JPS60161687A - Discharge starting method for high-output laser oscillator - Google Patents

Abstract

PURPOSE:To stabilize continuous-oscillation starting and intermittent-discharge pulse- oscillation of a laser, by generating auxiliary discharge between anodes and auxiliary electrodes before starting main discharge so that the auxiliary discharge causes the main discharge momentarily. CONSTITUTION:Auxiliary electrodes 9 are the same potential as cathodes 4 before the discharge starting, but a distance between the auxiliary electrodes 9 and anodes 3 is extremely short in comparison with one between the anodes 3 and the cathodes 4 so that the discharge between the auxiliary electrodes and the anodes is done positively for a very short time even at a low voltage. Between the auxiliary electrodes 9 and anodes 3, the discharge current is limited by resistors 10 with a high resistance to become the low-current discharge. Once the discharge has occurred, the potential of the auxiliary electrodes 9 is decreased by the resistors 10 and the main discharge which is induced by the low-current discharge between the auxiliary electrodes 9 and the anodes 3 is done between anodes 3 and cathodes 4. At this time, since an activating gas is caused to flow fast in the directions from the anodes 3 at the sides of the resonance mirrors 1 and 2 to the cathodes 4, gas ions which fill the important role for keeping the glow discharge have a fast moving speed and therefore can exert sufficient impact to the cathodes 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a method for starting a laser discharge in a high-output gas laser oscillator.

Most conventional high-output gas laser oscillators are of a type in which the working gas is made to flow, and there are low-speed axial flow types, high-speed axial flow types, orthogonal types, etc. depending on the flow rate of the working gas in one direction. Among these, high-speed axial flow oscillators have characteristics such as higher output per unit oscillation length, better output beam mode, and better electrical-to-optical conversion efficiency than other low-speed axial flow oscillators. There is. In addition, in high-speed axial flow oscillators, the gas pressure inside the oscillator is higher than in low-speed axial flow oscillators, but because the gas flow velocity is high, the gas flow becomes turbulent, and a uniform glow discharge can be obtained, making it possible to achieve continuous oscillation. In this case, stable laser oscillation can be obtained.

However, when a high-speed axial flow oscillator is used for pulse oscillation, the gas pressure inside the laser tube is still low.

The discharge starting voltage becomes distorted, making it difficult to instantaneously and reliably start the discharge, and thus making it difficult to obtain stable pulsed laser oscillation.

Therefore, in the case of pulse oscillation in a high-speed axial flow type oscillator, it is necessary to lower the working gas pressure and raise the discharge starting voltage than in the case of continuous oscillation. However, there is a drawback that when the working gas pressure is lowered, the electric power input to the discharge column is lowered and the maximum output of the laser oscillator is lowered. Therefore, in order to prevent this decrease in output as much as possible and ensure that pulse oscillation due to intermittent discharge is repeated instantaneously, a minute discharge is caused by a minute current (dark current) between one anode and cathode to be maintained even during the rest period of pulse oscillation. Although it has been considered to leave the laser oscillating in the same state, the set minute current causes laser oscillation even during the pause period of pulse oscillation, which is inconvenient in terms of processing. Furthermore, the working gas of the laser is constantly heated by discharge caused by a minute current, which causes the temperature of the gas to rise.

This increase in gas temperature results in a slight decrease in laser oscillation efficiency, which has the drawback of hindering the increase in laser oscillation efficiency due to pulsed discharge. Furthermore, attempts have been made to ensure that one discharge occurs instantaneously by increasing the voltage applied between the anode and cathode, but this method not only requires strengthening the dielectric strength of each part of the device, but also increases the input voltage. The disadvantage is that the % KVA and power losses increase.

