JPH02130975A - Microwave laser apparatus - Google Patents

Abstract

PURPOSE:To create glow discharge uniformly for improving overall efficiency and to reduce the size of a microwave laser apparatus by inserting insulator inserts into a discharge section of a waveguide for limiting a laser discharge section to a size equivalent to a diameter of laser beam. CONSTITUTION:Microwave power 2 is supplied into a waveguide 2 from a microwave oscillator 1 and enters into a discharge section 5 through a pressure barrier 4. Insulators 51, 52 of Teflon for example are applied on the periphery of the discharge section 5 so as to limit a glow discharge section to the central part 53 of the discharge section 5. The discharge section 5 terminates in closed- circuit wind tunnels 7, 7' and a vacuum vessel 8 is defined thereby. Laser gas is circulated in the vacuum vessel by a blower 10 and cooled by heat exchangers 9a, 9b. Internal gas pressure is controlled by a controller 15 through a supply valve 13 and an exhaust valve 14. Light pump by glow discharge in the glow discharge section 53 is emitted as laser light 18 through a semi-transparent mirror 16 and a total reflection mirror 17.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a high-output, compact 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 a laser medium, and this is particularly important when microwaves are used for discharge excitation. That is,
The pressure used in normal laser oscillation (20
~200 Torr).

Discharge occurs intensively near the entrance where 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, 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.

As a countermeasure against this, for example, literature (Appli, Phys, L
att.

37 (c), p. 673 (1980), there is something like the one shown in Figure 3. In Figure 3, the laser gas 3
1 is supplied at high pressure from the upper inlet 32, and as it passes through the nozzle 33 made of dielectric material, the gas speed increases and the gas pressure decreases.

On the other hand, the microwave 34 is supplied from the left side in the figure by a waveguide 35 and is supplied to the laser discharge section 41 through a pressure partition 36 that transmits the microwave. Since the cavity pressure is in the space 37 of the laser discharge section 41, no discharge occurs here.As mentioned above, the laser gas is accelerated in the dielectric nozzle 33, and the gas pressure decreases, so that no discharge occurs downstream of the nozzle 33. A microwave discharge 38 is generated. Since 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 oscillated by the optical resonator 39 configured on the downstream side. Exhaust gas 40 is discharged to the right in the figure by a vacuum pump.

(Problem to be solved by the invention) By the way, the first drawback of this method is that a vacuum pump is required to exhaust the entire amount of laser gas in order to adiabatically expand it through the nozzle, which requires a large amount of exhaust power for the vacuum pump. , the overall laser oscillation efficiency is extremely reduced.

The second drawback is that the discharge is concentrated near the exit of the nozzle. In other words, the pressure gradient downstream from the nozzle is lowest at the nozzle exit and gradually increases, and the microwave electric field strength is also maximum at the opposite side of the exit due to the effect of the insulator nozzle, so the discharge is concentrated near the nozzle exit. That's a big deal.

Furthermore, there was a problem in that the discharge was locally concentrated, the gas temperature rose, and the laser excitation efficiency was lowered, as well as the arc limit was lowered and the laser output was lowered. Therefore, these improvements have been desired.

An object of the present invention is to provide a compact microwave laser device with good overall efficiency, which is capable of producing a glow discharge of a certain type at normal gas pressures (20 to 200 Torr).

[Structure of the invention]

(Means for Solving the Problems) The microwave laser device of the present invention causes microwave discharge to occur directly in the microwave propagation direction inside a waveguide. Furthermore, in order to discharge only the part where the electric field is strong in the waveguide and the part from which the laser beam is extracted, an insulating material such as Teflon with low microwave loss is inserted around the waveguide to limit the glow discharge part, and the laser gas (Function) When the microwave power source, which is the main discharge power source, is activated and microwaves are supplied to the discharge section, the discharge section extends in the propagation direction and conducts as described above. Since the discharge is caused directly within the wave tube, a --like glow discharge is ignited and effective discharge excitation is performed. Furthermore, the discharge part in the waveguide is limited to the part from which the laser beam is taken out, and the glow discharge part is limited by inserting an insulator such as Teflon with low microwave loss in the peripheral part, so excitation of the laser gas is effective. I can hit the target.

(Embodiment) An embodiment of the present invention is shown in FIG. 1. In FIG. There is a pressure partition 4 inside the waveguide 3, which divides the waveguide 3 into an atmosphere side (microwave oscillator side) and a vacuum vessel side (microwave discharge tube side).

