JPH10190102A - Method for exciting discharge of gas laser and gas laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the oscillation output and oscillation efficiency of a gas laser. SOLUTION: A discharge tube 1a through which a laser gas 8 is made to flow is positioned in a state where the tube 1a is inserted into a cavity resonator 4a and microwaves outputted from a microwave oscillator 2 are led to the resonator 2 through a waveguide 3. Therefore, the light induced and emitted when the laser gas 8 is excited for discharge by the microwaves is reflected and amplified between mirrors 5 and 6 and outputted as a laser beam from the mirror 6. The resonator 4a is positioned on the upstream side of the tube 1a in the flowing direction of the gas 8. Therefore, the discharge excitation takes place in the upstream-side section of the resonator 4a and gas mixing is performed in the downstream-side section of the tube 1a having a length L.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas laser discharge excitation method and a gas laser device, and is effective when applied to a laser oscillator that excites a laser gas (laser medium) by high frequency discharge by electromagnetic waves in a high frequency range. .

[0002]

2. Description of the Related Art A conventional gas laser device will be described with reference to FIG. As shown in FIG. 1, in the conventional gas laser device, the discharge tube 1 in which the laser gas 8 is circulated and supplied.
Is installed in a state of being inserted in the axial direction of the cylindrical cavity resonator 4. The microwave oscillator 2 is connected to the cylindrical cavity resonator 4 via the waveguide 3. At both ends of the discharge tube 1, a total reflection mirror 5 and an output mirror 6, which constitute an optical resonator, are opposed to each other.

In the gas laser device having the above-described configuration, when the microwave output from the microwave oscillator 2 propagates through the waveguide 3 and is transmitted to the cylindrical cavity resonator 4, the cylindrical cavity The microwave is sealed in the space in the resonator 4 and thus in the space in the discharge tube 1. Therefore, the laser gas 8 in the discharge tube 1 is discharged and excited by the microwave electric field. As a result, stimulated emission light is generated from the laser gas 8, and the stimulated emission light is amplified by reciprocal reflection between the total reflection mirror 5 and the output mirror 6 constituting the optical resonator, and the output mirror 6 is amplified.
Can be taken out of the laser beam 7.

A gas laser device of the type shown in FIG. 4 has a gas flow direction of the laser gas 8 and an optical axis parallel to each other. It is called.

[0005] Discharge excitation of laser gas by microwave is described in Handy and Brandelik, J. Appl. Phys. Vol.
3753-3756 (1978).

[0006]

However, in the case of using a cavity resonator 4 in which microwaves are sealed, it is possible to discharge-excit a laser medium (laser gas 8). The discharge space is configured so that the laser gas 8 in the discharge tube 1 can stay on the optical axis as much as possible.

[0007] Therefore, even if the high-frequency power is increased in order to excite the molecules by increasing the electric field in the discharge space, the electric field intensity is not increased. There is a disadvantage that it cannot be raised so effectively.

Further, the discharge plasma generated by the electric field tends to absorb microwave energy. Therefore, focusing on the plasma generated by the laser gas 8 flowing in the discharge tube 1, more microwave energy is absorbed on the downstream side of the discharge tube 8 than on the upstream side of the discharge tube 8. As a result, despite the increase in the input power aimed at exciting the molecules, the output power did not increase much,
Most of the increased input power results in power loss, and there is a disadvantage that the temperature rise of the laser gas 8 cannot be avoided.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned disadvantages of the prior art, and is intended to reduce the laser output by causing discharge of molecules constituting a laser gas by a high-frequency electric field and excitation suitable for laser oscillation. It is an object of the present invention to provide a gas laser discharge excitation method and a gas laser device capable of increasing the oscillation efficiency and increasing the oscillation efficiency.

[0010]

According to the structure of the present invention, an electromagnetic wave output from a high-frequency oscillator is converted by a coaxial cable or a waveguide into a facing parallel plate electrode having a discharge tube installed therein or a parallel plate electrode. A discharge excitation method of an axial flow type gas laser that leads to an induction coupling coil or a cavity resonator and discharge-excites a laser medium gas sealed in a space in the discharge tube by an electric field by the electromagnetic wave to obtain a laser output. In this method, the discharge excitation is concentrated on the upstream side of the gas flow to generate plasma over the entire cross section of the discharge tube, and then the gas flow is maintained on the laser optical axis while being mixed at the downstream portion of the gas flow.

Further, in the discharge excitation method for a gas laser according to the present invention, immediately after the discharge excitation by the electromagnetic wave, a part of the laser gas before the discharge is supplied to a gas flow downstream of the discharge part, and the gas flow is cooled by gas mixing. It is characterized by strengthening.

Further, in the gas laser discharge excitation method according to the present invention, a cavity resonator is provided on an upstream side of a gas flow, and the cavity resonator is connected to a downstream cavity and an upstream cavity to which an electromagnetic wave is guided. It is characterized in that discharge is generated and gas molecules are excited by dividing into two.

