JPH0690042A - Laser discharge tube - Google Patents

Abstract

PURPOSE:To secure a stable base discharge region over a wide range. CONSTITUTION:A laser discharge tube is constituted of a discharge tube 10, main eletrodes 11 and 12, and a conductor 20 provided at a position a predetermined distance away from one end of each main electrode 11, 12. This conductor 20 is formed by vapor-depositing silver on the outer periphery of the discharge tube 10 by metallize in a ring form, where its width is about 20mm for example. When high frequency voltage is impressed across the main electrodes 11 and 12, a main discharge 100 develops across the main electrodes 11 and 12, and an auxiliary discharge 200 across the main eletrodes 11, 12 and the conductor 20. The main discharge 100 is a vertical discharge of high gain in the tube center to the tube axial direction, and a lateral discharge along this tube wall a discharge of low gain. Development of this auxiliary discharge weakens the main discharge 100 of high gain; as the result, a stable base discharge region free of laser output widens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser discharge tube for exciting a laser gas by discharging between electrodes, and more particularly to a laser discharge tube for improving discharge characteristics.

[0002]

2. Description of the Related Art In a laser oscillator, a high frequency voltage applied between electrodes causes a discharge in a discharge tube, and the discharge excites a laser gas to output a laser beam to the outside. The output control of the laser light is performed according to the output command value, and control from low output to high output is performed.

By the way, from the power-off state to the time when the power is turned on and laser light is output, it is necessary to excite the laser gas between the electrodes to start the discharge, and thus a high voltage is required. In the following description, the voltage required until the first discharge starts from the power-off state and the laser light is emitted is called the discharge start lighting voltage. On the other hand, once the discharge has started and the laser gas has started to discharge, after that, if the voltage is raised from the state of the base discharge by holding it in the low voltage state and performing the preliminary discharge (base discharge), it is not necessary to increase the voltage Can also obtain a predetermined laser output. that is,
This is because the resistance between the electrodes is lowered by shifting to the excited state.

Therefore, in the case of performing laser processing, usually, the resonator is set up in a base discharge state in advance, and the voltage and current are increased from the base discharge region. In the base discharge, since the laser light is not generated, the output of the resonator is 0 W, but the weak discharge to the extent that laser oscillation does not continue is maintained.

[0005]

However, in the region of this base discharge, the stable region is narrow and the change in ambient gas temperature
Due to factors such as a change in laser gas pressure and a change in laser gas composition, there is a problem that the gain of the resonator changes, a laser output is produced, or fluctuations occur in the discharge and the discharge is easily extinguished.

Further, the laser light pulse characteristic is a frequency response characteristic between the base discharge region of laser output 0 W and the rated output point, for example, but the laser light pulse characteristic also has a narrow base discharge stable region. In addition, there was a limit to the fall characteristic. That is, even if the voltage and current between the electrodes were reduced from the high output point to the base discharge region, it took some time for the laser output to reach 0 W. Further, when the laser gas temperature becomes high, the laser output becomes 0 even if the voltage and current between the electrodes are lowered to the base discharge region.
It did not become W and deteriorated the fall performance of the pulse characteristics. The deterioration of the pulse characteristics deteriorates the performance of laser processing and results in so-called sharp processing such as leaving a so-called marking line.

Further, in the above-mentioned conventional device, in order to start up the resonator directly from the power-off state to a predetermined output point,
It has been necessary to go through a process of once reducing the gas pressure and applying a high voltage discharge start lighting voltage to generate discharge between the electrodes and gradually returning to normal gas pressure, which requires a long time. Therefore, in practice, as described above, it was necessary to keep the laser oscillator always in the base discharge region.

The present invention has been made in view of the above circumstances, and it is possible to secure a stable base discharge region in a wide range, and to directly provide a short time even when the power is off without providing the base discharge region. It is an object of the present invention to provide a laser discharge tube capable of obtaining a predetermined output.

[0009]

In order to solve the above problems, the present invention provides a laser discharge tube in which a laser gas is excited by a discharge between electrodes, and a conductive material is provided on the outer circumference of the tube wall or inside the tube separately from the main electrode. Disclosed is a discharge tube for a laser provided with at least one body.

[0010]

In addition to the main electrode, at least one conductor is provided on the outer circumference of the tube wall or inside the tube. A horizontal electric field is formed between the main electrode and the conductor along the optical axis of the laser beam. Therefore, in the base discharge region where the voltage and current are low, the electric field formed in the discharge tube has not only the conventional vertical direction (vertical component) but also the horizontal direction (horizontal component). Unlike the vertical discharge, the horizontal discharge along the tube wall is a discharge in which the resonator gain is low and laser oscillation is difficult. Part of the voltage applied between the main electrodes is used for this horizontal discharge, and the voltage between the vertical main electrodes decreases. That is, the horizontal discharge weakens the high-gain vertical discharge. As a result, the base discharge area is expanded.

