JP2715949B2 - Ion laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion laser,
In particular, the present invention relates to an ion laser having a function of replenishing gas as a laser medium.

[0002]

2. Description of the Related Art An ion laser is one of gas lasers and is represented by an argon laser and a krypton laser. The argon laser continuously oscillates visible light from blue to green, and the krypton laser oscillates visible light from blue to red. In particular, since an argon laser laser can provide an output of several tens of watts in a single mode and is easy to handle, it has been widely applied as a light source for processing, medical treatment, printing, spectroscopy, holography, display, and other research.

An ion laser forms a population inversion by exciting a laser medium, such as argon or krypton, by discharge and oscillates. Excitation in an ion laser is performed by arc discharge, which is a major feature different from other gas lasers. The oscillation efficiency of an ion laser is very low, and a high current density is required. For laser oscillation, a discharge current of 1 to 100 A needs to flow through a discharge path having a diameter of 1 to 5 mm. As the discharge path is made smaller and the discharge current is increased, the current density increases and a high output is obtained. For such high-current-density arc discharge, it is important to select a material having resistance to spattering of plasma for components constituting the discharge path and the electrodes, and to take measures against gas consumption due to sputtering.

The structure of a conventional ion laser having a gas supply function will be described with reference to the block diagram of FIG. Here, an argon laser will be described, but the structure is the same for a krypton laser. As shown in FIG. 6 which is a schematic block diagram of an ion laser, a conventional argon laser includes a pair of mirrors 8a and 8b and mirrors 8a and 8b.
b, a laser oscillator 2 that supports and accommodates a discharge unit 9 that constitutes an oscillating unit, a gas supply unit 12 that supplies gas to the discharge unit 9, and supplies power to the discharge unit 9 to control its operation. The power supply / control unit 3 is provided. What is described here is an external mirror type argon laser,
An internal mirror type laser oscillator in which mirrors 8a and 8b are provided directly at both ends of the laser tube 1 instead of the Brewster window 7 is also known.

The discharge unit 9 includes an anode 4 on which electrons are incident, a cathode 5 from which electrons are emitted, a thin tube 6 serving as a discharge path, and a Brewster window 7 through which laser light is transmitted, and is filled with argon gas as a laser medium. It is configured to include the laser tube 1 described above. The gas supply unit 12 includes a gas reservoir 10 in which argon gas is sealed, and an electromagnetic valve 11 for controlling the release of the sealed gas. In addition, the power supply / control unit 3 includes:
Constant current circuit 14 for supplying a constant current between anode 4 and cathode 5
A discharge voltage measuring circuit 13 for measuring a voltage between the anode 4 and the cathode 5, and a gas replenishing circuit 1 for controlling opening and closing of the solenoid valve 11.
5 are accommodated.

The anode 4 is formed into a cylindrical shape using copper, nickel or graphite, while the cathode 5 is formed into a cylindrical shape.
An impregnated cathode made by impregnating porous tungsten with BaO or the like and working into a coil shape is used, and the thin tube 6 is formed of graphite, beryllium oxide, tungsten, silicon carbide, or the like. As described above, particularly, the cathode and the thin tube are formed of a sputter-resistant material.

In the arc discharge, even if the above-mentioned sputter-resistant material is used, the surrounding parts are sputtered, and argon is taken in at the time of deposition, so that the argon gas is gradually consumed. The lower the internal gas pressure, the more the gas is consumed, so that the gas consumption in the laser tube accelerates. Therefore, the gas supply function is prepared to Ru is stable long-term operation. This function is to open the solenoid valve 11 momentarily when the gas pressure in the laser tube 1 decreases to a certain reference value, and to supply argon gas from the gas reservoir 10.

The laser tube 1 is initially 0.1 to 10 To.
rr is sealed at an optimum gas pressure at which laser oscillation is most efficiently performed. This optimum gas pressure is determined by the structure and material of the laser tube 1. A gas reservoir 10 for gas storage is connected to the laser tube 1 and is piped, and a normally closed solenoid valve 11 is provided between the pipes. At the initial stage, the inside of the gas reservoir 10 is sealed with a gas pressure higher than that of the discharge unit 9.

