JPH0311684A - Microwave laser apparatus - Google Patents

Abstract

PURPOSE:To eliminate mismatching of an impedance and to match the impedance in any case by a method wherein a quarter-wave matching device is installed between a microwave power-supply and an electric discharge part and a size of this matching part is controlled so as to reduce reflected waves from the discharge part to a minimum. CONSTITUTION:A quarter-wave matching device 26 is installed between a microwave power supply and an electric discharge part 23; a size of this matching part is controlled so as to reduce reflected waves from the electric discharge part 23 to a minimum. Consequently, when microwaves are supplied to the electric discharge part 23, an impedance is matched to the electric discharge part 23 before an electric discharge; as a result, a microwave electric power is injected effectively to the electric discharge part 22. When the electric discharge is started, a characteristic impedance of the electric discharge part 23 is changed; the impedance is mismatched. At this time, the size of the matching part of the quarter-wave matching device 26 is changed immediately, and a matching state is maintained. Thereby, it is possible to match the impedance at any time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application) The present invention relates to a microwave laser device that performs microwave discharge excitation.

(Prior art) Generally, in order to obtain laser oscillation, it is necessary to generate a spatially uniform discharge in the laser medium, but this is especially important when microwaves are used for discharge excitation. Become. That is, when microwaves are used at the pressure used in normal laser oscillation (20 to 200 Torr), the discharge starting voltage is much higher than the discharge sustaining voltage, that is, the steady-state operating voltage, so it is not enough to generate a discharge. When high-intensity microwaves enter the discharge section, discharge occurs intensively near the entrance. Therefore, plasma with a cavity density is formed in this part, and the impedance is extremely reduced. As a result, almost 100% of the incident microwave is reflected as soon as it enters the discharge section, and no electrical input is effectively supplied to the discharge space.

In order to solve these problems, App 1i.

Phys, Let t,, 37 (8), p673 (
In 1980), a microwave laser device as shown in FIG. 4 was proposed. That is, in FIG. 4, laser gas 41 is supplied at high pressure from an upper part 42 of the discharge section, and as it passes through a nozzle 43 made of a dielectric material, the speed increases and the gas pressure decreases. On the other hand, microwaves 44 used for discharge excitation are supplied from the left side in the figure by a waveguide 45, and are supplied to the laser discharge section 51 through a pressure partition 46 that transmits microwaves.

Here, in the space of the laser discharge section 51, the space 47 in front of the nozzle 43 has a high pressure, so no discharge occurs in the space 47. On the other hand, the space 48 behind the nozzle 43
Since the gas pressure decreases in this area, microwave discharge occurs in this area.

The discharge in this part is uniform because it is a discharge in a low gas pressure, and the four optical resonators disposed downstream of the laser discharge section 51 cause the laser to pass through the laser gas excited by microwaves. Light is amplified and oscillated. Further, the exhaust gas 50 is discharged to the right in the figure by a vacuum pump.

(Problems to be Solved by the Invention) However, in the conventional microwave laser device having the above configuration, there were problems to be solved as described below.

That is, the laser gas 41 supplied at high pressure is passed through the nozzle 43.
A vacuum pump is required to evacuate the entire amount of laser gas in order to adiabatically expand it through the laser gas and lower the gas pressure. Moreover, the exhaust power of the vacuum pump becomes large, leading to an increase in the size of the device, and the overall laser oscillation efficiency is extremely reduced.

In order to solve these drawbacks, the present applicant has proposed a microwave laser device as shown in FIG. That is, the microwave power 2 sent out from the microwave oscillator 1 is configured to be radiated into the waveguide 3. A partition wall 4 is provided within the waveguide 3 to divide the waveguide 3 into a microwave oscillator side 3a and a microwave discharge tube side 3b. Furthermore, a discharge section 5 is connected to the waveguide 3b on the side of the microwave discharge tube. This discharge section 5
is composed of an introduction part 5a, a waveguide discharge part 5b, and an end part 5C, and the waveguide discharge part 5b is configured to have a smaller cross-sectional area than the introduction part 5a and the end part 5c.

Further, microwave shield tubes 7 and 7' are arranged coaxially with the laser optical axis 8 on both sides of the discharge section 5, and a total reflection mirror 9a and a semi-transmission mirror 9b are arranged facing each other at the ends thereof. The optical resonator is configured such that the laser beam 10 is emitted to the outside of the semi-transparent mirror 9b. Further, a laser gas circulation pipe 11 is connected to the end portion 5c of the discharge section, and a blower 12 is provided in the middle of the pipe to circulate the laser gas in the direction of an arrow 13. Furthermore, a plurality of cooling pipes 15 are arranged around the waveguide discharge section 5b.

However, in a microwave laser device having such a configuration, microwave energy is effectively injected into the waveguide discharge section, so a glow discharge is formed and the waveguide itself is discharged. Since it is a tube, it has the advantage that a robust and compact laser device can be obtained, but it has the following disadvantages.