A discharge section 5 is connected to the vacuum container side waveguide. Insulators 51 and 52 such as Teflon with low microwave loss are inserted into the waveguide discharge section 5 at its periphery to limit the glow discharge section to the central section 53 of the waveguide discharge section. The tip of the waveguide discharge section 5 becomes a circulating wind tunnel 7, 7', forming a vacuum container 8, in which heat exchangers 9a, 9b and a blower 10 are installed. After the whole is evacuated by a vacuum pump 11, laser gas is supplied from a cylinder 12.

The internal gas pressure is controlled by a gas supply valve 13 and an exhaust valve 14, and these controls are performed by a controller 15.

16 is a semi-transmission mirror, and 17 is a total reflection mirror.

Due to the optical resonator constituted by these pair of mirrors, laser light is excited by the glow discharge (shaded area) generated in the discharge section 53, and is extracted to the outside as laser light 18.

A major feature of the present invention shown in FIG. 1 is that the discharge occurs directly within the microwave waveguide 5. The inventor's research has revealed that the drawback of microwaves, which is described in FIG. 3 of the conventional example, is that they do not penetrate deeply into plasma.

That is, although the nozzle portion 33 must be made of an insulator that transmits microwaves as in the conventional example shown in FIG. 3, discharge also occurs in the nozzle portion 33 as shown.

Microwaves are said to propagate in space, but for this to happen, a wall current must flow.However, in the conventional example shown in FIG. It must flow within,
Therefore, a sheath having a high enough electron density to flow a strong internal current must be formed on the inner surface of the nozzle portion 33, which causes consumption of a large amount of microwave power and reflection of microwaves.

In view of the above, the waveguide 3 itself is used as a discharge tube, and furthermore, insulators 51 and 52 with small microwave loss are provided in the waveguide discharge section 5, so that the microwave glow discharge is It is limited to the central portion 53.

As can be seen in Figure 1(b), which shows the AA' cross section in Figure 1(a),
The microwave electric field A has a sinusoidal distribution and is strong at the center, and since laser light is usually circular, limiting the discharge part to the center part 53 makes effective use of the energy of the discharge part. possible. Laser light excited by the glow discharge (shaded area) in the center 53 of the discharge section by the optical resonator is extracted to the outside as laser light 18 by the semi-transmissive mirror 16.

Therefore, effective laser beam excitation becomes possible.

In this way, according to this embodiment, microwave energy is effectively injected into the discharge section 5, forming a --like glow discharge. Furthermore, since the waveguide itself is a discharge tube, it is robust and compact.

Furthermore, since the discharge portion is limited to the same shape as the laser beam, efficient discharge excitation is possible, resulting in a compact, high-output laser device.

FIG. 2 shows a second embodiment of the invention. That is, instead of inserting an insulator as shown in FIG. 1 into the microwave waveguide, a hollow container made of an insulator is inserted, and cooling air or a fluid such as insulator oil is circulated through the container for cooling.

In this case, since the discharge section is directly cooled, the discharge power density can be increased.

In addition, since the hollow container made of insulating material is filled with air or oil at atmospheric pressure, there is no possibility of electrical discharge.
Since the portion 2 is filled, there is no fear of voids occurring when a solid insulator is inserted.

〔Effect of the invention〕

As described above, according to the present invention, microwave energy is effectively injected into the discharge part to form a --like glow discharge, and furthermore, since the discharge part is limited to about the diameter of the laser beam, effective laser beam Amplified oscillation is performed, resulting in a laser oscillation device with good overall efficiency.

Furthermore, 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.
The efficiency of laser light excitation by discharge is increased.

[Brief explanation of drawings]

FIG. 1(a) is a sectional view of the microwave laser device of the present invention, FIG. 1(b) is a sectional view taken along the line AA' in FIG. 1(a), and FIG.
a) is a cross-sectional view showing the second embodiment of the present invention; FIG.
is a sectional view taken along line AA' in FIG. 2(a), and FIG. 3 is a sectional view showing the main parts of a conventional laser device. 1...Microwave oscillator board 2...Microwave power 3
... Waveguide 4 ... Pressure partition 5 ... Discharge part 6 ... Glow discharge 7 ... @ ring wind tunnel 8 ... Vacuum vessel 9a, Ob ... Heat exchanger 10 ... Blower 16, 17... Optical resonator agent Patent attorney Nori Chika Ken Yudo Ken Daishimaru

Claims (1)

[Claims] A laser medium gas containing CO_2 etc. is sealed in a vacuum container at low gas pressure, this gas is circulated through a heat exchanger to the discharge section using a blower, and microwaves are supplied from a microwave power source outside the discharge section, In a microwave laser device that excites a laser medium gas by direct glow discharge in a microwave waveguide, an insulating insert is inserted into the waveguide discharge part in order to limit the laser discharge part to the diameter of the laser beam. A microwave laser device characterized by: