JPH02132871A - Silent discharge type laser - Google Patents

Abstract

PURPOSE:Not only to increase a discharging power but also to improve a laser of this design in oscillation output power and oscillation efficiency by a method wherein the crosssectional width of a discharge space in a direction of the optical axis is almost equal to a gap length, and gap of a specified composition is used as a laser medium. CONSTITUTION:The crosssectional width of a silent discharge space 13, sandwiched in between electrodes 1a and 1b, in a direction of an optical axis is almost equal to a gap length d, and a gap medium, which contains at least three kinds of gases, CO2, N2 and He excluding H2O, is used as a laser medium, where the molar fractions of CO2 and N2 are 1-10% and 35-90% respectively. By this setup, a large discharging power can be applied and both an oscillation output power and an oscillation efficiency can be improved.

Description

[Detailed Description of the Invention] The present invention relates to a silent discharge laser. In particular, it relates to the optimization of the Ganu component used as the laser medium of a silent discharge type CO2 laser.

Silent discharge is a completely new discharge when it comes to laser excitation, and there is no precedent for it other than the inventors' research. The reality is that until now nothing was known about the optimal composition of the gas used as the laser medium. Before I explain, let me say something.

First, a silent discharge type C02 laser will be explained using an @cross laser as an example. What is the medium gas for the laser? Conventional.
100-square D, C, C used in discharge type CO2 laser
It has almost the same composition as the o2-co-N2-He mixed gas, with a mole fraction of 5-2-15-re% and a gas pressure of 100 Torr. Figure 1 shows silent discharge type CO2
Diagram of laser configuration. Figure 2 is 1-. of Figure 1. 1-line cross section is shown. In these figures, la and lb are electrodes with a width of 2 on and a length of 2 m, and 2a and 2b are electrodes la and lb.
A dielectric covering each outer surface of jb. These are about 10nF
It has a capacitance of

3 is a silent discharge space sandwiched between electrodes la and 1b,
The discharge gap length d==2Otsuru. That is, discharge space 3
The width of the cross section in the optical axis direction and the gap length are approximately equal. In addition, 4 is a gas guide made of an insulator, 5 is a heat exchanger, and 6 is a gas guide made of an insulator.
is the floor, and 7 is the metal container. The shortest distance to the electrode 1a is L=12). 8 is a power supply. 9 is the total internal reflection boundary,
Hl is a partially reflecting mirror. 11 is laser output light.

With the silent CO2 laser shown in Figures 1 and 2. Furthermore, when a sinusoidal voltage V is applied between the electrodes 1a and Ib to the current power source 8. As can be seen from Figure 3, which shows the time quality of the electrode voltage and current, the discharge period begins at time tA, where a pulsating current I superimposed on the pulsed ridge current flows, and the discharge stops at time tB. Then, tB-t( is the non-discharge period and Ce
tc-tl) is a discharge period of opposite polarity. The forming pressure vgap applied to the discharge space is as shown in Figure 3. During the discharge period, a constant value of v (approximately 2KV) is applied. This is called the discharge sustaining voltage.

Voltage V and '#t flow! What you get by multiplying is the instantaneous power. In this way, in silent discharge, discharge energy is injected discontinuously in time. Laser excitation. It is known that the oscillation output is approximately continuous in time under the conditions that the 1c source frequency is around 10 KHz and the gas pressure is around HIOTOrr.

The laser medium is excited by the silent discharge. Total reflection mirror9.
Oscillation occurs within the optical resonator made up of the partially reflecting mirror 10.
A part of the oscillated light is extracted to the outside as laser output 11. The laser medium gas is accelerated by the proar 6 and passes through the discharge space 3 at a high speed of several tens of ms-1. It is cooled by the heat exchanger 5 and circulated in the container T.

And mixed Ganu CO2-CO-N2-H2 = 5
- 2-15-78 (mole fraction). pressure, p=10
fl (peak-to-pe
ak l'i! ．． (hereinafter referred to as peak-to-beak)
FIG. 4 shows the relationship between Vpp, the time-averaged discharge power Wd, and the desired output i output wr. In Figure 4.
Ml) When I) = 15KV, pregnancy effect 1 ( =
Wr/Wd) = 6.2 CO oscillating at '16
2 lasers were prayed. If the applied voltage vpp is increased above the above-mentioned level, a discharge will occur between the container T and the electrode 1a, and wasteful discharge power will of course be consumed there. Inconveniences such as damage to the AC power supply 8 due to discharge noise occur.

The applied voltage vpp is increased. By increasing the launch power Wd, the lifting power is increased. Oscillation efficiency η (=Wr/Wd
) This is what I tried to do to further increase f. by this. It has been found that there is a problem in that it is difficult to increase the discharge power with the above gas composition.

