JPS6235278B2 - - Google Patents

Description

[Detailed description of the invention] This invention superimposes silent discharge on direct current discharge,
This invention relates to a laser device that aims to make the device smaller and have higher output.

Various types of CO ₂ laser equipment have been proposed,
Although it has been put into practical use, the most well-known type is the so-called glass tube.
The optical axis, discharge, and gas flow directions are in the same direction. FIG. 1 shows a longitudinal cross-sectional view of this conventional CO ₂ laser. In the figure, 1 is a total reflection mirror,
2 is a partial reflecting mirror, 3 is a laser tube, 4 is a jacket through which cooling water flows, 4a is an inlet for the cooling water, 4b is an outlet thereof, 5a is a laser gas supply port, 5b is an exhaust port, 6 is an anode, and 7 is a cathode, 8 is a discharge stabilization resistor,
9 is a DC power supply. Inside the laser tube 3, there is usually
A mixed gas consisting of CO ₂ , N ₂ , and He is constantly supplied through the supply port 5a and the exhaust port 5b, and the gas pressure is kept constant at 10 to 20 torr. A glow discharge is maintained between the anode 6 and the cathode 7 in this gas flow,
Used as an excitation medium for laser oscillation. The laser resonator is composed of two reflecting mirrors 1 and 2, and a part of the luminous flux within the resonator is extracted from the partial reflecting mirror 2 as an output beam.

In order to suppress the rise in gas temperature due to glow discharge, a typical glass tube CO ₂ laser has a double tube structure, and cooling water or oil is circulated within the outer jacket. With such a normal type of CO ₂ laser, an output of only 50 to 80 W can be obtained per 1 m of discharge length between the anode and cathode, and in order to obtain an output of 1 KW or more, even with a folded structure, the total length of nearly 20 m is required. It requires a long length, which inevitably increases the length of the device.

In order to increase the laser output per unit discharge length, it is sufficient to increase the discharge current or the discharge pressure, but in the former case, the gas temperature rises as the discharge current increases, and the laser output increases. saturation, requiring a method to increase the effectiveness of gas cooling to suppress this phenomenon. In the normal form mentioned above,
The flow velocity of the gas flowing inside the glass tube 3 is 1 m/s or less, which is meant to replenish CO ₂ dissociated by the discharge, but this gas flow velocity can be increased (>100 m/s).
s) A method of obtaining high output by increasing the cooling effect is also known. In addition, in order to increase the latter discharge pressure, it is necessary to increase the gas pressure.
When the gas pressure increases, the glow discharge tends to be focused near the center of the laser tube 3, and as the gas temperature in the center increases, it tends to shift to a strong brightness arc discharge, leading to a decrease or stop of the laser output. Therefore, in the case of a glass tube CO ₂ laser, when the gas flow velocity is low (1 m/s or less), it is operated at a gas pressure of 20 torr or less, and even when the gas flow velocity is high (100 m/s or more), the gas pressure is 40 torr or less. It is only operated by gas pressure.

As mentioned above, it is difficult for conventional CO ₂ lasers to operate at gas pressures of 40 torr or more, not only at low gas flow rates but also at high gas flow rates, and this problem limits their ability to be made smaller and more powerful. Ta.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by superimposing an alternating current silent discharge on the conventional direct current glow discharge, it can be uniformly diffused in the gas pressure range of 50 to 100 torr. The purpose of the present invention is to provide a CO ₂ laser device that maintains a stable discharge while achieving a smaller size and higher output.

FIG. 2 shows an embodiment of the present invention. In the figure, 10a and 10b are a pair of electrodes for silent discharge disposed opposite to each other, and 11 is an AC power source therefor.

FIG. 3 is a cross-sectional view of the laser tube 3 taken along the line in FIG. Silent discharge is alternating current discharge in a space with a dielectric between metal electrodes, and is well known as a so-called discharge for ozone generation. This discharge is a collection of local pulsed discharges, and since the current is limited by the presence of the dielectric, it is a stable discharge that does not transition to an arc. Furthermore, since this pulsed discharge has the characteristic of spreading over the entire surface of the metal electrode via the dielectric, it is possible to control the spread of the discharge space by changing the surface area of the electrode.

By using a silent discharge having such characteristics in combination with a direct current discharge, the drawbacks of laser excitation using a direct current discharge as described above can be overcome. That is, as shown in FIG.
is generated between the metal electrodes of the laser tube 3 through the glass wall of the laser tube 3, and is superimposed on the DC discharge in the optical axis direction. In this way, it was difficult to operate the laser at an operating pressure of about 20 torr with only DC discharge, but it is now possible to increase the operating pressure to 50 to 100 torr, making it possible to achieve a smaller size and higher output laser output. be done. This is because when the gas pressure increases with only DC discharge, the glow discharge converges closer to the central axis of the laser tube 3, and the laser output decreases.
Eventually, it will shift to filament-like arc discharge,
This is because by superimposing the phenomenon of stopping laser oscillation with a silent discharge that spreads in the tube diameter direction, it becomes possible to diffuse the DC discharge and maintain a uniformly spread DC discharge.