Further, according to the structure of the present invention, an electromagnetic wave output from a high-frequency oscillator is applied to a facing parallel plate electrode, an induction coupling coil or a cavity resonator having a discharge tube therein by a coaxial cable or a waveguide. In the gas laser device of the axial flow type in which the laser medium gas sealed in the space inside the discharge tube is excited by an electric field by the electromagnetic wave to obtain a laser output, discharge is performed to the discharge tube through which the laser gas flows. The mixing unit is provided upstream of the laser oscillation axis, and a mixing unit is provided downstream of the discharge unit.

In the present invention, two functions of a discharge part for discharging and exciting CO ₂ molecules and the like and a mixing part for enhancing gas cooling are separated. For this reason, according to the present invention, the high-frequency electric field is concentrated in the narrow space upstream of the gas flow, so that the high electric field acts on the laser gas with a small power, and the electric field does not act on the downstream portion of the discharge, thereby sufficiently mixing the gas. By doing so, by cooling the gas on the optical axis, a high laser oscillation gain can be obtained in the optical axis direction. And
In the present invention, the high frequency applied to the discharge unit is 1 MHz RF.
It can also be used in the microwave region from the region to several tens of MHz.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a gas (carbon dioxide) laser device according to a first embodiment of the present invention. As shown in the figure,
The discharge tube 1a in which the laser gas 8 is circulated and supplied,
It is installed so as to be inserted in the axial direction of a cylindrical (rectangular) cavity resonator 4a. Moreover, the cavity resonator 4a is arranged upstream of the discharge tube 1a with respect to the flow direction of the laser gas 8. The discharge tube 1a is provided with a cavity resonator 4
On the downstream side of the position where “a” is installed, the length of the discharge tube is set long so that sufficient gas mixing can be obtained.

One end of the waveguide 3 is connected to a side end of the cavity resonator 4 a, and the other end of the waveguide 4 is connected to the microwave oscillator 2. At both ends on the optical axis of the discharge tube 1, a total reflection mirror 5 and an output mirror 6, which constitute an optical resonator, are installed facing each other.

Here, more specific characteristics of each part of the first embodiment will be described. The microwave oscillator 2 is 2.45 GH
The microwave of z is oscillated, and the microwave of 1500 W is incident on the cavity resonator 4a. The gas composition of the laser gas 8 is a mixed gas of CO ₂ , N ₂ and He, and the pressure is 50 Torr. The inner diameter φ of the cavity resonator 4a is 8
3 mm, and the axial length is 100 mm. The inner diameter φ of the discharge tube 1a is 25 mm. In the discharge tube 1a, the downstream discharge tube length L downstream of the position where the cavity resonator 4a is installed is 200 mm (or 500 mm or 70 mm).
0 mm).

In the gas laser device having the above-described configuration, when the microwave output from the microwave oscillator 2 propagates through the waveguide 3 and is transmitted to the cavity resonator 4a, the microwave inside the cavity resonator 4a Microwave is sealed in the space of the discharge tube 1a and the space in the discharge tube 1a. Therefore, the laser gas 8 in the discharge tube 1a is discharge-excited by the microwave electric field. As a result, stimulated emission light is generated from the laser gas 8, and the stimulated emission light is amplified by reciprocal reflection between the total reflection mirror 5 and the output mirror 6 which constitute the optical resonator, and the laser light 7 transmitted through the output mirror 6 is converted to the stimulated emission light. Can be taken out. Moreover,
Since the downstream discharge tube length L is increased, gas mixing is sufficiently performed at the downstream discharge tube length L, the output of the laser beam 7 is increased, and the oscillation efficiency is improved.

The following Table 1 shows the laser output and the oscillation efficiency according to each downstream discharge tube length L.

[0021]

[Table 1]

In the conventional gas laser apparatus shown in FIG. 4, most of the central portion of the discharge tube 1 is covered with the cavity resonator 4, and most of the central portion of the discharge tube 1 emits laser light. Since it was used and there was almost no downstream discharge tube length, sufficient mixing was not performed, the laser output was small, and the oscillation efficiency was poor.

Next, a second embodiment of the present invention will be described with reference to FIG. In the second embodiment, the inner diameter of the cavity resonator 4a is φ83 mm, and its axial length is 100 mm. The inner diameter of the discharge tube 1a is 25 mm, and the length L of the downstream discharge tube is 500 mm. Further, a post-mixed gas supply unit 9 for supplying a fresh laser gas 8 is attached immediately downstream of a portion of the inner space of the discharge tube 1a where the cavity resonator 4a is disposed. The configuration of the other parts is the same as that of the first embodiment.

In the second embodiment, a fresh laser gas 8 is supplied by the post-mixed gas supply section 9 so that a rise in temperature can be suppressed by gas mixing. For this reason, the laser output is about 220 W, and the laser output is improved.

