JPS6339113B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas laser oscillator, and particularly to a device for generating pulsed laser oscillation.

A typical example of this type of laser is a three-axis orthogonal CO ₂ laser in which the laser optical axis, DC glow discharge path, and gas flow direction are substantially perpendicular to each other, so a conventional example will be described. Figure 1 is a vertical cross-sectional view of a 3-axis orthogonal laser, and Figure 2 is a vertical cross-sectional view of the 3-axis orthogonal laser.
FIG. In the figure, 1 is an anode, 2 is a cathode, 3 is a cathode substrate, 4 is a stabilizing resistor,
5 is a DC high voltage power supply, 6 is a discharge excitation unit, 7 is a total reflection mirror, and 8 is a partial reflection mirror.

Next, the operation will be explained. When a laser gas consisting of a mixed gas of CO ₂ , N ₂ , and He is flowed between the anode 1 and the cathode 2 at a flow rate of several tens of meters per second in the direction of the arrow, and a DC high voltage 5 is applied, a discharge occurs between the electrodes.
Since current flows through the stabilizing resistor 4, the discharge does not turn into an arc, and a gentle glow discharge is maintained. Discharge excitation part 6 generated by glow discharge
In this case, population inversion occurs between specific vibrational levels of CO ₂ molecules in the laser gas, and if a total reflection mirror 7 and a partial reflection mirror 8 having an appropriate reflectance are placed facing each other between the discharge excitation part 6. , laser oscillation occurs, and a laser beam comes out from the partially reflecting mirror 8. The laser output increases as the discharge power increases. For example, if the number of cathodes 2 is constant in the case shown in FIG. 1, an increase in the discharge power is equivalent to an increase in the discharge density. From the viewpoint of making the device more compact and reducing costs, it is desirable to increase the discharge density, but if the discharge power is increased beyond a certain level, a high temperature area will be generated locally in the discharge area, and the stabilizing resistor 4 will be present. However, the discharge will transition to an arc. When the discharge transitions to an arc, laser output is no longer obtained and the degradation of the laser gas increases significantly. Therefore, in order to make the oscillator more compact and to ensure reliability, laser oscillators are constructed so that the maximum output can be obtained before the discharge transitions to an arc.

By the way, when processing materials with high thermal conductivity, such as metals, with a laser beam, the thermal energy travels through the material and escapes to the outside, so if the average output is equal, the pulsed Generally speaking, a laser output with a large peak provides better machining energy, machining accuracy, etc.

For this reason, conventionally, with the configuration shown in FIG. 1, the output of the DC high voltage power supply 5 was made into the pulse output shown in FIG. 3a, and the pulsed laser output shown in FIG. 3b was obtained.

However, in such a pulsed laser oscillator, the peak laser output does not exceed the maximum output in the case of temporally constant laser output (continuous oscillation), and if you try to obtain the same average output as in the latter case, It is necessary to increase the number of cathodes 2 and make the oscillator larger.

For example, as shown in Figure 3a, if the voltage is applied for half of the period of the pulse power supply, that is, if the duty factor is 50%, then In order to obtain the same average output as the laser output, twice the size and twice the power supply capacity are required. Furthermore, in laser excitation using only glow discharge as shown in Figure 1, if the rise time of the pulse voltage is short, thermal diffusion is difficult to occur inside the glow discharge.
A thermal imbalance occurs, causing an arc to occur even if the current is less than the arc generating current. For this reason, a limit is placed on the rise time of the current, and in such a pulse output laser oscillator, the frequency of the pulse output has been limited to several tens of Hz at most.

On the other hand, in the field of laser processing, the higher the frequency of the pulse, the better the performance in processing accuracy, processing speed, etc., so it is desirable to develop a compact laser device that can obtain even higher frequencies and is easy to operate. It was rare.

This invention was made in view of the above request,
By using silent discharge as a pre-ionization means, the glow discharge is stabilized, and by utilizing the change in discharge characteristics of the glow discharge of the main discharge due to pre-ionization, it is compact, has a high pulse frequency, and has a high pulse rate. It is intended to provide an output laser oscillator.

Since this invention was born from deep consideration of the discharge characteristics of glow discharge as a main discharge when silent discharge is used as preliminary ionization, the operation of the invention will be explained while explaining these discharge characteristics.