The relationship between the discharge voltage Eb1 at the time of discharge at a certain discharge current Ib1 and the gas pressure in the laser tube 1 is shown by the solid line curve in FIG. Since the relationship between the gas pressure and the discharge voltage Eb1 has a one-to-one correspondence, the discharge voltage Eb1 can be used as a substitute for the gas pressure. The discharge voltage at the gas pressure P1 required for operation is set as the gas supply voltage Eg1, and the discharge voltage Eb1 during operation is compared with the gas supply voltage Eg1 to determine whether gas supply is necessary.

FIG. 8 shows a time change of the discharge voltage Eb1 when the discharge is performed at a certain constant discharge current Ib1. The solid line indicates the case where the gas supply function is operated, and the dashed line indicates the case where the gas supply function is not operated. When operated with the discharge current Ib1, the gas pressure decreases with the passage of time, so the discharge voltage Eb1 decreases. When the gas supply voltage Eg1 set in advance is divided, a gas supply signal is output from the gas supply circuit of the power supply / control section, and the solenoid valve 11 is instantaneously opened. By opening the solenoid valve 11, gas is introduced from the high-pressure gas reservoir 10 into the low-pressure laser tube 1, whereby the gas pressure in the laser tube 1 rises and the initial gas pressure is reproduced. This operation is repeated until the gas in the gas reservoir 10 decreases and becomes the same gas pressure as that of the laser tube 1, and finally reaches the discharge voltage Ed of the lowest gas pressure P3 for maintaining the discharge, and the discharge becomes impossible.

As a prior art relating to a gas laser, a laser output and a discharge input are measured to calculate an input / output characteristic, and the laser gas is refreshed based on a comparison between the characteristic and a predetermined reference characteristic. Kaihei 1-16
0070), in a gas laser using glow discharge, the output state of a power supply device is monitored, and when the state change exceeds a predetermined value, the supply of power to the gas laser is suppressed or stopped (Japanese Patent Application Laid-Open No. 62-62). Japanese Patent Application Laid-Open No. 1-184970), calculates the ratio between the discharge voltage and the set voltage and the ratio between the discharge current and the set current, and controls the gas pressure based on the integrated value of the difference between the two ratios. and so on.

[0012]

In the above-described conventional ion laser, the discharge voltage Eb1 is used instead of the gas pressure detection.
When the components of the discharge unit 9 such as the anode 4, the cathode 5, and the thin tube 6 deteriorate with time, the error between the true gas pressure and the detected value becomes large. There has been a problem that the gas pressure is reduced to a required gas pressure P1 or less and the life is shortened.

The arc discharge causes oxidation of the surfaces of the anode and the cathode 5, and in the cathode, the local temperature rise due to ion bombardment promotes the growth of tungsten grains. In addition, the shape and shape of the thin tube occur due to sputtering and deposition in the thin tube, and the impedance of the laser tube increases. Even if the gas pressure and the discharge current Ib1 are constant due to the increase in the impedance, the discharge voltage Eb1
Rises. When the operation is continued, the gas in the laser tube 1 is consumed and the discharge voltage Eb1 reaches the gas supply voltage Eg1. However, the relationship between the gas pressure at that time and the discharge voltage Eb1 is represented by a dotted curve in FIG.
It has dropped to 2.

FIG. 9 shows the discharge voltage Eb1 and the time change of the gas pressure in the laser tube 1 when the discharge is performed at a certain constant discharge current Ib1 in the case of such deterioration. When this operation is continued, the apparent gas pressure Eb1 operates within a certain range, but the gas pressure at which gas is supplied gradually decreases. The lower the gas pressure is, the larger the spatter amount is, and the deterioration of the components accelerates at an accelerated time, and the timing at which the gas pressure reaches the gas pressure P3 at which discharge becomes impossible is advanced.

Incidentally, in order to solve the above-mentioned problems, it is conceivable to directly measure the gas pressure in the discharge tube using a pressure detector. However, in a small laser such as an ion laser, providing a gas detector is not practical in terms of space and cost. In addition, when a general Pirani gauge is used as the pressure detector, the temperature rise due to arc discharge is large, and the risk of malfunction is increased. Further, accurate measurement of gas pressure on the order of 1/100 Torr is difficult.

