JPH06152029A - Exciting method for laser gas by use of microwave discharge - Google Patents

Abstract

PURPOSE:To improve the laser output and oscillation efficiency, by connecting a plurality of cavity resonators in coaxial with a discharge tube with a connecting plate and forming a nu/2 mode out of coupling modes generating a uniform microwave electric field in an axial direction of the discharge tube and forming the uniform electric field. CONSTITUTION:A laser gas is introduced into a discharge tube 1 through an inflow pipeline 10 and the laser gas heated by a discharge is ejected from the discharge tube 1 through an outflow pipeline 11 of the center and further is again circulated to the discharge tube 1 through the inflow pipeline 10 by a gas circulator 12. By propagating a microwave with a frequency of 2.45GHz from a microwave oscillator 2 to cylindrical cavity resonators 4 of the center through a waveguide 3 and an iris 13, the laser gas in the discharge tube 1 is discharged and excited. In this case, an electric field of pi/2 mode of a TM 010 is generated in the connected cylindrical cavity resonators 4, and a uniform discharge is generated in the two cavity resonators 4 of both ends out of the three cavity resonators 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of exciting a discharge by an electromagnetic wave in a microwave range.

[0002]

2. Description of the Related Art FIG. 2 shows a conventional laser device which is discharge-excited by electromagnetic waves in the microwave region. As shown in the figure, the cylindrical cavity resonator 4 is connected to the microwave oscillator 2 via the waveguide 3 and the iris 13, and end plates 9 are attached to both ends of the cylindrical cavity resonator 4, respectively. There is. The discharge tube 1 is inserted into the cylindrical cavity resonator 4 through the end plate 9, and a total reflection mirror 5 and an output mirror 6 which form an optical resonator are arranged at both ends of the discharge tube 1. ing.

Therefore, when a microwave is output from the microwave oscillator 2, the output microwave is
It propagates to the cylindrical cavity resonator 4 through the iris 13, and the laser gas in the discharge tube 1 is discharge-excited by the electric field of the microwave. As a result, stimulated emission light from the laser gas medium is obtained, amplified by reciprocal reflection between the total reflection mirror 5 and the output mirror 6, and the laser light 7 is emitted from the output mirror 6.
And output.

[0004]

A method of exciting a discharge of a laser gas by a microwave is already known (Handy and B).
randlelik, j.Appl.Phys., 49,3753-3756 (1978)), however, when oscillating a laser using a conventional cavity containing a microwave, the cavity length must be increased in order to increase the laser output. If the length is made longer, as shown in FIG. 3, the resonance frequency f of the electric field mode formed in the cavity resonator is changed by the discharge frequency due to the relationship between the resonance frequency f of the microwave electric field mode in the cavity resonator, the resonator length L and the inner diameter D. Approach the oscillation frequency of the microwave used for.

Therefore, TM ₀₁₀ forms an axially uniform magnetic field for inducing a uniform discharge of the laser gas in the discharge tube.
Various modes other than the mode (Transverse Magnetic Mode; "010" is a subscript represented by the Bessel function of the first kind) coexist. When various modes coexist in the cavity resonator as described above, the discharge becomes non-uniform, and it becomes impossible to excite the entire laser gas in the discharge tube, and the laser output decreases.

Further, when the microwave power is increased to increase the laser output, the temperature of the discharge tube rises, so there is a limit to the increase in laser output. The present invention has been made in view of the above-mentioned prior art, and by preferentially forming the TM ₀₁₀ mode inside the cylindrical cavity resonator, the entire laser gas in the cylindrical cavity resonator is formed. It is an object of the present invention to provide a method capable of uniformly discharging and improving laser output and oscillation efficiency.

[0007]

The structure of the present invention which achieves such an object is a discharge tube which introduces microwaves output from a microwave oscillator into a cylindrical cavity resonator and generates a discharge by its electric field. In the laser oscillator including an optical resonator including a total reflection mirror and an output mirror, a plurality of the cavity resonators are connected coaxially with the discharge tube by a connecting plate so that the cavity resonators are uniform in the discharge tube axial direction. It is characterized in that a uniform electric field is formed by forming a π / 2 mode among the coupled modes by TM ₀₁₀ which becomes a microwave electric field.

[0008]

A metal connecting plate is installed inside the cylindrical cavity resonator so as to be perpendicular to the electric field vector, and as shown in FIG. 4, only the TM ₀₁₀ π / 2 mode resonates. When a plurality of cavity resonators are coaxially connected, the entire laser gas in the discharge tube in the connected cavity resonators is uniformly discharged.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 1 shows one embodiment of the microwave discharge excitation method of laser gas of the present invention. In this embodiment, a cylindrical cavity resonator is used as the cavity resonator. As shown in the figure, the laser oscillator of the present embodiment has a laser gas (composition CO ₂
N _2, the He, as a target pressure 40 Torr), 3 pieces of cylindrical cavity resonator 4 (inner diameter 8.3 cm, length 10 cm) with two copper annular coupling plate 8 (inner diameter 4.0 cm, thickness 0.5 cm) And the end plates 9 are attached to both ends. As a result, the total length of the three connected cylindrical cavity resonators 4 is 3
It became 1 cm. Here, the microwave oscillator 3 is connected to the central cylindrical cavity resonator 4 through the waveguide 3 and the iris 13 (diameter 45 mm) (the diameter of the iris 13 is impedance matching, It was set so that the opposite microwave was zero when discharge occurred (standing wave ratio 1.1).