In order to solve the above drawback, an auxiliary electrode is provided near the cathode, an auxiliary discharge is generated between the auxiliary electrode and the cathode, and a main discharge between the anode and the cathode is induced by the diffusion of charged particles generated by this auxiliary discharge. A method has also been proposed. FIG. 1 is a schematic diagram showing an example of a device of this type. In the figure, 1 and 2 are laser resonant mirrors provided at both ends of the discharge tubes 8.8, and 3, 3 and 4, 4 are anodes and cathodes provided at both ends of the discharge tubes 8 and 8, respectively. It is. Reference numerals 5 to 7 denote a power supply, a power supply control circuit, and a ballast resistor for the laser oscillator, which are connected in series between the anode 3 and the cathode 4, respectively. 9.9 is the anode 3. an auxiliary electrode provided between and near the cathode 4, 10.10
is a high-resistance resistor connected between the auxiliary electrode 9 and the anode 3; 11 is the flow direction of the working gas for laser oscillation;
12 is an auxiliary glow discharge generated between the auxiliary electrode 9 and the cathode 4; 13 is a raw glow discharge generated between the anode 3 and the cathode 4; 14 is an electric glow discharge taken out from the discharge tube 8 by the laser resonator mirror 1; 15 is a blower for supplying and circulating the gas flow in the discharge tube 8; 16a is for removing the heat of the gas flow whose temperature has increased due to the discharge in the discharge tube; and 16b is for increasing the temperature by the compression heat of the blower 15. A heat exchanger for removing the heat content of the ascending gas stream.

In order to cause pulse oscillation in such a conventional high-speed axial flow oscillator, the power supply control circuit 6 intermittently controls opening and closing of a high voltage power supply circuit. Now, when the power supply control circuit 6 applies the output of the power supply 5 between each electrode, the auxiliary electrode 9 and the cathode 4
Since the distance between them is very close, the auxiliary glow discharge 1
2 starts.

The current caused by this auxiliary glow discharge 12 is extremely small because it is limited by the resistor 10, but the charged particles generated thereby diffuse toward the anode side, and this small current glow discharge causes the anode 3 and cathode to It is believed that the main glow discharge 13 is induced between 4 and 4. Such a structure is well known as a conventional discharge tube system, but it is different from the case where it is in a stationary gas like a general discharge tube, and the case where it flows at a speed close to the speed of sound, which is the object of the present invention. The situation is completely different from that in a gas, and as detailed above, the method shown in FIG. 1 has many drawbacks in a high-speed gas flow.

The first is that the auxiliary electrode is placed on the cathode side, which utilizes the diffusion of loaded particles toward the anode due to the auxiliary glow discharge generated between the auxiliary electrode and the cathode, which increases the direction of the gas flow. As shown in the figure, the direction is from one cathode to the anode. For this reason, all of the charged particles generated by the auxiliary glow discharge are subjected to a force in the direction of being swept away toward the anode.

However, before the gas laser oscillator starts oscillating,
Charged particles generated by the initial glow discharge are negatively charged electrons drawn from the cathode by an electric field and gas ions (cations) that emit their own electrons and become positively charged by collision of these electrons. As shown by the arrows in the figure, electrons move to the anode and gas ions move to the cathode, thereby establishing a current path. Such a process is seen at the start of discharge in a stationary gas as in a general discharge tube, but in a gas flowing at high speed, a large difference occurs in the motion of each particle. In other words, electrons with extremely small mass and volume are accelerated by the electric field and have a speed several orders of magnitude faster than the gas flow, so they are almost unaffected by the gas flow and move in almost the same way as in a stationary gas. On the other hand, gas ions, which are larger than electrons and have a large mass, do not increase in speed very much even if they are accelerated by an electric field, and remain at a speed on the same order as the gas flow. For this reason, the gas ions are greatly influenced by the force in the direction of being pushed back by the gas flow, and their moving speed becomes extremely low.

For this reason, the time the gas ions remain between the electrodes becomes longer, causing a large charge imbalance within the discharge tube, which hinders the maintenance and development of the discharge.

