JP2700822B2 - Gas laser device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a gas laser device in which a discharge space for exciting a laser gas has a flat slab shape.
In particular, it relates to improvement of the stability of the laser resonator.

[Prior Art] FIG. 5 is a schematic sectional view of a conventional gas laser device disclosed in JP-A-63-192285, and FIG. 6 is a schematic plan view showing a configuration of a resonator of the 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, and (73) and (74) are electrode surfaces polished to an optical reflection surface. (75) is the discharge gap,
(76) and (77) are spacers that insulate the electrodes (71) and (77), and (78) is a U-shaped base, and the electrodes (71) and (72)
The base (78) is an assembly consisting of a spacer (76) and (77)
Mounted on top, the U-shaped base (78) is closed by a lid (79) and a ceramic insulator (80) is disposed between the lid (79) and the electrode (71). In addition, as shown in FIG. 6, the laser resonator is constituted by 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 (11) passes through the cable (22) via the power matching unit (21) and the electrodes (71), ( 72) applied during The discharge gap (75) between the electrodes (71) and (72) is filled with laser gas.
The laser gas is discharge-excited by the high frequency applied between the electrodes (71) and (72). As described above, since the excited laser gas is present in the laser resonator constituted by the reflecting mirrors (52) and (53), laser oscillation is performed. At this time, the distance between the electrodes (71) and (72) was set to 2 mm, and the electrodes (7
The distance between the edge of 1) and (72) and the edge of the convex mirror (53) is 2mm
As a result, a square beam having a side of about 2 mm can be obtained. 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. In addition, it is difficult to adjust the inclination of the reflecting mirror, and it is difficult to adjust the inclination due to deformation due to temperature, so that it is difficult to secure the stability of the resonator.

The present invention has been made in order to solve such a problem, and an object of the present invention is to provide a gas laser device which is insensitive to the inclination of a reflecting mirror, can easily adjust the inclination of the reflecting mirror, and has good stability.

[Means for Solving the Problems] In a gas laser device according to the present invention, a discharge space is formed in a flat slab shape having different vertical and horizontal dimensions of a cross section perpendicular to a laser optical axis direction. A laser resonator mirror is disposed at each end, and at least one of the mirrors is an asymmetric concave mirror having a reflecting surface having a first curvature in one direction and a reflecting surface having a second curvature in a direction perpendicular to the mirror.
For the one dimension having a longer dimension in the cross section of the discharge space, a reflecting surface having a first curvature is applied to form an unstable resonator having a negative branch, and for the one dimension having a shorter dimension in the cross section of the discharge space, the second dimension is used. An optical waveguide resonator is formed by acting a reflecting surface having the following curvature, and a laser beam is extracted from one end having a longer dimension in the cross section of the discharge space.

[Operation] In the present invention, in the one dimension having a longer dimension in the cross section of the discharge space, an unstable type resonator having a negative branch is formed by acting a reflecting surface having a first curvature, and the dimension of the dimension in the cross section of the discharge space is reduced. For the shorter one dimension, the optical waveguide resonator is formed by applying the reflecting surface of the second curvature, so that the resonator has a focal point, but the light concentrates not at one point but at one line, The ratio of light concentration is greatly reduced as compared with the case where a normal cylindrical axisymmetric resonator is used as a negative branch,
The feature of being free from problems due to concentration of light such as optical damage and being insensitive to the inclination of the reflecting mirror of the unstable resonator of the negative branch is maximized. Further, a high-quality beam mode can be obtained also on the optical waveguide resonator side.

Embodiment FIG. 1 (a) is a perspective view showing a resonator according to an embodiment of the present invention, and FIG. 1 (b) is an outline of the resonator shown in FIG. 1 (a) on the unstable type resonator side. FIG. 1 (c)
FIG. 3 is a side view showing an outline of the optical waveguide resonator side of the resonator shown in FIG.

1 (a), 1 (b) and 1 (c), reference numeral 50 denotes a total reflection mirror. The total reflection mirror (50) is an asymmetric concave mirror having a reflection surface having a first curvature optimum for an unstable resonator and a reflection surface having a second curvature optimum for an optical waveguide resonator. In this embodiment, a toroidal mirror is used. It is a mirror. (51) is an exit total reflection mirror. This exit total reflection mirror (51)
This is also an asymmetric concave mirror having a reflection surface of the first curvature and a reflection surface of the second curvature similar to the mirror (50). In this embodiment, it is a cylindrical mirror. The first curvature and the second curvature are curvatures in directions orthogonal to each other. In addition, a concave mirror having a reflection surface having the first curvature and the second curvature as described above will be referred to as an asymmetric concave mirror in this specification.

(67) is a discharge space, and the electrodes (71),
This is a space corresponding to the discharge gap (75) surrounded by the surface of (72). The discharge space (67) is formed in a flat slab shape having different vertical and horizontal dimensions (A and B) in a cross section perpendicular to the laser optical axis direction, and the dimension B is the dimension of the optical waveguide with respect to the laser wavelength. There is. The illustration of the discharge space (67) is simplified and only the outline is shown. This discharge space (67)
On the other hand, the mirrors (50) and (51) face the reflecting surfaces of the first curvature so as to expand the light one-dimensionally in the direction A when viewed in the plan view shown in FIG. And place the first
As shown in FIG. 1B, when viewed from a direction orthogonal to FIG. 1A, the reflecting surfaces of the second curvature are arranged to face each other.

