JPS63186483A - Gas laser device - Google Patents

Abstract

PURPOSE:To enable a laser operation of a high efficiency and a large output by causing a microwave circuit to form a microwave mode having a field component vertical to the boundary a dielectric opposed to the conductor wall and a plasma, thereby generating a spatially uniform microwave discharge plasma. CONSTITUTION:In a gas laser device wherein a plasma is generated by microwave discharge in a microwave circuit to give laser excitation, a laser gas generating a plasma 70 is sealed in a space 67 formed between a conductor wall 65 constituting part of said microwave circuit and a dielectric 66 provided opposite the conductor wall 65. And, said microwave circuit is adapted to form a microwave mode having a field component vertical to the boundary of the dielectric 66 and the plasma 70. With this, a spatially uniform microwave discharge plasma can be generated, the whole discharge can be put in a condition suitable for laser excitation, the overlapping of the laser resonator mode and the plasma becomes good, whereby a high-efficiency and large-output gas laser device is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas laser device that performs laser excitation using microwave number it.

[Conventional technology]

Figure 8 shows, for example, Journal of Applied
Physics Vol, 49, No. 7, Ju1
7111713, P, 3753 is a sectional view showing a conventional gas laser device.

FIG. 10 is a sectional view taken along line BB in FIG. 9.

In the figure, (3) is a waveguide that transmits microwaves.

C11l is a waveguide taper provided in a part of this waveguide.

The opening is a Pyrex glass laser discharge tube installed in the space of the tapered part of the waveguide, and (g) is the laser gas inlet provided at the end of the laser discharge tube.

The trowel is also the laser gas outlet, and the field is the laser discharge tube (
A cooling gas air pipe arranged to enclose the

The plane is a cooling gas inlet provided at the end of this cooling gas supply pipe, C (1 is also a cooling gas outlet, (to) is a Brewster window provided at both ends of the laser discharge tube,
1 is a cathode for DC broadcasting, and (4) is also an anode.

In a conventional gas laser device as described above.

A laser gas such as CO2 laser gas is introduced into the laser discharge from the laser gas inlet a,
On the other hand, a TEIQ mode microwave is excited in the waveguide; g (3). This waveguide (3) has a waveguide taper C3)1 inside, and the inner diameter of the waveguide (3) is minimum at the position where the laser discharge tube (2) is installed. The electric field of the microwave is maximum when it is upright. This strong microwave electric field causes the laser gas in the laser discharge tube (2) to radiate and rupture, generating plasma and exciting the laser medium. At this time, for example, low-temperature N2 gas is flowed at high speed into the cooling gas supply pipe (towards), and the discharge tube is
Laser oscillation conditions can be obtained by cooling 3 from the outside and appropriately selecting discharge conditions such as the pressure of the laser gas, and by providing a mirror for laser oscillation (not shown) outside the Brewster window. Laser oscillation is performed.

[Problem that the invention seeks to solve]

In the conventional gas laser device described above, since a closed laser discharge tube (2) is used, when conductive plasma is generated, a coaxial mode with the plasma in the laser discharge tube Q as an inner conductor is generated. Microwave mode becomes dominant,
The microwave-electric field in the plasma is an electric field whose main component is parallel to the tube wall of the laser discharge tube (2),
The microwave entering the plasma becomes a mode in which it is substantially perpendicular to the tube wall of the laser discharge tube, that is, the plasma boundary.

In this way, in a discharge generated by microwaves incident perpendicularly to the plasma boundary, the microwave electric field decreases from the discharge tube wall toward the inside, but because the discharge plasma has constant voltage characteristics, the microwave electric field decreases slightly. The difference in electric field causes a large change in current density, resulting in the generation of a significantly non-uniform plasma concentrated near the wall of the discharge tube.

This situation is shown in the sectional view of FIG. cll in the figure
l is the waveguide taper, C33 is the laser discharge tube, (69
) is the electric force of the microwave electric field, and (7) is the plasma. In conventional gas laser devices that use microwave discharge, non-uniform plasma is generated as shown in Figure 11, so the entire discharge It is difficult to create a suitable state for laser excitation, and there is also the problem that the laser resonator mode and plasma do not overlap, resulting in low laser output and efficiency.

