Microwave excited gas laser oscillator

Abstract: In one discharge tube (3) in which laser gas flows, a plurality of microwave generating units composed of microwave power sources (4), magnetrons (1) and waveguides (2) are disposed, and each magnetron (1) oscillates intermittently by switching drive of the microwave power source (4). A main controller (6) gives a reference clock to a power source unit (5) composed of said plurality of microwave power sources (4). By this reference clock, adjacent microwave power sources (4) in the power source unit (5) are switched and driven at a predetermined phase difference through a phase shifter (7). Accordingly, discharge interference in adjacent discharge areas (10) is avoided, so that a stable laser beam output may be obtained.

Description: FIELD OF THE INVENTION The present invention relates to a microwave excited gas laser oscillation control method for exciting by discharging laser gas by microwave, and a microwave excited gas laser oscillator. BACKGROUND OF THE INVENTION Recently, the gas laser oscillator tends to be reduced in size. To achieve this object, the exciting frequency for discharging gas laser becomes gradually a higher frequency. Hitherto, as the frequency for such gas laser oscillation, a high frequency power source of 100 kHz to scores of megahertz has been used. To reduce in size, however, problems are price and control performance. To solve the problems, various studies have been made on the microwave excited gas laser oscillator (hereinafter called MEGLO) for exciting by discharging laser gas by microwave. Fig. 6 is a schematic diagram for explaining a constitution of a conventional MEGLO, and it is described below while referring to the drawing. A microwave power source (hereinafter called power source) 4 is a switching power source of about 20 kHz, and a high voltage is applied so that a magnetron 1 may produce a microwave. The microwave emitted from the magnetron 1 is injected into a discharge area 10 which is part of a discharge tube 3 in which laser gas flows, through a waveguide 2. In the discharge area 10, the laser gas is discharged and excited by the microwave. The excited and generated laser beam is amplified in a laser resonator composed of an output mirror 8 which is a partial reflector and a total reflector 9. Part of the laser beam amplified in the laser resonator is delivered outside through the output mirror 8. As shown in Fig. 6, supposing the magnetron 1, waveguide 2 and power source 4 to be one microwave generating unit (hereinafter called MGU) 200, plural MGUs 200 are used in one discharge tube 3. Further supposing one discharge tube 3 and a plurality of MGUs 200 to composed one microwave output unit (hereinafter called MOU) 300, the number of MOUs used in one MEGLO is determined by the laser output of the MEGLO. Fig. 7 shows an example of using four MGUs 200 in one discharge tube 3, in which four microwave output timings are shown simultaneously. As shown in Fig. 7, each MGU 200 outputs intermittently so as to issue a microwave for a period of Ton 101, and cut off for a period of Toff 102. The microwave output timings from four MGUs 200 are nearly simultaneous. In order to stabilize the microwave output, pulse-width modulation (hereinafter called PWM) control of a specific off time is effected. In the conventional MEGLO, the output of each magnetron 1 is controlled at a specific off time by the PWM control. However, when plural MGUs 200 for composing one MOU 300 are disposed closely, the microwave output of each MGU 200 is issued at the same time as shown in Fig. 7, and discharges in the discharge area 10 may interfere with each other. In the event of such phenomenon, the continuous output of laser beam contains ripples, and the peak output of the laser beam in pulse operation fluctuates largely. At the same time, the laser beam output decreases. The conventional MEGLO had such problems. Reference may also be made to JP-A-09 205 241 (relative to which the present invention is characterised), and to JP-A-02 078 285. In particular, JP-A-02 078 285 discloses a microwave excited gas laser where the MGUs are successively staggered in switching phase in order to make the laser output stable. SUMMARY OF THE INVENTION It would be desirable to present a small-sized MEGLO capable of delivering a continuous output of stable laser beams and a high pulse peak output. The MEGLO of the invention comprises: plural discharge tubes disposing laser gas inside, plural microwave generating units (MGUs) each comprising microwave supply means for supplying microwaves, a power source for driving the microwave supply means, and a waveguide for guiding the microwaves to a said