JPH084165B2 - Gas laser device - Google Patents

Description

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

[Conventional technology]

Figure 9 shows, for example, the Journal of Applied Physics Vol.49,
No. 7, July 1978, P. 3753, a cross-sectional view showing a conventional gas laser device, and FIG. 10 is a cross-sectional view taken along the line BB in FIG. In the figure, (3) is a waveguide that transmits microwaves, (31) is a waveguide taper provided in a part of this waveguide, and (32) is installed in the space of this waveguide taper part. The laser discharge tube made of pyrex glass (33) is a laser gas inlet provided at the end of this laser discharge tube,
Similarly, (34) is a laser gas discharge port, (35) is a cooling gas gas pipe arranged so as to surround the laser discharge pipe (32),
(36) is a cooling gas inlet provided at the end of the cooling gas supply pipe, (37) is also a cooling gas outlet, and (38) is a bridge provided at both ends of the laser discharge pipe (32). A star window, (39) is a cathode for DC discharge, and (40) is an anode.

In the conventional gas laser device as described above, the laser gas is introduced into the laser discharge tube (32) through the laser gas inlet (33), for example.
Laser gas such as CO ₂ laser gas is introduced, while
A TE ₁₀ mode microwave is excited in the waveguide (3). The waveguide (3) has a waveguide taper (31) inside.
Since the inner diameter of the waveguide (3) is minimum at the position where the laser discharge tube (32) is installed, the microwave electric field is maximum at this position. This strong microwave electric field discharges and destroys the laser gas in the laser discharge tube (32), generating plasma and exciting the laser medium. At this time, for example, low-temperature N ₂ gas or the like is caused to flow through the cooling gas supply pipe (35) at high speed to cool the laser discharge pipe (32) from the outside and to appropriately select the discharge conditions such as the pressure of the laser gas. Thus, laser oscillation conditions are obtained, and laser oscillation is performed by providing a laser oscillation mirror (not shown) outside the Brewster window (38).

[Problems to be solved by the invention]

In the conventional gas laser device as described above, since the closed laser discharge tube (32) is used, when conductive plasma is generated, the plasma in the laser discharge tube (32) is coaxial with the inner conductor. The microwave mode of the mode becomes dominant, and the microwave electric field in the plasma is
An electric field whose main component is a component parallel to the tube wall of 2), and the microwave that penetrates into the plasma becomes a mode in which it is substantially perpendicular to the tube wall of the laser discharge tube (32), that is, the plasma boundary. . In this way, the microwave electric field decreases inward from the wall of the discharge tube in the discharge generated by the microwave incident perpendicularly to the plasma boundary, but because the discharge plasma has a constant-voltage characteristic. A slight difference in the electric field causes a large change in the current density, resulting in the generation of extremely nonuniform plasma concentrated near the wall of the discharge tube. This situation is shown in the sectional view of FIG.
In the figure, (31) is the waveguide taper, (32) is the laser discharge tube, (69) is the electric field lines of the microwave electric field, and (70) is the plasma. In a conventional gas laser device using microwave discharge, it is difficult to put the entire discharge into a state suitable for laser excitation due to the generation of non-uniform plasma as shown in Fig. 11. The mode and plasma did not overlap, and the laser output and efficiency were low.

The present invention has been made to solve the above problems, and obtains a gas laser device that generates a spatially uniform microwave discharge plasma and enables high-efficiency and high-power laser operation. The purpose is to

[Means for solving problems]

The gas laser device according to the present invention is a space formed between a conductor wall forming a part of a microwave circuit, such as a waveguide, and a dielectric provided so as to face the conductor wall. A laser gas for generating plasma due to microwave discharge is enclosed in the microwave circuit, and the microwave circuit forms a microwave mode having an electric field component perpendicular to the boundary between the dielectric and plasma.

[Action]

In the gas laser device according to the present invention, since there is a conductor wall having a higher conductivity than plasma facing the dielectric material that is the microwave entrance window, the terminal current of the incident microwave flows through this conductor wall. A current that penetrates between the dielectric and the conductor wall flows in the plasma, and a spatially uniform plasma is generated.

