JP2002050819A - Metal vapor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal vapor laser device for controlling a discharge tube temperature rapidly, safely, and reliably. SOLUTION: The metal vapor laser device 1 supplies a pulse voltage of 20 kV with a repeating frequency of 0.5 kHz, for example, in 45 minutes after a high-voltage pulse with a specific repeating frequency where the frequency has been changed appropriately by a repeating frequency-control device 25 is subjected to power supply failure, re-applies a pulse voltage of 20 kV with a repeating frequency of 0.2 kHz in additional 75 minutes, and safely turns off power when the temperature of the discharge tube reaches approximately 200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal vapor laser device, and more particularly to a mechanism for reducing thermal stress caused by a metal vapor source adhering to an inner wall of a discharge tube and maintaining the integrity of the discharge tube.

[0002]

2. Description of the Related Art FIG. 3 is a schematic view showing an example of a known metal vapor laser device. As shown in FIG. 3, the metal vapor laser device 1 includes a cylindrical ceramic tube 2 serving as a main portion of a discharge tube 5 and connection portions 2 a and 2 b at both ends on the axis of the ceramic tube 2. It has an anode 3 and a cathode 4 connected to both ends of a ceramic tube 2.

A pair of electrode flanges 6a and 6b are provided on the axis of the discharge tube 5 and outside the anode 3 and the cathode 4, respectively. Each of the electrode flanges 6a and 6b is provided on an outer cylinder 9 that supports an insulating tube 8 that covers the outer periphery of a heat insulating material 7 that is provided so as to surround the outer surface of the discharge tube 5.

A pair of Brewster tubes 10 is located outside the axis of the electrode flanges 6 a and 6 b and on the axis of the discharge tube 5.
a and 10b are connected. These Brewster tubes 10
a, 10b (on the axial extension of the discharge tube 5)
A pair of windows 11a and 11b are attached, and an output mirror 12 and a total reflection mirror 13 provided outside the windows 11a and 11b form a laser resonator.

[0005] A gas supply pipe 14 for supplying, for example, a neon (Ne) gas as a discharge gas into the discharge tube 5 is connected to the Brewster tube 10b shown on the left side of FIG.
A gas exhaust pipe 15 for exhausting gas in the discharge tube 5 is connected to the blaster tube 10a shown on the right side of FIG.

A pressure gauge 16, a flow regulating valve 17, and a vacuum pump 18 are connected to the gas exhaust pipe 15, and the gas pressure in the discharge tube 5 is controlled to be constant, for example. The pressure gauge 16, the flow control valve 17, and the vacuum exhaust pump 18 also manage the evacuation at the time of exchanging a plurality of metal evaporation sources 19 arranged inside the discharge tube 5.

[0007] A buffer gas supply source (not shown) is connected to the gas supply pipe 14, and a predetermined amount of buffer gas is supplied into the discharge tube 5 through a supply valve 20.

The outer cylinder 9 is provided at a substantially central portion in the longitudinal direction or at the center thereof in order to provide a predetermined potential difference between the electrode flange 6a for supplying power to the anode 3 and the electrode flange 6b for supplying power to the cathode 4. It is divided into two parts in the vicinity and functions as voltage supply flanges 21a and 21b.

The voltage supply flanges 21a and 21b are connected to each other by a charging resistor 22, and the two flanges 21a and 21b are connected to each other.
A high-voltage pulse power supply 23, which includes a capacitor, an inductor, a high-speed switching element, and the like, is turned on / off at a predetermined repetition frequency in synchronization with the pulse generated by the pulse reshaping device 24 at a high speed during a period 21b. A high pulse voltage is applied.

In such a metal vapor laser device 1, a discharge buffer gas is supplied into the discharge tube 5, and a high-speed pulse voltage is applied between the anode 3 and the cathode 4 from the pulse power supply 23 to discharge plasma. To form The pulse power source 23
Generates a pulse voltage having a repetition frequency of several thousand times per second, for example, in synchronization with the pulse timing signal supplied from the pulse shaper 24.