That is, in general, when microwaves are applied to a laser device, impedance matching becomes a big problem because when microwaves are used to generate a discharge, the impedance at the discharge section changes significantly. In other words, when an ionized gas, that is, plasma is formed in the discharge part due to discharge, this plasma acts as a dielectric substance with equal polarization with respect to the microwave electric field,
The dielectric constant decreases as the electron density of the plasma increases. In particular, as the electron density increases and the plasma frequency approaches the frequency of the incident microwave, the dielectric constant approaches zero.

By the way, the characteristic impedance of a waveguide filled with a dielectric is proportional to fT7T, where μ is the magnetic permeability of the dielectric and ε is the dielectric constant. Therefore, when a discharge occurs, the impedance of the discharge section becomes extremely large, and the impedance matching between the microwave power source and the discharge section serving as the load is greatly lost, and a considerable portion of the incident power from the microwave power source is reflected. It turns out. On the other hand, if the dimensions of the waveguide and the discharge section are configured so that impedance matching can be achieved in the discharge state, the impedance matching will be lost when no discharge is occurring, and there will be an increase in reflections, causing damage in areas other than the discharge section. There was a drawback that electric discharge occurred.

In this way, the characteristic impedance of the discharge section changes greatly depending on the discharge state, that is, the degree of ionization, so even if the impedance is matched at one operating point, it will be mismatched at other operating points, so it is difficult to maintain a good discharge state. was extremely difficult. Further, there are also disadvantages in that not only the capacity of the microwave power source becomes large, but also discharge occurs in areas other than the discharge section.

The present invention was proposed in order to eliminate the drawbacks of the prior art as described above, and its purpose is to eliminate impedance mismatch and provide highly accurate microwaves that can achieve impedance matching in any case. The purpose of the present invention is to provide a laser device.

[Structure of the Invention] (Means for Solving the Problems) The present invention is characterized in that a laser medium gas is sealed in a vacuum container at a low gas pressure, the gas is circulated to a discharge section, and the gas is disposed outside the discharge section. In a microwave laser device that excites a laser medium gas by supplying microwaves from a microwave power source that discharges and excites a laser medium gas, a
The present invention is characterized in that a /4 wavelength matching device is provided, and the dimensions of the matching portion are controlled so as to minimize the reflected waves from the discharge portion.

(Function) According to the microwave laser device of the present invention, when the microwave power source is activated and microwaves are supplied to the discharge section,
Since impedance matching with the discharge section is achieved before discharge, microwave power is effectively injected into the discharge section.

Furthermore, when the discharge starts, the characteristic impedance of the discharge section changes, resulting in impedance mismatch, but at this time, the dimensions of the matching section of the 1/4 wavelength matching device immediately change, acting to maintain the matching state. .

(Example) Hereinafter, an example of the present invention will be specifically described based on FIGS. 1 and 2.

In this embodiment, as shown in FIG. 1, the microwave oscillator 21 is connected to a directional coupler 22 via a waveguide 24a.
is connected to the directional coupler 22, and a waveguide 24 is connected to the directional coupler 22.
The discharge section 23 is connected via b and 24c. Furthermore, a pressure partition 25 is provided between the directional coupler 22 and the discharge section 23.
The left side of the figure is the atmosphere side, and the right side is the vacuum side.

Further, a 1/4 wavelength matching device 26 is disposed within the discharge section 23, and is configured to achieve impedance matching between the discharge section 23 and the microwave power source by changing the dimensions of this matching section. ing.

On the other hand, an incident microwave power meter 27 and a reflected microwave power meter 28 are connected to the directional coupler 22 and are configured so that their respective outputs are supplied to a controller 29. The controller 29 controls to minimize the ratio of the reflected power to the incident power, or to minimize the reflected power, and this control output is converted to the 1/4 wavelength by the converter 30. It is configured to be converted into a driving force for the matching device 26 and perform an impedance matching operation.

Next, FIG. 2 shows an example of a 1/4 wavelength matching device built into the discharge section 23. That is, a quarter wavelength matching device 26 is disposed between the microwave waveguide section 24c and the discharge section 23. Further, the 1/4 wavelength matching device 26 is composed of an electrode portion 26a and a drive rod 26b, and a bellows 31 that can be expanded and contracted is disposed around the drive rod 26b to maintain airtightness inside the container. ing. Note that the length L of the electrode portion 26a is set to 1/4 wavelength.

In the microwave laser apparatus of this embodiment having such a configuration, the impedance matching operation is performed as described below.

That is, in general, the lateral dimension (longitudinal) of a rectangular waveguide is a,
The vertical dimension (short side) is b, the magnetic permeability of the waveguide medium is μ,
If the dielectric constant is ε, then the characteristic impedance Z. is given by the following equation.

