JP2002050810A - Metal vapor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal vapor laser device for obtaining stable and efficient laser output for a long time. SOLUTION: The metal vapor laser device 1 is provided with a discharge tube 5 that retains a metal vapor source 19 inside and is filled with a discharge gas having a specific pressure, an anode 3 and a cathode 4 provided at both ends of the discharge tube 5, and extension tubes 10a and 10b for mounting a window that are provided at both ends on the extension line of the axial line of the discharge tube 5 and retain windows 11a and 11b for transmitting a laser beam. The windows 11a and 11b are located at distance L that is at least seven times larger than the inner diameter of the discharge tube from the end of the discharge tube 5.

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 metal vapor laser device capable of efficiently obtaining a laser output for a long time.

[0002]

2. Description of the Related Art A known metal vapor laser apparatus has a cylindrical ceramic tube and a discharge tube comprising an anode and a cathode provided at both ends of the ceramic tube. On the outward extension along the optical axis of the discharge tube, portions located outside each of the anode and the cathode are connected to a pair of window mounting extension tubes via an electrode flange. .

[0003] A pair of windows for transmitting laser light made of quartz glass are attached to the outer opening of the window attachment extension tube in a non-perpendicular, that is, obliquely hermetically joined to the optical axis.
Further, an output mirror and a total reflection mirror which constitute a laser resonator are arranged outside each window.

A gas supply pipe for supplying a buffer gas for discharge control, for example, a neon (Ne) gas, is connected to one of the extension pipes for attaching a window, and a discharge pipe is connected to the other extension pipe for attaching a window. A gas exhaust pipe for exhausting the pipe is connected.

[0005] A pressure gauge, a flow regulating valve and a vacuum exhaust pump are connected to the gas exhaust pipe, and the gas pressure in the discharge tube is maintained at a predetermined value. The evacuation at the time of exchanging a plurality of metal evaporation sources arranged inside the discharge tube and the like is also managed by the pressure gauge, the flow control valve, and the vacuum exhaust pump.

In such a metal vapor laser device, a discharge plasma is formed by supplying a buffer gas into the discharge tube and applying a high-speed pulse voltage between the anode and the cathode by a high-voltage pulse power supply. You.

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

[0008]

In the above-described metal vapor laser apparatus, a large number of metal vapors exist in a high temperature region where discharge plasma can be generated in the discharge tube, and a part of the metal vapors is used as an extension pipe for window mounting. And fly to windows attached to both ends thereof.

Further, since a part of the heat insulating material covering the outer surface of the discharge tube is structurally exposed to the discharge plasma at the connection between the anode and the cathode and the discharge tube, it is damaged by the discharge plasma. It is also known that damaged insulation scatters into windows at both ends.

As described above, when the metal vapor and the damaged heat insulating material adhere to the window outside the window-mounting extension pipe, the transmittance of the window decreases, and the transmittance gradually decreases through the output mirror and the total reflection mirror of the laser resonator. There is a problem that the laser output is reduced.

An object of the present invention is to provide a metal vapor laser device capable of efficiently obtaining a laser output for a long period of time.

[0012]

SUMMARY OF THE INVENTION The present invention provides a discharge tube in which a metal vapor source is held and filled with a discharge gas of a predetermined pressure, an anode and a cathode provided at both ends of the discharge tube, And a window-mounting extension tube that is provided to extend outward from the position of the cathode further along the optical axis of the discharge tube,
In a metal vapor laser device having a window for transmitting a laser beam mounted near the end of the window mounting extension tube, the window mounted on the window mounting extension tube receives the discharge from the end of the discharge tube. This is a metal vapor laser device installed at a position that is at least seven times the inner diameter of the tube.

[0013]

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 discharge tube 5 having a cylindrical ceramic tube 2 and an anode 3 and a cathode 4 connected to both ends of the ceramic tube 2 via connecting portions 2a and 2b. have.

A pair of electrode flanges 6a and 6b are provided at portions located outside the anode 3 and the cathode 4, respectively. In addition, each electrode flange 6a, 6b
Are provided on outer cylinders 9a and 9b that support an insulating tube 8 that covers the outer periphery of a heat insulating material 7 provided so as to surround the outer surface of the discharge tube 5.

