JPH04321289A - Gas laser - Google Patents

Abstract

PURPOSE:To contrive the improvement of the oscillation efficiency of a gas laser. CONSTITUTION:A gas laser is provided with a double tube 16 made of a dielectric, a gas circulator 5 which is connected to an inner tube of the double tube and supplies later medium gas, a cooling medium circulator 17 which is connected to an outer tube of the tube 16 and supplies a cooling medium having an insulator property, a microwave cavity resonator 1 encircling at least one part of the tube 16, a microwave generator 8, which is connected to the resonator, and a totally reflecting mirror 11 and a partial reflecting mirror 12, which are arranged in opposition to each other at both end parts of the tube 16. A discharge tube 2 is cooled in such a way, whereby the oscillation efficiency of the gas laser is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas laser device which excites a gas by discharge and oscillates laser light by irradiating the gas with microwaves.

0002

2. Description of the Related Art FIG. 2 shows the basic configuration of a conventionally proposed microwave-excited gas laser. An example of this is shown in Japanese Patent Publication No. 61-220486. Microwaves 7 output from a microwave generator 8 operated by power supply from a power source 6 are guided to a cavity resonator 1 via a waveguide 9, and a discharge tube 2 passes through the cavity resonator 1. Microwave discharge 10 of laser medium gas 3 sealed inside
The total reflection mirror 11 and the partial transmission mirror 12
Laser oscillation is caused and laser light 13 is extracted through the oscillator. In addition, in order to prevent the temperature of the laser medium gas from increasing, which would cause a decrease in laser oscillation efficiency, the laser medium gas 3 is drawn out from one end of the discharge tube 2, and after being cooled through the gas circulator 5 and the heat exchanger 4, It is returned to the other end of the discharge tube 2 again.

0003

SUMMARY OF THE INVENTION The conventional device described above has the following problems. (1) Since the specific heat of the laser medium gas is generally small, a relatively small amount of energy injection by discharge can easily raise the gas temperature. Therefore, if an attempt is made to suppress the gas temperature below a predetermined value, the flow rate of the laser medium gas may be increased or a special cryogenic medium such as liquid nitrogen may be used in the heat exchanger 4 to maintain the temperature of the laser medium gas 3 sufficiently. After lowering it, it is necessary to return it to the discharge tube. In addition, in order to increase the laser output while keeping the microwave input and laser output per unit length of the discharge tube approximately constant, the length of the discharge tube must be lengthened, but on the other hand, the temperature increase of the laser medium gas Since it is approximately proportional to the tube length, in order to ensure discharge at a temperature below a predetermined temperature leading to laser oscillation over the entire length of the discharge tube, the length of the discharge tube cannot be longer than the length that corresponds to the capacity of the heat exchanger 4.

As mentioned above, in the conventional apparatus, in order to prevent the temperature of the laser medium gas from rising, it is necessary to increase the gas flow rate, which leads to an increase in the power required for gas circulation and the heat exchanger. Disadvantages include the need to increase capacity and the inability to increase the length of the discharge tube. (2) In the process of transmitting microwaves from the outside of the discharge tube to cause discharge of the laser medium gas inside the discharge tube, a wall boundary layer that absorbs the microwaves is formed on the inner wall surface of the discharge tube. The thickness of this wall boundary layer is a function of the microwave frequency and the collision frequency between electrons and molecules, and has the characteristic that it becomes thinner as the gas pressure becomes higher and the degree of ionization becomes higher. During microwave discharge excitation, a strongly absorbing wall boundary layer with high electron density is formed in the discharge section of the discharge tube 2, and the gas temperature within the boundary layer rises rapidly, thereby rendering the laser operation ineffective. is known (publication “Schock, W., L.
aser-Kolloquium 85,13DFV
LR-Institute fuel Techn
(3) Due to the discharge of the laser medium gas, the gas is ionized and a plasma is formed in the discharge tube. Although recombination of ions and electrons is difficult to occur in the plasma, ions and electrons are discharged. A possible phenomenon is that recombination is promoted on the wall surface when it collides with the inner wall of the tube.When the above-mentioned recombination occurs on the wall surface, heat equivalent to ionization energy is given to the wall surface, so the temperature of the wall surface increases. This results in a decrease in laser output.

[0005]

[Means for Solving the Problems] The present invention takes the following means to solve the above problems.

That is, as a gas laser device, (1)
a dielectric double tube; a gas supply means connected to the inner tube of the double tube to supply a laser medium gas; and a cooling medium connected to the outer tube of the double tube to supply an insulating cooling medium. a supply means, a microwave cavity resonator surrounding at least a portion of the double tube, a microwave source connected to the cavity resonator for supplying microwaves, and disposed opposite to both ends of the double tube. A total reflection mirror and a partial transmission mirror are provided. (2) In claim 1, the length of the double tube is made longer than the length of the cavity resonator.