This invention... In view of the gas composition problem mentioned above. It is possible to increase the discharge power. In order to pray for a silent discharge laser with high output power and efficiency. This is a comparison made with the aim of optimizing the gas composition.

As a result of researching the electrical characteristics of discharge, we found that the discharge power Wd of silent discharge, the peak-to-beak value of applied pressure vpp, the discharge sustaining pressure of silent discharge v*. It has become clear that the following equation approximately holds true between the power supply frequency f and the electrode capacitance CdO.

Wd = f-Cd II2V* (Vpp-2
V1) - Song... (1) And. The discharge sustaining voltage V* is determined by the gas pressure p. Discharge gap length d and 2V1: Apd -1+ B ・
・・・・・・・・・(2) (However, A and BFi are constants of gas). Also, B is small (usually can be ignored). 2V*: Apd =--
131. In addition. Hereinafter, A will be referred to as the gas constant. Similar to vppmaxIIi that can be applied, and 5
Considering the safety car of 0chi, Vppmax=-, (ApL+B) = iApL -
・It became clear that it can be expressed as ``i41'' (where L is the shortest distance between the high-voltage silent discharge electrode and the container or other grounded metal part).

Putting the above results together. Upper limit Wdma of discharge power Wd
X is. becomes.

Based on the formula [5] above. Do not change the structure of the laser.
．． In order to increase Wdfna .

However, increasing the power supply frequency f in {1) increases the cost of manufacturing the power supply and also increases the cost of manufacturing the power supply. This has the disadvantage that the energy efficiency of the power source deteriorates. In order to increase the capacitance Cd of the ``carp'' electrode, increasing the electrode area would result in an increase in the size of the device. Furthermore, if the thickness of the dielectric is made thinner, the voltage resistance of the dielectric will decrease, and if the permittivity of the dielectric is increased, materials with high dielectric constants will generally have poor pressure resistance. C. It is necessary to take one of the above methods. Some drawbacks arise. +lv) How to increase the gas pressure p. Although this has the effect of increasing the upper limit of the discharge power WdmaX, the minimum discharge power WO required for simultaneous K oscillation also increases approximately in proportion to the square of the gas pressure p2, so in the end the efficiency of the laser cannot be increased. It's not a good method.

Therefore. In this invention, a medium gas composition with a large gas constant A and suitable for laser oscillation K is obtained, and high output is achieved. The aim is to realize a highly efficient silent discharge type CO2 laser.

by the way. The dependence of the gas constant A on the type of gas will be clarified for the first time here. To date, there has been no research that provides any basis for understanding this dependence. This is c
The application of silent discharge to the o2 laser is based on the fact that it was first made by the inventors K.

Silent discharge. As shown in Figure 3. A discharge period and a non-discharge period are different during one cycle of voltage application. The temporal and spatial average discharge voltage during the discharge period is V*. During the discharge period. In addition, minute pulse-like discharges with κ dispersion occur and disappear repeatedly. Silent discharges in air and oxygen have been revealed. It is presumed that a similar phenomenon occurs in the medium gas of the C02 laser. Namely. Silent discharge. This itself includes all of the phenomena of ignition of the discharge, maintenance of the discharge, and extinction of the discharge, which are all very different from each other, so the absolute value of the voltage V mentioned above. Dependence on gas class 1. All of their existence is spark-filled. Extrapolation from research fields such as glow discharge was impossible.

The dependence of the gas constant A on the gas composition will be explained below based on the experimental results K.

Co
2 is in charge of 5. Figure 5 shows an example of a change in the 2v* value of 7' (increase) by changing the mole fraction of N2 while keeping CO at 2. FIG. 6 shows changes in the upper limit Wdmax.

moreover. The minimum discharge power WO required for oscillation in each case, the ratio of the increase in the oscillation output wr and the eccentric power Wd qo (
= ΔWr/Δwd) from the results of the oscillation experiment.
As shown in the figure. Using WO and η0, the upper limit of the oscillation output W
rmax and the upper limit of discharge power Wdma)C are wr”ax=(Wd”ax−WO)1o “””
``'《6', and the upper limit ηmax of the oscillation efficiency η is as follows.

Figure 6. FIG. 8 shows the results of determining the upper limit ηmax of the oscillation efficiency and the upper limit W rIna X of the oscillation output from the results shown in FIG. As you can see from this Figure 8. From the viewpoint of discharging power input, it is expected that the effect will be more than twice that of the comparative example when the molar amount of N2 is 35% or more. tdN26Q% from the perspective of increasing pumping efficiency
~To%KaJisuit, N2 3 5~! IO 9
6 can achieve 80% of the optimum value.