In the resonator configured as described above, one dimension having a longer dimension in the cross section of the discharge space, that is, A
As for the direction, it is an indefinite type resonator having a negative branch in which the reflecting surfaces of the first curvatures of the mirrors (50) and (51) are combined. In the B direction, the optical waveguide resonator is formed by the reflecting surface having the second curvature.

By the way, when a spherical concave mirror having a curvature suitable for an unstable resonator is used for the mirrors (50) and (51), the curvature on the optical waveguide resonator side is not suitable for the optical waveguide resonator. However, there is a possibility that a high-order mode of the optical waveguide is excited and a strong side lobe is generated, and it is difficult to form a so-called lowest-order single mode. On the other hand, this resonator changes the curvature in the B direction, and In order to achieve a curvature that efficiently excites the lowest single mode among the optical waveguide modes in the shorter dimension, laser oscillation should be performed in a circular high-quality mode in which higher-order optical waveguide modes are not easily excited. Can be.

Further, in the unstable resonator of the negative branch, the laser optical axis is shifted from the central axis of the discharge space in order to extract the laser beam (8) only from the one end (671) having the longer dimension of the cross section of the discharge space. . That is, mirrors (50) and (51)
At least one of them is arranged to be inclined with respect to the central axis of the discharge space. The mirror (51) is provided with a beam extraction unit (511). This laser beam extraction part (5
In this embodiment, a part of the mirror (51) is cut out to form a linear aperture.

In the above embodiment, the mirror (50) is a toroidal mirror,
The mirror (51) uses a cylindrical mirror,
Both may use a toroidal mirror.Also, even when only one is a toroidal mirror or a cylindrical mirror and the other is a spherical concave mirror, both optical mirrors have a lower optical waveguide resonator side than those using a spherical concave mirror. Mode can be improved.

In the drawing, P _L0 indicates the laser beam intensity distribution extracted from the mirror (51), R _T1 and R _T2 are the first and second radii of curvature of the mirror (50), and R _P1 and R _P2 are the mirrors. (51) is the first and second radii of curvature. A and b show the effective length of the mirror.

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

FIG. 2 is an explanatory view for explaining the misalignment sensitivity of the positive branch unstable type resonator, and FIG. 3 is an explanatory view for explaining the misalignment sensitivity of the negative branch unstable type resonator. 2 and 3, (1) and (2) are mirrors, and FIG. 2 shows the mirror (52) and the mirror (53) of FIG. 5, and FIG. 3 shows the mirror (1) of FIG. 50) and a mirror (51). e is the center of curvature of the mirror (2), f is the center of curvature of the original mirror (1), g is the center of curvature of the mirror (1), θ is the deviation angle of the mirror (1), and φ is the deviation angle of the optical axis. It is. The optical axis is a line connecting the centers of curvature, that is, a line perpendicular to both mirror surfaces. When the mirror (1) is displaced, that is, when the mirror (1) is inclined.
Changes from ▼ to ▲ ▼. d shows an off-axis.

The sensitivity of an unstable resonator to misalignment is
Journal (IEEE JOURNAL OF QUANTUM ELECTRONICS, DECEMB
As described in ER 1969, p.579), the following (1)
To (3).

Here, m is a magnification and can be considered as a curvature ratio of a mirror in a confocal resonator.

R ₁ and R ₂ are the radii of curvature of the mirrors (1) and (2), and the expression (5) is negative because the convex curvature and the concave curvature are distinguished by ± signs.

This m is a ratio of the effective length of the mirror (a and b shown in FIGS. 1 and 6) limited geometrically (optically) by the edge and the aperture.

Note that the effective length of the mirror is a portion of the mirror which is limited by edges and apertures and is actually exposed to light. (In the case of axial symmetry, the effective diameter is obtained.) That is, the expansion ratio is the ratio of the size of the beam before expansion to the size of the beam after expansion in the resonator.

In the example of the prototype CO ₂ laser according to FIG. 1, the discharge space length is 400 mm, the cross-sectional dimension is 2 × 20 mm, and the appropriate output coupling ratio
Magnification factor m is set so that 10% and symmetry of output beam are compatible.
Designed around 1.1. In this case _{M +} 22, _{M -}
It becomes 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 tilt of the mirror is much smaller in the negative branch. Therefore, the stability of the resonator is improved.

In the present invention, the enlargement factor m is defined only on the unstable side (cross section dimension A), and has no relation on the optical waveguide side (cross section dimension B).

