JPS637036B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas laser oscillation device, and more particularly to a gas laser oscillation device having a means for cooling a laser medium gas.

In general, a laser is a device that generates and amplifies light by activating a laser medium by some method (e.g., electric discharge, optical pumping, etc.) and utilizing the transition between its quantum mechanical states with stimulated emission. This uses gas as the laser medium.

In the following, we will discuss the case of CO ₂ gas laser in particular.
The laser oscillation mechanism will be briefly explained.

In the _case of a CO ₂ gas laser, as is well known, the quantum states involved in laser oscillation are the 000 level, which basically corresponds to the ground state, and the 010 energy state higher than this, among the vibrational levels of the CO 2 molecule. ,
They are 100, 200, and 001 levels. Among these, the 001 level corresponds to an excited state. CO ₂ laser has oscillation lines of 10.4 μm band and 9.4 μm band, but the 10.4 μm band ranges from the above 001 level.
This is due to the 100 level transition, and the 9.4 μm band is due to the transition from the 001 level to the 200 level.

On the other hand, due to the above transition, molecules at the 100 level and 200 level make a transition to the 010 level without emitting light, and this transition speed is said to be more than an order of magnitude faster than the transition speed between other levels. . Therefore, a population inversion occurs between the 001 level and the 100 and 200 levels.

However, since the transition of _CO2 molecules from the 010 level to the 000 level is slow at high laser output, the number of molecules at the 010 level increases, resulting in an increase in the number of molecules at the 100 and 020 levels. Eventually, the difference between the number of molecules at the 001, 100, and 020 levels, that is, the population inversion number, decreases, and the laser output decreases. On the other hand, as is known, 010
The number of laser molecules can be reduced by removing energy by cooling the molecules to the 010 level.

In addition, in the above explanation, the 9.4μm band
We have been dealing with laser oscillations in the 10.4μm band in parallel, but in reality, in the case of CO ₂ lasers, oscillation in the 10.4μm band takes priority, and oscillation in the 9.4μm band can be obtained by inserting a dispersion element into the resonator. .

Therefore, in the following description, the transition process between the 001 and 100 levels that causes 10.4 μm band oscillation will be explained, but this is not intended to essentially limit the content in any way.

It is also well known that the output of laser oscillation increases as the difference in the number of CO ₂ molecules between the 001 and 100 levels increases, as described above. Many CO ₂ molecules are excited from the ground state to the 001 level or other higher energy levels due to electrical discharge, but as the laser medium gas temperature increases, the distribution number of CO ₂ molecules also decreases to the 100 level. is increasing. Therefore, if the laser medium gas is cooled, the 010
The number of molecules at the level decreases, and as a result, the number of molecules at the 100 level decreases, and the difference in the distribution number of molecules between the 001 and 100 levels increases, so the transition from the 001 level to the 100 level becomes more frequent. That is, the laser light output is increased.

On the other hand, in the case of a CO ₂ laser, it is common to add N ₂ gas or He gas to CO ₂ gas. Among these, the first vibration level of _N2 gas is the same as that of _CO2 .
The 001 level and energy value match well,
For this reason, both energy levels create a kind of resonance, which serves to increase the number of CO ₂ molecules at the 001 level. In addition, He molecules contribute to cooling the gas as described later.

When trying to obtain a large output by injecting large amounts of energy into the resonator by means such as discharging,
It is important to quickly transition the CO ₂ molecules distributed at the 100 level to the 000 level. To this end, various methods have been proposed to enhance the cooling effect of the laser medium gas.
Some of these methods will be briefly explained below.

Conventional cooling methods include (1) an indirect diffusion cooling method in which the tube wall of the discharge tube is cooled from the outside and heat exchange is performed by the medium gas colliding with the inner wall of the discharge tube, and (2) a cooling method in which the medium gas is cooled from the outside. The two main methods were the high-speed convection cooling method, which cools the discharge tube by flowing it at high speed.

As is well known, the thermal energy Q generated by discharge in a cylindrical discharge tube with radius r is axially
Then, according to the following equation, the gas is diffused in the radial direction and is discharged outside the tube by the axial movement of the gas inside the tube (High Energy Lasers and Their
Applications (page 247)Edited by Stephen
Jacobs.Murray Sargant Marlon O.
Scully).