Further, the electric field strength distribution becomes dense due to the electric field formed between the main electrode and the conductor. Therefore, the discharge start lighting voltage becomes low, and a predetermined output can be obtained directly in a short time even when the power is off.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram schematically showing the structure of a laser discharge tube of the present invention. In the figure, only one end side of the laser discharge tube 1 is shown. The laser discharge tube 1 includes a discharge tube 10, main electrodes 11 and 12 provided on the outer periphery of the discharge tube 10, and the main electrode 1 thereof.
It is composed of a conductor 20 provided separately from the components 1 and 12.

The discharge tube 10 is a pipe made of quartz glass and having a circular cross section, and is used, for example, in a 1.5 KW carbon dioxide laser. Main electrodes 11 and 12 are provided on the outer peripheral surface of the discharge tube 10. The main electrodes 11 and 12 are formed by depositing silver on the outer peripheral surface of the discharge tube 10 by metallization. Radiators 14 and 15 are provided in contact with the main electrodes 11 and 12, respectively.

The conductor 20 is provided at a position separated from the one ends of the main electrodes 11 and 12 by a predetermined distance D (for example, 5 mm). This conductor 20 is the same as the main electrodes 11 and 1 described above.
Similar to 2, the silver is deposited on the outer peripheral surface of the discharge tube 10 by metallization to form a ring shape, and the width thereof is, for example, about 20 mm. Here, the conductor 20 is provided on the laser gas downstream side of the discharge tube 10, but it may be provided on another place of the discharge tube 20 if necessary.
Although one conductor 20 is provided, a plurality of conductors 20 may be provided. Further, the conductor 20 is connected to the discharge tube 1
It may be configured so as to be provided in the 0 tube.

In the discharge tube 10, laser gas is supplied with an arrow 30.
Flow in the axial direction of the main electrode 1 by the high frequency power source 13.
When a high frequency voltage is applied between 1 and 12, a discharge is generated between the main electrodes 11 and 12, and the laser gas is excited. At both ends of the discharge tube 10, a total reflection mirror and an output coupling mirror (not shown here) are provided to form a Fabry-Perot type resonator, which amplifies light emitted from the excited laser gas. Output as laser light.

When a high frequency voltage is applied, a discharge (auxiliary discharge) is also generated between the main electrodes 11 and 12 and the conductor 20. This auxiliary discharge will be described below. FIG. 2 is an explanatory diagram of the auxiliary discharge. When a high frequency voltage is applied between the main electrodes 11 and 12, a main discharge 100 occurs between the main electrodes 11 and 12, and an auxiliary discharge occurs between the main electrodes 11 and 12 and the conductor 20, as shown in the figure. 200 is generated. The main discharge 100 is a discharge in the vertical direction with respect to the tube axis direction. On the other hand, the auxiliary discharge 200 is a discharge in the lateral direction with respect to the tube axis direction, and this lateral discharge is a discharge in which laser light is hard to be generated.

In the base discharge region where the voltage and current are low, a part of the voltage applied between the main electrodes 11 and 12 is used for the auxiliary discharge in the horizontal direction, and the voltage in the vertical direction is correspondingly increased. The voltage between the main electrodes 11 and 12 drops.
That is, the generation of the auxiliary discharge weakens the main discharge 100 in which the laser light is likely to be generated. As a result, a stable base discharge region where laser light is not generated is expanded. Also,
By disposing the conductor 20 between the main electrodes 11 and 12, the electric field strength distribution becomes dense. Therefore, the discharge start lighting voltage becomes low. The base discharge region and the discharge starting lighting voltage will be described in detail below with reference to FIG.

FIG. 3 shows a high frequency current RF applied to the main electrode.
It is a figure which shows the relationship between I and the high frequency voltage RFV. In the figure, first, a case of a conventional discharge tube will be described using a broken line 51 and the like. In a conventional discharge tube not provided with the conductor 20, when an attempt is made to raise the resonator from the power-off state to a high output point, first, the voltage is a high voltage discharge start lighting voltage V ₄ ( For example, it is necessary to raise it to 4150V). When the discharge starting lighting voltage V ₄ is reached, the first dielectric breakdown occurs in the discharge tube and the discharge starts. When the discharge starts, the voltage once sharply decreases along the broken line 52. After that, the voltage and the current may be raised along the solid line 64 to a predetermined output point. In the resonator in which the discharge has started once, if the voltage and the current are held in the base discharge region 58 after that, the base discharge region 5
It is possible to rise along the solid line 64 from 8 to a predetermined output point at any time.