Thereafter, the inside of the discharge tube 5 is heated to a high temperature by the discharge plasma, and vaporized copper particles, ie, metal vapor, as a laser medium are generated from the metal vapor source 19, and the metal vapor diffuses into the discharge tube 5. The laser beam is oscillated when the excited metal vapor transitions to a low energy level by being excited by the free electrons in the discharged discharge plasma.

[0012]

By the way, when the laser device is disassembled and installed, such as the installation of a metal vapor source, and immediately after a long-time operation that may cause air intrusion, the operation is restarted immediately after the air has been introduced into the buffer gas. Water and the like, which adhere to the structural material of the ceramic tube 2 which is the main part of the discharge tube 5 and increase the discharge resistance and make the discharge unstable, so that the discharge tube reaches a temperature at which laser oscillation is possible. Until the internal temperature of 5 rises and a stable discharge can be obtained at that time, after visually confirming whether or not the discharge state has deteriorated, the buffer gas mixed with air, moisture, or the like is evacuated, and then a new gas is discharged. A so-called bake-out process and a deaeration operation are required in which the operation of injecting a buffer gas into the gas and restarting the discharge is repeated.

However, the discharge may be deteriorated in the metal vapor laser device, and the deterioration of the discharge may cause breakage of the ceramic tube 2 due to the discharge plasma coming into contact with the inner wall of the discharge tube 5, that is, the ceramic tube 2. In addition, an increase in the discharge resistance of the electric energy generated by the discharge causes damage to the electric elements in the discharge circuit due to abnormal overheating, so if the discharge deteriorates, it is necessary to immediately lower the temperature of the discharge tube. Yes, the discharge must be stopped.

As described above, the soundness of the laser device can be obtained by performing the operation of immediately lowering the discharge tube temperature due to the deterioration of the discharge. However, since the temperature change of the discharge tube and the like becomes large,
In addition to problems with soundness, such as damage to the discharge tube,
During the deaeration operation, personnel for monitoring and operating the discharge of the laser device are required.

When laser oscillation is not required, the discharge is stopped and the temperature of the discharge tube or the like is cooled down to room temperature in order to stop the laser oscillation operation from the viewpoint of soundness and energy saving of the apparatus or from the viewpoint of safety. However, it is conceivable that a large thermal stress is applied between the metal vapor source and the ceramic discharge tube in the process of cooling from the temperature at which metal vapor is generated to room temperature, and the discharge tube is damaged.

In order to lower the discharge tube temperature when the discharge deteriorates, there is a method of lowering the applied voltage. The discharge is performed under predetermined conditions such as the distance between the electrodes, the pressure of the discharge gas, the impurity gas concentration, and the like. In this case, since a discharge does not occur unless a voltage of a predetermined magnitude, for example, about 5 kV / m is applied in the example of the copper vapor laser device, it is difficult to lower the discharge tube temperature, and the discharge itself is substantially reduced. It is required to stop.

However, when the laser device is stopped, the discharge tube may be rapidly cooled and may be damaged, and replacement of the discharge tube due to the damage requires a great deal of cost.

An object of the present invention is to provide a metal vapor laser device capable of controlling a discharge tube temperature quickly, safely and reliably.

[0019]

SUMMARY OF THE INVENTION The present invention has been made based on the above-mentioned problems, and has a metal vapor source and heats a discharge tube filled with a discharge gas at a predetermined pressure by high-speed pulse discharge. A metal vapor laser device for generating a laser beam by generating a metal vapor by providing a control device capable of controlling the repetition frequency of the pulse discharge to control the temperature of the discharge tube. It is a metal vapor laser device.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram showing an example of a metal vapor laser device to which an embodiment of the present invention is applied. As shown in FIG. 1, a metal vapor laser device 1 includes a cylindrical ceramic tube 2 serving as a main part of a discharge tube 5.
And connecting portions 2a at both ends on the axis of the ceramic tube 2.
An anode 3 and a cathode 4 are connected to both ends of the ceramic tube 2 via 2b.

A pair of electrode flanges 6a and 6b are provided on the axis of the discharge tube 5 and outside the anode 3 and the cathode 4, respectively. Each of the electrode flanges 6a and 6b is provided on an outer cylinder 9 that supports an insulating tube 8 that covers the outer periphery of a heat insulating material 7 that is provided so as to surround the outer surface of the discharge tube 5.

A pair of Brewster tubes 10 are located outside the axis of the electrode flanges 6 a and 6 b and on the axis of the discharge tube 5.
a and 10b are connected. These Brewster tubes 1
A pair of windows 11a and 11b are attached to openings (on the extension on the axis of the discharge tube 5) of the openings 0a and 10b, and an output mirror 1 provided outside the windows 11a and 11b.
An optical oscillator is formed by 2 and the total reflection mirror 13.

A gas supply pipe 14 for supplying, for example, neon (Ne) gas as a discharge gas into the discharge tube 5 is connected to the blaster tube 10b shown on the left side of FIG.
A gas exhaust pipe 15 for exhausting gas in the discharge tube 5 is connected to the blaster tube 10a shown on the right side of FIG.

The gas exhaust pipe 15 is connected to a pressure gauge 16, a flow control valve 17, and a vacuum exhaust pump 18 so that the gas pressure in the discharge tube 5 is controlled to be constant, for example. The evacuation of the plurality of metal evaporation sources 19 arranged inside the discharge tube 5 is also controlled by the pressure gauge 16, the flow control valve 17, and the vacuum exhaust pump 18.

A buffer gas supply source (not shown) is connected to the gas supply pipe 14, and a predetermined amount of buffer gas is supplied into the discharge tube 5 through a supply valve 20.

The outer cylinder 9 is provided at a substantially central portion in the longitudinal direction or at the center thereof in order to give a predetermined potential difference between the electrode flange 6a for supplying power to the anode 3 and the electrode flange 6b for supplying power to the cathode 4. It is divided into two parts in the vicinity and functions as voltage supply flanges 21a and 21b.

The voltage supply flanges 21a and 21b are connected to each other by a charging resistor 22, and the two flanges 21a and 21b are connected to each other.
Between 21b, for example, a high-speed pulse from a high-voltage pulse power supply 23, which is constituted by a capacitor, an inductor, a high-speed switching element, and the like, is turned on / off at a predetermined repetition frequency in synchronization with a pulse generated by the pulse shaper 24, , A high voltage pulse voltage is applied.

The high-voltage pulse power supply 23 uses a high-speed switch element to charge the electric charge stored in a capacitor (not shown) with a rise time of approximately 10 ⁻⁷ seconds or less, a voltage of several tens to several tens of kV, and a repetition frequency of Several kHz to tens of k
It is configured to be able to output a high-voltage pulse voltage at a high speed of Hz. The high-voltage pulse power supply 23 controls the pulse voltage generation timing in synchronization with the pulse supplied from the pulse reshaping device 24. Further, the pulse reshaping device 24 is configured to be able to output a pulse signal having an arbitrary width and cycle according to a pulse frequency input from the repetition frequency control device 25 and having an arbitrary width and cycle.

Next, the operation of the above-described metal vapor laser device 1 will be described. First, the exhaust pump 18 is operated to evacuate the inside of the discharge tube 5, and thereafter, for example, neon gas is injected into the discharge tube 5 from the gas supply tube 14. At this time, the pressure of the buffer gas in the discharge tube 5 which has been increased by the injection of the buffer gas for discharge is measured by the pressure gauge 16, and a gas pressure control (not shown) is performed so that the measured value becomes a preset pressure value. The automatic flow control valve 17 is operated by the vessel,
The discharge amount of the buffer gas in the discharge tube 5 is adjusted, and the pressure in the discharge tube 5 is controlled to a set value.

