JPH07105541B2 - Gas laser device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas laser device that performs laser excitation by using microwave discharge.

[Prior Art] FIG. 6 is a perspective view showing a conventional gas laser device (Japanese Patent Application No. 62-225224) filed by the applicant of the present application on September 10, 1987, and FIG. It is a VV line sectional view.

In the figure, 2 is a laser head part having a ridge waveguide type microwave cavity structure, which is a kind of microwave circuit for generating plasma in laser gas by microwave discharge and performing laser excitation. A magnetron as a microwave oscillator, 4 is a waveguide for guiding the microwave output from the magnetron 3 to the laser head portion 2, and 6 is a microwave coupling window for coupling the microwave from the waveguide 4 to the laser head portion 2. , 7 are reflectors for laser oscillation attached to the laser head unit 2. Further, 20 is a cavity wall following the microwave coupling window 6 in the laser head portion 2, and 21 and 22 are provided in the central portion of the cavity wall 20, each constituting a part of a microwave circuit. Ridge, 23
Is a conductor wall formed on one ridge 21. In this conventional example, the bottom wall surface of the groove 28 provided on the upper surface of the ridge 21 is used. The reference numeral 24 designates a dielectric made of, for example, alumina, which is provided so as to face the conductor wall 23 and acts as a microwave entrance window.
By covering the groove 28 on the upper surface, it is a discharge space which is formed between the conductor wall 23 and the dielectric 24 and in which a laser gas such as a carbon dioxide laser gas is sealed.

Next, the operation will be described. The microwave generated by the magnetron 3 propagates through the waveguide 4 and the microwave coupling window 6
By matching the impedance with, the laser head 2 is efficiently coupled. The laser head portion 2 has a ridge cavity shape as shown in the drawing, and microwaves are concentrated near the ridges 21 and 22 to generate a very strong microwave electromagnetic field. Due to this strong microwave electromagnetic field, the laser gas enclosed in the discharge space 25 is destroyed by discharge, plasma is generated, and the laser medium is excited. Here, cooling water is caused to flow in the cooling water passage 27 to cool the discharge plasma, and the laser oscillation condition is obtained by appropriately selecting the discharge condition such as the pressure of the laser gas, and the reflecting mirror 7 shown in FIG. Laser oscillation light can be obtained by forming a laser resonator with a reflecting mirror that does not appear in the drawing and that faces the drawing.

At this time, the ridge 21 forming part of the microwave circuit
Microwave discharge is performed in the discharge space formed between the conductor wall 23 formed in and the dielectric wall 24, which is arranged so as to face the conductor wall 23 and serves as a microwave entrance window.
Since the microwave is incident only from one side of the plasma, the phenomenon that the microwave mode of the coaxial mode with the plasma as the inner conductor becomes dominant does not occur, and the desired microwave is not generated. Discharge in the wave mode can be performed. When the microwave circuit forms a microwave mode having an electric field component perpendicular to the boundary between the dielectric 24 and the plasma, like the ridge cavity of the laser head portion 2 shown in the figure, the dielectric 24 and the conductor are Since it faces the wall 23, it also has an electric field component perpendicular to the conductor wall 23, and an electric field penetrating the plasma can be formed. Therefore, even if a plasma having conductivity is generated, the conductive material wall 23 having a conductivity several orders of magnitude higher than that of the plasma is arranged so as to face the dielectric 24 as the microwave incident window, so that the incident microwave The termination current flows through the conductor wall 23, and the electric field in the vicinity of the conductor wall 23 is forced to be perpendicular to the surface of the conductor wall 23, so that the electric field penetrating the generated plasma is maintained. Therefore, the microwave penetrates into the plasma and a current flows through the plasma, and a spatially uniform discharge plasma is generated due to the continuity of the current. In this way, since a spatially uniform discharge can be obtained, it becomes easy to put the entire discharge in a state suitable for laser excitation. Further, a laser head portion 2 which is a microwave circuit and a waveguide 4 which is a microwave transmission path are arranged in parallel in a direction along the laser optical axis, and a long micro-wave provided in the longitudinal direction of the laser head portion 2. Microwaves can be supplied through the wave coupling window 6 to cause the laser to uniformly generate a strong microwave electromagnetic field over the ridges 21 and 22 of the head portion 2. Therefore, without increasing the size of the entire device, it is long in the laser optical axis direction,
A uniform discharge can be obtained, and the optimum state for the entire discharge and laser excitation can be obtained.

