JPH0276276A - Microwave laser device - Google Patents

Abstract

PURPOSE:To achieve a uniform glow discharge under normal gas pressure by making the direction of flow of laser medium gas in the discharge part to be equal to that of propagation of microwave and by providing a preliminary ionization part at the upstream part of discharge part. CONSTITUTION:Gas discharged from a discharge part 7 is cooled by heat exchangers 9a and 9b provided at the front and rear of a roots blower 8. Then, a preliminary ionization part 10 consisting of an inner electrode 10a and an outer electrode 10b coated with crystal is provided at the upstream of the discharge part 7. Thus, by applying a pulsative high voltage to this preliminary ionization part 10 from an external pulse power supply 11, laser gas before entering the discharge part 7 is ionized to at least 10 (ion pair/cm) or more. It reduces discharge start voltage at the discharge part 7, allows ionization to proceed readily even if the electric field is approximately the same as discharge maintaining voltage when microwave incides the discharge part 7, and forms a uniform glow discharge under normal gas pressure (20-200Torr) 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 emission, it is necessary to generate a spatially uniform discharge in the laser medium, and this condition is particularly important when microwaves are used for discharge excitation. . In other words, microwaves are used at the pressure (
20 to 200 Torr), discharge occurs intensively near the entrance where the microwave enters the discharge section. Therefore, high-density plasma is formed in this portion, and impedance is extremely reduced in this portion. As a result, the incident microwave becomes almost 100% as soon as it enters the discharge part.
is reflected, and no electrical input is effectively supplied to the discharge space.

As a countermeasure for this, for example, literature (Appli, Phys
, Lett, 37(8), p673 (1980
According to ), there exists something like the one shown in Figure 3. In FIG. 3, the laser gas 21 is connected to the upper population 22.
The gas is supplied at a higher pressure, and as it passes through the nozzle 23 made of dielectric material, the gas 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. The discharge here occurs 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) The biggest drawback of the above method is that a vacuum pump is required to exhaust the entire amount of the laser gas 21 in order to adiabatically expand it 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 excavation efficiency of the entire apparatus is extremely reduced.

Therefore, a configuration in which the gas pressure is drastically changed as in the above system is not preferable, and it has been desired to develop a microwave excitation 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 71' chroma wave 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 structure 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 direction of the discharge section is A feature of the structure is that a pre-ionization section is provided in the section.

(Function) In the present invention having the above configuration, when microwaves are supplied to the discharge part, the discharge part is ionized in a negative manner by the pre-ionization part, and the spatial resistance is lowered. , -like ionization immediately progresses and the spatial resistance value decreases, making it possible to match the impedance of the incident space, so that the 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. In general, since the preliminary ionization energy is small compared to the total discharge energy, energy efficiency is improved. In particular, in pre-ionization power sources for microwaves, −
If the microwaves are ignited evenly by performing pre-ionization at different angles, all that is needed is to replenish the amount lost due to diffusion into walls, etc., so 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 adapted to be 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 section 10 consisting of an internal electrode 10a and an external electrode 10b covered with quartz or the like is provided upstream of the discharge section 7. By applying a pulsed high voltage from the pulse power source 11, the laser gas before entering the discharge section 7 is ionized to at least 10 (ion pairs/cm) or more.

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 the microwave laser device of this embodiment having the above-described configuration, the laser gas can be pre-ionized to at least 10 ion pairs/Cm in the pre-ionization section 10 upstream of the discharge section 7. Since the discharge starting voltage can be reduced, when microwaves are incident on the discharge section 7, ionization proceeds quickly even if the electric field is about the discharge sustaining voltage, and a --like microwave glow discharge is established in the discharge section 7. do.

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 the entrance of the discharge section 7. No such inconvenience will occur.

In this case, the resistance value of the discharge section 7 during discharging can be adjusted to a value that is 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. The waves 12 are only slightly reflected near the entrance of the discharge section 7, and most of the microwave energy is injected into the discharge section. In this way, the discharge section 7
By the microwave energy efficiently injected into
Ionization of the pre-ionized laser gas further progresses, and the generated ions and electrons are ionized by the flow of the laser gas.
Since it is sent downstream, a -like discharge occurs within the discharge tube. Note that the excited laser gas causes the optical resonator 15 to amplify and emit laser light.

As described above, it can be seen that in this embodiment, the microwave energy is effectively injected into the discharge section 7, resulting in a --like glow discharge, and effective amplification and excavation of the laser beam is performed. In addition, since the pre-ionization power source only needs to form an appropriate space charge (for example, 10 ion pairs/Cm) in the discharge part, the pre-ionization energy is small compared to the total discharge energy, resulting in good energy efficiency. It becomes a microwave laser device.

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 the microwaves are ignited evenly by performing pre-ionization in various ways, only a small amount of pre-ionization energy is sufficient as it is only necessary to replenish the dissipation valve by diffusion into walls etc. .

It should be noted that the present invention is not limited to the above-mentioned embodiment, and the configuration of the preliminary ionization section can be selected as appropriate. For example, an embodiment as shown in FIG. 2 is possible. In FIG. 2, an insulator-coated thin metal wire 18 coated with an insulator such as quartz is arranged inside the laser discharge tube 1 located upstream of the laser discharge tube 1 and at the entrance 17 of the waveguide 16. has been done.

In this embodiment with such a configuration, when the microwave 12 is incident, the electric field near the thin wire is strengthened, the laser gas is pre-ionized by partial discharge, and the electron density is 10' to 10'.
108 (1/cm3) is obtained. Immediately after the entrance section 17 of the waveguide 16, a concave section 19 is provided over a certain length, although it varies depending on the gas conditions, so that electrons and ions generated by corona discharge are diffused in a weak electric field and become uniform. and enters the discharge section 7.

In this embodiment, as in the previous embodiment, uniform preliminary ionization can be performed, so that a --like glow discharge can be formed in the discharge section 7, and the laser gas can be excited favorably.

[Effects of the invention] As described above, in the present invention, a preliminary @
With the simple configuration of providing a female part, microwave energy can be effectively injected into the discharge part, and it can be used at normal gas pressure (20 to 200 Torr) without changing the pressure.
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 sectional view showing a discharge section of another embodiment of the invention, and FIG. 3 is a sectional view of a conventional microwave laser device. FIG. 3 is a sectional view showing main parts. 1... Laser electric tube, 2... Vacuum pump, 3゜4... Pulp, 5... Laser gas cylinder, 6...
... Gas controller, 7... Discharge section, 8... Roots blower, 9a, 9b... Heat exchanger, 10... Pre-ionization section, 10a... Internal electrode, 10b... External electrode, 1
1...Pulse power supply, 12...Microwave, 13...
・Microwave power supply, 14... Waveguide part, 15... Vanguard (Tatsuki, 15a, 15b... Mirror, 16... Waveguide, 17... Waveguide entrance part, 18... ...Insulator-coated thin metal wire, 19...Waveguide recess. 1st r: lJ 1'6 Sash 2 Fig.

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 device characterized in that a pre-ionization section is provided in the microwave laser device.