On the other hand, the discharge tube 1 provided with the conductor 20
At 0, when trying to raise the resonator from the power-off state to the high output point, the voltage may be raised along the solid line 61, and the discharge start lighting voltage V ₃ thereof is a relatively low voltage (eg, 3550V). As described above, the discharge start lighting voltage V ₃ becomes significantly lower than the conventional discharge start lighting voltage V ₄ as described above.
Auxiliary discharge 20 formed between the conductors 1 and 12 and the conductor 20
This is because the distribution of the electric field strength becomes dense due to 0.

When the discharge is started at the discharge start lighting voltage V ₃ , the voltage once sharply decreases along the solid line 62 as in the case of the above-mentioned conventional case. After that, the voltage and the current may be raised along the solid line 64 to a predetermined output point.

Further, in the case of the discharge tube 10 provided with the conductor 20, the base discharge area 68 thereof is greatly expanded as compared with the conventional base discharge area 58. In this way, the base discharge region 68 is greatly expanded because, as described above, the generation of the auxiliary discharge 200 causes the vertical main electrodes 11 and 1 to extend.
This is because the voltage between the two drops and the main discharge 100 is weakened accordingly. The base discharge region 68 is more stable than the conventional base discharge region 58, with no fluctuation or disappearance of the discharge. Therefore, the resonator can be more surely held in the base discharge state.

When the resonator is started up, it can be started up along the solid line 64 from the stable base discharge region 68 to a predetermined output point at any time. Alternatively, by utilizing the fact that the discharge start lighting voltage is greatly reduced from V ₄ to V ₃ , the discharge start lighting voltage V ₃ and the solid line 64 are directly passed from the power-off state to a predetermined high output point. It can also be set up by launching. In that case, it becomes unnecessary to hold the voltage and the current in the base discharge region 68. Therefore, when laser processing is not performed, the power may be turned off. Further, since the discharge starting lighting voltage V ₃ is low, the rise time of the resonator can be shortened accordingly.

Further, in the conventional narrow base discharge region 58, when the laser gas pressure is high, the base discharge becomes unstable. Therefore, it is necessary to set the laser gas pressure low when holding the resonator in the base discharge. On the other hand, since the base discharge region 68 can be widened, the base discharge can be maintained even when the laser gas pressure is high. If the laser gas pressure is high, a high output can be obtained accordingly, and from this point as well, the base discharge can be started up to a high output state in a shorter time.

Next, the effect associated with the expansion of the base discharge region will be described with reference to FIGS. 4 and 5. FIG. 4 is a laser light pulse characteristic diagram. The laser light pulse characteristic is a frequency response characteristic between the base discharge region of 0 W of laser output and the rated output point, for example. Here, the frequency is 2KH
z, the case of rated output 1500W is shown. A waveform 70 shown by a broken line is a laser light pulse characteristic in the conventional discharge tube, and a waveform 80 shown by a solid line is a laser light pulse characteristic in the discharge tube 10 provided with the conductor 20. As shown in the figure, the trailing edge of the waveform 80 is steeper than that of the waveform 70 and is greatly improved. This is due to the following reasons. That is, in the conventional discharge tube, the command current when the laser output command is 0 W is I _{2 as} shown in FIG.
It could not be lowered below the value. On the other hand, in the discharge tube 10 provided with the conductor 20, the base discharge region 68 is greatly expanded, so that it is possible to lower the I ₁ value. Therefore, in the case of the discharge tube 10 provided with the conductor 20, the laser output 0W command can be performed with a lower command current. Therefore, as shown by the waveform 80, the laser output is controlled to 0W with a sharp fall. can do.

Further, as shown in the figure, the waveform 80 surely decreases to the laser output of 0 W, whereas the waveform 70 does not completely decrease to 0 W. This is because, as described above, in the conventional discharge tube, the current of the laser output 0 W command can be reduced only to the I ₂ value, and in that region, when the laser gas temperature becomes high, the gain of the resonator becomes high. This is because a false laser output is generated. On the other hand, the conductor 20
In the discharge tube 10 provided with the current of the laser output 0 W I ₁
Can be lowered to a value. Therefore, the current can be reliably reduced to the region where the laser output is not output.

As described above, the laser light pulse characteristic is improved and the laser output is increased, so that the laser processing performance is improved and so-called sharp cutting can be performed without generating so-called marking lines.

