirror (50), and a cylindrical mirror is used for the mirror (51), but both may be toroidal mirrors, or only one is a toroidal mirror or a cylindrical mirror, and the other is a spherical mirror. Even when a concave mirror is used, the mode on the optical waveguide resonator side can be made better than when a concave mirror with both spherical surfaces is used.

In the figure, PLO indicates the laser beam intensity distribution taken out from the mirror (51), and RTl and R1
□ are the first and second radii of curvature of the mirror (50), R and R
P2 is the first and second 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 5 are shown.
3), and FIG. 3 shows the mirror (50) and mirror (51) of FIG. e is the center of curvature of mirror (2>), f is the center of curvature of the original mirror (1), g is the center of curvature of the displaced mirror (1), θ is the deviation angle of mirror (1), and φ is the deviation angle of the optical axis. Note that the optical axis is a line connecting the centers of curvature, that is, a line perpendicular to both mirror surfaces.
1) is shifted, that is, the mirror (1) is tilted, ef
changes from to i. d indicates a shifted optical axis.

The sensitivity of unstable resonators to misalignment is described in the IEEE JOURNAL OF QUANTU
MELECTRONIC8, DECEMBER1913
9, P, 579), as described below (1)
~(3) Expression.

M-- θ...(L) Here, m is the magnification and confocal (Confocal I)
) In a resonator, it can be considered as the curvature ratio of the mirror.

R 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 6) limited by edges and apertures.

m=- (6) 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.) In other words, the magnification rate is
It is the ratio of the size of the beam before being expanded and the size of the beam after being expanded within the resonator.

In the example of the COz laser prototyped according to Figure 1, the discharge space length is 400 mm, the cross-sectional dimensions are 2 x 20 mm, and the magnification factor m is set to about 1.1 in order to achieve both an appropriate output coupling rate of 10% and symmetry of the emitted beam. Designed.

In this case, M222 and M21.

+ 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 stability of the resonator is improved.

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

By the way, an unstable negative branch resonator has a focal point within the resonator, and if it is used in a normal cylindrical axis-symmetrical resonator, there will be a single point where light is concentrated within the resonator, causing problems such as optical damage. , is rarely used in general. In contrast, the present invention applies an unstable resonator with a negative branch in a conventional resonator that is not symmetrical about the cylindrical axis and constitutes an optical 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 (L in Figure 1 (b) and (C)), and when applied to a normal cylindrical axis-symmetrical resonator. The rate of light concentration is greatly reduced compared to the previous model, and there are no problems due to light concentration such as optical damage, and the feature of being insensitive to the tilt of the negative branch unstable reflector can be maximized. becomes.

In an example of a discharge space length of 400 mm and cross-sectional dimensions of 2 x 20 mm,
As shown in Figure 4, the output of the positive branch resonator is 25W.
Although the mode was distorted due to the distortion of the mirror and the output was saturated, more than 80 W was obtained with the negative branch resonator. Even in the negative branch, when a concave spherical mirror was used, an output of 80 W or more was obtained, but a strong side lobe occurred in the optical waveguide direction (the one-dimensional direction with the shortest dimension), and a circular mode could not be obtained. On the other hand, by using a toroidal mirror as the mirror, a good round-shaped mode 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 CO2 laser mentioned above, a mirror with a diameter of about 3hm is used with a shape error of ±0.5μ plays, but in the case of a negative branch, the curvature of the unstable type is about 4
00, the error is ±0.5 degrees, but in the case of the positive branch, the curvature is about 9000, resulting in an error of ±200*+m, and in the positive branch, the deviation from the confocal point is large, the magnification rate also deviates from the target, and the light Control did not work as designed.

In the above embodiment, a discharge is generated by a high frequency electric field to excite the laser gas.
As disclosed in Publication No. 3, a cross section perpendicular to the laser optical axis direction is formed between a conductive wall that constitutes a part of a microwave circuit and a dielectric material provided opposite to this conductive wall. The same effect can be obtained by implementing 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, the present invention achieves unstable resonance of the negative branch by applying a reflection surface of the optimum first curvature to the unstable resonator for the longer one dimension in the cross section of the discharge space. As for the shorter one dimension in the cross section of the discharge space, the optical waveguide resonator is constructed by applying a reflecting surface of the second curvature that is most suitable for the optical waveguide resonator. Although there is a focal point, the light is concentrated on a line rather than on one point, so there are no optical damage or other problems caused by the concentration of light, and the main feature is that it is insensitive to the tilt of the reflector of the unstable negative branch resonator. Furthermore, a high-quality beam mode can be obtained on the optical waveguide resonator side, and the stability of the resonator is improved overall.

[Brief explanation of drawings]

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 optical waveguide 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 type resonator. , Fig. 3 is an explanatory diagram explaining the misalignment sensitivity of a negative branch unstable type resonator, Fig. 4 is a graph showing the characteristics of a CO2 laser oscillator using a positive branch and negative branch unstable type resonator, and Fig. 5 is a graph showing the characteristics of a CO2 laser oscillator using a conventional negative branch unstable type resonator. A schematic sectional view of the gas laser device, and FIG. 6 is a schematic plan view showing the configuration of a resonator of the gas laser device shown in FIG. In the figure, (50) is a total reflection mirror (asymmetric concave mirror)
, (51) is the exit total reflection mirror (asymmetric concave mirror), (
511) is the laser beam extraction part, <B7> is the discharge space, (8) is the laser beam, A is the longer dimension in the discharge space cross section, and B is the shorter dimension in the discharge space cross section. In addition, in the figures, the same reference numerals indicate the same or corresponding parts. Figure 2

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 at least one of the mirrors is asymmetrical with a reflecting surface of a first curvature in one direction and a reflecting surface of a second curvature in a direction perpendicular to this. Using a concave mirror, the reflecting surface of the first curvature acts on the one dimension with the longer dimension in the cross section of the discharge space to form an unstable negative branch resonator, and the one dimension with the shorter dimension in the cross section of the discharge space The gas laser is characterized in that an optical waveguide resonator is formed by using the reflecting surface of the second curvature, and further, the laser beam is extracted from one end of the longer dimension in the cross section of the discharge space. Device.