Outside the electrode flanges 6a and 6b, a pair of extension pipes 10a and 10b for window attachment are connected. A pair of windows 11a, 11b made of, for example, quartz glass for transmitting a laser beam is formed in a vacuum on the outer openings of the window mounting extension tubes 10a, 10b, that is, the extensions along the optical axis of the discharge tube 5. Installed airtight. An output mirror 12 and a total reflection mirror 13 are arranged outside these windows 11a and 11b, and constitute an optical resonator.

Therefore, the distance L from the position of the windows 11a, 11b attached to the window attachment extension tubes 10a, 10b to the end of the discharge tube 5 is equal to the discharge tube 5, ie, the ceramic tube 2
Is set to be 7 times or more of the inner diameter D (that is, the effective inner diameter). Note that the end of the discharge tube 5 that defines the distance L means the end of each region on the window side that functions as an insulating discharge tube during operation of the laser device. Therefore, as shown in the figure, in the structure in which the open end of the cylindrical anode 3 or the cylindrical cathode 4 projects in the direction of the ceramic tube 2,
The distance L is defined as a dimension from the position of the windows 11a and 11b to the opening end of the cylindrical anode 3 or the cylindrical cathode 4 on the ceramic tube 2 side.

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 window-mounting extension 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 window-mounting extension tube 10a shown on the right side of FIG.

A pressure gauge 16, a flow control 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 maintained at a predetermined value. The pressure gauge 1
6, by the flow control valve 17 and the vacuum pump 18
Exhaust when the plurality of metal evaporation sources 19 arranged inside the discharge tube 5 are replaced is also managed.

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

The outer cylinders 9a and 9b are arranged substantially at the center in the longitudinal direction 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. Alternatively, the conductive member is divided into two parts in the vicinity thereof, and also functions as the 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-speed pulse from a high-voltage pulse power supply 23 which is constituted by, for example, a capacitor, an inductor, and a high-speed switching element and is turned on / off at a predetermined repetition frequency in synchronization with the pulse generated by the pulse shaper 24 is provided between the high-speed pulse generator 21b A high 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 tens of kV. kHz to tens of kilohertz
It is configured to be able to output a high-voltage pulse voltage at a high speed of Hz. Note that the high-voltage pulse power supply 23 is
The pulse voltage generation timing is controlled in synchronization with the pulse supplied from.

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 after the evacuation, 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 heater, and the discharge amount of the buffer gas in the discharge tube 5 is adjusted and controlled.

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 1400 ° C. when is copper.

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 beam generated in the discharge tube 5 is
While the laser beam passes through a and 11b and is reflected by the output mirror 12 and the total reflection mirror 13 constituting the laser resonator, its amplitude is amplified, and a laser beam is output from the output mirror 12 in due course.

By the way, the metal vapor laser device 1 uses a resonance mirror composed of the output mirror 12 and the total reflection mirror 13 so that free electrons in the discharge plasma collide with each other and the excited metal vapor transitions. The laser light to be output resonates. As the distance between the mirrors 12 and 13 and the discharge tube 5 is narrower, that is, as the mirrors are closer to the discharge tube 5, a larger laser output is obtained. As a technique for reducing the distance between the resonance mirrors 12 and 13 to obtain a large laser output, it is effective to reduce the distance between the windows 11 a and 11 b and the discharge tube 5.
If the discharge lamps 1a and 11b are too close to the discharge tube 5, the windows 11a and 11b may be damaged by the discharge itself.

For this reason, conventionally, it is best to set the distance L from the windows 11a, 11b to the end of the discharge tube 5 to about two to three times the inner diameter (ie, the effective inner diameter) D of the discharge tube 5. However, as described above, the metal vapor from the inside of the discharge tube 5 and the impurities caused by damage of the heat insulating material 7 exposed between the anode 3 and the cathode 4 and the ceramic tube 2 by the discharge plasma, It has been confirmed that when the impurity particles adhere to the inner surfaces of the windows 11a and 11b, the laser output gradually decreases. The number O of the impurity particles adhering to the windows 11a and 11b is represented by k as a constant, D as the inner diameter of the discharge tube,
When L is the distance from the window to the end of the discharge tube, it can be obtained by O = kD ² / L ² .

