JPH1117247A - Microwave-excited gas laser oscillator and control method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the life of a magnetron and raise the rise time of a pulse in a pulse operation mode by specifying the value of the quotient of the division of the mean current by the peak current given by a magnetron current at least at a max. magnetron power. SOLUTION: A magnetron drive circuit 25 constructs a microwave generator 12 with a magnetron 6 to drive a magnetron in a pulse mode according to a signal from a controller 13. The applied voltage is varied with a const. duty of the magnetron current so that D=(mean current/peak current)×10 of the magnetron current is always over 40. The drive circuit 25 may be composed of a PEM or resonance type drive circuit which always provides the D value of the magnetron current over 40 at a max. power while the magnetron current duty ratio varies according to a signal from the controller 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas laser oscillating device for obtaining a laser beam by exciting a laser gas with a microwave.

[0002]

2. Description of the Related Art An example of a microwave-excited gas laser oscillation device is disclosed in the document APPLIED PHYSICS L.
ETTER, 37 (8), P673 (1980) and the like are known.

FIG. 5 shows a schematic diagram of the configuration of a microwave-excited carbon dioxide laser oscillation device which the present inventors have studied so far based on the above-described gas laser oscillation device.

In FIG. 5, reference numeral 12 denotes a microwave generator including a magnetron for generating microwaves, 13 denotes a control unit for controlling the microwave generator, 11 denotes a discharge tube formed of a dielectric such as glass, and 14 denotes a discharge tube. This is a waveguide that supplies microwaves into the discharge tube 11. The discharge tube 11 is the waveguide 1
4, the laser gas in the discharge tube 11
Excited by microwaves. The discharge section 15 is where the laser gas is excited. A total reflection mirror 16 is disposed at one end of the discharge tube 11 and a partial reflection mirror 17 is disposed at the other end to form an optical resonator. The laser beam 18 from the partial reflecting mirror 17
Is emitted. An air supply pipe 19 is connected to both ends of the discharge tube 11, and an intake pipe 20 is connected to the center of the discharge tube 11. Heat exchangers 21 and 22 and a blower 23 are connected between the intake pipe 20 and the air supply pipe 19 to circulate the laser gas. The heat exchangers 21 and 22 are provided to cool the laser gas whose temperature has been increased by the discharge of the discharge unit 15 and the blower 23. The arrow 24 indicates the direction in which the laser gas flows, and the laser gas circulates in the gas laser oscillation device shown in the figure.

[0005] The operation of the carbon dioxide laser oscillation device configured as described above will be described. First, the control unit 13 controls the microwave generator 12 to generate a microwave. FIG. 6 shows a magnetron current waveform of the microwave generator 12 at this time. Discharge tube 11 through waveguide 14
A microwave is applied to the discharge unit 15 in the inside to generate a glow discharge in the discharge unit 15. The laser gas passing through the discharge unit 15 is excited by obtaining this discharge energy, and the excited laser gas is brought into a resonance state between the optical resonator formed by the total reflection mirror 16 and the partial reflection mirror 17, and the partial reflection mirror 1 is turned on.
7 and a laser beam 18 is emitted.

[0006]

In this microwave-excited gas laser oscillator, a phenomenon called "moding" tends to occur as the magnetron of the microwave generator 12 deteriorates, the microwave output decreases, and the predetermined laser No output can be obtained. Therefore, it is determined that the life of the magnetron has expired due to the occurrence of the moding, and in that case, the magnetron needs to be replaced. Moreover, in the carbon dioxide laser oscillation device shown in FIG. 5, since a plurality of magnetrons are usually used, a short magnetron life results in an increase in maintenance cost of the entire laser oscillation device.

Further, in the case of performing a pulse operation for generating a pulse-like laser output by repeatedly interrupting the generation of a continuous pulse-like microwave, the rising speed of the pulse is slow with the laser output due to the constant interruption of the microwave. Adversely affects processing.

