JPH0133956B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is a discharge-excited CO that does not require low-temperature cooling.
The present invention relates to a gas laser excitation method and a laser device thereof. A discharge-excited CO gas laser (hereinafter referred to as a CO gas laser) applies an electric field to a CO mixed gas to excite CO molecules and extract laser light. That is, the CO gas laser is excited by an excitation process due to discharge electron collision and a vibrational quantum exchange excitation process between CO molecules (hereinafter simply referred to as V-V excitation). With a normal CO gas laser,
The population inversion is not generated only by the electron equilibrium excitation process, and the generation of the population inversion is largely due to the V-V excitation process. This V-V excitation process can be expressed as follows. CO (m) + CO (n) kf krCO (m-1) + CO (n + 1) + ΔE (1) However, n and m are vibrational quantum numbers, and n is higher than m
It's bigger. k _f and k _r are forward and reverse velocity coefficients, respectively. ΔE is the excess energy due to the anharmonicity of CO molecules. There is the following relationship between k _f and k _r . k _f =k _r ·exp (ΔE/kT) (2) Here, T is the translational temperature and k is the Boltzmann constant. According to equation (2), at kTΔE, the values of k _f and k _r become close, and the V-V excitation process expressed by equation (1) is nullified. Therefore, the smaller T is, the larger the forward velocity coefficient of the V-V excitation process becomes. Therefore, CO gas lasers generally require low-temperature cooling for efficient operation. Normal CO gas lasers operate at low temperatures, so
Cooling methods using refrigerants such as liquid air (LN ₂ ) or cooling methods using adiabatic expansion are used. Cooling using a refrigerant is not practical because the amount of refrigerant used increases as the equipment becomes larger, and adiabatic expansion cooling using a supersonic nozzle is difficult because it is difficult to generate an excited discharge in a supersonic flow. Or, it is difficult to create a closed gas cycle. The point that this low temperature cooling is necessary is
This is the biggest obstacle when using CO gas lasers. In addition, subsonic flow using conventional self-sustaining discharge
In the CO gas laser, the laser optical axis, discharge, and gas flow were coaxial. This coaxial structure was required to ensure uniform cooling, since low-temperature cooling was essential for conventional CO gas lasers. Due to the coaxial structure mentioned above, conventional CO gas lasers
The electrode spacing is relatively long (more than 50 cm), so CO
It was not possible to increase the pressure of the mixed gas. This is because the product of pressure and electrode spacing is generally constant in CO gas lasers. In addition, in the above coaxial structure,
Since the tube wall was being cooled, in order to equalize the temperature of the gas flowing inside the laser tube, the inner diameter of the laser tube was
Since the discharge needs to be as small as 2 cm to 2 cm, and the discharge depends on bipolar diffusion, it was not possible to increase the pressure and N ₂ concentration at the same time. For this reason, conventional laser devices have had to perform low-temperature cooling. In view of the above-mentioned conventional drawbacks, the present invention minimizes low-temperature cooling and increases the operating temperature, thereby eliminating the need for complex cooling methods and cooling devices, and providing a highly efficient and high characteristic output CO gas laser excitation method and laser. The purpose is to provide equipment. The present invention is characterized in that in a CO gas laser, the discharge and gas flow are perpendicular to the laser optical axis, and in a CO gas mixture, the concentration of _N2 gas (volume %, hereinafter referred to as volume %) is The concentration should be at least 6 times the concentration of the gas, and the total pressure of the mixed gas should be
The height was set at 20 torr or more. Still another feature of the present invention is that the cathode electrode is configured to be separated from the main gas flow path by a predetermined distance from the inner tube wall of the laser tube. The present invention will be explained below with reference to the drawings. In FIG. 1, a rectangular parallelepiped laser tube 1 made of acrylic resin consists of an upper tube wall 2, a lower tube wall 3, and a rectangular parallelepiped hollow duct portion 4 formed therebetween.
The gas stream 5 flows in the direction of the arrow in the hollow duct section 4 by being evacuated by a pump (not shown) provided at its end. A flat anode electrode 6 made of stainless steel is embedded in the lower tube portion 3. An insulating body 7 made of alumina is buried in the upper tube wall 2, and a plurality of cylindrical hollow holes 8 are arranged linearly apart from each other in the insulating body 7 as shown in FIG. A cylindrical cathode electrode 9 made of brass is adhered to the inner periphery of the electrode. This cathode electrode 9 is buried inside the hollow hole 8 at a predetermined distance, for example, 3 mm, from the inner wall of the upper tube wall, that is, the upper wall surface of the hollow duct portion 4 . At this time, here,
The cathode electrode 8 is arranged directly above the anode electrode 5. The plurality of cathode electrodes 9 correspond to one flat anode electrode 6. Opening windows 10 and 11 for extracting laser light are provided on both sides of the laser tube at the portion where the linearly arranged cathode electrode 9 and anode electrode 6 are provided. Laser light propagation ducts 12 and 13 are provided in the opening windows 10 and 11, and laser mirrors 14 and 15 are fitted at the tips of the ducts. In the laser tube 1 configured as described above,
First, the inside of the tube is evacuated, gas is introduced, and a voltage of 400V to 1kV is applied between the electrodes via a stabilizing resistor.The laser beam is emitted in the direction of arrow 16, that is, the gas flow and the discharge current flowing between the electrodes. The CO gas laser is generated in a direction perpendicular to the CO gas laser direction and operates as a triaxial CO gas laser. As mentioned above, in the CO gas laser device according to the present invention, each cathode electrode has a diameter of 3 mmφ, for example.
For example, 49 brass tubes are used on the upper tube wall 2 of the laser tube.
Since the divided cathode electrode is embedded in an insulating object 7 provided in a strip shape in a direction perpendicular to the direction, the electric field between each cathode electrode 9 and anode electrode 6 is Since they are restricted at the exit, mutual interference can be suppressed and a good electric field distribution can be obtained. Therefore, it was possible to increase the concentration of N ₂ and achieve a high discharge input density. That is, FIG. 3 shows the change in laser output when the N ₂ concentration is changed. The optimal composition of _N2 is 30%. This is more than five times larger than other CO gas lasers. The concentration of N ₂ shall be at least 6 times the concentration of CO. FIG. 4 shows the change in the output spectrum when the N ₂ concentration is changed. _N2 concentration is 21.3%,
It was changed into four levels: 26.5%, 31.7%, and 37.5%.
As the N ₂ concentration increases, the observed oscillation lines increase. This indicates that N ₂ contributes to the excitation process and is effective in increasing the laser gain. Furthermore, when the N ₂ concentration was 37.5%, an oscillation line with a vibrational quantum number _{of 8 or less, which is considered to be vibrational quantum exchange from excited N 2 molecules} , was observed. This shows that there is excitation energy injected into the CO molecule. In this way, this device has improved discharge electrodes.
By operating a CO gas laser with an _N2 concentration more than 6 times the CO concentration, self-sustaining discharge can be used.
An excitation process occurs in which N ₂ is first excited and then CO molecules are excited by vibrational quantum exchange between N ₂ and CO. Further, according to the present invention, the discharge input density is
10w/cm3 or ^more can be achieved. Increasing the discharge input density increases the temperature rise in the discharge section. However, in the embodiment of the present invention described above, by using a triaxial discharge arrangement with a strong convection cooling effect, internal consumption of energy due to temperature rise is prevented. That is, in the above embodiment, since the gas flow, the discharge current, and the laser beam are all perpendicular to each other, the heating of the gas flow is limited to the portion perpendicular to the discharge current, so that temperature rise is suppressed. Furthermore, since the electrode spacing can be made small, the gas pressure can be increased, and a gas pressure of 20 Torr or more can be used at the discharge outlet. Since both the N ₂ concentration and the gas pressure can be increased, both the characteristic output energy and the electrical conversion efficiency of the gas laser device can be improved. The table below shows a comparison between the characteristics of the subsonic CO gas laser device according to the present invention and the characteristics of a conventional CO gas laser device. The composition used here is CO/N ₂ /
He=3.8/31.8/64.4 (all are capacity %).