This invention was made to solve the above-mentioned problems, and provides a gas laser device that generates spatially uniform microwave discharge plasma and enables high-efficiency, high-output laser operation. The purpose is to

[Means for solving problems]

A gas laser device according to the present invention is provided in a space formed between a conductor plate, such as a waveguide, which constitutes a part of a microwave circuit, and a crown body provided opposite to the conductor plate. In addition to enclosing a laser gas that generates plasma by microwave discharge, the microwave circuit is configured to form a microwave mode having an electric field component perpendicular to the boundary between the dielectric and the plasma.

[Effect]

C(7) In the gas laser device according to the invention, there is a conductive plate having higher conductivity than the plasma opposite to the dielectric which is the microwave incidence window, so the terminal current Mt of the incident microwave is higher than that of this conductor. mA flows through the plate and passes through the space between the dielectric and conductive plate, and a spatially uniform plasma is generated.

〔Example〕

FIG. 1 shows a gas laser device ii according to one embodiment of the present invention.
, where (1) is a magnetron which is a microwave oscillator, (2) is a waveguide, and (3) is a waveguide (2).
), (4) is the microwave coupling window, (5) is the mirror for laser oscillation, (6: is the laser head part, and Fig. 2 shows the laser head s (6; 1 is a cross-sectional view taken along the line A-A in FIG. 1 showing the details.As shown in FIG. have.

In Figure 2, (61) is the microwave coupling window (4)
(62) and (63) are formed at the center of the cross section of this cavity wall.

(64) is a groove formed in one of the glue holes (62), and (65) is a conductor plate that constitutes a part of the microwave circuit, and in this example, #J1 (64) is a wall surface. is used. (66) is a dielectric material such as alumina provided opposite to this conductor board (65),
(67) This dielectric (66) covers the above #I (6), so that the above conductive plate (65) and the dielectric (66)
A discharge space formed between this discharge space (
67) is filled with laser gas such as CO2 laser gas (68), bridges (62) and (63).
) is a cooling waterway formed in the

In the gas laser device according to the present invention configured as described above, the microwave generated by the magnetron +1+ passes through the waveguide (2) and is expanded by the horn waveguide (3), and the microwave coupling window +4) By performing impedance matching at , the laser beam is efficiently coupled to the laser head section (6). As shown in the cross-sectional view in Fig. 2, the laser head section (61) has a ridge cavity shape, and the microwaves are concentrated between the ridges (52) and (63). The electromagnetic field destroys the laser gas sealed in the discharge space (67), generates plasma, and excites the laser medium.Here, the cooling channel (68)
Cooling water is added to cool the discharge plasma, and
The laser oscillation conditions can be obtained by appropriately selecting the discharge conditions such as the pressure of the laser gas, and the mirror (5) in Figure 1
8 and another mirror not shown to form a laser resonator, laser oscillation light can be obtained. At this time, in the gas laser resonator according to the present invention (8G), a conductor plate (65) forming a part of the microwave circuit and a conductor plate (65) are provided opposite to this conductor plate (65).

In order to cause a microwave discharge to occur in the discharge space (67) formed between the dielectric material (66) and the dielectric material (66) that serves as the microwave incidence window, the microwave is incident only from one side of the plasma, and the plasma A phenomenon in which the microwave mode of the coaxial mode with the inner conductor becomes dominant does not occur, and discharge can be performed in the desired microwave mode.

Furthermore, when the microwave circuit forms a microwave mode having an electric field component perpendicular to the boundary between the dielectric (66) and the plasma, as in the ridge cavity shown in FIG. Since the plates (65) are placed facing each other, the conductive plate (65) also has a vertical electric field component, creating an electric field that penetrates the plasma. At this time, even if conductive plasma is generated, there is a conductive plate (65) that is several orders of magnitude higher in conductivity than the plasma, which faces the dielectric (66) that is the microwave incidence window, so that the incident microwave The terminal current flows through this conductor plate (65), and
The nearby electric field is forced to be perpendicular to the surface of the four-electric wall (65), and the above-mentioned plasma-purchasing electric field is maintained.