The present invention has been made in view of such a situation, and an object of the present invention is to solve the problem of detecting a gas pressure higher than an actual gas pressure due to deterioration of a laser tube. It is an object of the present invention to prevent a vicious cycle of shortening the life of the laser tube from increasing spatter due to a decrease in the gas pressure and further reducing the gas pressure, thereby extending the life of the laser tube.

[0017]

According to the present invention, a laser medium is sealed and a pair of arc discharge electrodes (4, 4) are provided to excite the laser medium.
A laser tube (1) in which 5) is arranged, a gas reservoir (10) in which gas serving as a laser medium is sealed, and a control valve (11) for controlling the flow of the laser medium in the gas reservoir into the laser tube. And a gas supply circuit (15) for outputting a gas supply signal for opening the control valve when the gas pressure in the laser tube is insufficient. arc discharge path outside is formed by a pair of arc discharge electrodes huge
Outside the extension of the arc discharge path and the arc discharge path
A pair of glow discharge electrodes (18) are disposed adjacent to each other on an extension of the line, and the gas supply circuit detects a discharge voltage between the glow discharge electrodes, and turns off the control valve when the discharge voltage is equal to or less than a reference value. An ion laser, which outputs a gas supply signal for opening, is provided.

[0018]

Next, embodiments of the present invention will be described with reference to the drawings. [First Embodiment] FIG. 1 is a schematic block diagram of an ion laser according to a first embodiment of the present invention. As shown in FIG. 1, the ion laser includes a discharge unit 9, a laser oscillator 2 having a pair of mirrors 8 a and 8 b disposed outside the discharge unit 9, a gas supply unit 12, and a power supply / control unit 3. .

In the discharge section 9, a pair of electrodes for arc discharge for exciting and exciting argon gas, that is, a hollow cylindrical copper anode 4 and a coil-shaped impregnated cathode 5 are provided in the laser tube 1. A narrow tube 6 made of a ceramic material having a hollow cylindrical shape and high thermal conductivity is arranged therebetween, and these constitute an arc discharge portion. Brewster windows 7 made of optical quartz glass are provided on extensions of both ends of the arc discharge portion. In the gas supply unit 12 connected to the discharge unit 9, several tens Torr is stored in the gas reservoir 10.
Of argon gas is sealed and sealed by the electromagnetic valve 11. The mirrors 8a and 8b, which are disposed at both ends of the laser oscillator 2 and constitute a resonator, are formed by depositing a dielectric multilayer film on optical quartz glass.

A constant current circuit 1 is provided between an anode 4 and a cathode 5 to cause an arc discharge in an arc discharge path in the laser tube 1.
4 supplies a constant current, and the discharge voltage is measured by a discharge voltage measuring circuit 13. A glow discharge electrode 18 for generating a glow discharge is provided outside (left side) of the anode 4.
Are provided as a pair. This may be outside the cathode 5 (right side). A constant current is supplied between both ends of the glow discharge electrode 18 by a glow discharge constant current circuit 17 to generate a glow discharge. The discharge voltage is the glow discharge voltage measurement circuit 1
6 measured.

At this time, the glow discharge voltage Eb2 between the glow discharge electrodes 18 and the internal gas pressure in the laser tube 1 are one-to-one as shown in FIG. 2 as in the case of the arc discharge shown in FIG. Yes, it is. A glow discharge voltage Eg2 corresponding to the gas pressure P1 necessary for operation is set in the gas supply circuit 15 as a gas supply voltage. The glow discharge voltage Eb2 is compared with the gas supply voltage Eg2. When the relationship of Eb2 ≦ Eg2 is satisfied, a gas supply signal is output from the gas supply circuit 15 and the solenoid valve 11 is opened for 0.1 ms or less. Thereby, the gas pressure and Eb2 are restored to the initial values.

FIG. 3 shows the change over time in the discharge voltage (arc discharge voltage) Eb1 and the gas pressure in this embodiment. Replenishing the gas by using the discharge voltage of the glow discharge instead of the gas pressure means that the actual gas pressure is erroneously detected higher because there is no deterioration of the electrodes and thin tubes due to arc discharge as in the conventional technology. , And can always be operated at the initial gas pressure each time gas is supplied.