ρV _x C _p ∂T/∂ _x +1/r(∂/∂rrK∂T/∂r)=Q
………(1) However, ρ: gas density, T: temperature, C _p : specific heat,
K: thermal conductivity coefficient, V _x : gas flow velocity, r: radius of cylindrical discharge tube As is clear, the first term in equation (1) corresponds to the increase in temperature in the gas flow direction. . By the way, the heat propagation corresponding to the second term in equation (1) is usually 2~
About 20ms (Introduction To Gas Lasers:
Population Inversion Mechanisms (No. 271-272)
Page): By Colins Willett, B.Sc.ph.D., Inst.P.)
When the gas velocity V _x is small, heat propagation due to the second term becomes dominant. Cooling under such conditions corresponds to the indirect diffusion cooling method described above, and
The case where the first term in equation (1) is large corresponds to the fast convection cooling method. Usually, when the first term is dominant, the V _x needs to be at or above the sonic speed or subsonic speed.

In the case of indirect diffusion cooling, there is a temperature gradient (∂T/∂r) in the radial direction, and the larger the thermal energy Q, the larger the temperature gradient ∂T/∂r, which increases the temperature at the center of the discharge tube. That is clear. As described above, the indirect diffusion cooling method described above has a problem in that the laser medium gas present near the central axis of the discharge tube is not sufficiently cooled due to the low thermal conductivity of the laser medium gas.

As a countermeasure, He gas is generally used to replace the CO ₂
A method has been adopted in which the cooling effect of the laser medium gas is increased by adding it to gas or N ₂ gas. That is, the thermal conductivity coefficients of CO ₂ , N ₂ , and He gas mentioned above are respectively (1.66; 2.61; 15.1) at 300K.
×10 ^-4 W/cm・deg. However, since the surface areas of the inner and outer walls of the discharge tube that are involved in cooling are constant, there is a limit to the cooling effect, and if the medium temperature becomes even higher, effective cooling will no longer be possible. . In this way, high cooling efficiency cannot be obtained with the indirect diffusion cooling method,
Not suitable for high power lasers.

On the other hand, in the high-speed convection cooling method, as mentioned above, the laser medium gas is passed through the discharge tube at high speed, and the gas is discharged outside the tube before it is heated beyond a predetermined limit due to discharge, etc., and the laser medium gas is This suppresses temperature rise. With this high-speed convection cooling method, the laser medium gas can be sufficiently cooled and high output can be obtained relatively easily, but the system to flow the gas at high speed becomes large and the amount of gas used is enormous. There is a drawback that it becomes.

Today, in laser oscillation equipment, it is extremely beneficial to realize high-power laser oscillation output with a smaller system, which also reduces the equipment floor space and occupied space at the place of use. There was naturally a limit to the ability to simultaneously achieve smaller size and higher output depending on the method.

SUMMARY OF THE INVENTION An object of the present invention is to return to the basic principles of a laser system, particularly its cooling system, and to realize a new idea, thereby providing a gas laser oscillation device with higher output and smaller size.

The present invention employs an unprecedented method for cooling the laser medium gas, and accordingly adds new improvements to the laser medium gas supply system.
That is, in the present invention, a high pressure generating section, that is, a gas compression means that has not been used conventionally, is provided in the laser medium gas supply system, and the high pressure gas that is sent from the high pressure generating section is introduced into the laser discharge tube. The thermodynamic cooling effect accompanying gas expansion is used to directly cool the medium gas.

Another object of the present invention is to provide a simple and efficient laser oscillation device by devising a means for introducing the laser medium gas into the laser discharge tube.

Hereinafter, the present invention will be described in detail using a CO ₂ laser oscillation device as an example, based on the accompanying drawings.

FIG. 1 is a schematic diagram of a gas laser oscillation device equipped with a laser medium gas supply system according to the present invention. The basic structure of the present invention is a gas high pressure section A, a resonator section B, a low pressure section C, and an intermediate pressure section D. Here, as shown in Fig. 1, the entire system constitutes one circulation system. The following is an example of a case in which there is one.

The high pressure section A includes a pressurizer (or compressor) 6 for pressurizing the gas in the system to a high pressure, a catalyst 7 for removing reaction products generated during the laser process and reducing the laser oscillation output, A reservoir 8 for adjusting the capacity of the high-pressure section, a heat exchanger 9 for cooling the medium gas 11, and the like are provided.

The resonator section B is provided with a discharge tube 1, a gas introduction port 14 for introducing gas into the discharge tube 1, and a gas exhaust port 12.

A vacuum pump 2 is provided in the low pressure section C. Further, the intermediate pressure section D is provided with a laser medium gas cylinder 3, an oil trap filter 4, and an intermediate pressure section capacity adjustment reservoir 5.