[Problems to be Solved by the Invention] In the conventional gas laser device as described above, the laser head portion 2 which is a microwave circuit and the waveguide 4 which is a microwave transmission path are arranged in parallel in the direction along the laser optical axis. Microwaves are supplied through the long microwave coupling window 6 arranged in the longitudinal direction of the laser head portion 2 to uniformly generate a strong microwave electromagnetic field over the ridges 21 and 22 of the laser head portion 2. At the same time, it is long in the laser optical axis direction and enables a uniform discharge, so that more stable and uniform plasma can be generated in the discharge space, but since the microwave itself changes sinusoidally, The distribution of the electric field strength in the width direction of 24 is a sine wave distribution in which the electric field in the central portion of the dielectric 24 becomes strong, and the discharge in the discharge space 25 is not started unless the electric field strength becomes a predetermined value or more. Therefore, there is a problem that discharge is generated only in the central portion in the width direction of the discharge space 25, the discharge distribution in the width direction becomes non-uniform, and plasma may not be generated uniformly in the discharge space 25.

In order to solve such a problem, it is considered to increase microwave energy. For example, in the case of exciting a CO ₂ laser gas, the efficiency is lowered if the gas temperature rises excessively locally, and therefore the local discharge is generated. The power density has an upper limit value, and the microwave energy could only be increased until the discharge power density in the central portion of the discharge space 25 reached the upper limit value.

The present invention has been made to solve the above-mentioned problems, and it causes a uniform discharge in the width direction in the discharge space to make the generated microwave discharge plasma stable and spatially uniform. An object of the present invention is to obtain a gas laser device capable of high efficiency and high power laser operation.

[Means for Solving the Problems] The gas laser device according to the present invention is configured such that at least the width of the tip of the ridge facing the groove serving as the discharge space via the dielectric is narrower than the width of the groove. . Furthermore, the width of at least the tip of the ridge facing the groove serving as the discharge space via the dielectric is made narrower than that of the groove, and the dielectric contact portion is divided into a plurality of portions having a concave portion at least in the center. There is.

[Operation] In the gas laser device according to the present invention, since the width of at least the tip of the ridge facing the groove serving as the discharge space via the dielectric is made narrower than the width of the groove, it changes sinusoidally. The electric field strength in the width direction of the microwave dielectric is due to the edge effect of focusing the microwave energy on both side corners of the dielectric because the width of the tip of the ridge is narrower than the width of the groove. Both sides in the width direction become stronger, and the central part becomes weaker accordingly. This also applies to the distribution of electric field strength in the discharge space. Therefore, the microwave energy can be increased by the weakened electric field in the central part of the dielectric, and the increase in this energy causes the electric field strength on both sides in the width direction of the dielectric to be equal to or higher than a predetermined value at which discharge can be started. , The dielectric, that is, the dischargeable electric field intensity region in the discharge space has a uniform electric field intensity distribution that spreads from the center to both sides.

Further, the tip of the ridge, which is opposed to the groove serving as the discharge space via the dielectric, has a width narrower than the width of the groove, and is formed by dividing the tip into a plurality of parts having a recessed portion at least in the center. Therefore, the electric field strength in the width direction of the microwave in the discharge space is due to the width of the tip of the ridge being narrower than the width of the discharge space, and the fact that the tip is divided with a recessed portion at least in the center. Microwave energy is focused on both side corners of the tip and the corners of the tip that are divided. Due to the edge effect, both sides in the width direction of the dielectric and the portions corresponding to the corners of the tip are divided. Becomes stronger, and at least the central recess becomes weaker. Therefore, the microwave energy can be increased by the amount of the weakened electric field in the central recessed portion, and the increase in this energy causes the electric field strength in the width direction of the dielectric material other than the predetermined value at which discharge can start. The electric field region in the dielectric, that is, the discharge space, in which discharge is possible, has a uniform distribution of the electric field strength that extends from the center to both sides.

