JPH0276277A - Microwave laser device - Google Patents

Abstract

PURPOSE:To achieve a uniform glow discharge under normal gas pressure by making the direction of flow of a laser medium gas in a discharge part to be equal to that of propagation of microwave, by providing a preliminary part at the upstream of the discharge part, and then providing a magnetic field producing means for producing magnetic field which crosses the direction of propagation of microwave at right angle at the outside of the discharge part. CONSTITUTION:A magnet for preliminary ionization (preliminary ionization part) 10 is provided at the outside of a waveguide 16 in the upstream part of a discharge part 7, a magnetic field crossing the microwave electric field at right angle is formed, a preliminary glow is formed, and an electronic density exceeding at least 10 ion pair/cm<2> is formed. Also, a microwave power supply 13 for supplying a microwave 12 to the waveguide 16 through a waveguiding part 14 is provided at the upstream side of the waveguide 16. Also, a magnet for producing magnetic field (magnetic-field producing means) 17 is provided at the outside of the waveguide 16 of the discharge part 7 to form a magnetic field crossing the direction of propagation of the microwave 12. It allows energy of microwave to be effectively impregnated into the discharge part 7, thus forming a uniform glow discharge at normal gas pressure without changing pressure.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a discharge-excited laser device, and particularly to a high-output, compact microwave laser device that performs microwave discharge excitation. .

(Prior Art) Generally, in order to obtain laser excavation, it is necessary to generate a spatially uniform discharge in the laser beam, and this condition is
This is particularly important when microwaves are used for discharge excitation.

That is, when microwaves are used at a pressure (20 to 200 Torr) used in normal laser excavation, discharge occurs intensively near the entrance where the microwaves enter the discharge section. Therefore, high-density plasma is formed in this portion, and impedance is extremely reduced in this portion. As a result, as soon as the incident microwave enters the discharge part, it becomes almost 100%
% will be reflected and no electrical input will be effectively supplied to the discharge space.

As a countermeasure for this, for example, literature (AI) E) li, ph
ys, Lett, 37(8), p673(19
80)), there exists something like the one shown in Figure 3. In FIG. 3, laser gas 21 is supplied at high pressure from an upper inlet 22, and passes through a nozzle 2 made of a dielectric material.
3, the speed increases and the gas pressure decreases.

On the other hand, the microwave 24 is supplied from the left side in the figure by a waveguide 25, and is supplied to the laser discharge section 31 through a pressure partition 26 that transmits the microwave.

Since the space 27 of the laser discharge section 31 is under high pressure, no discharge occurs here. The laser gas 21 is accelerated at the nozzle 23 as already mentioned and the gas pressure is reduced so that a microwave discharge 28 is generated downstream of the nozzle 23. Since the discharge here is a discharge in a low gas pressure -
The laser beam excited by the microwave and passing through the laser gas is amplified and excavated by the optical resonator 29 configured on the downstream side. The exhaust gas 30 is discharged to the right side in the figure by a vacuum pump.

(Problem to be Solved by the Invention) By the way, the biggest drawback of the above method is that a vacuum pump is required to exhaust the entire amount of laser gas 21 in order to perform heat-insulating engraving through the nozzle 23. in this case,
A large amount of power is required to exhaust the vacuum pump, and as a result, the laser oscillation efficiency of the entire device is extremely reduced.

Therefore, a configuration in which the gas pressure is greatly changed as in the above system is not preferable, and it has been desired to develop a microwave-excited laser that can operate under the same operating conditions as a normal laser.

The present invention was proposed to solve the problems of the prior art, and its purpose is to maintain normal gas pressure (20 to 200 T) without significantly changing the gas pressure.
It is an object of the present invention to provide a compact microwave laser device with good overall efficiency and capable of generating a glow discharge of - orr ).

[Structure of the Invention] (Means for Solving the Problems) The microwave laser device of the present invention has a configuration in which the flow direction of the laser medium gas in the discharge section and the propagation direction of the microwave are the same, and the upstream section of the discharge section The structure is characterized in that a preliminary ionization section is provided in the discharge section, and a magnetic field generating means for generating a magnetic field perpendicular to or parallel to the propagation direction of the microwave is disposed outside the discharge section.

(Function) In the present invention having the above configuration, when microwaves are supplied to the discharge section, the discharge section is electrified in a negative manner by the pre-ionization section, and the spatial resistance is low. , --like ionization immediately progresses and the spatial resistance value decreases,
Since it is possible to match the impedance of the incident space, microwave energy is effectively consumed here.

Furthermore, since the discharge occurs at a discharge sustaining voltage, which is much lower than the normal dielectric breakdown voltage, a stable and -like glow discharge is formed in the discharge section, making it possible to optimally excite the laser gas.

Furthermore, in the present invention, since the magnetic field generating means is provided outside the discharge section, the effect of the magnetic field causes the microwave to
The so-called cut-off frequency shifts to the lower frequency side.