By the way, the unstable type of the negative branch resonator has a focal point in the resonator, and if it is used for a normal cylindrical axis symmetric resonator, a point where light is concentrated in the resonator occurs and there is a problem such as optical damage. , And are rarely used in general. In contrast,
In the present invention, the one-dimensional one having the shorter dimension in the cross section of the discharge space is an ordinary resonator which is not cylindrically symmetric with respect to the cylindrical axis and constitutes an optical waveguide resonator, to which an unstable resonator having a negative branch is applied. For this reason, although the focal point exists in the resonator, the light is concentrated not at one point but at one line (FIGS. 1 (b) and (c)).
L), the ratio of light concentration is greatly reduced as compared with the case where the present invention is applied to an ordinary cylindrically symmetric resonator, and there is no problem due to light concentration such as optical damage. The feature that is insensitive to the inclination of the reflector can be maximized.

In the example of a discharge space length of 400 mm and a cross-sectional dimension of 2 × 20 mm, the fourth
As shown in the figure, the output of the positive branch resonator is about 25 W and the mode is distorted due to the distortion of the mirror, and the output is saturated. However, the negative branch resonator obtained 80 W or more.
Even with the negative branch, when a concave spherical mirror is used as the mirror, an output of 80 W or more was obtained, but a strong side lobe occurred in the optical waveguide direction (one-dimensional direction with smaller dimensions), and a circular mode could not be obtained. On the other hand, when the mirror was a toroidal mirror, a nearly circular favorable mode was obtained.

Further, since the radius of curvature of the mirror is smaller in the negative branch, the curvature is large and the curvature error with respect to the shape error is small. For the same shape error (accuracy), the error of the radius of curvature (accuracy) increases substantially by the square of the target radius of curvature, and the negative branch is more advantageous in terms of the accuracy of mirror fabrication. For example, in the example of the above CO ₂ laser, a mirror of about φ30 mm is used with a shape error of ± 0.5 μm, but in the case of a negative branch, the curvature of the unstable type is about 400 and an error of ± 0.5 mm, Curvature is about 900 for a positive branch
At 0, the error was ± 200 mm, and the deviation from the confocal point was large in the positive branch, the enlargement ratio also deviated from the target, and the light control was not as designed.

In the above embodiment, a laser gas is excited by generating a discharge by a high-frequency electric field. However, as disclosed in JP-A-63-186483, a conductor wall constituting a part of a microwave circuit is disclosed. A space having different vertical and horizontal dimensions of a cross section perpendicular to the laser optical axis direction is formed between the substrate and the dielectric provided opposite to the conductor wall. The same effect can be obtained even if the present invention is applied to a gas laser apparatus that excites a laser gas by generating a plasma by causing a discharge breakdown by a wave electric field.

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

[Effects of the Invention] As described above, in the present invention, in the one dimension having a longer dimension in the cross section of the discharge space, the unstable surface of the negative branch is acted on by the reflecting surface having the first curvature optimal for the unstable type resonator. The optical waveguide resonator is formed by applying a reflection surface having a second curvature that is optimal for the optical waveguide resonator in the one dimension having the shorter dimension in the discharge space cross section. Although there is a focus on light, light concentrates not on one point but on a line, and there is no problem due to light concentration such as optical damage, and it is insensitive to the inclination of the reflector of the unstable resonator of the negative branch. Beam mode on the optical waveguide resonator side.
There is an effect that the stability of the resonator is improved overall.

[Brief description of the drawings]

FIG. 1 (a) is a perspective view showing a resonator according to one embodiment of the present invention, and FIG. 1 (b) is a plan view showing an outline of an unstable resonator side of the resonator shown in FIG. 1 (a). FIG. 1 (c) is a side view showing an outline of the optical waveguide resonator side of the resonator shown in FIG. 1 (a), and FIG. 2 is an explanatory view for explaining the misalignment sensitivity of the positive branch unstable type resonator. FIG. 3 is an explanatory view for explaining the misalignment sensitivity of the negative branch unstable resonator. FIG. 4 is a graph showing the characteristics of the CO ₂ laser oscillator using the positive branch and the negative branch unstable resonator.
FIG. 1 is a schematic sectional view of a conventional gas laser device, and FIG.
FIG. 2 is a schematic plan view illustrating a configuration of a resonator of the gas laser device illustrated in FIG. In the figure, (50) is a total reflection mirror (asymmetric concave mirror),
(51) is an exit total reflection mirror (asymmetric concave mirror), (511)
Is a laser beam extraction part, (67) is a discharge space, (8)
Is the laser beam, A is the longer dimension in the cross section of the discharge space, and B is the shorter dimension in the cross section of the discharge space. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] In a gas laser apparatus in which a laser gas is excited by a discharge, a discharge space in which the laser gas is excited by the discharge is formed by a flat slab having different vertical and horizontal dimensions in a cross section perpendicular to a laser optical axis direction. And a laser resonator mirror is disposed at each end of the discharge space, and at least one of the mirrors has a first curvature reflection surface in one direction and a second curvature reflection surface in a direction orthogonal thereto. By using an asymmetric concave mirror having the following structure, the reflecting surface having the first curvature is applied to one dimension having a longer dimension in the cross section of the discharge space to form an unstable resonator having a negative branch. For the shorter dimension of the above, a reflecting surface of the second curvature is applied to form an optical waveguide resonator, and a laser beam is taken from one end of the longer dimension in the cross section of the discharge space. Gas laser apparatus being characterized in that the Suyo.