Second, in a laser oscillator, the current is limited by a resistor to cause a glow discharge, whereas the electron emission from the cathode to maintain the glow discharge is thermionic, similar to an arc discharge. Since this is done not by emission or field emission but by the impact of cations flowing into the cathode, if the movement speed of these cations is reduced by the gas flow as described above, the necessary amount of electron emission cannot be secured. gone,
It becomes difficult to maintain the glow discharge itself, and it tends to become difficult to induce the main discharge.

Thirdly, one of the mechanical drawbacks of the conventional device shown in FIG.
In order to facilitate the start of the auxiliary discharge, it is necessary to use the cathode 4 as a needle-like electrode to improve the electric field strength at the time of starting the discharge. For this reason, the impact of gas ions during the main discharge concentrates on the tip of this needle-like electrode, making the cathode susceptible to damage and making it impossible to increase the current capacity, which ultimately improves the output of the oscillator. This means that you will not be able to do so. As described above, the conventional method of providing an auxiliary electrode close to the cathode side has many drawbacks in principle, and it has been almost impossible to cause the output laser to oscillate in a pulsed manner.

The present invention provides a method for starting a discharge in a high-power gas laser oscillator with a high gas pressure, including increasing the gas pressure by one step,
without increasing the applied voltage between the anode and cathode.
The object of the present invention is to stably perform pulse oscillation by instantaneously and reliably causing intermittent repeating glow discharge between an anode and a cathode.

SUMMARY OF THE INVENTION The present invention provides a discharge starting method for a laser oscillator that generates a main discharge between an anode and a cathode to produce a high-output laser discharge. An auxiliary electrode is provided near the anode to generate an auxiliary discharge between the anode and the auxiliary electrode before the main discharge starts, and this auxiliary discharge ensures that the main discharge occurs instantaneously, thereby starting the continuous oscillation of the laser. This paper proposes a method for starting a Sekide karlaser discharge that stably performs intermittent discharge pulse oscillation.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 is a schematic configuration diagram showing an example of an apparatus for carrying out the discharge starting method for a high-power laser oscillator according to the present invention. In the figure, parts having the same functions as the conventional apparatus shown in FIG. 1 are designated by the same reference numerals. shown below. Also, Figure 3 shows "I" of one of the devices in Figure 2.
- “A” is a cross-sectional view taken along arrows.

In FIG. 2, the auxiliary electrode 9 is a rod-shaped electrode and the resonant mirror 1.2
It is provided near the anode 3 provided on the side, and has the same potential as the cathode 4 before starting discharge, but the distance between the auxiliary electrode 9 and the anode 3 is smaller than the distance between the anode 3 and the cathode 4. , is extremely small, so the discharge between the auxiliary electrode 9 and the anode 3 occurs reliably in a very short time even at a low voltage (compared to the discharge between the anode 3 and the cathode 4). Between the electrode 9 and the anode, a high-resistance resistor 10 limits the discharge current, resulting in a minute discharge. The main discharge occurs between the anode 3 and the cathode 4 due to the micro discharge between the auxiliary electrode 9 and the anode 3. At this time, the gas ions that play an important role in maintaining the glow discharge are the working gas. As shown in the figure, since it flows at high speed in the direction from the anode 3 on the side of the resonant mirror 1.2 to the cathode 4, the moving speed is high and a sufficient impact can be applied to the cathode 4. Electrons can be emitted by the impact of the inflowing gas ions after they have been sufficiently accelerated, so there is no need to create a needle-like shape to increase the electric field strength at the start of discharge, as in the conventional method, as shown in Figure 2. In this way, the main discharge is instantaneously followed by the minute discharge between the auxiliary electrode 9 and the anode 3, so that continuous discharge is possible. In the case of intermittent discharge, that is, a pulsed laser that repeats the discharge start in short cycles, it is necessary to use a stable pulsed laser to ensure instantaneous discharge for each pulse. I get the output.

