JPH06140694A - Microwave discharge exciting laser - Google Patents

Abstract

PURPOSE:To provide a microwave discharge exciting laser having large outputs and a lower power loss. CONSTITUTION:One end of a wave guide 1 is connected with a microwave oscillator 11 and the other end is connected with a metal container 2, and an opening 2a is provided in a part superimposing on an internal radius part of the wave guide 1 in a wall surface of the metal container 2 and a symmetrical pair of cylindrical metal projections 3, 9 is provided in the direction of crossing the axial direction of the wave guide 1 within the metal container 2. An oscillating pipe closing one end 4a and the other end 4b is inserted into the symmetrical cylindrical metal projections 3, 9, and the oscillating tube 4 is connected with a laser gas circulating pipe 8 between the one end 3a of the cylindrical metal projection 3 located in the external side of the metal container 2 and the one end 4a of the oscillating tube 4, and the oscillating tube 4 is connected with a laser gas circulating pipe 10 between one end 9a of the cylindrical metal projection 9 located in the external side of the metal container 2 and the other end 4b of the oscillating pipe 4, in order to circulate laser gas 5 within the oscillating tube 4 through the pipes 8, 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser oscillated by microwave discharge excitation.

[0002]

2. Description of the Related Art A conventional microwave discharge pumped laser is a method of supplying microwaves by directly connecting a microwave power source to an oscillation tube to cause laser oscillation, or connecting a waveguide directly to the oscillation tube. A method of supplying a microwave through this waveguide to cause laser oscillation has been used.

FIG. 2 shows an example of a conventional microwave discharge excitation laser. Electrodes 22 and 23 are provided on both sides on the outer circumference of the oscillation tube 21 to supply electric power to the oscillation tube 21, and the oscillation tube 21 is provided with electrodes 22 and 23. A total reflection mirror 26 and a semi-reflection mirror 27 are provided on the long axis at positions sandwiching the oscillation tube 21.
2 is a microwave power source 28 and a choke coil 2 for pre-ionizing the laser gas 29 prior to laser oscillation.
4 and the preionization circuit 25 are connected.

[0004]

However, in the above-mentioned microwave discharge excitation laser, the microwave is generated in the oscillation tube 2 as the ratio of the longitudinal dimension to the lateral dimension of the oscillation tube 21 approaches 1.
Since it is uneconomical because it leaks from No. 1, and microwaves leak from the oscillation tube 21 to cause radio interference, it is necessary to make the vertical dimension of the cross section of the oscillation tube 21 smaller than the horizontal dimension. As a result, the cross-sectional area of the oscillation tube 21 cannot be increased, and a large output cannot be obtained. In order to obtain a large laser output in a state where the vertical dimension of the cross section of the oscillation tube 21 is smaller than the horizontal dimension, it is conceivable to increase the total length of the oscillation tube 21 to increase the volume of laser gas. In this case, Since the total length is too long to be practical, this method is not suitable for high output. Further, glow discharge for causing laser oscillation is easy if the gas pressure is lowered to 1 atm or less, but it is not easy at 1 atm or more, so the laser gas pressure is set to 1 atm or more to increase the laser output. If it is necessary to provide the above structure, it is necessary to provide the choke coil 24 and the preionization circuit 25 in the above-described structure, but this complicates the structure. Therefore, the present invention realizes a microwave discharge pumped laser with a large output and a low power loss by generating a uniform high electric field only in a necessary portion to enable laser oscillation in a laser gas of 1 atm or more. . In addition, since the discharge device has a closed structure, there is no leakage microwave so that other devices are not damaged.

[0005]

According to a first aspect of the present invention, a microwave oscillator 11 is connected to one end of a waveguide 1 and a metal container 2 is connected to the other end thereof. Wave tube 1
A pair of cylindrical metal projections 3, 9 facing each other in the direction intersecting the axial direction of the cylindrical metal projections 3, 9 are provided.
Oscillation tube 4 is inserted in 9 and laser gas 5
Then, the total reflection mirror 6 and the semi-reflection mirror 7 are arranged so as to face each other at a position sandwiching the oscillation tube 4 on the long axis of the oscillation tube 4.

In the invention of claim 2, the metal container 2 is grounded in the invention of claim 1. According to the invention of claim 3, in the invention of claim 1 or 2, a gas or a derivative of a kind that hardly causes an electric discharge is put in the metal container 2. In the invention of claim 4, in the invention of claim 1 or 2, the metal container 2
The inside is evacuated to high vacuum. In the invention of claim 5, claim 1
Alternatively, in the second aspect of the invention, the pressure inside the metal container 2 is made higher than the gas pressure inside the oscillation tube 4.