An object of the present invention is to provide a microwave-excited gas laser oscillating device capable of extending the life of a magnetron and increasing the pulse rising speed during pulse operation.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, a first means of the present invention is to provide a microwave generator for generating a microwave by a magnetron, and to convert a microwave from the microwave generator into a laser gas. A discharge unit that supplies and excites the laser gas, an optical resonator that resonates the laser gas excited in the discharge unit to generate a laser beam, and a control unit that controls an operation of the microwave generation device; In the section, the value of D = (average current / peak current) × 100 expressed by the magnetron current is set at least at the maximum of the magnetron output, and D is set to 40 or more.

A second means of the present invention is to perform a pulse operation for generating a pulsed laser output by repeatedly intermittently generating a pulsed microwave, and to generate a magnetron current at the rising portion of each pulse. The current is controlled to be larger than the flat portion and to be controlled substantially during the rising section.

According to a third aspect of the present invention, in the second aspect, the magnetron current at the rising portion of the pulse is 1.5 times or more the flat portion of the pulse during the pulse operation,
It is controlled by the current for 150 μs or more.

A fourth means of the present invention is to independently control an enhanced portion in which a magnetron current at a pulse rising portion is larger than a pulse flat portion and a pulse flat portion during a pulse operation.

[0013]

According to the first aspect of the present invention, the peak value of the magnetron current can be reduced, the occurrence of moding can be reduced, and the life of the magnetron can be extended while securing a predetermined laser output. .

The above reason will be considered. The relationship between the magnetron current (instantaneous value) generated by the moding and the magnetron deterioration (use time) decreases with the deterioration of the magnetron as shown in FIG. On the other hand, the relationship between the average value of the magnetron current and the laser output is almost proportional as shown in FIG. FIG. 3C shows the relationship between the value of D and the laser output during the use time when the desired magnetron life has been reached.
Magnetron moding occurs in the following areas,
Although the laser output is reduced, the moding is eliminated when the value of D is approximately 40 or more, and a predetermined laser output is obtained. Therefore, in order to suppress the moding while securing a predetermined laser output, the duty of the pulse signal for driving the magnetron should be increased, and the peak value should be reduced while maintaining the average value of the magnetron current. In order to obtain a microwave output with a desired magnetron life, it becomes possible by setting the value of D to 40 or more.

According to the second means of the present invention, the pulse can be started up at a high speed during the pulse operation.

According to the third means of the present invention, the pulse rise time can be reduced to 50 μs or less.

According to the fourth aspect of the present invention, the pulse rising speed can be stably improved even if there is a variation or fluctuation of the microwave generator.

Consider the above reason. The pulse rise time of the laser output waveform when a constant magnetron current is intermittently becomes substantially the same even if the laser output setting is changed as shown in FIG. Therefore, by supplying a current larger than the magnetron current in the pulse flat portion during the pulse rising time, the rising speed can be increased as shown in FIG. 4B.

In the microwave-excited carbon dioxide laser oscillation device shown in FIG. 5 which we have studied, if the pulse rise time shown in FIG. 4A is about 150 μs and the target rise time is 50 μs, As shown in FIG. 4A, when a magnetron current of about 1.5 times the set value is passed, tr ′ ≒ tr / 3 ≒ 50 μs. Therefore, if the magnetron current at the rising portion of the pulse is 1.5 times or more the flat portion of the pulse and the current is controlled for 150 μs or more, the target rising time of 50 μs can be obtained.

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG. (Embodiment 1) In FIG. 1, reference numeral 25 denotes a magnetron driving circuit, which constitutes the microwave generator 12 together with the magnetron 26. The magnetron drive circuit 25 drives the magnetron in a pulsed manner by a signal from the control unit 13. The duty of the magnetron current is kept constant, the applied voltage is changed, and the D of the magnetron current is changed.
= (Average current / peak current) × 100 is always 40
The configuration is as described above.

(Embodiment 2) In FIG. 1, the magnetron drive circuit 25 is constituted by a drive circuit such as a PWM type or a resonance type.
The duty of the magnetron current changes, but at the maximum output, the value of D = (average current / peak current) × 100 of the magnetron current becomes 40 or more.