[0007]

[Function] (1) By the above means, the laser medium gas in the inner tube of the double tube is discharge-excited by the microwave of the cavity resonator and emits light. This light causes laser oscillation between the total reflection mirror and the partial transmission mirror, and is output as a laser beam from the partial transmission mirror.

During this time, the cooling medium is supplied from the cooling medium supply means to the outer pipe of the double pipe and flows therethrough. This prevents a rise in the temperature of the laser medium gas and prevents a decrease in efficiency. At this time, since the laser medium gas in the inner tube is cooled from the outer circumferential surface, the wall boundary layer portion, where the temperature rises, is efficiently cooled. Further, the laser medium gas is also cooled by supplying cooling circulation from the gas supply means, thereby preventing a decrease in luminous efficiency. (2) Due to the double tube coming out from the cavity resonator,
The energy excited within the cavity resonator is efficiently transferred to the light emitting medium gas in the laser medium gas, improving oscillation efficiency.

[0009]

[Embodiment] An embodiment of the present invention will be explained with reference to FIG.

[0010] The parts explained in the conventional example are given the same numbers and the explanation thereof is omitted, and the explanation will mainly be given to the parts related to the present invention.

A dielectric double tube 16 is provided passing through the cavity resonator 1. The inner tube of the double tube 16 is used as the discharge tube 2. That is, a gas cycle pipe 20 is provided which is connected from one end to the other end and has a gas circulator 5 and a heat exchanger 4 (gas supply means). Further, a refrigerant cycle pipe 15 is provided which is connected from one end of the outer pipe of the double pipe 16 to the other end and has a refrigerant circulator 17 and a radiator 18 (coolant supply means).

The double tubes 16 are all made of quartz glass and have an inner diameter of 18.5 mmφ x outer diameter of 21.5 mmφ, an inner diameter of 31.5 mmφ x an outer diameter of 35.5 mmφ, an effective length of the discharge section of 200 mm, and a total length of 400 mm ( (twice the length of the discharge section). In addition, the cavity resonator for microwaves is made of copper.
The inner diameter was 100 mmφ×the length of the discharge section was 200 mm. The cooling medium to be circulated through the outer tube portion of the double tube 16 is CC.
The flow rate in the inner tube was adjusted to approximately 5 cm/s using the l4 liquid. As the laser medium gas, CO2/N
Using a mixture of
The pressure and temperature at the upstream entrance of the discharge tube 2 were 10 Torr and 20° C., respectively.

Furthermore, the microwave generator 8 used is
We focused on the frequency of 2.45 GHz, which is often used in industrial heating furnaces and household microwave ovens, and by operating it continuously, we obtained continuous microwaves with ripples of ±105% or less, and introduced them into the cavity resonator 1. The laser oscillated.

In the above configuration, the microwave 7 output from the microwave generator 8 driven by the power source 6 is guided to the cavity resonator 1 through the waveguide 9. A double tube 16 is arranged inside the cavity resonator 1, and the microwave 7 penetrates through the outer tube wall of the double tube 16, then propagates through the refrigerant liquid, and further passes through the discharge tube 2. The laser medium gas sealed inside is discharged and excited. In the microwave propagation process as described above, it is important to select a discharge tube material and a cooling medium that do not reflect or absorb microwaves.

In this example, quartz and CCl4 were used, but other examples of such materials include high-purity alumina, beryllium oxide, etc., and liquids such as SF6, which is a spherically symmetric molecule with no polar moment. You can.

Since the wall of the discharge tube 2 is constantly cooled by the cooling medium 3, it is possible to keep cooling the laser medium gas in contact with the inner wall of the discharge tube 2. Cooling medium 15
is taken out at the right end of the double tube 16, passed through the coolant circulator 17, radiated by the radiator 18, and then returned to the left end of the double tube 16, thereby completing the cooling cycle using the coolant 15.

In the above-mentioned cooling cycle, in order to enhance the cooling effect, the flow rate of the laser medium gas inside the discharge tube 2 is increased, and the flow rate of the cooling medium outside the discharge tube 2 is increased, thereby increasing the film heat transfer coefficient. It is effective to do so. Since it is effective to use a liquid cooling medium outside the discharge tube 2 and use a heat transfer mode that involves evaporation of the liquid, the rate-determining step of heat transfer is found to exist in the gas film on the inner wall surface of the discharge tube. become. Therefore, the flow rate of the cooling medium 15 can be two orders of magnitude lower than the flow rate of the laser medium gas in the discharge tube. Thus, in order to obtain a sufficient cooling effect, the laser medium gas 3 is returned to the discharge tube 2 via the gas circulator 5 and the heat exchanger 4, and the high-speed flow of the laser medium gas 3 within the discharge tube 2 is controlled. It is possible. In the case of a relatively low output laser, a sufficient cooling effect can be obtained only by the cooling cycle of the discharge tube wall using the cooling medium 15, so the heat exchanger 4 is omitted in the laser medium gas cycle system. It is also possible.