Next, a third embodiment of the present invention will be described with reference to FIG. In the third embodiment, a cavity resonator 4b having an upstream cavity 10 and a downstream cavity 11 for excitation is connected to a discharge tube 1
It is arranged on the upstream side of a. One end of the waveguide 3 is connected to the upstream cavity 10 of the cavity resonator 4b.

In the third embodiment, the inner diameter φ of the cavity resonator 4b is
Is 83 mm, and the axial length of the upstream cavity 10 is 50 mm.
And the axial length of the exciting downstream cavity 11 is 100
mm. The inner diameter φ of the discharge tube 1a was 25 mm, and the length L of the discharge tube on the downstream side was 500 mm.

In the third embodiment, the length of the upstream cavity 10 in the axial direction is reduced, and the length of the downstream cavity 11 for excitation is increased.
Is provided downstream of the upstream cavity 10. For this reason, a strong electric field enabling discharge at a high pressure is obtained in the upstream cavity 10 on the upstream side, and the excitation of the CO ₂ molecule can be controlled in the excitation downstream cavity 11 to be suitable for oscillation. Thus, the cavity resonator 4a having the upstream cavity 10 and the excitation downstream cavity 11
The pressure of the laser gas 8 to 70 To
Even if it is rr, the laser output becomes as large as about 250 W. That is, the output is improved due to the effect of the two cavities 10 and 11 of the cavity resonator 4b.

In each of the above embodiments, excitation and laser oscillation by microwave discharge have been described as examples of high-frequency discharge. However, similar effects can be obtained by high-frequency discharge having a frequency range of 13.56 MHz or the like.

In the above embodiment, the laser device in which the discharge tube is arranged in the cavity resonator is shown. However, the laser device in which the discharge tube is arranged in the opposed parallel plate electrode for discharge, or the discharge device in the induction coupling coil. Naturally, the present invention can be applied to a laser device having a tube.
Further, a coaxial cable may be used instead of the waveguide.

[0030]

According to the present invention, in a gas laser device, a discharge can be generated by an appropriate electric field with respect to laser gas molecules in the direction of its optical axis, and the gas can be sufficiently mixed downstream of the discharge portion. Thereby, an excited state suitable for oscillation of the laser gas can be effectively formed. Also,
In the conventional method, an appropriate electric field is not formed, and the energy that only heats the gas can be effectively used, so that the laser oscillation efficiency can be increased.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a gas laser device according to a first embodiment of the present invention.

FIG. 2 is a front sectional view showing a gas laser device according to a second embodiment of the present invention.

FIG. 3 is a front sectional view showing a gas laser device according to a third embodiment of the present invention.

FIG. 4 is a front sectional view showing a conventional gas laser device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1a Discharge tube 2 Microwave oscillator 3 Waveguide 4, 4a, 4b Cavity resonator 5 Total reflection mirror 6 Output mirror 7 Laser light 8 Laser gas 9 Rear mixed gas supply part 10 Upstream cavity 11 Excitation downstream space Body L Downstream discharge tube length

Claims (4)

[Claims] 1. An electromagnetic wave output from a high-frequency oscillator is guided by a coaxial cable or a waveguide to an opposed parallel plate electrode, an induction coupling coil, or a cavity resonator in which a discharge tube is installed, and the inside of the discharge tube. In a discharge excitation method of an axial flow type gas laser in which a laser medium gas enclosed in a space is discharge-excited by an electric field by the electromagnetic wave to obtain a laser output, the discharge excitation is concentrated on an upstream side of a gas flow. A discharge excitation method for a gas laser, comprising: generating a plasma over an entire cross section; and maintaining a gas flow on a laser optical axis while mixing at a downstream portion of the gas flow. 2. The discharge excitation method for a gas laser according to claim 1, wherein immediately after the discharge excitation by the electromagnetic wave,
A discharge excitation method for a gas laser, wherein a part of a laser gas before discharge is supplied to a gas flow downstream of a discharge part, and cooling of the gas flow is enhanced by gas mixing. 3. The gas laser discharge excitation method according to claim 1, wherein a cavity resonator is provided upstream of the gas flow,
A discharge excitation method for a gas laser, wherein the cavity resonator is divided into a downstream cavity and an upstream cavity to which an electromagnetic wave is guided to generate discharge and excite gas molecules. 4. An electromagnetic wave output from a high-frequency oscillator is guided by a coaxial cable or a waveguide to an opposed parallel plate electrode, an induction coupling coil, or a cavity resonator in which a discharge tube is installed. In a gas laser device of an axial flow system in which a laser medium gas enclosed in a space is excited by an electric field by the electromagnetic wave to obtain a laser output, a discharge unit is provided with a laser oscillation axis with respect to a discharge tube for flowing a laser gas. A gas laser device, which is installed upstream with respect to the upper part and secures a mixing part downstream of a discharge part thereof.