To make it easier to understand. As an example, the molar content of N2 is 6
Comparing the 0% actual example and the 15th comparative example, wd,
The relationship between Wr, Vl)1) is shown in Figure 9.

In the example of N260%, Vl)p can be applied up to 28KV, Wd is maximum 6.4KW, and Wr is maximum 0.
．． 72KW. η:1 1. 2-chi silent discharge type c
o2 Just in case you can use the laser to its fullest potential.

As clearly explained above, according to the above-mentioned Example K, selecting the molar fraction of N2 from 35 to 9096 K is better than K. It is possible to input a large amount of discharge power. and oscillation efficiency,
It becomes possible to realize a silent discharge type CO2 laser with a large oscillation output.

The optimization of the gas composition in the above example is as follows. In the apparatus shown in Fig. 1 and 2. On the condition that the discharge riIJ11 is not lost between the electrode 1a and the container T or other grounded metal part,
One of the starting points was M.

The structure of the device. When the distance IfIL between the electrode 1a and the container T or other grounded metal part is configured to be sufficiently long, yppmax becomes a large value (#40 KV) determined by the withstand voltage performance of the dielectrics 2a and 2b.

In this case, in equation (1) above, vppmaX ) 2y*
As is clear, if we assume that WdmaX ”ot.

Due to the gas composition with a large gas constant A. Increase discharge power. The effect of obtaining a laser with high oscillation efficiency can also be achieved in this case.

next. Other embodiments of this invention will be described.

The above-mentioned example FiCO2 5 L CO 2 '
As mentioned above, when the mole fraction of N2 is varied at a constant mole fraction of 16. The component co in the gas is. Originally co
This was used to improve the laser gas composition by dissociating 2 into CO and 02, and to prevent the oscillation efficiency from decreasing under conditions of long-term gas shut-off.

Then... When operating while exchanging gas,
CO is not always necessary. Also. If you want to perform efficient and stable operation for a long time by shutting off the gas. C.O.
It is desirable to set the mole fraction element to an optimal value.

The case where CO is not included and the case where co is included will be described below.

First, Figure 10 shows the relationship between the gas constant A and the composition of a CO2-N2-He mixed gas. In FIG. 10, it can be seen that 11iii of the gas constant A is determined exclusively by N2, and the influence of the molar fraction of CO2 and He is small. Therefore, the purpose of increasing W d m a
The above can be achieved. The effect of simultaneously increasing the K of the oscillation effect source can be achieved when C02 is in the range of 1 to 1 (l). When the mole fraction of C02 is outside this range, 40 becomes 1 (1 or less).
This makes it less practical as a laser emitter.

next. When using a CO2 -CO-N2-He mixed gas, as shown in Figure 11, the mole fraction of CO is 0 to 5. The gas constant A increases rapidly. on the other hand. η0 is CO
If the molar fraction exceeds 10 Ti, it becomes less than 10 Ti. C0
Combining the results for different states of 2 molar height. Say the following: In other words. The molar fraction of CO is in the range of 0 to 2 times the molar height of CO2, and the molar fraction of N2 is 35
~If it is within the range of Lochi. Increase ydmaX. and ηm
The result of increasing a* can be achieved. Furthermore, a CO2 laser with stable oscillation output for a long time can be obtained even under K gas-filled operating conditions.

Furthermore, some of the He was replaced with Ar and the next gas was also used. This invention is effective. That is, CO2-CO-N
FIG. 12 shows an example of the effect that the molar fraction of Ar has on the gas constant AK in a 2-He-Ar mixed gas. This twelfth
From the figure, the mole component of Ar is the value of the gas constant A. Therefore, it can be seen that no residual shadow Wt is given to Wd m a X.

10,000, if the mole fraction of Ar exceeds 174t-, that is, the mole fraction of He. η0 is less than 10%)
The effect of increasing ηmax becomes smaller. And C0
The situation was almost the same regardless of the range K where the mole fraction of 2 was 1 to 10% and the mole fraction of co was 0 to 2 times that of 002. That is, the molar fraction of CO2 is 1 to 10 cm,
CO is 0 to 2 times that of CO2, and the mole fraction of N2 is 35 to 2.
90% of the vortex, and in the range of 0 to 1 times that of Ar or He, increase WdmaX, and increase ηmax.
A gas composition that increases the And, He is ArKf! If! Since He is an expensive gas, replacing it has a great practical effect of reducing the operating cost of the laser.

In the example described above. In both cases, a silent open-circuit C02 laser is shown in which the gas flow and the optical axis direction intersect with each other. Even in the case of an axial flow type configuration, the present invention can be applied and the effect is the same, only that the location targeted by the distance L that determines yppmaX is different.