[0007]

In the microwave discharge pumped laser according to the first aspect of the present invention configured as described above, TM110 mode is used when the metal container 2 is a rectangular parallelepiped cavity resonator, and TM010 mode is used when the metal container 2 is a cylindrical cavity resonator. When the mode is excited into the metal container 2 through the waveguide 1, the mode is sandwiched between the pair of cylindrical metal projections 3 and 9 in the vicinity of the axes of the pair of cylindrical metal projections 3 and 9 in the metal container 2. Since a high electric field of microwaves is generated in the space, glow discharge occurs in the laser gas 5 inside the oscillation tube 4 inserted in the cylindrical metal projections 3 and 9 even if the gas pressure is 1 atm or more, The laser light thus generated reciprocates between the total reflection mirror 6 and the semi-reflection mirror 7 and is amplified to cause laser oscillation.

In the microwave discharge excitation laser of the second aspect of the present invention, since the metal container 2 is connected, there is no risk of electric shock even if the metal container 2 is accidentally touched during operation. In the microwave discharge excitation laser of the invention of claim 3,
There is no discharge near the outside of the oscillation tube 4, and efficient and stable oscillation can be performed. In the microwave discharge pumped laser according to the invention of claim 4, discharge is not generated near the outside of the oscillation tube 4, and efficient and stable oscillation can be performed. Also in the microwave discharge pumped laser of the fifth aspect of the present invention, discharge is not generated near the outside of the oscillation tube 4, and efficient and stable oscillation can be performed.

[0009]

FIG. 1 is an example of a microwave discharge pumped laser according to the present invention, in which a microwave oscillator 11 is connected to one end of a waveguide 1 and a metal container 2 is connected to the other end thereof, and a wall surface of the metal container 2 is connected. A window 2a is opened in a portion that overlaps the inner diameter portion of the waveguide 1, and a pair of cylindrical metal projections 3 facing each other in a direction intersecting the axial direction of the waveguide 1 are formed in the metal container 2. 9 are provided, and one end 4a and the other end 4b are provided in the cylindrical metal projections 3 and 9 facing each other.
The oscillating tube 4 closed is inserted, and the one end 3a of the cylindrical metal protrusion 3 and the one end 4 of the oscillating tube 4 located outside the metal container 2 are inserted.
Piping 8 for laser gas circulation in oscillation tube 4 between
And a pipe 10 for laser gas circulation is connected to the oscillation tube 4 between one end 9a of the cylindrical metal projection 9 located on the outside of the metal container 2 and one end 4b of the oscillation tube 4 to connect the pipe 8 , 10 to circulate the laser gas 5 in the oscillation tube 4. The end faces of the oscillating tube 4 at the one end 4a and the other end 4b are sufficiently smooth so that the direction of the laser light running from the inside of the oscillating tube 4 along the major axis of the oscillating tube 4 cannot be changed. A total reflection mirror 6 and a semi-reflection mirror 7 are provided on the outside of each of the four. The metal container 2 is grounded. A gas or a dielectric material that is unlikely to cause an electric discharge is placed in the metal container 2, the inside of the metal container 2 is evacuated to a high vacuum, or the pressure inside the metal container 2 is set sufficiently higher than the gas pressure inside the oscillation tube 4. Make it higher

In this microwave discharge excitation laser, TM110 mode is used when the metal container 2 is a rectangular parallelepiped cavity resonator, and TM010 mode is used when the metal container 2 is a cylindrical cavity resonator.
When microwaves are sent into the metal container 2 through the waveguide 1 by using the mode, the pair of cylindrical metal projections 3 and 9 in the metal container 2 are in the vicinity of the axial center of the pair of cylindrical metal projections. Since a high electric field is generated in the space between the protrusions 3 and 9, glow discharge occurs inside the oscillation tube 4 in this high electric field space, and the light generated in the oscillation tube 4 due to this glow discharge is reflected by the total reflection mirror 6. Laser light is generated by repeating back and forth between the semi-reflecting mirrors 7.

According to this embodiment, glow discharge is uniformly generated in the oscillation tube 4, and a large output laser beam with little power loss can be obtained. Further, since the portion to which the high electric field is applied is inside the metal container 2, by grounding the metal container 2, the metal container 2 becomes equipotential with the ground, and there is no fear of electric shock.
Further, the leakage microwave does not affect other devices, and the preliminary ionization circuit is unnecessary.

FIG. 2 shows another example of the microwave excitation laser of the present invention. In the oscillation tube 4, between the one end 3a and the one end 4a and between the other end 9a and the other end 4b, respectively, the preliminary discharge electrode 4 is provided.
c and 4d are provided, a low density plasma is used, and the resonance frequency at the time of plasma formation is adjusted to the microwave frequency in advance. Others are the same as the example of FIG. Since the resonance frequency shift is small in low density plasma,
By adjusting the resonance frequency at the time of plasma formation to the microwave frequency in advance, laser oscillation is continuously performed without stopping discharge even if the resonance frequency of the resonator shifts to a higher direction after the start of discharge.