When operating the gas laser oscillator, a predetermined amount of gas is supplied from the gas cylinder 3 to the main cooling system, and after the valve 3a is closed, the gas is supplied to the pressurizer 6.
After being pressurized to a high pressure by the catalyst 7 and refreshed as described above by the catalyst 7, it is once cooled by the heat exchanger 9. In this case, whether to employ water cooling or air cooling for the heat exchanger shall be appropriately selected depending on the laser output and the scale of the system. Furthermore, it goes without saying that the arrangement order of the heat exchanger 9, the capacity adjustment reservoir 8, the catalyst 7, etc. may differ depending on the specifications of each.

The gas cooled by the heat exchanger 9 is discharged into the discharge tube 1 through a gas inlet 14 provided in the discharge tube 1, and then through a gas outlet 10, which will be described later. At this time, the laser medium gas is further cooled to minus several tens of degrees by the cooling effect accompanying gas expansion, as will be described later, and then diffused into the tube 1. The laser medium gas 11 heated in the laser process by electrical excitation is drawn out from the discharge tube 1 through the exhaust port 12 by the vacuum pump 2, and then sent to the intermediate pressure section D. As described above, the intermediate pressure section D is provided with the oil trap filter 4 in order to remove the oil discharged from the vacuum pump 2 from the laser medium gas 11. The filter 4
The laser medium gas 11 that has passed through is sent to the high pressure section A again through the pressurizer 6, and is circulated by repeating the above-mentioned process.

FIG. 2 is a system diagram of another embodiment of the present invention, showing a gas supply system in which the laser medium gas 11 supplied to the discharge tube 1 is not reused. The same symbols as in FIG. 1 represent the same parts. Its structure and operation will be most easily understood from the description with respect to FIG.

As described above, the gas laser device according to the present invention utilizes the cooling effect accompanying the gas expansion that occurs when the gas 11 sent from the high-pressure part A of the gas supply system is introduced into the discharge tube 1 through the gas inlet, It is characterized in that the laser medium gas 11 is directly cooled.

FIG. 3 shows a schematic cross-sectional view of one specific example of a gas laser resonator employing the cooling method according to the present invention.

In the figure, a discharge tube 1 constituting a resonator is made of a highly insulating material such as glass, and is composed of a double tube consisting of an outer tube 1a and an inner tube 1b. The outer tube 1a is a glass tube (for example, made of quartz), and the inner tube 1b is provided with a large number of gas ejection ports 10, which are micro holes, in its tube wall.

As described above, the arrangement of the gas jet ports 10 provided in the inner tube 1b has the following aspects.

(1) When the gas outlets 10 made of micro holes are provided evenly over the entire surface of the wall of the inner tube 1b; (2) When the gas outlets 10 are provided evenly on the wall of the inner tube 1b;
(3) When the gas jet ports 10 are provided irregularly on the pipe wall (4) In (1) to (3) above, In the case where the gas outlet 10 is provided at a certain angle with respect to the normal line on the inner wall of the tube, the inner tube 1b of the discharge tube 1 may be made of a porous highly insulating and highly thermally conductive material instead of glass. It is also effective and within the scope of the present invention. In this way, the flanges 13, which also serve as electrodes, are fixed to both ends of the discharge tube 1 constructed of a double tube with an O-ring or an adhesive. The flange 13 has a gas inlet 14 for introducing the laser medium gas 11 sent from the high-pressure part A of the gas supply system into the discharge tube 1, and a gas inlet 14 for discharging the gas 11 diffused into the discharge tube 1 to the outside of the tube. gas exhaust port 1
2, optical mirrors 15 and 18, and an electrode terminal 16 are provided.

In this case, an outer tube (not shown) is further provided outside the discharge tube 1 composed of the double tube, and water is allowed to cool the discharge tube by flowing water between the outer tube 1a and the outer tube. It is also possible to use them together.

The laser medium gas 11 compressed to a high pressure by the pressurizer 6 in the gas supply system is once cooled by the heat exchanger 9, and then passes through the gas inlet 14 provided in the flange 13 and enters the discharge tube 1. be introduced.
That is, the laser medium gas 11 introduced into the discharge tube 1 flows into the gap between the outer tube 1a and the inner tube 1b from the gas introduction ports 14 provided at both ends of the discharge tube 1, and is brought to a high pressure in the gap. keep it. What is important at this time is that the pressure within the double pipe gap is kept sufficiently high (normally around 7 kg/ ^cm2 is desirable), and the cross-sectional area of the gas outlet 10 is determined accordingly. The dimensions must be selected so that the pressure will not decrease. Otherwise, the gas cooling effect due to gas expansion will be reduced, and practically sufficient cooling will not be achieved.