〔Example〕

FIG. 1 is a schematic view showing a gas laser device according to an embodiment of the present invention. (1) is a magnetron which is a microwave oscillator, (2) is a waveguide, (3) is a waveguide (2). A horn waveguide that expands the width of the microwave, (4) is a microwave coupling window,
(5) is a mirror for laser oscillation, (6) is a laser head portion, and FIG. 2 is a sectional view taken along the line AA in FIG. 1 showing the details of the laser head portion (6). As shown in FIG. 2, the laser head portion (6) has a structure of a ridge waveguide type microwave cavity which is a kind of microwave circuit. Second
In the figure, (61) is a cavity wall following the microwave coupling window (4), (62) and (63) are ridges formed in the center of the cross section of this cavity wall, and (64) is one of these. Ritsuji (62)
And (65) is a conductor wall forming a part of the microwave circuit. In this embodiment, the groove (64) is formed.
Walls of are used. (66) is a dielectric such as alumina provided facing the conductor wall (65),
(67) is a discharge space formed between the conductor wall (65) and the dielectric (66) by covering the groove (64) with the dielectric (66). (67) for example CO
₂ Laser gas such as laser gas is enclosed. Also (6
8) is the cooling water channel formed in the ridges (62) and (63).

In the gas laser device according to the present invention configured as described above, the microwave generated by the magnetron (1) is propagated through the waveguide (2) and expanded by the horn waveguide (3), and the microwave coupling window By performing impedance matching in (4), the laser head section (6) is efficiently coupled. The laser head portion (6) is in the shape of a cavity of the ridge as shown in the sectional view of FIG. 2, and the microwave is concentrated between the ridges (62) and (63). The concentrated electromagnetic field of the microwaves causes the laser gas enclosed in the discharge space (67) to be destroyed by electric discharge, generating plasma and exciting the laser medium. Here, the cooling water channel (68) is caused to flow cooling water to cool the discharge plasma, and the laser wave oscillation condition is obtained by appropriately selecting the discharge condition such as the pressure of the laser gas. Laser oscillation light can be obtained by forming a laser resonator with the mirror (5) and another mirror (not shown). At this time, in the gas laser device according to the present invention, the conductor wall (65) forming a part of the microwave circuit and the dielectric wall which is provided so as to face the conductor wall (65) and serves as a microwave incident window. Body (6
Since microwave discharge is generated in the discharge space (67) formed between the microwave and the discharge space (6), microwaves are incident only from one surface of the plasma, and microwaves in the coaxial mode with plasma as the inner conductor are used. The phenomenon in which the mode becomes dominant does not occur, and the desired microwave mode discharge can be performed. Further, when the microwave circuit forms a microwave mode having an electric field component perpendicular to the plasma boundary of the dielectric (66) like the ridge cavity shown in FIG. Since the walls (65) are installed to face each other, the electric conductor wall (65) also has a vertical electric field component, and an electric field penetrating the plasma can be generated. At this time, even if a conductive plasma is generated, there is a conductor wall (65) that is several orders of magnitude more conductive than the plasma, facing the dielectric (66) that is the microwave entrance window. Terminating current flows through the conductor wall (65), the electric field near the conductor wall (65) is forced to be perpendicular to the surface of the conductor wall (65), and the electric field penetrating the plasma is maintained. . For this reason, microwaves penetrate into the plasma, and a current flows through the plasma, resulting in a spatially uniform discharge plasma due to the continuity of the current. This state is shown in the enlarged sectional view of FIG. In the figure, (69) is the electric field lines of the microwave electric field, and (70) is the discharge plasma. According to the gas laser device of the present invention, a uniform discharge as shown in FIG. 3 can be obtained, so that the entire discharge can be easily put into an optimal state for laser excitation, and the laser resonator mode and plasma The overshoot is improved, and it is possible to obtain laser oscillation with high efficiency and high output, which is orders of magnitude higher than that of the conventional gas laser device using microwave discharge. Fig. 4 is a graph of the experimental results when the device with a discharge length of 300 mm is applied to the CO ₂ laser in the configuration shown in Fig. 1 and Fig. 2, the horizontal axis is the microwave input of frequency 2.45 GHz, and the vertical axis is Is CO ₂
Laser power and efficiency. As shown in Fig. 4, a maximum output of 24 W and a maximum efficiency of 10.5% were obtained, and the CO ₂ laser output of 15 mW reported in the conventional example shown in Figs. Also, in the conventional example, only pulse oscillation is obtained, whereas in the device according to the present invention,
It was confirmed that CW oscillation was possible.