Therefore, since microwaves can pass through plasma with high electron density, stable uniform discharge is possible.

In addition, in the present invention, the preliminary ionization energy is small compared to the total discharge energy, resulting in good energy efficiency. In particular, with pre-ionization power sources for microwaves, if you perform pre-ionization at -degrees and -degrees to ignite the microwaves evenly, all you need to do is replenish the vanishing valve by diffusion into walls, etc. Therefore, the pre-ionization energy can be reduced in this respect as well.

(Embodiment) An embodiment of the microwave laser device according to the present invention as described above will be specifically described below with reference to FIG.

In FIG. 1, reference numeral 1 denotes a quartz laser discharge tube forming a vacuum vessel, which is evacuated to vacuum via a valve 3 by an evacuation pump 2. After being evacuated to vacuum, valve 3 is closed, valve 4 is opened, and laser gas is injected into this vacuum container from laser gas cylinder 5, and after being injected to a constant pressure (for example, 50 Torr). , valve 4 is closed.

In this case, the valves 3 and 4 are normally controlled by a laser gas controller 6, as shown by broken lines in FIG. 1, and injection and exhaust are performed alternately or continuously by this valve control. 1. The laser gas inside the laser discharge tube 1 is constantly replaced in small amounts. In the discharge section 7 in the laser discharge tube 1, the upstream side of the waveguide 16 is tapered so that the electric field is higher than that before and after the discharge section 7.

The laser gas is circulated by a Roots blower 8. In this case, the gas sent out from the discharge section 7 has a high temperature due to the heating effect of the microwave discharge, so it is cooled by heat exchangers 9a and 9b provided before and after the Roots blower 8.

In this embodiment, a pre-ionization magnet (pre-ionization section) is provided outside the waveguide 16 in the upstream portion of the discharge section 7.
10 are arranged, thereby creating a magnetic field orthogonal to the microwave electric field, creating a preliminary glow, and creating an electron density of at least 10 ion pairs/Cm3.

Further, on the upstream side of the waveguide 16, a microwave power source 1 that supplies microwaves 12 to the waveguide 16 via the waveguide section 14 is provided.
3 is provided.

Furthermore, a pair of mirrors 15a, 1
An optical resonator 15 made up of 5b is arranged.

In addition, in this embodiment, a magnetic field generating magnet (magnetic field generating means) 17 is disposed outside the waveguide 16 of the discharge section 7 to form a magnetic field perpendicular to the propagation direction of the microwave 12. It has become.

In the microwave laser device of this embodiment having the above configuration, the preliminary ionization magnet 10 upstream of the discharge section 7
When a magnetic field perpendicular to the microwave electric field is formed, the microwave discharge starting voltage decreases and a preliminary glow is formed, as shown in FIG. In this case, an electron density of at least 10 ion pairs/Cm3 is formed in the preliminary glow, so when the + microwave is incident on the discharge section 7, ionization progresses quickly even if the electric field is about the discharge sustaining voltage. However, --like microwave glow discharge is generated in the discharge section 7.

That is, in this embodiment, the electric field strength of the microwave 12 can be made low enough to prevent glow discharge from occurring in the discharge section 7 when there is no pre-ionization, so that a strong discharge is formed near sunset in the discharge section 7. This will not cause any inconvenience.

In this case, the resistance value of the discharge section 7 during discharge can be adjusted to a value equal to or close to the characteristic impedance of the waveguide section 14 that couples the microwave power source 13 and the discharge section 7, so that the incident microwave 12 Very little of the microwave energy is reflected near the entrance of the discharge section 7, and most of the microwave energy is injected into the discharge section. Then, due to the microwave energy efficiently injected into the discharge section 7 in this way, the ionization of the pre-ionized laser gas progresses roughly, and the generated ions and electrons are sent downstream by the flow of the laser gas. As a result, a -like discharge occurs within the discharge tube. Note that the excited laser gas is in the optical resonator 1.
5, the laser beam is amplified and oscillated.

Furthermore, in this embodiment, a magnetic field perpendicular to the microwave electric field is generated also in the discharge mold part 7 by the magnetic field generating magnet 17 provided outside the discharge part 7, so that the layer is stable and flexible. A discharge can be formed.

That is, according to the introductory book on plasma physics, ``Introduction to Plasma Physics'' translated by Uchida, when electron mass m, charge F, and electron density n, the plasma frequency ωp is ωp = (4πne/m
) is given by. It is known that microwaves with a frequency lower than the plasma frequency ωp cannot propagate in the plasma.

Here, when a magnetic field B exists, the cyclotron frequency ωG is defined as ωc = e B/m. Using this cyclotron frequency ωC, a cutoff frequency ωR1ωL equal to the resonance frequency ωh is given by the following equation.