FIGS. 4 to 6 are diagrams showing the main parts of another apparatus for carrying out the high-power laser discharge starting method of the present invention. FIG. 4 shows a case where the anode 3 and the auxiliary electrode 9 are arranged substantially at right angles instead of facing each other as shown in FIG. FIG. 5 shows a case where the auxiliary electrode 9 is arranged in the same gas flow path as the anode 3 so that the tip of the auxiliary electrode 9 is near the tip of the anode 3.

Furthermore, FIG. 6 shows a case where an auxiliary electrode 9 is provided between the anode 3 and the cathode 4 (!l) near the anode and within the main discharge path. No matter where it is placed in the vicinity, the Ichigo discharge is instantaneously and reliably performed.

Effects of the present invention As described above, according to the high-power laser discharge starting method of the present invention, even if the gas pressure is controlled more than before, the voltage applied between the anode and the cathode remains the same as before, and the auxiliary electrode Following the micro discharge between the anode and the anode, the main discharge between the one anode and the cathode is instantaneously and reliably performed. Therefore, continuous wave oscillation, in some cases laser oscillation, is performed smoothly, and by lowering the output voltage of the power supply circuit, it is possible to lower the input KVA, reduce the dielectric strength, and reduce the cost of equipment. can. In addition, in the case of intermittent discharge pulse oscillation, stable pulsed laser output can be obtained because the discharge is instantaneously and reliably performed for each pulse, especially in the high output range where the gas pressure is effective such as in a high-speed axial flow oscillator. Pulse oscillation is also possible. Furthermore, according to the discharge starting method of the present invention, heat is supplied by the minute discharge even during the pulse oscillation period, unlike an oscillator that maintains a minute discharge between the anode and the cathode during the pulse oscillation pause period. A complete cooling effect can be obtained, and there is no disadvantage of inconvenience, and a wide range of processing can be performed. Also,
Because the main glow discharge between the anode and the cathode occurs instantaneously and reliably, the period of transient streamer discharge before transitioning to glow discharge is extremely short, and noise due to streamer discharge is reduced, especially the pulse oscillation of intermittent discharge. The noise reduction effect is large in the case of

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus for carrying out a conventional discharge starting method for a laser oscillator, FIG. 2 is a block diagram of an apparatus for carrying out a discharge starting method for a laser oscillator according to the present invention, and FIG. The "A"--A cross-sectional views from Figure 4 to Figure 6 are as follows:
It is a figure which shows the principal part of another apparatus which carries out the discharge starting method of the laser oscillator of this invention. 3... Anode, 4... Cathode, 5... Laser oscillator power supply 6... Power supply control circuit, 8... Discharge tube, 9...
Auxiliary electrode, 11... Gas flow, 12... Auxiliary discharge, 1
3...Main discharge agent Patent attorney Hiroshi Nakai Drawing CJ (no internal changes) Fig. 2 Fig. S Fig. 4 Fig. 5 Fig. 6 Te U Gone city official manuscript (self-produced) March 68, 1981 1. Indication of matter 1!4 1981 Patent Application No. 181'28 2. Name of the invention Method for starting discharge of high-power laser oscillator 3. Relationship with amendment overturner case Patent applicant Osaka Osaka Transformer Co., Ltd. 4, 2-1-11 Tayo, Yodoyo-ku, Osaka (026) Address: 2-1-11 Tayo, Yodoyo-ku, Osaka 532 [Contact information: Telephone (0(i)) 301-1212]5,
? ``Day of direct command'' spontaneously

Claims (1)

[Claims] 1. A main discharge is generated between an anode and a cathode and flows upward, an auxiliary electrode is provided near the anode, and an auxiliary discharge is caused between the anode and the auxiliary electrode before the main discharge starts. A method for starting a discharge in a high-power laser oscillator, in which a main discharge is started by the auxiliary discharge. ,