Therefore, the number O of the impurity particles is proportional to the square of the inner diameter D of the discharge tube 5 (the ceramic tube 2), and the distance L from the end of the discharge tube 5 (the ceramic tube 2) to the windows 11a and 11b. Is inversely proportional to the square of

Therefore, in order to reduce the number of impurity particles adhering to the windows 11a and 11b, the inner diameter D of the discharge tube 5 must be reduced or the discharge tube 5 (the ceramic tube 2) must be reduced.
It is beneficial to increase the distance L from the end of the window 11a to the window 11b.

However, since the inner diameter (diameter) D of the discharge tube 5 is usually determined in advance based on the output specifications of the laser device, the number of impurity particles adhering to the windows 11a and 11b is substantially reduced. For this purpose, it is practical to increase the distance L from the windows 11a, 11b to the end of the discharge tube 5, that is, the length of the window-mounting extension tubes 10a, 10b, for example.

FIG. 2 shows the distance L between the windows 11a and 11b and the anode 3 and the cathode 4 of the discharge tube 5 and the number of impurity particles adhering to the windows 11a and 11b when the laser device is operated for a predetermined time. 6 is a graph showing the relationship between the above and the actual measurement. From this result, when the distance L between the windows 11a and 11b and the end of the discharge tube 5 is set to 600 mm, compared to a conventional general laser apparatus having a distance L of 450 mm, the distance L is about 0.5 mm. Can be reduced by a factor of two. Also, windows 11a and 11b
When the distance L between the discharge tube 5 and the end of the discharge tube 5 is 1000 mm, it can be recognized that the distance L can be reduced by 0.2 times.

FIG. 3 shows the ratio (L / D) between the distance L between the windows 11a, 11b and the end of the discharge tube 5 and the inner diameter D of the ceramic tube 2 shown in FIG. 6 is a graph showing a relationship between window transmittances of laser light. From this data, if the ratio (L / D) is 7 or more, the laser light transmittance of the windows 11a and 11b after continuous operation for 1000 hours, which is an index of the non-stop time required for the laser device, is 95%. %
It was confirmed that the above could be maintained.

Thus, the extension pipes 10a and 10
b through the windows 11a, 11b attached to the ends of the discharge tube 5
If the distance L to the end of the discharge tube 5 is at least seven times the inner diameter D of the discharge tube 5, impurity particles generated in the discharge tube will
Thus, a metal vapor laser device capable of suppressing the amount adhering to b and obtaining a stable and efficient laser output over a long period of time is obtained.

[0035]

As described above, according to the present invention, a stable and efficient laser output can be obtained for a long period of time. Thereby, the operating cost of the metal vapor laser device is also 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 a relationship between a distance L from a window to an end of a discharge tube and the number of impurity particles adhering to the window in the metal vapor laser device shown in FIG.

3 is a distance L from the window shown in FIG. 2 to the end of the discharge tube;
4 is a graph showing a relationship between the laser light, the inner diameter D of the discharge tube, the ratio, and the window transmittance of the laser beam when the operation target time of the laser device has elapsed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Metal vapor laser apparatus, 2 ... Ceramic tube, 3 ... Anode, 4 ... Cathode, 5 ... Discharge tube, 10a ... Extension tube for window attachment, 10b ... Window Mounting extension tubes, 11a, 11b: window, 12: output mirror, 13: total reflection mirror, L: distance from window to end of discharge tube.

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Ryoichi Otani 1385-1, Higashiyama, Shimoishi-kami, Otawara-shi, Tochigi Prefecture F-term in Toshiba Nasu electron tube factory (reference) 5F071 AA03 DD06 DD07 JJ02 JJ08 JJ09

Claims (1)

[Claims] 1. A discharge tube in which a metal vapor source is held and which is filled with a discharge gas of a predetermined pressure, anodes and cathodes provided at both ends of the discharge tube, and the discharge from the positions of the anode and the cathode. A metal vapor having a window mounting extension tube extending outwardly along the optical axis of the tube, and a laser beam transmitting window mounted near an end of the window mounting extension tube. In the laser apparatus, the window attached to the window attachment extension tube is attached to a position at a distance from the end of the discharge tube at least seven times the inner diameter of the discharge tube. Laser device.