[Embodiment] FIG. 1 is a sectional view showing a gas laser device according to an embodiment of the present invention. In the figure, the same configurations as those of the conventional example are denoted by the same reference numerals as those of the conventional example, and the description of the duplicated configurations is omitted. 20 is a microwave coupling window 6 in the laser head section 2
Cavity wall, 21 and 22 are provided in the central portion of the cavity wall 20, each of which constitutes a part of the microwave circuit, and 23 is a groove 28 provided on the upper surface of one ridge 21. , 24 is a dielectric provided opposite to the conductor wall 23, and 25 is the dielectric 24 covering the groove 28 on the upper surface of the ridge 21 so that the conductor wall 23 and the dielectric 24 are provided. It is the discharge space formed between and. Reference numeral 221 denotes the tip of the other ridge 22 facing the groove 28 via the dielectric 24, the width of which is narrower than the width of the groove 28.

In the gas laser device configured as described above, the ridge facing the groove 28 that becomes the discharge space 25 via the dielectric 24.
Since the width of the tip portion 221 of 22 is formed to be narrower than the width of the groove 28, the electric field strength in the width direction of the dielectric 24 of the microwave from the magnetron 3 which changes sinusoidally is the ridge 22. Since the width of the tip portion 221 of each of the two is narrower than the width of the groove 28, the microwave energy is focused on the both side corners of the tip portion 221 by the edge effect. become weak. This also applies to the distribution of electric field strength in the discharge space 25. Therefore, the microwave energy can be increased by the weakened electric field in the central portion of the dielectric 24. Therefore, by increasing the microwave energy of the magnetron 3, the electric field strength of both sides in the width direction of the dielectric 24 becomes equal to or higher than a predetermined value at which discharge can be started, and the electric field strength region in the dielectric 24, that is, the discharge space 25 where discharge is possible. Spreads from the center to both sides, and as shown in the graph of FIG. 3, the electric field strength distribution curve c is gentler than the electric field strength distribution curve c of the conventional example, and the electric field strength distribution is uniform. Therefore, the discharge distribution due to the microwave energy becomes uniform over the entire width in the discharge space 25, and stable and uniform plasma is generated in the discharge space, so that the laser output can be obtained with high efficiency and large output.

FIG. 2 is a sectional view of a gas laser device according to another embodiment of the present invention.

In this embodiment, the structure of the other ridge 22 facing the groove 28 via the dielectric 24 is different from that of the above embodiment. That is, the tip end portion 222 of the ridge 22 of this embodiment has a width narrower than the width of the groove 28, and has a groove 223 which is a recessed portion at the center of the cross section and is formed by being divided into left and right. Therefore, the electric field strength in the width direction of the microwave dielectric is such that the width of the tip portion 222 is the discharge space 2
Microwave energy is narrower than the width of 5 and the tip portion 222 has a groove 223 that is a recessed portion at least in the center and is divided into left and right sides. Due to the edge effect focused on the portion of the dielectric portion, both side portions in the width direction of the dielectric 24 and the portions corresponding to the corner portions of the divided tip end portion 222 become strong and the recessed portion corresponding to the central groove 223 becomes weak. Become. Therefore, the microwave energy can be increased by the amount of the weakened electric field in the central recess of the dielectric 24. for that reason,
By increasing the microwave energy of the magnetron 3, the electric field strength other than the central portion in the width direction of the dielectric 24 becomes equal to or higher than a predetermined value at which discharge can be started, and the dielectric 24, that is, the dischargeable electric field region in the discharge space 25 is in the center. As shown in the graph of FIG. 3, the curve further spreads to both sides, and the curve is gentler than the electric field strength distribution curve c of the conventional example, and the electric field strength distribution curve b is dented in the center, resulting in a uniform electric field strength distribution. Therefore, the discharge distribution by the microwave energy becomes uniform over the entire width of the discharge space 25, and stable and uniform plasma is generated in the discharge space.

The tip portion 222 of the ridge 22 of this embodiment has a groove 223 in the center of the cross section and is divided into two parts on the left and right sides. Of course, it may be divided into the above.

Further, in the above-described embodiment, only the tip portion of the ridge 22 is formed to be narrower than the width of the groove 28. However, as shown in still another embodiment of the present invention in FIGS. A similar effect can be obtained even if the groove is narrower than the width of the groove 28.