The above-mentioned gas outlet 10 is provided on the wall of the inner tube 1b.
is provided, so that the laser medium gas 11 flows into the inner tube 1b from the gas outlet 10. On the other hand, since the inner tube 1b is suctioned by the vacuum pump 2 in the gas supply system through the gas exhaust port 12, its internal pressure is sufficiently low, and the laser medium gas 11 flowing into the inner tube 1b instantly diffuses into the tube. do. As described above, the temperature of the CO ₂ gas 11 ejected into the pipe decreases to several tens of degrees below zero due to the cooling effect accompanying gas expansion.

When introducing gas into the discharge tube 1, a large number of gas jet ports 10 provided on the wall surface of the inner tube 1b in the manners (1) to (4) above emit gas at right angles or obliquely to the central axis of the discharge tube 1. The medium gas 11 is ejected in the direction and is cooled. In this manner, due to the gas expansion around each gas outlet, the cooled gas flows toward the center of the discharge tube 1 and creates turbulent flow.

Therefore, the low-level CO ₂ molecules that have been diffused as the laser medium gas 11 is warmed by the discharge exchange heat by colliding with low-temperature (ground level) neutral CO ₂ molecules. As a result, the deficiency in cooling the gas temperature at the center of the discharge tube 1, which is a drawback of the diffusion cooling method, is improved, and a further cooling effect is produced. Therefore, it is easy to obtain a cooling effect close to that of conventional high-speed convection cooling without increasing the pumping speed of the vacuum pump, that is, with a smaller vacuum pump.

The cooled laser medium gas 11 is heated by a laser process due to electrical excitation while flowing through the tube toward the gas exhaust port 12, but the gas exhaust port is heated before the number of molecules distributed at the "100" level increases sufficiently. 12 to the outside of the tube.

As mentioned above, the resonator employing the cooling method according to the present invention ejects high-pressure medium gas into the discharge tube,
The cooling effect associated with gas expansion is used to effectively cool the medium gas. In the above-mentioned embodiments, several modes of microholes formed in the wall of the discharge tube were shown, but in all of them, the output per unit length of the discharge tube was increased several times compared to the conventional indirect diffusion cooling method. is obtained.

That is, in the process of flowing into the inner tube 1b,
The ejected gas is reflected on the opposing inner tube walls, causing mutual turbulence, and the gas is cooled and released, suppressing the increase in the number of low-level CO ₂ molecules mentioned above and increasing the laser oscillation output. This results in an increase in

FIG. 4 is a schematic cross-sectional view of another specific example of a gas laser resonator suitable for the present invention, in which a high-pressure medium gas 11 is introduced into the discharge tube 1 from a locally provided gas jet port 10. This figure shows the case where it is introduced into a pipe.

In this specific example, the discharge tube 1 is composed of a tube body having high thermal conductivity and high insulation properties (for example, BeO (beryria), etc.), and flanges 13 are fixed to both ends of the tube body. The flange 13 also serves as an electrode as in the case of FIG. 3, and is provided with an electrode terminal 16, optical mirrors 15, 18, a gas inlet 14, a gas exhaust port 12, etc.

In this case, as is clear from the cross-sectional view of the flange 13 shown in FIG. As such, the inlet 1
4 is preferably positioned and drilled. With this configuration, interference between the ejected gases is also added, making it possible to generate more significant gas turbulence, which is even more effective in terms of improving heat exchange characteristics, making the discharge more uniform, and increasing the output. There is an effect.

As a modification of the resonator shown in FIGS. 4 and 5, (1) a plurality of gas jet ports are provided in the center of the discharge tube 1;
The tube is drilled in the same manner as described above, and the gas ejected into the tube is diffused and discharged from the gas exhaust ports provided at both ends of the discharge tube.

(2) On the contrary, multiple gas outlets are provided at both ends of the discharge tube, and an exhaust port is provided in the center of the tube.

(3) Distribute the gas jet ports and exhaust ports appropriately along the axial tube wall of the discharge tube.

Such a modification has the advantage that the ejected gas diffuses within the pipe and travels a short distance and time before being exhausted, so that the temperature rise of the medium gas is small.

As described above in detail, the present invention skillfully utilizes the cooling effect associated with the gas expansion of the gas flowing into the tube through the gas jet port as a cooling method for the laser medium gas, and the above cooling method is put to practical use. The system is characterized in that it is equipped with a gas supply system consisting of a low pressure section, an intermediate pressure section, and a high pressure section. As mentioned above, if a recycling system is adopted in which the gas supply system is equipped with a catalyst and an oil trap filter, and the medium CO ₂ gas is circulated within the system, operating costs can be reduced when operating the equipment. can contribute.
Furthermore, for the circulation of the laser medium gas within the system, a pressurizer for generating high pressure and a pump for generating vacuum are separately provided, so even if small devices are used for each, high circulation efficiency can be achieved. This makes it possible to achieve miniaturization of the entire device.