The embodiment shown in Fig. 2 shows an example in which a pair of silent discharges is provided with poles, but in order to further diffuse the DC discharge in the tube radial direction and to realize an axially symmetric excitation space, it is necessary to As shown in FIG. 4, two pairs of electrodes 10a to 10d may be provided, and if a plurality of pairs of electrodes are further provided to superimpose silent discharges, the result will be more complete. This is particularly suitable for the generation of TEMoo modes, which require an axisymmetric excitation space.

Moreover, according to this invention, not only can the gas pressure be increased, but even when compared at the same gas pressure,
The linear region of the laser output with respect to the injection discharge stream is expanded, and efficiency is increased. FIG. 5 is a diagram showing this difference in characteristics. As is clear from the figure, with only DC discharge, the laser output tends to be saturated when the discharge current becomes larger than I _Dc1 , whereas by superimposing silent discharge, the linear region of output increase expands up to I _Dc2 . Even after subtracting the laser output equivalent to the silent discharge power, an increase in efficiency is achieved. This is the result of spatially uniformizing and suppressing the increase in gas temperature due to the effect of uniformly diffusing the discharge in the direction of the glass tube wall.

The effects of the present invention described above are of course effective for a so-called diffusion cooling type CO ₂ laser with a normal low gas flow rate, but they are further enhanced in the case of a high gas flow rate. That is, high gas flow rate (>
In the case of a glass tube type CO ₂ laser (100 m/s), gas cooling depends only on the high-speed flow, and there is almost no cooling effect on the glass tube wall. Therefore, in order to suppress the rise in gas temperature and obtain high output, it is effective to increase the gas pressure and the mass flow rate of the gas flow. However, as mentioned above, when the gas pressure is increased, the DC glow discharge is narrowly focused in the direction of the central axis, causing a rise in gas temperature.
If it is close to the current, arc discharge tends to occur, and oscillation may even stop. On the other hand, when silent discharge is superimposed, high gas pressure operation at 50 to 100 torr can be realized under high gas flow velocity, and laser oscillation is even more effective in the high current and high gas pressure region than in the case of low gas flow velocity. This makes it possible to significantly reduce the size and increase the output of the device.

This invention relates to a discharge tube having electrodes disposed at both ends, through which a laser medium gas is passed in the axial direction, and configured to apply a DC voltage between the two electrodes to generate a DC glow discharge. and an optical resonator constituted by a total reflection mirror and a partial reflection mirror disposed on both sides of the axis of the discharge tube, and configured to extract a laser beam through the partial reflection mirror. In the discharge tube, an electrode for silent discharge extending in the axial direction is provided on the tube wall surface of the discharge tube so as to face each other across the space in which the DC glow discharge is generated, and between the electrodes. It is characterized by being equipped with an AC power supply that applies an AC voltage, and generating a silent discharge in a direction crossing the DC glow discharge by superimposing it, making it possible to increase the gas pressure and input a large amount. Therefore, the device can be made smaller or have higher output.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a conventional glass tube type CO ₂ laser device, FIG. 2 is a longitudinal sectional view showing an embodiment of the present invention, and FIG. 3 is a sectional view taken along the line of FIG.
FIG. 4 is a sectional view of another embodiment of the present invention, and FIG. 5 is a characteristic diagram showing the relationship between discharge current and laser output. In the figure, 1 is a total reflection mirror, 2 is a partial reflection mirror,
3 is a laser tube, 4 is a jacket, 5a is a laser gas supply port, 5b is an exhaust port, 6 is an anode, 7 is a cathode, 9 is a DC power supply, 10a to 10d are electrodes for silent discharge, 1
1 is an AC power supply. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A device having electrodes disposed at both ends, configured to allow laser medium gas to be vented in the axial direction, and to apply a DC voltage between the two electrodes to generate a DC glow discharge. an optical resonator configured with a total reflection mirror and a partial reflection mirror disposed on both sides of the axis of the discharge tube, and a laser beam is taken through the partial reflection mirror. electrodes for silent discharge extending in the axial direction and provided on the tube wall surface of the discharge tube so as to face each other across the space in which the DC glow discharge is generated; A gas laser device comprising: an AC power source that applies an AC voltage between the electrodes, and generates a silent discharge in a direction crossing the DC glow discharge by superimposing the same. 2. The gas laser device according to claim 1, wherein the discharge tube is formed of a glass tube, and an electrode for silent discharge is provided on the outer wall surface of the glass tube. 3. The gas laser device according to claim 1 or 2, comprising a plurality of pairs of silent discharge electrodes.