Next, the discharge circuit, that is, the high-speed pulse power supply 23 and the pulse shaper 24 are operated to generate plasma in the discharge tube 5, and the plasma causes the metal vapor source 19 to reach a temperature at which the metal vapor source 19 can generate metal vapor. Raise the temperature. The temperature required for laser oscillation is, for example, a metal vapor source 19
Is about 1500 ° C.

By maintaining this state, the metal vapor is uniformly distributed in the discharge tube 5. Free electrons in the plasma collide with the metal vapor to excite the metal vapor, and the inside of the discharge tube 5 eventually assumes a population inversion state. In this state,
A laser beam is generated when the excited metal vapor transitions to a low energy level.

The laser light generated in the discharge tube 5 is
While passing through a and 11b and being reflected by the output mirror 12 and the total reflection mirror 13 constituting the laser resonator, the amplitude increases and the power is increased, and the laser light is output from the output mirror 12 soon.

However, immediately after the maintenance of the metal vapor laser apparatus 1 such as replenishment of the metal vapor source 19 or when the operation is stopped for a long time, the amount of metal vapor that can be generated from the metal vapor source 19 by electric discharge is reduced by the metal vapor laser light. By the time the temperature rises to a temperature at which the temperature rises, air and moisture adhering to the structural material such as the discharge tube 5 and the heat insulating material 7 are released into the buffer gas due to the temperature rise, and the discharge is deteriorated due to the increase in the discharge resistance. Therefore, the temperature in the discharge tube 5, particularly the temperature in the inner wall of the discharge tube where the metal vapor source is placed and the vicinity thereof is lowered by temporarily lowering the repetition frequency of the discharge, and the discharge is repeated again as the discharge is improved. Increase the frequency to discharge tube 5
It is necessary to raise the temperature inside.

When the laser oscillation operation is stopped, as shown in the example of FIG. 2, the discharge voltage and the repetition frequency are gradually reduced while being relaxed on the way, so that the thermal stress between the metal vapor source 19 and the ceramic tube 2 is reduced. It is preferable to suppress a rapid increase in

More specifically, as shown by a curve A in FIG.
The high-speed pulse voltage supplied to the anode 3 and the cathode 4 of
Once turned off, for example, after about 45 minutes, the repetition frequency is changed under the control of the repetition frequency control device 25, and the repetition frequency is applied again at, for example, 0.5 kHz and the pulse voltage is applied again at, for example, 20 kV.

Subsequently, after a lapse of about 45 minutes, for example, about 75 minutes later (about 2 hours after the power is turned off), a repetition frequency of, for example, 0.2 kHz and a pulse voltage of, for example, 20 kV are again applied. Apply.

Hereinafter, after a lapse of the previous two hours (a total of 45 minutes and 75 minutes), for example, after a lapse of about one hour and thirty minutes (about three and a half hours after the power is turned off), the temperature in the discharge tube 5 is reduced. When the temperature falls to about 200 ° C., the high-speed pulse power supply 23, the pulse reshaping device 24 and the repetition frequency control device 25 are completely turned off once again, whereby the discharge tube 5 is safely cooled.

In FIG. 2, a curve B shows a temperature change in the discharge tube 5 due to a normal power-off without the control of the present application. As described in the section of the related art, the rapid thermal stress changes between the metal vapor source 19 and the ceramic 2 tube, and in the worst case, the discharge tube 5 may be damaged. It is on the street.

By the way, in the curve A of FIG. 2, the repetition frequency is set to 0.5 kHz after approximately 45 minutes have elapsed since the power was turned off.
z, the pulse voltage was set to 20 kV, and after a lapse of about 75 minutes from the lapse of the previous 45 minutes, the repetition frequency was set to 0.2.
kHz, but the repetition frequency is 0.5 kHz as it is.
When z is maintained, the temperature in the discharge tube 5 is maintained at about 300 ° C. as in the case where the repetition frequency is set to 0.5 kHz from the beginning shown in the curve C. In that case, it is observed that the temperature from about 300 ° C. to about 200 ° C. drops rapidly.