Therefore, the microwave penetrates into the plasma, the current passing through the plasma is distorted, and the continuity of the flow makes it possible to obtain a spatially uniform discharge plasma. This situation is shown in the enlarged sectional view of FIG. In the figure, (69) is the electric field line of the microwave electric field, and (70) is the discharge plasma. According to the gas laser device according to the invention.

Since a uniform discharge as shown in Fig. 3 can be obtained, it is easy to bring the entire discharge into an optimal state for laser excitation, and the overlap between the laser resonator mode and the plasma is good, making it possible to It is possible to obtain laser oscillation with an order of magnitude higher efficiency and higher output than gas laser devices that use electric discharge. Figure 4 is a graph of experimental results when the device with the configuration shown in Figures 1 and 2 and a discharge length of 300n is applied to a CO2 laser, where the horizontal axis is frequency 2,
45 GHz microwave input, vertical axis is CO2 laser power and efficiency. As shown in Fig. 4, a maximum output of 24 W and a maximum efficiency of $1 (15%) were obtained, and the CO2 laser output 1 reported in the conventional example shown in Fig. 8.10 was obtained.
It was confirmed that an output three orders of magnitude higher than that of 57 HW was obtained, and that the device according to the present invention was capable of CW oscillation, whereas the conventional example could only obtain pulse oscillation.

According to the configuration of the present invention, since the metal wall that confines microwaves and the discharge plasma are in close contact with each other, effective cooling can be freely performed from outside the metal wall.1 For example, cooling of laser gas such as CO2 laser This is advantageous when applied to lasers that require M.

Since it does not use the effect of a magnetic field, it can also be applied to high-pressure lasers such as excimer lasers, and has the advantage that it does not require a device for generating a magnetic field, making the device compact and simple.

Although one embodiment has been described above, various device configurations can be taken depending on the type of microwave circuit and the method of configuring the discharge space (67). Figure 5 is a sectional view showing an example of how to configure a discharge space when a microwave cavity or waveguide is used as a microwave circuit. In Figure 9, (65) shows a part of the microwave path. Constituting the same gas wall, (66) is a dielectric, and (67) is a discharge space. Figure 5(a) shows a microwave cavity with a 9% body plate (66).
A space (67) is formed by partitioning the space (67), which has the advantage of being easy to manufacture. Figure 5 (
1)) The space other than the discharge space (67) is a dielectric (66)
It is filled with

It functions to prevent unnecessary discharge outside the discharge space (67). Figure 5(e) shows the groove formed in the cavity wall in the discharge space (67
A discharge space of arbitrary size (6
7). Figure 5(d) is shown in Figure 5(d).
This is the same as the one shown in Q) with a ridge (63) added, and can discharge a higher pressure laser gas than the one shown in FIG. This has advantages such as easier matching. Figure 5(e) shows a dielectric material (66) with a recess.
It has the advantage that a discharge space (67) of any size can be formed using a standard-shaped microwave cavity. FIG. 5(f) is the same as the one shown in FIG. 5(e) with a ridge (63) added thereto, and can discharge a higher pressure laser gas than the one shown in FIG. 5(e). This has advantages such as easier matching. Figure 5 (
gJ, (h) indicates a combination of these. As shown in Figure M5, considerable freedom can be achieved by appropriately selecting the conductor board (65) that forms part of the microwave circuit and the v1 electric body (66) provided opposite to this conductor board. The discharge space (67) can be designed.

A uniform discharge similar to that shown in FIG. 3 above 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. 6th
Figures (al) show an example in which the outer conductor of the coaxial line is used as a conductive board (65) constituting a part of the microwave circuit, and Figure 6 (1) shows an example in which the inner conductor of the coaxial line is used as the conductive board (65) that constitutes a part of the microwave circuit. (65
), and FIG. 6(C) shows an example using a sl-IJ tubular line. The coaxial line and strip line shown in Figure 6 do not have a cutoff frequency, so when using microwaves of 145 GHz, for example, the entire device has a smaller configuration than a device using a microwave cavity. There is an advantage that it can be done. It goes without saying that for each of the cases in FIGS. 6(a), (1)), and (C), various device configurations can be adopted in accordance with the method of configuring the discharge space shown in FIG. 5.