FIG. 4 is a vertical sectional view of one embodiment of the present invention, and FIG.
The figure is a cross-sectional view taken from the line in Figure 4, where 9 is a dielectric electrode, 10 is a cooling water inlet for cooling this electrode, 11 is a cooling water outlet, 12 is a high voltage terminal, and 13 is a silent discharge. This is an AC high voltage power supply for generating electricity. FIG. 6 is a cross-sectional view of the dielectric electrode 9, in which 9-1 is an iron tube and 9-2 is a dielectric, usually made of glass. In such a configuration, when the high-current, high-voltage power supply 13 is operated, a gentle discharge called a silent discharge occurs between the dielectric electrode 9 and the anode 1 and cathode 2. This discharge current is 1/20 of the glow discharge current of the main discharge described below. When the DC high voltage power supply 5 is operated in this state, the anode 1
A glow discharge occurs between the electrode 2 and the cathode 2, and a discharge portion 6 as shown in FIG. 5 is generated. When preliminary ionization is performed by silent discharge, the so-called V-i characteristics of the current and voltage of glow discharge change greatly.

An example of its characteristics is shown in FIG. The vertical axis is the discharge sustaining voltage V of glow discharge, and the horizontal axis is the glow discharge current i
It is. The characteristic curve in the figure is the V-i characteristic when silent discharge is not performed, and the characteristic curve is the V-i characteristic when silent discharge is performed steadily (13 AC high voltages are always applied). It is a characteristic.

The flat part of the characteristic curve (constant current characteristic) indicates that glow discharge is occurring, and the part where V rapidly drops as i increases indicates transition to arc discharge. In a laser device, the maximum operating point is just before the transition to an arc. Comparing the characteristic curves and characteristic curves, it can be seen that when a silent discharge is performed and pre-ionization is performed, the current until it transitions to an arc increases several times, and the sustaining voltage of the glow discharge decreases. By the way, as mentioned above, the glow discharge current flows through the stabilizing resistor 4, and the electric circuit thereof is shown in FIG. 8. In the figure, E represents the output voltage of the DC high voltage power supply 5, i represents the current flowing in the glow discharge, and V represents the discharge sustaining voltage of the glow discharge. It is easy to understand that the following equation holds true from this circuit system.

=E-iR The characteristic curve of this equation is drawn as a broken line in FIG. 7, and the intersection of the characteristic curve and the characteristic curve becomes the operating point _P1 when silent discharge is not performed. The voltage×current at this operating point _P1 becomes the glow discharge power _P1 , and a laser output corresponding to the power of _P1 =6KV×2A=12KW is obtained. However, when silent discharge is performed using the same device (same resistance value R), the operating point moves to point _P2 where the characteristic curves intersect. The discharge power _P2 at this time is
P ₂ = 5.5 KV x 6.25 A ≒ 34 KW, which means that approximately 2.9 times the power of P ₁ can be obtained, and the laser output will also be larger than this. An example of the relationship between discharge power P and laser output is shown in Figure 9, and at operating point P ₁ it is 12KW.
A laser output of 0.7KW was obtained for a discharge power of , and at operating point P ₂ a laser output of 0.7KW was obtained for a discharge power of
A laser output of 5.3KW can be obtained.

As explained above, when silent discharge is used as pre-ionization, the glow discharge characteristics change greatly, but
The present invention utilizes this characteristic to input large pulsed discharge power to obtain large pulsed laser output.

FIG. 10 is a waveform diagram for explaining an embodiment of the present invention. FIG. 10a is an output voltage waveform diagram when the AC high voltage power supply 13 is pulsed, and FIG. Waveform diagram, figure c is a waveform diagram of the laser output. A high AC voltage is applied for a certain period of time to cause silent discharge, and then paused for a certain period of time, thereby repeating fp = frequency. As mentioned earlier, the power of silent discharge is a few percent of the main discharge (glow).
Therefore, waveform control is easy. When such a voltage is applied, silent discharge also occurs only when a voltage is applied corresponding to this fp. Therefore, if the transition from operating point P ₁ to P ₂ shown in Figure 7 occurs with a period fp and the DC high voltage power supply is a constant voltage type, the power input changes as shown in Figure 10b, and the As a result, the pulsed laser output shown in figure c is obtained. In this method, preliminary ionization is performed by silent discharge, so thermal diffusion becomes active and no thermal imbalance occurs inside the glow discharge, so an extremely stable glow can be maintained even if the glow discharge current changes. Therefore, experiments have shown that, for example, at a laser gas pressure of 200 Torr, the pulse repetition frequency fp can be up to about 10 KHz.

The example shown in Fig. 10 shows a case where a laser output of about 0.7KW is obtained even when the silent discharge is at rest, but depending on the value of resistor 4, the 7th
Since the operating points P ₁ and P ₂ in the figure move, the combination of Figures 7 and 9 shows that the laser output during this rest period can be adjusted arbitrarily (it can even be set to zero). Needless to say.

The above explanation was for the case where the DC high voltage power supply 5 was a constant voltage type, but the other embodiment of the invention shown in FIG. 11 uses a constant current type DC high voltage power supply 5. , 14 are capacitors connected in parallel to the DC high voltage power supply 5.