In the figure, a certain section of the right side of the double tube 16 is not housed inside the cavity resonator 1. This is due to the following reason. A general carbon dioxide laser will be explained as an example. The laser medium of a carbon dioxide laser uses a mixture of He+N2+CO2 with a certain composition ratio, but the process of discharge excitation of this is such that the N2 molecules are first excited rather than the CO2 molecules being directly excited by collision with electrons. , then in the collision between N2 and CO2, N2 to CO
It is known that energy transfer occurs in CO2 molecules, and population inversion is formed in the excited state of CO2 molecules, leading to laser oscillation. Therefore, in order to fully utilize the excited N2 molecules and increase the laser oscillation efficiency, the length of the cooling section should be longer than the length of the discharge tube, and the section of the double tube 16 that protrudes from the cavity resonator 1. In this case, it is effective to transfer energy from excited N2 molecules to CO2 molecules while cooling the discharge tube 2 wall.

Further, at both ends of the cavity resonator 1, microwave leakage prevention tubes 16 are provided at the end plate portions through which the double tubes 16 pass.
Needless to say, the purpose of this is to prevent external leakage of microwaves from the viewpoint of human safety and prevention of radio wave interference.By adjusting the diameter and length of the prevention tube, it is possible to The amount of wave leakage can be reduced to a predetermined value or less. Furthermore, in an actual device, the configuration shown in FIG. 1 is housed in a casing, and measures are taken to completely contain microwaves.

In the above, how much does the laser output differ between when the cooling medium CCl4 is forced to flow through the outer tube portion of the double tube 16 and when the cooling medium is completely discharged from the outer tube portion? I tried measuring. As a result, when the microwave input was 300 W, the laser output was 35.5 W when the discharge tube 2 was cooled with the laser configuration of this example, whereas the laser output was 18.5 W when the discharge tube was not cooled.
A phenomenon in which the power was halved to 3W was observed. Even when the microwave input was increased or decreased by about 50% from the above value, the cooling effect described above was almost the same.

Next, in order to see the effect of making the double tube 16 longer than the discharge length, the total length of the double tube 16 was set to 400 mm.
When comparing the case of mm and the case of 300 mm, the laser output of the former was about 20% higher.

As mentioned above, it is clear that the laser radiation is different when the cooling medium is passed through the outer tube space outside the discharge tube 2 and when the cooling medium is discharged from the same space, that is, when the discharge tube is not forcibly cooled. A difference was observed in the output, confirming the effect of increasing the laser output by cooling the discharge tube through cooling medium flow.

Furthermore, by extending a discharge tube whose tube wall is forcibly cooled with a cooling medium to the downstream side of the discharge section, energy transfer from excited N2 molecules to CO2 molecules occurs in the extended section, resulting in laser oscillation. The effect of increasing laser output was confirmed because the necessary population inversion formation of excited CO2 molecules was promoted.

[0024]

[Effects of the Invention] As explained above, according to the present invention,
It has the following effects. (a) The inner tube is cooled by the cooling medium passing through the outer tube, effectively preventing a rise in the temperature of the laser medium gas, resulting in a significant improvement in oscillation efficiency. (b) By making the length of the double tube longer than the length of the cavity resonator, energy was effectively transferred to the luminescent medium gas, and oscillation efficiency was significantly improved.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional example.

[Explanation of symbols]

1 Cavity resonator 2 Discharge tube 4 Heat exchanger 5 Gas circulator 8 Microwave generator 11 Total reflection mirror 12 Partially transparent mirror 16 Double pipe 17 Cooling medium circulator 18 Heatsink

Claims (2)

[Claims] [Claim 1] A double pipe made of dielectric; a gas supply means connected to the inner pipe of the double pipe for supplying a laser medium gas;
a cooling medium supply means connected to the outer tube of the double tube for supplying an insulating cooling medium; a microwave cavity resonator surrounding at least a part of the double tube; What is claimed is: 1. A gas laser device comprising: a microwave source that supplies a microwave source; and a total reflection mirror and a partial transmission mirror that are placed opposite to each other at both ends of the double tube. 2. The gas laser device according to claim 1, wherein the length of the double tube is longer than the length of the cavity resonator.