[Table] Although this device can be configured to be relatively small, its performance in the gas flow center is also shown. The gas temperature uses the value at the center of the flow. The operating pressure for both is approximately 30 Torr. According to the table above, this device uses simple self-sustaining discharge, does not add gases with low ionization voltage such as Xe or O ₂ , and has high efficiency at a gas temperature of 185K to 200K, which is relatively high for a CO gas laser.
It can be seen that high characteristic output can be obtained. According to the present invention, due to the above-mentioned characteristics, a good subsonic self-sustaining discharge CO at high temperatures of 100 K or higher can be achieved.
Since a gas laser can be realized, it has the remarkable effect of eliminating the need for complicated cooling methods and cooling devices, which were an obstacle in conventional CO gas lasers. As described above, according to the present invention, since a CO gas laser can obtain high efficiency and high characteristic output at high temperatures, it is possible to provide a subsonic CO gas laser excitation method and a laser device that do not require complicated and expensive cooling means. .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, and FIG.
The figure is a perspective view of the above embodiment, Figure 3 is a characteristic diagram showing the relationship between the N ₂ flow rate, N ₂ concentration and laser output of the laser device according to the present invention, and Figure 4 shows the observed oscillation line intensity with respect to the N ₂ concentration. FIG. DESCRIPTION OF SYMBOLS 1... Laser tube, 2... Upper tube wall, 3... Lower tube wall, 4... Hollow duct part, 5... Gas flow, 6...
Anode electrode, 7... Insulator object, 8... Hollow hole,
9...Cathode electrode, 10...Laser light.

Claims (1)

[Claims] 1. In a method of operating a discharge-excited CO gas laser, the directions of the gas flow and the discharge current are orthogonal to the direction of the laser beam, and the concentration (capacity %) of the N ₂ gas that composes the gas is adjusted. A method for exciting a discharge-excited CO gas laser, in which the concentration (volume %) of CO gas is 6 times or more and the total pressure of the gas is 20 Torr or more. 2. The method for exciting a discharge-excited CO gas laser according to claim 1, wherein the flow rate of the gas is subsonic. 3. The method for exciting a discharge-excited CO gas laser according to claim 1, wherein the CO gas laser is self-sustaining. 4 A triaxial flow type CO that has a cathode electrode and an anode electrode arranged so that a discharge current is generated in a direction perpendicular to the gas flow in the laser tube, and extracts laser light in a direction perpendicular to the gas flow and discharge current. 1. A discharge-excited CO gas laser device, characterized in that the cathode electrode is formed in a hollow shape and is spaced apart from the interior surface of the laser tube toward the inside of the laser tube wall. 5. An insulating object is provided on the laser tube wall, and a plurality of the cathode electrodes are spaced apart from each other and buried within the insulating object, thereby suppressing the interference of the discharge electric field between each cathode electrode and the anode electrode. A discharge-excited CO gas laser device according to claim 4.