In a laser oscillator configured in this way,
When a silent discharge is not formed, the terminal voltage of the capacitor 14 is _E1 , but when a silent discharge is formed, a large glow discharge current flows, so that it cannot be supplied only by the DC high voltage power supply 5 (constant). (since it is a current source), it is also supplied from the capacitor 14, and a pulsed laser output similar to that shown in FIG. 10c above is obtained. Furthermore, if the capacitance of the capacitor 14 is sufficiently large at this time, the terminal voltage will hardly drop, and a large current can be supplied during silent discharge formation.

In this embodiment, since the DC power supply 5 is of a constant current type, in combination with the capacitor 14, the maximum current capacity of the DC high voltage power supply 5 may be the average current value of the glow discharge current.

On the other hand, even if the DC high voltage power supply 5 is a constant voltage type, the maximum current capacity of the DC high voltage power supply 5 can be increased by connecting between the output side of the coil 15 and the capacitor 14 as shown in FIG. can be set to the glow discharge current value, and the installed capacity of the power supply can be reduced.

As explained above, when silent discharge is performed as a preliminary ionization source in direct current glow discharge, pulsed laser output can be obtained by using a pulse output as the silent discharge power source, and this output is higher than when glow discharge is used alone. It will be 2 to 3 times more. Moreover, since the silent discharge requires about 1/20 of the current of the glow discharge of the main discharge, silent discharge can be controlled extremely easily, and the laser pulse output can be easily controlled. Moreover, since silent discharge is used as preliminary ionization, a stable glow is formed even if the rise of the glow discharge current is accelerated, and the frequency of the laser pulse can be increased to several KHz.

In the above embodiment, a high DC voltage that does not generate a glow discharge by itself is applied between the anode and the cathode, and a pulsed AC high voltage is applied to the dielectric electrode to generate a silent discharge. Although we have shown a configuration that generates a glow discharge as a trigger to output a laser pulse, even if a high DC voltage that generates a glow discharge is applied between the anode and cathode, it is possible to output a similarly large laser output in the form of a pulse. can be released. This state can be understood as corresponding to the state of transition from operating point P ₁ to P ₂ in the characteristic diagram of FIG.

This invention comprises: an anode and a cathode which are arranged to face each other across a laser gas airflow and to which a DC high voltage is applied; an anode and a cathode which are arranged in the laser gas airflow and to which a pulsed AC high voltage is applied; In a gas laser oscillator that is equipped with a dielectric electrode that generates a silent discharge between the anode and the cathode, and that excites the laser by the glow discharge that occurs between the anode and the cathode, the voltage is intermittently applied from an AC high voltage power source. By intermittently changing the discharge power of the silent discharge, the power of the glow discharge is induced to change intermittently, and the laser output is pulsed. The excellent effect of making it possible to control the high-frequency pulse laser output was achieved.

[Brief explanation of the drawing]

Figure 1 is a vertical cross-sectional view of a conventional horizontal gas laser oscillator, Figure 2 is a cross-sectional view along the line shown in Figure 1, and Figures 3 a and b are power supply voltage waveforms when a DC high voltage power supply is used as a pulse output. and a laser output waveform diagram, FIG. 4 is a longitudinal cross-sectional view of one embodiment of the present invention, FIG. 5 is a cross-sectional view taken along the line shown in FIG. Figure 8 is an equivalent circuit diagram of DC glow discharge, Figure 9 is a characteristic diagram showing the relationship between discharge power and laser output in this example, and Figure 10a is a diagram showing the relationship between AC power and laser output. Figure 11 is a circuit diagram of another embodiment of the present invention, and Figure 12 is a diagram of another embodiment of the present invention. FIG. 3 is an example circuit diagram. In the figure, 1 is an anode, 2 is a cathode, 5 is a DC high voltage power supply, 6 is a discharge excitation part, 9 is a dielectric electrode, 9-
1 is an iron pipe, 9-2 is glass, and 13 is an AC high voltage power supply. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An anode and a cathode arranged opposite to each other across the laser gas airflow and connected to a DC high voltage power supply, and an anode and a cathode arranged in the laser gas airflow and connected to an AC high voltage power supply, In a gas laser oscillator that is equipped with a dielectric electrode that generates a silent discharge between an anode and a cathode, and that excites the laser by the glow discharge that occurs between the anode and the cathode, the voltage application from the AC high voltage power source is intermittently applied. A gas laser oscillator characterized in that the gas laser oscillator is configured to induce intermittent changes in the power of the glow discharge and pulse the laser output by intermittently changing the discharge power of the silent discharge. 2. The gas laser oscillator according to claim 1, wherein the DC high voltage power supply is a constant current type, and a capacitor is connected in parallel to the output end of the constant current high voltage power supply. 3. The gas laser oscillator according to claim 1, comprising a coil connected in series to the output end of a constant voltage type high voltage power supply, and a capacitor that grounds the output side of this coil.