According to the configuration of the present invention, since the metal wall for confining the microwave and the discharge plasma are in close contact with each other, effective cooling can be freely performed from the outside of the metal wall, and for example, a laser gas such as a CO ₂ laser can be cooled. It is advantageous when applied to lasers where cooling is important, and because the effect of the magnetic field is not used,
For example, it can be applied to high-pressure lasers such as excimer lasers, and there is an advantage that a device for generating a magnetic field is unnecessary and the device is small and simple.

Although one embodiment has been described above, various device configurations can be adopted depending on the type of microwave circuit and the method of configuring the discharge space (67). FIG. 5 is a cross-sectional view showing an example of the method of constructing the discharge space when a microwave cavity or a waveguide is used as the microwave circuit. In the figure, (65) constitutes a part of the microwave circuit. Conductor wall, (66) is a dielectric, and (67) is a discharge space. FIG. 5 (a) shows a discharge space (67) formed by partitioning a microwave cavity with a dielectric plate (66), which has an advantage of easy manufacture. Figure 5 (b) shows the discharge space (67).
The space other than that is filled with the dielectric (66) and has a function of preventing unnecessary discharge in the space other than the discharge space (67). Fifth
In FIG. 6C, the groove formed on the cavity wall is used as the discharge space (67), and there is an advantage that the discharge space (67) having an arbitrary size can be formed. FIG. 5 (d) is the one shown in FIG. 5 (c) with a ridge (63) added, and can discharge a laser gas having a higher pressure than that shown in FIG. 5 (c). There are advantages such as easy matting. Fifth
The figure (e) uses a dielectric (66) having a depression, and has an advantage that a discharge cavity (67) of any size can be formed by using a microwave cavity having a standard shape. . FIG. 5 (f) is the one shown in FIG. 5 (e) to which the ridge (63) is added, and the laser gas having a higher pressure than that in FIG. 5 (e) can be discharged. There are advantages such as easy matching. FIGS. 5 (g) and 5 (h) show a combination of these. As shown in FIG. 5, by appropriately selecting the conductor wall (65) forming a part of the microwave circuit and the dielectric (66) provided facing the conductor wall, The discharge space (67) can be designed quite freely, and a uniform discharge similar to that shown in FIG. 3 can be obtained.

FIG. 6 is a sectional view showing an embodiment in which a coaxial line or a strip line is used as the microwave circuit. FIG. 6 (a) shows an embodiment in which the outer conductor of the coaxial line is used as a conductor wall (65) forming a part of the microwave circuit, and FIG. 6 (b) shows the inner conductor of the coaxial line being made conductive. Body wall (65)
FIG. 6 (c) shows an example using a strip line. Since the coaxial line and the strip line shown in FIG. 6 do not have a cutoff frequency, for example, when a microwave of 2.45 GHz is used, the entire device has a smaller device configuration than a device using a microwave cavity. There is an advantage that can be. Note that FIG. 6 (a),
It goes without saying that various device configurations can be taken according to the method of configuring the discharge space shown in FIG. 5 for each of the cases (b) and (c).

FIG. 7 is a sectional view showing an embodiment in which a surface wave line is used as a microwave circuit. FIG. 7 (a) shows an embodiment in which a conductor plate is used as a conductor wall (65) and a dielectric plate is used as a dielectric (66) to form a discharge space (67) and at the same time to form a surface wave line. In FIG. 7 (b), the conductor cylinder is used as the conductor wall (65), and the dielectric tube surrounding the conductor cylinder is used as the dielectric (66) to form the discharge space (67) and simultaneously construct the surface wave line. An example will be shown. Seventh
As shown in the figure, the surface wave line enables the microwave circuit and the discharge space to be constructed at the same time with the minimum number of components.
This has the advantage of simplifying the device. FIG. 7 (a),
Also in the embodiment of (b), various device configurations can be adopted in accordance with the method of configuring the discharge space shown in FIG.