Figure 13 is a diagram showing the principle of construction of an axial flow type silent discharge laser. The portions of the insulating tube 15, which has an annular cross section and are covered with the electrodes 1a and 1b, are used as dielectric materials 2a and 2b. electrode l
a, lb are wrapped with insulation 1-14. Nine. Since the discharge gap length d is equal to the distance between the dielectrics 2a and 2b, the width of the cross section of the discharge space 30 in the optical axis direction is equal to the gap length. Furthermore, a total reflection mirror 9. The partial reflector is held in a grounded metal mirror holder 13. A heat exchanger and a blower (not shown) are connected to the gas guide 4 made of an insulating material. In this embodiment, the shortest distance between the electrode 1a and the mirror holder 13 is the distance L that determines yp and max.

As explained above. According to this invention, it can be used as a gas medium for a silent discharge laser. At least C02-N2-He
Contains three types of gas components. and the mole fraction of CO2 is 1
~10% and N2 molar enrichment range of 135-90%. A large amount of discharge power can be input. The oscillation effect is large. In other words. This has the effect of realizing a high-output laser.

In addition. In this invention K. The CO2- as a gas medium
CO'kflS is added to the N2-He mixed gas, and CO
By making the mole fraction of K less than twice the mole fraction of C02. It is possible to provide a stable high-output laser for a long period of time under gas-filled conditions. Also. The above CO2-N2-He or fIico2-co-N as a gas medium
Partially replacing He in the 2-He mixed gas with Ar,
By making the molar fraction of Ar less than 1 times that of He, it is possible to provide an inexpensive gas for a high-output silent discharge C02 laser.

[Brief explanation of the drawing]

Figure 1 is a side view showing an example of a silent discharge type C02 laser.
Figure 2 is a cross-sectional view along the summer-1- of Figure 1, and Figure 3 is a cross-sectional view along the
An explanatory diagram of the laser current and voltage shown in Fig. 2. Figure 4 shows the discharge power for the gas composition of the comparative example. Diagram showing peak-to-peak values of lifting power and applied voltage. Figure 5 is 1! Maintenance voltage v and gas pressure p. Figure 6 is a diagram showing the relationship between the discharge gap length d and pci, Figure 6 is a diagram showing the relationship between the molar fraction of N2 in the gas, the maximum discharge power WdmaX, and the gas constant A, and Figure T is the relationship between the molar fraction of N2 in the gas and the gas constant A. Lifting power η versus mole fraction and discharge power
A diagram showing the relationship between 0 and the minimum discharge power WO required for liftoff. Figure 8 shows the mole fraction of N2 in the gas and the maximum lift efficiency ηmax
Diagram showing the relationship between. The ninth factor is a diagram showing the relationship between the discharge power Wd, the oscillation output wr, and the peak-to-peak value vpp of the applied voltage in the gas of one embodiment of the present invention in comparison with the gas of the comparative example. A diagram showing the influence of the mole fraction of C02 on the constant A for a CO2-N2-He mixed gas. Figure 11 shows the influence of the mole fraction of CO on the gas constant A for a CO2-CO-N2-He mixed gas, and Figure 12 shows the influence of the mole fraction of Ar on the gas constant AK on the CO2-CO -N2 -He-Ar mixed gas, and Figure 13 is a side sectional view and a transverse sectional view showing an example in which the present invention is applied to an al and lbld axial flow type silent discharge two O2 laser. la, lb... electrode, 2a, 2b... dielectric. 3.
...discharge space. 4... Gas guide, 5... Heat exchanger. 6... Prowa. T... Container, 8... AC power supply.
9... Total reflection mirror. 10...partial reflecting mirror. 13...
Mirror holder. 15...Insulating tube. In addition. The same reference numerals in the figures indicate the same or corresponding parts.

Claims (2)

[Claims] (1) At least one side is covered with a dielectric material 1
In a silent discharge laser in which an AC voltage is applied between a pair of electrodes to generate a silent discharge in a discharge space sandwiched between the two electrodes, the width of the cross section in the optical axis direction of the discharge space and the gap length are and the gas medium contains at least three types of gas components, CO_2-N_2-He, excluding H_2O, and the mole fraction of CO_2 is 1 to 10%, and N_2
A silent discharge laser characterized in that the molar fraction of is in the range of 35 to 90%. (2) The gas in the discharge space is at least C less than H_2O
The silent discharge laser according to claim 1, characterized in that it contains four types of gas components: O_2-CO-N_2-He. (3) The silent discharge laser according to claim 1 or 2, wherein the gas in the discharge space contains at least four types of gas components, CO_2-N_2-He-Ar, excluding H_2O. .