Further, in the above-described embodiment, the microwave circuit has a so-called double ridge cross-sectional shape, and one ridge is provided with the groove 28 forming the discharge space 25.
It is needless to say that the microwave circuit may have a so-called single ridge cross-sectional shape, and the groove 28 may be provided on the wall surface of the conductor facing the ridge.

[Effects of the Invention] As described above, according to the present invention, the width of at least the tip portion of the ridge facing the groove serving as the discharge space via the dielectric is formed so as to be narrower than the width of the groove. In the electric field strength in the width direction at, the microwave energy is focused on both side corners of the tip portion, so that both side portions in the width direction of the dielectric body are strengthened and the central portion is weakened accordingly. By increasing the microwave energy by the amount of the weakened electric field in the central part, the electric field strength on both sides of the dielectric is made higher than a predetermined value at which discharge can be started. The uniform electric field strength distribution spreads on both sides of the discharge space, which makes the discharge distribution due to the microwave energy in the width direction uniform in the discharge space. A stable and uniform plasma is generated in the space, and the laser output can be obtained with high efficiency and large output.

Another aspect of the present invention is to form a ridge tip portion having a width narrower than the width of a groove by dividing it into a plurality of portions having a recessed portion at least at the center, and to determine the electric field strength in the width direction in a microwave dielectric material by using microwave energy. By the edge effect that is focused on both side corners of the tip and the corners of the tip that is divided,
Both sides of the dielectric in the width direction and the part corresponding to the corners of the divided tip are strengthened and the recessed part including at least the center is weakened. By increasing the wave energy, the electric field strength other than the central part of the dielectric is made higher than a predetermined value at which discharge can be started. As a result of this distribution, the discharge distribution by the microwave energy in the width direction in the discharge space becomes uniform, and a stable and uniform plasma is generated in the discharge space, so that the laser output can be obtained with high efficiency and large output. Have.

[Brief description of drawings]

1 is a sectional view of a gas laser device according to an embodiment of the present invention, FIG. 2 is a sectional view of a gas laser device according to another embodiment of the present invention, and FIG. 3 is a conventional view in the width direction of a dielectric. An example and a graph for explaining the electric field intensity distribution of the present invention, FIG. 4 is a sectional view of a gas laser device which is still another embodiment of the present invention, and FIG. 5 is still another embodiment of the present invention. FIG. 6 is a sectional view of the gas laser device, FIG. 6 is a perspective view showing a conventional gas laser device, and FIG. 7 is a sectional view taken along line VV of FIG. 21 …… ridge, 22 …… ridge, 23 …… conductor wall, 24 ……
Dielectric, 25 ... Discharge space, 28 ... Groove, 221, 222 ... Tip, 223 ... Recessed part. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] 1. A microwave oscillator that oscillates microwaves, a microwave transmission line that transmits microwaves, and a plasma generated in a laser gas by the discharge of the microwaves transmitted by the microwave transmission line to excite the laser. A microwave entrance window provided with a microwave circuit for forming a groove in a conductor wall forming the microwave circuit and facing the conductor wall forming the groove bottom to close the groove. Microwave mode having an electric field component perpendicular to the boundary between the dielectric and plasma generated in the laser gas by the microwave circuit, by enclosing the laser gas in a discharge space formed between the dielectric and the dielectric. In a microwave excitation type gas laser device configured to form a ridge, a ridge is formed on a portion of a conductor wall facing the groove via a dielectric, and A gas laser device characterized in that the width of the tip is formed to be narrower than the width of the groove. 2. A microwave oscillator that oscillates microwaves, a microwave transmission line that transmits microwaves, and a microwave that is transmitted through the microwave transmission line to generate plasma in the laser gas for laser excitation. A microwave entrance window provided with a microwave circuit for forming a groove in a conductor wall forming the microwave circuit and facing the conductor wall forming the groove bottom to close the groove. Microwave mode having an electric field component perpendicular to the boundary between the dielectric and plasma generated in the laser gas by the microwave circuit, by enclosing the laser gas in a discharge space formed between the dielectric and the dielectric. In a microwave excitation type gas laser device configured to form a ridge, a ridge is formed on a portion of a conductor wall facing the groove via a dielectric, and A gas laser device characterized in that the width of the tip portion is made narrower than the width of the groove at least, and the tip portion is divided into a plurality of portions having a recessed portion at least in the center.