[0013]

According to the first aspect of the present invention, it is possible to realize a laser having a large output, a small power loss, and excellent efficiency even in laser oscillation by microwave discharge excitation. Here, the electric field in the vicinity of the oscillation tube is increased by arranging the pair of cylindrical metal objects 3 and 9. As a result, the discharge can be performed without unnecessarily increasing the output of the microwave oscillator. In addition, the TM110 mode is used when the metal container 2 is a rectangular parallelepiped cavity resonator, and the TM010 mode is used when the metal container 2 is a cylindrical cavity resonator. Enhanced, microwave discharge becomes even easier. These resonance modes have a microwave electric field only in the axial component of the container, and the electric field distribution is strongest at the center axis and weaker near the container wall, so that the electric field only near the oscillation tube necessary for discharging the laser gas can be strengthened. The output of the microwave oscillator can be remarkably reduced, and power consumption can be reduced, oscillation efficiency can be increased, and the device can be downsized. Therefore, the most promising application is for an excimer laser or a carbon dioxide laser, which requires high-density and high-energy electrons. When used in an excimer laser, the discharge stops when the discharge starts and the high resonance frequency of the resonator shifts to the number side, so that there is no microwave input to the resonator. This extinguishes the plasma and stops the laser oscillation. At the same time, the resonance frequency of the resonator returns to its original value, so that the microwave is absorbed again in the resonator and discharge is started. In this way, since the microwave input to the resonator is cut off and the discharge is extinguished after the glow discharge is formed at the beginning of the discharge and before the arc discharge is formed,
The deterioration of the laser gas is small, and efficient laser starting is possible. The blinking cycle of the discharge here is determined by the time constants of rise and disappearance of the plasma density.

The pair of cylindrical metal projections 3 and 9 in the metal container 2 looks like electrodes at first glance, but this is not an electrode, but near the axial center of the cylindrical metal projections 3 and 9 and the pair of cylindrical metal projections 3 and 9. Since it is for generating a high electric field in the space between the cylindrical metal projections 3 and 9, it has the same advantage as other types of microwave discharge pumped lasers in that impurities are not generated from the electrodes due to discharge. To have.

According to the second aspect of the invention, since the metal container 2 is grounded, there is no risk of electric shock even if the metal container 2 is accidentally touched during operation. According to the third aspect of the present invention, it is possible to perform efficient and stable oscillation without causing discharge of gas or the dielectric near the outside of the oscillation tube 4. According to the invention of claim 4, efficient and stable oscillation can be performed without causing discharge near the outside of the oscillation tube 4. According to the invention of claim 5, the gas near the outside of the oscillation tube 4 can perform efficient and stable oscillation without causing discharge.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a microwave discharge excitation laser of the present invention.

FIG. 2 is a diagram showing another example of the microwave discharge excitation laser of the present invention.

FIG. 3 is a diagram showing an example of a conventional microwave discharge excitation laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Waveguide 2 Metal container 3 Cylindrical metal projection 4 Oscillation tube 5 Laser gas 6 Total reflection mirror 7 Semi-reflection mirror 8 Piping 9 Cylindrical metal projection 10 Piping

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masahiko Adachi 3-chome, Yoshinocho, Nishibiwajima-cho, Nishibashijima-cho, Nishikasugai-gun, Aichi Takadake Works Nagoya Works

Claims (5)

[Claims] 1. A microwave oscillator 11 is provided at one end of a waveguide 1.
And a metal container 2 is connected to the other end, and a pair of cylindrical metal projections 3 and 9 facing each other in a direction intersecting the axial direction of the waveguide 1 are provided in the metal container 2. The oscillation tube 4 is provided in the pair of cylindrical metal projections 3 and 9 and
A microwave discharge excitation laser in which a laser gas 5 is put inside, and a total reflection mirror 6 and a semi-reflection mirror 7 are arranged so as to face each other at a position sandwiching the oscillation tube 4 on the long axis of the oscillation tube 4. 2. The microwave discharge excitation laser according to claim 1, wherein the metal container 2 is grounded. 3. The microwave discharge excitation laser according to claim 1, wherein the metal container 2 contains a gas or a dielectric material of a kind that does not easily generate a discharge. 4. The microwave discharge excitation laser according to claim 1, wherein the inside of the metal container 2 is evacuated to a high vacuum. 5. The microwave discharge pump laser according to claim 1, wherein the pressure inside the metal container 2 is set higher than the gas pressure inside the oscillation tube 4.