In the above-described embodiments, the discharge space (67) formed between the conductor wall (65) forming a part of the microwave circuit and the dielectric provided facing the conductor wall is almost the same. An example of generating plasma throughout was shown, but the discharge space (67)
It is also possible to generate plasma only in a part of. 8th
The figure shows an embodiment in which a convex portion (71) is provided in a part of the microwave circuit, and a plasma (70) is generated in the strong electromagnetic field portion generated in a part of the discharge space (67) by the convex portion (71). Fig. 8 (a) shows an example in which a convex portion (71) is provided outside the discharge space (67), and Fig. 8 (b) shows inside the discharge space (67). The example which provided the convex part (71) is shown. 8th
With the configuration shown in the figure, the discharge plasma can be concentrated only in a part of the discharge space (67), which makes it easy to obtain a three-axis orthogonal laser device. There are advantages such as being able to discharge high-pressure laser gas and facilitating generation of plasma with high discharge power density.

〔The invention's effect〕

As described above, according to the present invention, the microwave discharge is generated in the space formed between the conductor wall forming a part of the microwave circuit and the dielectric provided so as to face the conductor wall. Since the laser gas for generating plasma is enclosed and the microwave circuit is configured to form a microwave mode having an electric field component perpendicular to the boundary between the dielectric and plasma, a spatially uniform microwave is generated. The discharge plasma can be generated, the entire discharge can be put into a state suitable for laser excitation, the laser cavity mode and plasma overlap can be improved, and a gas laser device with high efficiency and high output can be obtained. There is.

[Brief description of drawings]

FIG. 1 is a schematic view showing a gas laser device according to an embodiment of the present invention, FIG. 2 is a sectional view of the same FIG. 1A-A, and FIG. 3 is a sectional view for explaining the state of discharge in the same embodiment. 4 and 5 are graphs showing laser oscillation characteristics in the same embodiment, FIG. 5 is a sectional view showing another embodiment of the present invention, and FIG. 6 is a sectional view showing another embodiment of the present invention. FIG. 7 is a sectional view showing still another embodiment of the present invention, FIG. 8 is a sectional view showing still another embodiment of the present invention, FIG. 9 is a sectional view showing a conventional gas laser device, and FIG. The figure is also FIG. 9B-
FIG. 11 is a sectional view taken along the line B, and FIG. 11 is a sectional view for explaining the state of discharge in the conventional gas laser device. In the figure, (65) is a conductor wall forming a part of the microwave circuit, (66) is a dielectric, (67) is a discharge space, and (70) is a discharge space.
Is discharge plasma, and (71) is a convex part provided in a part of the microwave circuit. The same reference numerals in each figure indicate the same or corresponding parts.

Front page continuation (72) Inventor Yoshihiro Ueda 8-1-1 Tsukaguchihonmachi, Amagasaki City, Hyogo Prefecture Sanryu Electric Co., Ltd. Applied Equipment Laboratory (72) Inventor Tadashi Yanagi 8-1-1 Tsukaguchihonmachi, Amagasaki City, Hyogo Prefecture No. 1 Sanritsu Electric Co., Ltd. Applied Equipment Laboratory

Claims (5)

[Claims] 1. In a gas laser device for generating plasma by microwave discharge in a microwave circuit to excite laser, a conductor wall constituting a part of the microwave circuit, and a conductor wall facing the conductor wall. A laser gas for generating the plasma is sealed in a space formed between the dielectric and the microwave circuit, and the microwave circuit has a microwave mode having an electric field component perpendicular to a boundary between the dielectric and the plasma. A gas laser device for forming a gas laser device. 2. The gas laser device according to claim 1, wherein the microwave circuit is a microwave cavity or a waveguide. 3. The gas laser device according to claim 1, wherein the microwave circuit is a coaxial line or a strip line. 4. The gas laser device according to claim 1, wherein the microwave circuit is a surface wave line. 5. A microwave circuit according to claim 1, wherein a convex portion is provided in a part of the microwave circuit, and the strong electromagnetic field generated by the convex portion is filled with laser gas for generating the plasma. Gas laser device.