(Embodiment 3) In FIG. 2A, the control unit 13 includes a control circuit 27 for controlling an enhanced portion which is larger than a pulse flat portion of a pulse rising portion of a magnetron current during pulse operation, and the magnetron. It has a control circuit 28 for controlling the flat portion of the current pulse, and a switching circuit 29 for switching between the current detection signal and the control signal in synchronization. Switching circuit 2
9 shows the magnetron current shown in FIG.
The enhanced portion of the pulse shown in FIG.
The current detection signal and the control signal are synchronously switched in the flat portion shown in FIG. 1D, so that the enhanced portion and the flat portion can be controlled independently.

In the above description, the axial-flow type gas laser oscillation device is used, but the effects can be obtained with other types of gas laser oscillation devices.

[0024]

As described above, according to the present invention, the peak value of the magnetron current is reduced, the occurrence of moding is reduced, and the life of the magnetron can be extended. Further, the pulse rising speed during the pulse operation is improved, and the effect of improving the processing performance is obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a microwave-excited gas laser oscillation device according to an embodiment of the present invention.

2A is a schematic configuration diagram of a microwave-excited gas laser oscillation device according to an embodiment of the present invention. FIG. 2B is a diagram showing a magnetron current waveform during pulse operation. FIG. 2C is only a magnetron current in an enhanced portion. (D) is a diagram showing a current waveform in which only the magnetron current in the flat portion of the pulse is selected.

3A is a diagram showing a relationship between magnetron degradation and a magnetron current generated by moding. FIG. 3B is a diagram showing a relationship between an average value of the magnetron current and laser output. FIG. 3C is a target magnetron use time. Showing the relationship between the value of D and the laser output in FIG.

4A is a diagram showing a laser output waveform at the time of pulse operation; FIG. 4B is a diagram showing a magnetron current waveform and a laser output waveform at the time of enhancement;

FIG. 5 is a schematic configuration diagram of a conventional microwave-excited gas laser oscillation device.

FIG. 6 is a diagram showing a magnetron current waveform;

[Explanation of symbols]

 REFERENCE SIGNS LIST 12 Microwave generator 13 Control unit 15 Discharge unit 25 Magnetron drive circuit 26 Magnetron 27 Control circuit for pulse enhancement part 28 Control circuit for pulse flat part 29 Switching circuit

Claims (4)

[Claims] 1. A microwave generator for generating microwaves by a magnetron, a discharge unit for supplying microwaves from the microwave generator to a laser gas to excite the laser gas, and a laser unit for exciting the laser gas in the discharge unit. An optical resonator that resonates to generate a laser beam;
A control unit for controlling the operation of the microwave generating apparatus, wherein the control unit sets a value of D = (average current / peak current) × 100 expressed by magnetron current at least at the maximum of the magnetron output, and sets D to 40 or more. Microwave-excited gas laser oscillator set to. 2. A microwave generator for generating continuous pulsed microwaves by a magnetron, a discharge unit for supplying microwaves from the microwave generator to a laser gas to excite the laser gas, and An optical resonator that resonates the excited laser gas to generate a laser beam, and a control unit that controls the operation of the microwave generation device, wherein the control unit repeatedly and intermittently generates continuous pulsed microwaves. When performing a pulse operation for generating a pulse-like laser output, the magnetron current at the rising portion of each pulse is set to be larger than the flat portion of the pulse, and the microwave-excited gas laser controlled by the current during the almost rising section. Oscillator. 3. The microwave-excited gas laser oscillation device according to claim 2, wherein, during the pulse operation, the magnetron current at the rising portion of the pulse is set to 1.5 times or more of the flat portion of the pulse, and is controlled by the current for 150 μs or more. 4. A control unit for controlling the operation of a microwave generator for generating a continuous pulsed microwave, wherein the control unit controls a magnetron current at a pulse rising portion during a pulse operation to generate a pulse flat portion. A method for controlling a microwave-excited gas laser oscillation device that independently controls a larger enhancement portion and a pulse flat portion.