FIG. 7 is a sectional view showing an embodiment of a microwave circuit using a surface wave line as a microwave circuit. In Fig. 7(a), the conductor plate is a conductor plate (65), and the dielectric plate is a dielectric plate (66).
An embodiment is shown in which a discharge space (67) is formed and a cinnabar wave combination is formed at the same time, and FIG. 7(b) shows a conductor plate (65) formed of a conductor cylinder.

An embodiment will be shown in which a dielectric tube surrounding this conductor cylinder is used as a dielectric (66) to form a discharge space (67) and at the same time constitute a surface wave line. 2 as shown in Figure 7.
The advantage of using a surface wave line is that the microwave circuit and the discharge space can be constructed simultaneously with a minimum number of components, and the VcR can be simplified. In the embodiments shown in FIGS. 7(a) and 7(L), various device configurations can be adopted in accordance with the method of configuring the discharge space shown in FIG. 5.

In the embodiments so far, a discharge space (67) is formed between a four-electric wall (65) that constitutes a part of a microwave circuit and a dielectric provided opposite to this four-electric wall. We have shown an example of generating plasma in almost the entire area, but if the radiation 1 is spaced (
It is also possible to generate plasma only in a part of 67). Figure 8 shows that a convex portion (7) is provided in a part of the microwave circuit.
FIG. 8(a) is a sectional view showing an embodiment in which plasma (70) is generated in a strong electromagnetic field generated in a part of the discharge space (67) by the convex portion (7). ) shows an example in which a convex part (71) is provided on the outside of the eighth part.
Figure (b) shows an example in which a convex portion (7) is provided inside the discharge space (67).The configuration shown in Figure 8 allows discharge plasma to be concentrated only in a part of the discharge space (67).

It becomes easy to obtain a three-axis orthogonal laser device.

High pressure laser gas can be discharged. Advantages such as easy generation of plasma with high discharge force density arise.

〔Effect of the invention〕

As described above, according to the present invention, microwave discharge is generated in the space formed between the conductor board that constitutes a part of the microwave circuit and the ejt body provided opposite to the conductor board. In addition to enclosing the laser gas that generates the plasma, the microwave circuit is configured to form a microwave mode having an electric field component perpendicular to the boundary between the dielectric and the plasma, so that the microwave circuit is spatially uniform. It is now possible to generate micro-temporary cage plasma, and the entire discharge can be brought into a state suitable for laser excitation, resulting in good overlap between the laser resonator mode and the plasma.

This has the effect of providing a gas laser device with high efficiency and high output.

[Brief explanation of the drawing]

FIG. 1 is an overview diagram showing a gas laser device according to an embodiment of the present invention, FIG. 2 is a sectional view taken along the line A-A in FIG. 4 is a graph showing the laser oscillation characteristics in the same implementation side. FIG. 5 is a cross-sectional color showing another embodiment of the present invention. FIG. 6 is a cross-section 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 another embodiment of the present invention, and FIG. S is a sectional view showing a conventional gas laser device. , Figure 10 is also Figure 9B
11 is an m'r plane view illustrating the state of discharge in a conventional gas laser device. In the figure, (65) is a conductive board that forms part of the microwave circuit, (6 is a dielectric, (67) is a discharge space, (70) is a discharge plasma, and (71) is a part of the microwave circuit. It is a convex part provided in the part. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (5)

[Claims] (1) In a gas laser device that generates plasma and excites laser by microwave discharge in a microwave circuit,
A laser gas that generates the plasma is filled in a space formed between a conductive board constituting a part of the microwave circuit and a dielectric provided opposite to the conductive board. A gas laser device characterized in that the microwave circuit forms a microwave mode having an electric field component perpendicular to the boundary between the dielectric and the plasma. (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 convex portion is provided in a part of the microwave circuit, and a laser gas that generates the plasma is sealed in a strong electromagnetic field generated by the convex portion.
The gas laser device described in Section 1.