FIG. 5 is an explanatory diagram for improving the electric shutter function. The electric shutter function here is a base discharge response characteristic for switching from a high output point such as a rated output to a base discharge region where the laser output is 0 W. Here, the rated output is 15
The case where 00W is turned off to 0W is shown. A waveform 90 shown by a broken line is a base discharge response characteristic in a conventional discharge tube,
The waveform 95 shown by the solid line is the discharge tube 1 provided with the conductor 20.
It is a base discharge response characteristic at 0. As shown in the figure, the fall of the waveform 95 is steeper than that of the waveform 90, and the electric shutter function for switching to the laser output 0 W is greatly improved. This is due to the expansion of the base discharge region 68, as in the case of the above laser light pulse characteristics.
This is because the command current when the laser output 0 W is commanded can be greatly reduced. By improving the electric shutter function, an incomplete cutting portion such as a marking line that is left at the end of the conventional cutting processing does not remain, and a more complete cutting processing can be performed. Also, the cutting processing time can be shortened.

FIG. 6 is a diagram showing a second embodiment of the laser discharge tube of the present invention. The discharge tube 10A of this embodiment has two spiral electrodes 11A and 12A, and a conductor 20A is provided on one end side of the spiral electrodes 11A and 12A.

FIG. 7 is a view showing a third embodiment of the laser discharge tube of the present invention. Although this drawing is drawn schematically as compared with FIG. 6 described above, the discharge tube 10B also corresponds to the discharge tube 10 of FIG.
Similar to A, it has two spiral electrodes 11B and 12B. The conductor 20B is similarly provided spirally between the two electrodes 11B and 12B. That is,
The conductor 20B is provided in the entire discharge region of the discharge tube 10B. Therefore, the auxiliary discharge can be generated more reliably and stably.

In the above description, the conductor is provided to generate the auxiliary discharge, but a ferroelectric may be provided in place of this conductor. In this case, the ferroelectric substance may be, for example, a dielectric constant ε = 1000 and a thickness of 0.5 mm.
Barium titanate or the like can be applied.

Further, the conductor may be constructed as a discontinuous resistor connected to the main electrode. Further, an electrode may be provided on the conductor, and the divided voltage may be supplied to the electrode so that the base discharge can be performed more stably.

[0032]

As described above, in the present invention, at least one conductor is provided outside the main wall of the discharge tube or inside the tube in addition to the main electrode. A lateral discharge is formed between the main electrode and the conductor along the optical axis of the laser light. Unlike the vertical discharge, the horizontal discharge is a discharge with a low resonator gain. A part of the voltage applied between the main electrodes is used for this lateral discharge,
The voltage between the main electrodes in the vertical direction drops. That is, the horizontal discharge weakens the vertical discharge having a high resonator gain. Therefore, the stable base discharge region without laser output is expanded, and the resonator can be more surely held in the base discharge state.

Further, as the base discharge area becomes wider, the command current for the laser output 0 W can be set lower, and as a result, the laser light pulse characteristic and the electric shutter function can be greatly improved. . Further, the laser gas pressure can be increased to improve the oscillation efficiency as the base discharge region is widened.

Further, the electric field strength distribution becomes dense due to the electric field formed between the main electrode and the conductor. Therefore, the discharge start lighting voltage becomes low, and a predetermined output can be obtained directly in a short time even when the power is off. Therefore, it is possible to eliminate the need for holding the base discharge during laser processing.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of a laser discharge tube of the present invention.

FIG. 2 is an explanatory diagram of auxiliary discharge.

FIG. 3 is a diagram showing a relationship between a high frequency current RFI applied to a main electrode and a high frequency voltage RFV.

FIG. 4 is a laser light pulse characteristic diagram.

FIG. 5 is an explanatory diagram of an electric shutter function improvement.

FIG. 6 is a diagram showing a second embodiment of the laser discharge tube of the present invention.

FIG. 7 is a diagram showing a third embodiment of the laser discharge tube of the present invention.

[Explanation of symbols]

 10, 10A, 10B Discharge tube 11, 11A, 11B Main electrode 12, 12A, 12B Main electrode 13 High frequency power source 20 Conductor 100 Main discharge 200 Auxiliary discharge

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Manabe 3580, Kobaba, Oshinomura, Minamitsuru-gun, Yamanashi Prefecture FANUC CORPORATION (72) Inventor, Ryoki Fujioka 3580, Kobaba, Oshinomura, Minamitsuru-gun, Yamanashi Local FANUC Co., Ltd.

Claims (6)

[Claims] 1. A laser discharge tube for exciting a laser gas by a discharge between electrodes, wherein at least one conductor is provided on the outer circumference of the tube wall or inside the tube in addition to the main electrode. tube. 2. The laser discharge tube according to claim 1, wherein the conductor is provided in a ring shape on the outer circumference of the tube wall. 3. The laser discharge tube according to claim 1, wherein an electrode for supplying power is provided on the conductor. 4. The laser discharge tube according to claim 1, wherein the conductor is provided in the entire discharge region. 5. The laser discharge tube according to claim 1, wherein a ferroelectric substance is provided instead of the conductor. 6. The discharge tube for laser according to claim 1, wherein the conductor is a resistor.