Zo=(π2 φb/8a)・Z-work Z1=η・λg/λ η=-f7iwa7...(1) λg=
Guide wavelength λ: Microwave wavelength Therefore, when there is no discharge, there is no change in the medium, so in FIG. is Zx, and the characteristic impedance of the discharge section is z
If b, then Za oCa, Zx ocx, Zb oc
b - = (2), and the impedance matching condition is Zx - f = 1, so x = f = T lower (3).

On the other hand, when discharge occurs in the discharge section 23, the following occurs. Due to the generation of discharge, the inside of the discharge section 23 is filled with ionized gas, that is, plasma, but this plasma is considered to be a dielectric substance with equal polarization to the microwave electric field, and the dielectric constant ε is ε=ε, -neφe 27m 4ω2
・°゛ (4 ε.: Vacuum dielectric constant ne: Electron density e: Electron charge m: Electron mass ω: Microwave angular frequency 1.

Therefore, as the electron density ne increases, the dielectric constant ε decreases, and as the plasma frequency ωp (-ne*e 7m ・ε0) approaches the power supply frequency ω, the dielectric constant ε approaches zero from equation (4),
From equation (1), since the characteristic impedance approaches infinity, the matching will deviate.

When an impedance mismatch occurs in this way, the reflected power resulting from the impedance mismatch is detected by the reflected power meter 28, and control signals are sent from the two controllers to match the impedance via the converter 30 shown in FIG. A driving force for adjusting the dimensions of the section is applied to the quarter wavelength matching device 26. This driving force is
The drive rod 26b shown in FIG. 2 is moved up and down to align the microwave power source and the microwave glow discharge plasma 32.

In this manner, according to the present embodiment, microwave energy is efficiently injected into the discharge section 23, so that a --like glow discharge is obtained, and effective amplification and oscillation of laser light is performed. In addition, since a metal bellows 31 is disposed in the quarter wavelength matching doubler 26,
Not only is airtightness maintained, but there is also the advantage that there is no leakage of radio waves.

Note that the present invention is not limited to the above-described embodiment, and the quarter wavelength matching device 26 may be provided outside the vacuum container as shown in FIG. In this case, in order to limit the discharge within the discharge section 23, it is necessary to set a>b. Further, the position of the 1/4 wavelength matching device is set at a distance where the standing wave generated by the reflected wave from the discharge plasma section 32 is maximized or minimized. Furthermore, in this case, since the 1/4 wavelength matching device 26 is placed on the atmosphere side, there is no need to make the matching section airtight, and its control becomes easy.

"Effects of the Invention" - As stated above, according to the present invention, a 1/4 wavelength matching device is disposed between the microwave power source and the discharge section, and the dimensions of the matching section are adjusted to match the dimensions of the matching section. By simply controlling the reflected waves to a minimum, it is possible to eliminate impedance mismatching and provide a highly accurate microwave laser device that can achieve impedance matching in any case.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the microwave laser device of the present invention, FIG. 2 is a sectional view showing an example of a quarter wavelength matching device in the microwave laser device of the present invention, and FIG. FIG. 4 is a sectional view showing a main part of a conventional example, and FIG. 5 is a configuration diagram showing an example of a conventional microwave laser device. 1...Microwave oscillator, 2...Microwave power,
3... Waveguide, 4... Partition wall, 5... Discharge part, 5a
...Introduction part, 5b... Waveguide discharge part, 5c... End part, 6... Glow discharge, 7, 7'... Microwave shield tube, 8... Laser optical axis, 9a... Total reflection mirror, 9b... Half-transmission mirror 10... Laser light, 1
1... Laser gas circulation piping, 12... Blower, 15
...Cooling pipe, 21...Microwave oscillator, 22...
- Directional coupler, 23... discharge section, 24... waveguide,
25... Pressure bulkhead, 26... 1/4 wavelength matching device, 2
6a... Electrode part, 26b... Drive rod, 27... Incident microwave power meter, 28... Reflection microwave power meter, two... Controller, 30... Converter , 31... Bellows, 32... Microwave glow discharge plasma, 41... Laser gas, 42...''-
Portion inlet, 43... Nozzle, 44... Microwave, 4
5... Waveguide, 46... Pressure partition, 49... Optical resonator, 50... Exhaust gas, 51... Laser discharge section.

Claims (1)

[Claims] A laser medium gas is sealed in a vacuum container at low gas pressure, this gas is circulated to a discharge section, and a microwave is supplied from a microwave power source disposed outside the discharge section to generate a discharge. In a microwave laser device that excites a laser medium gas, a quarter-wavelength matching device is disposed between the microwave power source and the discharge section, and the dimensions of the matching section are adjusted to match the reflected waves from the discharge section. A microwave laser device characterized in that it is controlled to minimize.