discharge tube, the waveguides of the plural microwave generating units being positioned close to each other for supplying microwaves to respective areas of the discharge tubes; control means for driving and controlling each one of said microwave generating units, characterised in that said control means drives the microwave generating units with a phase difference such that mutually adjacent microwave generating units for each discharge tube are not turned on simultaneously. For example, in the case of two adjacent MGUS, while one is issuing microwaves, the other stops microwaves. Next, at the time when the hitherto busy MGU stops output of microwaves, the other MGU issues microwaves. In this way, the controller controls the switching phase of the microwaves supplied to each discharge tube. Therefore, in the case of the MEGLO of the invention, if plural MGUs are disposed closely, mutual discharge interference can be decreased, and a stable laser beam small in ripple content may be issued. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of a microwave output unit explaining the principles of a microwave excited gas laser oscillator of the type of the invention. Fig. 2 is a block diagram explaining the constitution of an embodiment of the microwave excited gas laser oscillator of the invention. Fig. 3 is a diagram showing microwave output timing of one microwave power source of Fig. 2. Fig. 4 is a diagram showing output timing of microwave output of each microwave power source in Fig. 2. Fig. 5 is a diagram showing output timing in other example of microwave output of each microwave power source in the embodiment of the invention. Fig. 6 is a block diagram explaining the constitution of a conventional microwave excited gas laser oscillator. Fig. 7 is a diagram showing output timing of microwave output of each microwave power source in the prior art. DESCRIPTION OF THE PREFERRED EMBODIMENT (Embodiment) Embodiment of MEGLO of the invention is described below while referring to the drawings. Fig. 1 is a block diagram explaining one MOU showing the constitution of the embodiment. Fig. 2 is a block diagram of the MEGLO of the invention using a plurality of MOUs shown in Fig. 1. Same constituent elements as in the prior art in Fig. 6 are identified with same reference numerals, and their description is omitted. For the sake of simplicity of description, supposing four MGUs shown in Fig. 1 to be first MGU 201, second MGU 202, third MGU 203, and fourth MGU 204, a discharge tube 3 in which laser gas flows is inserted into a waveguide 2 for composing MGU 201, MGU 202, MGU 203, and MGU 204. In Fig. 1, four sets of closely disposed MGUs are shown as an example, but the invention is not limited to four sets; the number of MGUs to be used may be two sets or more per discharge tube. Referring now to Fig. 1 and Fig. 2, the embodiment is described below. The microwaves generated from the magnetron 1, in the discharge area 10 form a microwave glow discharge. Also, as shown in Fig. 1, each power source 4 of plural MGUs composed in one discharge tube 3 forms one power source unit 5. The power source unit 5 has a reference clock input terminal 18 for receiving a reference clock, and also includes a phase shifter 7 for setting the phase difference of the switching phase of each power source 4. This phase shifter 7 controls the switching phase of each power source 4. A main controller 6 shown in Fig. 2 controls the power source units 5 composed in a plurality of MOUs 400 in batch, and issues a reference clock to each power source unit 5 through the input terminal 18. A laser resonator is composed of an output mirror 8, which is a partial reflector, and a total reflector 9. A laser beam is delivered from the output mirror 8. In Fig. 2, two sets of MOUs 400 are shown, but the MEGLO of the. embodiment is not limited to two sets only. A further multiplicity may be used depending on the required output of the MEGLO. The operation of the MEGLO in thus constituted embodiment of the invention is described below. A reference clock of about 20 kHz is sent from the main controller 6 to each power source unit 5. The power source 4 is switched by at the frequency of this reference clock, and each magnetron 1 issues intermittent microwaves, as shown in Fig. 3, for turning on for a period of Ton 101, and turning off for a period of Toff 102. In order to stabilize the microwave output, PWM control of a specific off time is effected. Its frequency is about 20 kHz. The reference clock is put into the power source 4 through the phase shifter 7. Then; as shown in Fig. 4, the microwave outputs of MGU 201, MGU 202, MGU 203, and MGU 204 each have a phase difference α. For example, as