ωh-LT case; 7 lower ωR=[ωc+(ωc+4ωp)]/2ωL=[-ω
c+(ωc+4ωp)]/2 When the phase velocity Vφ with respect to the microwave frequency ω is drawn according to the above-mentioned introductory book, it becomes as shown in FIG. From FIG. 3, when the plasma density n and the magnetic field B are fixed, microwaves cannot pass through the plasma at frequencies ω=O to ωL, which are shaded in the figure. When the frequency ω becomes 01 or more, the microwave can pass through the plasma, and the microwave can pass through the plasma up to the resonance frequency ωh. In this region, depending on whether ω is smaller or larger than ωp, the microwave speed is faster than C,
Or it may propagate slowly, and as seen from Figure 3, ω=ωp
Then microwaves propagate at a speed C. When the frequency ω exceeds ωh, the microwave cannot propagate up to ωR again, and ω
Everything beyond R becomes a propagation region.

In this way, even if the microwave frequency ω is lower than the plasma frequency ωp, due to the action of the magnetic field, 01
It can be seen that since the above frequencies can propagate in the plasma, stable and negative-like discharge is possible.

As described above, it can be seen that in this embodiment, microwave energy is effectively injected into the discharge section 7, resulting in a --like glow discharge, and effective amplification and excavation of laser light is performed. In addition, in pre-ionization, it is sufficient to simply form an appropriate space charge (for example, 10 ion pairs/cm) in the discharge area, so compared to the total discharge energy,
The pre-ionization energy is small and a special power source for pre-ionization is not required, resulting in a microwave laser device with good energy efficiency.

In particular, a feature of microwaves is that space charges are trapped in the discharge space, so unlike normal DC or AC lasers, there is no need for a cathode fall section to supply electrons, which improves the efficiency of laser light excitation by discharge. There is also the advantage that the pre-ionization energy can be further reduced. That is,
As mentioned above, in the pulse power source 11 for pre-ionization, - degrees,
- If pre-ionization is performed to ignite the microwaves evenly, all that is needed is to replenish the extinction valve by diffusion into walls, etc., so a small amount of pre-ionization energy is sufficient.

Note that the present invention is not limited to the above embodiments, and the configuration of the magnetic field generating means can be selected as appropriate. For example,
An embodiment as shown in FIG. 4 is possible. In the embodiment shown in FIG. 4, the magnetic field generating magnet 17 disposed outside the laser discharge tube 1 is tilted by an angle θ, and the magnet 17 is directed downstream.
The spacing between the two is narrowed. In this embodiment with such a configuration, the magnetic field becomes stronger toward the downstream of the discharge section 7, so as the microwave 12 is incident and attenuated by the discharge, the discharge voltage decreases, and the electrons are more uniformly distributed. Density is obtained.

Furthermore, instead of using the magnetic field generating magnet 17, it is also possible to arrange a coil outside the discharge section 7 to generate a magnetic field in the microwave propagation direction, and the same can be done. You can get the effect of

[Effects of the Invention] As described above, in the present invention, microwave energy can be effectively injected into the discharge part by providing a pre-ionization part upstream of the discharge part, and it is possible to inject the microwave energy into the discharge part normally without changing the pressure. At a gas pressure of (20 to 200 Torr) -
Since a glow discharge of various types can be formed, effective amplification of laser light can be performed, and a compact microwave laser device with good overall efficiency can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a microwave laser device according to the present invention, FIG. 2 is a characteristic diagram showing discharge starting voltage characteristics with respect to magnetic field strength, and FIG. 3 is a graph showing phase velocity with respect to microwave frequency. FIG. 4 is a sectional view showing a discharge section of another embodiment of the present invention, and FIG. 5 is a sectional view showing the main parts of a conventional microwave laser device. DESCRIPTION OF SYMBOLS 1...Laser discharge tube, 2...Evacuation pump, 3゜4...Valve, 5...Laser gas cylinder, 6...
...Gas controller, 7...Discharge unit, 8...Roots blower, 9a, 9b...Heat exchanger, 10...Preliminary ionization magnet, 11...Pulse power supply, 12...・Microwave, 13...Microwave power supply, 14...Wave guide, 15
... Optical resonator, 15a, 15b... Mirror, 16.
... Waveguide, 17... Magnet for generating magnetic field.

Claims (1)

[Claims] Laser medium gas is sealed in a vacuum container at low gas pressure, and this gas is circulated by a blower to a discharge section via a heat exchanger, and this discharge section is supplied with an external microwave power source. In a microwave laser device that excites a laser medium gas by supplying microwaves and causing a discharge, the flow direction of the laser medium gas in the discharge section and the propagation direction of the microwave are the same, and the upstream section of the discharge section A microwave laser characterized in that a pre-ionization section is disposed at the discharge section, and a magnetic field generating means for generating a magnetic field perpendicular to or parallel to the microwave propagation direction is disposed outside the discharge section. Device.