As a result, an increase in the amount of sputtering and an increase in impedance due to the lowering of the gas pressure are eliminated, and the speed of gas consumption is suppressed, so that a longer life is achieved. In addition, since the glow discharge has a low discharge voltage and a small spatter amount as compared with the arc discharge, providing the glow discharge path in the laser tube 1 does not adversely affect the laser operation or the service life.

[Second Embodiment] FIG. 4 is a schematic block diagram showing a second embodiment of the present invention as an enlarged view of only the anode portion. The other parts are common to the first embodiment and are not shown. In this embodiment, one glow discharge electrode 18 also serves as an anode support member 19 that supports the anode 4. Since a trigger voltage of several kV is applied to the anode 4 at the start of the arc discharge, a countermeasure is required for the glow discharge circuit, but other configurations and operations are the first.
This is the same as the embodiment.

Third Embodiment FIG. 5 shows a schematic block diagram of a third embodiment of the present invention as an enlarged view of only a cathode portion. The other parts are common to the parts of the first embodiment and are not shown. In the present embodiment, one glow discharge electrode 18 supports the cathode 4.
Yin electrode support member 20 also serves. Other configurations and operations are the same as those of the first embodiment. In the above second and third embodiments, the number of parts can be reduced, and a low-priced product can be supplied.

[0026]

As described above, according to the present invention, in an ion laser having a gas replenishing function, glow discharge is performed in addition to arc discharge for laser excitation, and the discharge voltage is detected to obtain a gas pressure value. Since it is used, the gas pressure is not detected high due to the deterioration of the laser tube, and as a result, the disadvantage that the gas supply is performed after the pressure becomes lower than the planned gas supply pressure is caused. Can be avoided. Therefore, according to the present invention, it is possible to suppress the increase in the amount of sputtering and the acceleration of gas consumption due to the lower gas pressure, and to achieve a longer life of the laser tube.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of a first embodiment of the present invention.

FIG. 2 is a characteristic diagram of a glow discharge voltage Eb2 with respect to a gas pressure in the embodiment of FIG.

FIG. 3 is a graph showing the change over time in gas pressure and discharge voltage Eb1 inside the laser tube of the embodiment of FIG. 1;

FIG. 4 is an enlarged view of an anode part in a schematic block diagram according to a second embodiment of the present invention.

FIG. 5 is an enlarged view of a cathode portion of a schematic block diagram according to a third embodiment of the present invention.

FIG. 6 is a schematic block diagram of a conventional example.

FIG. 7 is a characteristic diagram of a discharge voltage Eb1 with respect to a gas pressure in a conventional example.

FIG. 8 is a graph showing a change with time of a discharge voltage Eb1 in a conventional example.

FIG. 9 shows gas pressure and discharge voltage Eb inside a laser tube of a conventional example.
FIG.

[Explanation of symbols]

 Reference Signs List 1 laser tube 2 laser oscillator 3 power supply / control unit 4 anode 5 cathode 6 thin tube 7 Brewster window 8a, 8b mirror 9 discharge unit 10 gas reservoir 11 solenoid valve 12 gas supply unit 13 discharge voltage measurement circuit 14 constant current circuit 15 gas supply circuit Reference Signs List 16 glow discharge voltage measuring circuit 17 glow discharge constant current circuit 18 glow discharge electrode 19 anode support member 20 cathode support member

Claims (2)

(57) [Claims] 1. A laser tube in which a laser medium is enclosed and a pair of arc discharge electrodes for exciting the laser medium is provided, a gas reservoir in which gas as a laser medium is enclosed, and a gas reservoir in the gas reservoir. A control valve for controlling the flow of the laser medium into the laser tube, and a gas supply circuit that outputs a gas supply signal for opening the control valve when the gas pressure in the laser tube is insufficient. in ion laser having, arc discharge path outside which is formed by the pair of arcing electrodes in the laser tube and extending in the arc discharge path
Outside the long line and adjacent to the extension of the arc discharge path
A pair of glow discharge electrodes is disposed at a position, and the gas replenishment circuit detects a discharge voltage between the glow discharge electrodes and, when the discharge voltage is equal to or less than a reference value, outputs a gas replenishment signal for opening the control valve. An ion laser characterized by output. 2. The ion laser according to claim 1, wherein a support member of one of the pair of arc discharge electrodes also serves as one of the pair of glow discharge electrodes.