In these three cylindrical cavity resonators 4,
The discharge tube 1 is inserted through the end plate 9,
A total reflection mirror 5 and an output mirror 6, which form an optical resonator, are arranged at both ends of each. A discharge conduit 11 for discharging the laser gas from the discharge tube 1 is inserted into the central cylindrical cavity resonator 4 and communicates with the center of the discharge tube 1. Further, inflow pipes 10 communicate with both ends of the discharge tube 1, and these inflow pipes 11 and 10 are connected via a gas circulator 12 such as a heat exchanger.

Therefore, the laser gas flows through the inflow line 10.
Laser which is guided to the discharge tube 1 and heated by the discharge
The gas is discharged from the discharge tube 1 through the central discharge line 11.
Is discharged, and the inflow conduit 10 is further supplied by the gas circulator 12.
It will be circulated through the discharge tube 1 again. here,
Microphone with frequency of 2.45 GHz from microwave oscillator 2
B wave through the waveguide 3 and iris 13
By propagating to the resonator 4, an electric field of microwave is generated.
As a result, the laser gas in the discharge tube 1 is discharge-excited. At this time,
The cylindrical cavity resonator 4 connected as shown in FIG.
₀₁₀Π / 2 mode electric field is generated and three cavity resonators
The two cavity resonators 4 at the two ends of 4 can be uniformly discharged.
Becomes In the central cavity resonator 4, TM₀₁₀of
When the 0 mode and the π mode form an electric field, the discharge tube 1 and
Electric discharge is generated also in the connection portion with the discharge pipe line 11.
Therefore, in the present invention, the connecting plate 8 is devised in the present invention.
More, as shown in the figure TM ₀₁₀Of the π / 2 mode electric field
Only the center cavity resonator 4 does not discharge.
It is a scam.

Table 1 shows the laser output and laser oscillation efficiency obtained in this example.

[Table 1] As shown in Table 1, when three cylindrical cavity resonators 4 are connected by a connecting plate to increase the resonator length, the laser oscillation is increased as compared with the conventional single cylindrical cavity resonator. It can be seen that the efficiency is almost unchanged, but the laser power increases proportionally. Further, by changing the thickness and the inner diameter of the annular connecting plate 8, it is possible to control the injection amount of microwave power for each resonator.

On the other hand, according to the conventional method, the laser gas was discharged in the cavity resonator having the cavity length of 30 cm as shown in FIG. 2 without using the coupled cavity resonator forming the π / 2 mode of the present invention. In this case, since the discharge temperature of the laser gas increased, the laser output and the oscillation output did not rise so much as shown in Table 1. Comparing these results, in order to increase the laser power, the π / 2 mode of TM ₀₁₀ according to the present invention is used, and the laser gas is fed from the central cylindrical cavity 4 into which microwave is introduced. It can be seen that it is effective to introduce and distribute to adjacent cylindrical cavity resonators 4.

The present invention is not limited to the above-mentioned embodiment, and a cylindrical cavity resonator in which a π / 2 mode electric field of TM ₀₁₀ is not formed may be combined with an antenna or an iris for introducing microwaves. good. For example, when a coaxial waveguide or a coaxial cable is used instead of using an iris for connecting the waveguide and the cavity resonator, an antenna coupling (an inner conductor inserted in the cavity resonator or an inner conductor and The outer conductor may be partially short-circuited to form a loop) so that the same impedance (standing wave ratio) as when an iris is used can be obtained.

[0015]

As described above in detail with reference to the embodiments, according to the present invention, the discharge is performed while maintaining the discharge of the laser gas in the discharge tube installed in the cylindrical cavity resonator uniformly. Since the volume can be increased, the laser output can be increased. In addition, the laser power can be further increased by effectively inflowing and distributing the laser gas.

[Brief description of drawings]

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

FIG. 2 is a front sectional view showing a conventional laser device.

FIG. 3 is a graph showing the relationship between the resonance frequency and the cavity length.

FIG. 4 is an explanatory diagram showing a coupled mode of TM ₀₁₀ in a cylindrical cavity resonator.

[Explanation of symbols]

 1 Discharge Tube 2 Microwave Oscillator 3 Waveguide 4 Cylindrical Cavity Resonator 5 Total Reflection Mirror 6 Output Mirror 7 Laser Light 8 Ring Connection Plate 9 End Plate 10 Inlet Pipeline 11 Exhaust Pipeline 12 Gas Circulator 13 Iris

Claims (1)

[Claims] 1. A discharge tube for introducing microwaves output from a microwave oscillator into a cylindrical cavity resonator to generate a discharge by an electric field thereof, and an optical resonator including a total reflection mirror and an output mirror. in the laser oscillator is, by multiple connected by the connecting plate the cavity resonator to the discharge tube coaxially, a uniform microwave electric field in the discharge tube axis TM ₀₁₀ of coupled mode by [pi / A microwave discharge excitation method for laser gas, which comprises forming a uniform electric field by forming two modes.