shown in Fig. 4, in the microwave OFF time Toff 102 between MGU 201 and MGU 203, the adjacent MGU 202 and MGU 204 issue microwaves. To the contrary, in the microwave OFF time Toff 102 between MGU 202 and MGU 204, the adjacent MGU 201 and MGU 203 issue microwaves. In this way, by keeping an appropriate phase difference in the microwave output of adjacent MGUs, mutual discharge interference between adjacent discharge areas 10 can be avoided. The microwaves emitted from each magnetron 1 are injected through each waveguide 2 into the discharge area 10, which is part of the discharge tube 3 in which laser gas flows. In the discharge area 10, the laser gas is discharged by the microwave, and is excited. The stimulated laser beam is amplified in the laser resonator composed of the output mirror 8, a partial reflector, and the total reflector 9. Part of the laser beam amplified in the laser resonator is delivered outside from the output mirror 8. As a result, mutual discharge interference of adjacent discharge areas 10 is avoided, so that a stable laser beam may be emitted. The phase differences of the microwave outputs is sufficient that the microwave outputs of the adjacent MGUs do not overlap, and as shown in Fig. 5, for the microwave outputs of MGU 201, MGU 202, MGU 203, and MGU 204, a phase difference β between adjacent MGUs is provided. For example, as shown in Fig. 5, in the overlapped microwave OFF time of MGU 201, MGU 203, and MGU 204, the MGU 202 adjacent to MGU 201 and MGU 203 issues a microwave. Next, in the overlapped microwave OFF time of MGU 201, MGU 202, and MGU 204, the MGU 203C adjacent to MGU 202 and MGU 204 issues a microwave. Also, in the overlapped microwave OFF time of MGU 202 and MGU 203, the MGU 201 and MGU 204 adjacent to MGU 202 and MGU 203 issue microwaves. In this way, by keeping an appropriate phase difference in the microwave outputs of adjacent MGUs, mutual discharge interference in adjacent discharge areas 10 can be avoided. As a result, a stable laser beam is issued. In the foregoing embodiment of the invention, the MGUs are described to be adjacent in an integral structure, but actually the waveguide for composing the MGUs are desired to be disposed to be adjacent to each other. The magnetron and power source are not required to be disposed adjacently to each other. In the embodiment of the invention, the microwave output is described so as to be controlled by PWM in a specific off time, but, for example, in the case of two adjacent MGUs, while one is issuing a microwave, the other is stopping microwave. Next, at the timing when the hitherto busy MGU stops output of microwaves, the other MGU issues microwaves. As the microwave generator, the magnetron is used, but other means having microwave-generating function by semiconductor or others may be also used. The microwave power source may be selected so as to be suited to the above or other microwave generating function. As evident from the description herein, in the MEGLO of the. invention, since mutual discharge interference of adjacent discharge areas 10 can be avoided, a small-sized gas laser oscillator can be presented at a stable laser beam output.

Claims: A microwave excited gas laser oscillator comprising: plural discharge tubes (3) disposing laser gas inside, plural microwave generating units (200) each comprising microwave supply means (1) for supplying microwaves, a power source (4) for driving the microwave supply means, and a waveguide (2) for guiding the microwaves to a said discharge tube (3), the waveguides (2) of the plural microwave generating units being positioned close to each other for supplying microwaves to respective areas (10) of the discharge tubes; control means (6, 7) for driving and controlling each one of said microwave generating units, characterised in that said control means (6, 7) drives the microwave generating units (200) with a phase difference such that mutually adjacent microwave generating units (200) for each discharge tube (3) are not turned on simultaneously. A microwave excited gas laser oscillator of claim 1, wherein a reference clock for controlling the switching phase of microwave is sent from the control means (6, 7) to each microwave generating unit, for each one of plural discharge areas of each discharge tube. A microwave excited gas laser oscillator of claim 1, wherein the oscillator is organised to include: a unit (5) comprising at least a first and a second of said power sources (4) and a phase shifter (7) associated therewith.

Inventors: IWASAKI YUTAKA, YAMANE SHIGEKI, IWASAKI, YUTAKA, YAMANE, SHIGEKI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1999
Main classification: H01S3
IPC codes: H01S3