In addition, in the gas supply system of the present invention, the medium gas flowing in the system passes through a heat exchanger, a reservoir, a catalyst, etc. during the circulation process, so that the pressure pulsations generated from the pressurizer are alleviated, and the medium gas flows inside the discharge tube. The gas pressure can be kept constant before the gas is introduced into the tank. As a result, the CO ₂ gas injected into the pipe from the gas outlet is always kept in a stable state.

The features of the present invention can be summarized as follows.

(1) A laser oscillation power supply with specifications equivalent to those of the conventional diffusion cooling method can be used.

(2) The flow velocity of the laser gas medium in the discharge tube is determined by the pumping speed of the vacuum pump and the conductance of the pumping system as a whole, but when viewed in the radial direction of the discharge tube's cross section, it is determined by the gas cooling effect due to gas expansion. Since it has a high gas outflow rate, it has an effect similar to convection cooling method.

(3) By increasing the laser medium gas pressure to a high pressure, we adopted a physical gas cooling method in which the gas is expanded at the gas injection port into the laser discharge tube. (4) The gas injection By devising the shape of the exit,
The pressure difference can be increased and the gas outflow rate can be further increased.

As described above in detail, according to the present invention, the laser system can be kept small and the laser oscillation output can be increased several times (about five times). This will contribute to the application of lasers in many fields and to the development of industry.

[Brief explanation of the drawing]

1 and 2 are schematic system diagrams of embodiments of the present invention, FIGS. 3 and 4 are longitudinal sectional views of gas laser resonators suitable for the present invention, and FIG.
The figure is a sectional view taken along the - line in FIG. 4. 1... Discharge tube, 2... Vacuum pump, 3... Medium gas cylinder, 6... Pressurizer, 9... Heat exchanger, 1
1...Medium gas, 12...Gas exhaust port, 13...
Flange, 14...Gas inlet.

Claims (1)

[Claims] 1. A laser discharge tube, optical mirrors disposed at both ends thereof, and a gas supply system for introducing and discharging a laser medium gas into the discharge tube, the gas supply system comprising: , a laser medium gas pressurizer, a heat exchanger for cooling the laser medium gas, an introduction section for introducing the laser medium gas into the laser discharge tube, an exhaust section for the laser medium gas from the laser discharge tube, and an exhaust pump, The discharge tube is a double tube, and the inner tube is formed with a gas introduction part consisting of a plurality of small holes, and the space between the inner tube and the outer tube is supplied with laser medium gas at a high pressure. A laser oscillation device characterized in that the laser medium gas is configured to cool the laser medium gas as the gas expands when the laser medium gas is introduced into the discharge tube. 2. The laser oscillation device according to claim 1, further comprising an outer tube that covers the outer tube, and a coolant is supplied to a space between the outer tube and the outer tube. 3. The laser oscillation device according to claim 1 or 2, wherein the small hole formed in the inner tube is provided on the entire surface of the tube wall. 4. The laser oscillation device according to claim 1 or 2, wherein the small holes formed in the inner tube are arranged with regularity. 5. The laser oscillation device according to claim 1 or 2, wherein the small holes formed in the inner tube are arranged irregularly. 6 At least a portion of the small hole formed in the inner tube,
Claim 1, characterized in that the inner tube is opened in a direction that does not coincide with the normal to the inner surface of the tube wall.
6. The laser oscillation device according to any one of Items 5 to 5. 7. The laser oscillation device according to claim 1 or 2, wherein the inner tube is made of a porous, highly insulating, and highly thermally conductive material. 8. The laser oscillation device according to claim 1, wherein the introduction portion of the laser medium gas into the discharge tube is a plurality of gas jet ports. 9. The laser oscillation device according to claim 8, wherein the plurality of gas jet ports are provided at one end of the discharge tube, and the discharge port is provided at the opposite end. 10. The introduction part of the laser medium gas into the discharge tube is a plurality of gas jet ports arranged at both ends of the discharge tube, and the discharge port is provided at the center of the discharge tube. A laser oscillation device according to claim 1. 11. The scope of the above claims, characterized in that the introduction part of the laser medium gas into the discharge tube is a plurality of gas jet ports provided at the center of the tube, and the discharge ports are provided at both ends of the discharge tube. The laser oscillation device according to item 1. 12. The laser oscillation device according to claim 8, wherein the gas ejection port and the discharge port are distributed in an axial direction of the discharge tube.