On the other hand, as shown by the curve D, when the repetition frequency is set to, for example, 0.2 kHz from the beginning,
The time required for the temperature of the discharge tube 5 to fall to about 200 ° C. is substantially the same as the control method of the present application, but is from 400 ° C. to 200 ° C.
Since the time until the temperature drops to ° C is short, it should be avoided from the viewpoint of protecting the discharge tube 5.

According to the present invention, it is possible to control the temperature of the discharge tube 5 which cannot be controlled only by the voltage control, to maintain the soundness of the metal vapor laser device 1, and to reduce the number of personnel required for the operation. Reduction is also possible.

The metal vapor laser device 1 shown in FIG.
In the temperature control of FIG. 1, the temperature inside the discharge tube 5 near the metal vapor source is set by the thermometer shown in FIG. 1, for example, a radiation thermometer 26 of an infrared type or the like, and repeated based on the measured temperature information. The frequency may be controlled. In this case, the temperature information in the discharge tube 5 measured by the radiation thermometer 26 is taken into the computer 27, and the computer 27 controls the pulse width and the cycle input from the repetition frequency controller 25 to the pulse reshaping device 24. Is also good.

The result of detection of the temperature inside the discharge tube 5 by the radiation thermometer 26 is stored in advance in the computer 27, and the width and cycle of the pulse input from the repetition frequency control device 25 to the pulse shaper 24 by the computer 27 alone. May be controlled.

As described above, in the metal vapor laser device of the present invention, the discharge tube temperature can be freely and accurately controlled, and the soundness of the laser device such as the discharge tube can be reliably maintained, and automation can be performed. Therefore, the operating cost can be reduced.

[0045]

As described above, according to the present invention, the discharge tube temperature is controlled by controlling the repetition frequency of the high-speed, high-voltage pulse output from the high-speed pulse power supply. Tubes can be controlled quickly and safely.

Further, the soundness of the laser device can be reliably obtained, automation can be performed, and the operating cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a metal vapor laser device to which an embodiment of the present invention is applied.

FIG. 2 is a graph showing an example of the temperature control of a discharge tube when the metal vapor laser device shown in FIG. 1 is stopped (in the case of a copper vapor laser).

FIG. 3 is a schematic diagram showing a known example of the metal vapor laser device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Metal vapor laser device, 2 ... Ceramic tube, 5 ... Discharge tube, 23 ... High voltage pulse power supply, 24 ... Pulse shaper, 25 ... Repetition frequency control device, 26 ... a thermometer 27 ... a calculator.

Claims (5)

[Claims] 1. A metal vapor laser apparatus for holding a metal vapor source and heating a discharge tube filled with a discharge gas of a predetermined pressure by high-speed pulse discharge to generate a metal vapor and obtain a laser beam. A metal vapor laser device, comprising: a control device that controls a temperature of the discharge tube by controlling a repetition frequency of discharge. 2. The metal vapor laser device according to claim 1, wherein the pulse repetition frequency is set to a smaller repetition frequency than at the time of laser oscillation when stopping the laser oscillation of the metal vapor laser device. 3. A method for measuring a temperature drop of the discharge tube with a thermometer,
The metal vapor laser device according to claim 1, wherein a repetition frequency of the pulse discharge is controlled based on the measured temperature information. 4. The metal vapor laser device according to claim 3, wherein said pulse repetition frequency is changed by a computer. 5. A metal vapor laser apparatus for holding a metal vapor source and heating a discharge tube filled with a discharge gas at a predetermined pressure by high-speed pulse discharge to generate a metal vapor and obtain a laser beam. When the discharge tube is discharge-heated and evacuated to remove the impurity gas adhered to the discharge tube, when the discharge resistance increases due to an increase in the generation amount of the impurity gas and the discharge deteriorates, the high-speed pulse is repeated. A device for controlling the temperature of the discharge tube by lowering the frequency, and when the generation amount of the impurity gas decreases, increasing the repetition frequency of the high-speed pulse to increase the temperature of the discharge tube. Metal vapor laser device.