JPS6035838B2 - Silent discharge laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a silent discharge laser, and in particular to optimization of gas components used as laser soot for a silent discharge C02 laser.

Silent discharge is a completely new type of discharge in terms of excitation of Caesar, and there are no precedents other than the research of the inventors.

Before proceeding with the explanation, it should be stated that the fact is that the optimum components of the gas used as the caesar medium have not been known at all until now. First, a silent discharge type C02 laser will be explained using an orthogonal laser as an example.

Sooty gas for lasers has conventionally been produced using orthogonal D, C discharge type C0.
The composition is almost the same as the C02-CO-N2-He mixed gas used in the 2-laser, and the molar fraction of these is 5-2-
15-78%, gas pressure is 100Ton. FIG. 1 is a block diagram of a silent discharge type C02 laser, and FIG. 2 is a sectional view taken along the low zero line of FIG. 1. In these figures, la, lb
is an electrode having a width of 2 arcs and a length of 2h, and 2a and 2b are dielectric materials covering the outer surfaces of the electrodes la and lb, and these have a capacitance of about 1 F. 3 is both armies pole la, lb
The silent discharge space is sandwiched by the discharge gap length d=2.

Further, 4 is a gas guide made of an insulator, 5 is a heat exchanger,
6 is a blower, 7 is a metal container, the shortest distance to the electrode la is L = 12 skin, 8 is an AC power supply, 9 is a total reflection mirror, 1
Kawama partial reflecting mirror 11 is the laser output light. Figure 1,
In the silent discharge type C02 laser shown in Fig. 2, when a sinusoidal voltage V is applied between the electrodes la and lb by the AC power supply 8, as can be seen from Fig. 3, which shows the temporal variation of the electrode voltage-crab flow. , the discharge period begins at time t^, a pulsed discharge current 1 flows, and the discharge stops at time tB, and tB
-tc is a non-discharge period, and tc-to is a discharge period of opposite polarity. As shown in FIG. 3, the voltage Vgap applied to the discharge space is a constant value V* (approximately V) during the discharge period, and this is called a discharge sustaining voltage. Multiplying the voltage V and the current 1 gives instantaneous power. In this way, in silent discharge, the discharge energy is injected discontinuously in time, but the excitation and oscillation output of the laser are both temporally injected under conditions of a power frequency of around 1 HZ and a gas pressure of around 100 tons. It is known that it is mostly continuous. The laser soot is excited by the silent discharge, oscillation occurs within the optical resonator constituted by the total reflection mirror 9 and the partial reflection mirror 10, and a part of the oscillation light is taken out as a laser output 11.

The laser quality gas is accelerated by the blower 6, passes through the discharge space 3 at a high speed of several plates/s-1, is cooled by the heat exchanger 5, and circulates in the container 7. And mixed gas C02-C
O-N2-5 = 5-2-15-78 (mole fraction), pressure p = 10 Morr, frequency 10 KHz, the value from the maximum positive value to the maximum negative value of the applied voltage (-pe of peak-
FIG. 4 shows the relationship between the ak value (hereinafter referred to as peak value) Vpp, the time-averaged discharge power Wd, and the obtained oscillation output Wr.

In FIG. 4, when Vpp=1 arc V, the oscillation efficiency (
A C02 laser oscillating at =Wr/Wd)=6.2% was obtained. If the applied voltage Vpp is increased above the above-mentioned level, a discharge will occur between the container 7 and the electrode la, and not only will the discharge power be wasted, but also the AC power source 8 will be damaged due to discharge noise.
This may cause inconvenience such as damage to the Applied voltage Vpp
The reason for increasing the discharge power is to increase the oscillation output by increasing the discharge power Wd, and to further increase the oscillation efficiency (=Wr/Wd). It has been found that there is a problem in that it is difficult to increase.

In view of the above gas composition problem, this invention was made with the aim of optimizing the gas composition in order to obtain a silent discharge laser that is capable of increasing discharge power, and has high oscillation output and oscillation efficiency. It is.

As a result of researching the electrical characteristics of discharge, we found that the discharge power Wd of silent discharge, the peak-to-peak value of the applied voltage Vpp, the discharge sustaining voltage V* of silent discharge, the power supply frequency f, and the capacitance of the power supply Cd
It became clear that the following equation holds approximately between .

Wd=f・Cd・2V*(Vpp-2V*)...m
Then, the discharge sustaining voltage V* is the gas pressure p, the discharge gap length d
and 2V*=Apd+B
...'21 (However, A and B are constants of gas).

Also, since B is small and can usually be ignored, 2V*
=Apd...can be expressed as '3'.

Note that A is hereinafter referred to as a gas constant. VppMX that can be applied
Similarly, and assuming a safety factor of 50%, Vppma
It has been found that X=(APL+B)= can be expressed as pL ---'41 (where L is the shortest distance between the high-voltage silent discharge electrode and the container or other grounded metal part).

Combining the above results, the upper limit Wdm of the discharge power Wd is
-Cd-A2p2d (wife L-d)...(5).

In order to increase the Wdm sensitivity without changing the structure of the laser by filling in the above formula '5}, {i} Increase the power supply frequency f {ii} Increase the capacitance Cd of the power supply Wind Increase the gas constant A Four means of increasing the gas pressure p can be considered.

However, increasing the power supply frequency f of 'i} not only increases the production cost of the power supply but also has the disadvantage that the energy efficiency of the power supply deteriorates.

In order to increase the capacitance Cd of the power supply (ii), increasing the electrode area will result in an increase in the size of the device, and decreasing the thickness of the dielectric will reduce the withstand voltage performance of the dielectric. If the dielectric constant of the dielectric is increased, the material with a high dielectric constant generally has the disadvantage of poor withstand voltage performance, and it is necessary to find one of the above-mentioned means, resulting in one of the disadvantages.
Another way to increase the gas pressure p is to increase the upper limit Wdm of the discharge power.
Although this method has the effect of raising the rock, at the same time, the minimum discharge power Wo required for oscillation also increases approximately in proportion to the square of the gas pressure p2, so it is not possible to increase the efficiency of the laser after all, so it is not a good means. Therefore, in this invention, a sooty gas composition having a large gas constant A and suitable for laser oscillation is obtained,
The aim is to realize a silent discharge type C02 laser with high output and high efficiency.

By the way, the dependence of the gas constant A on the type of gas is being clarified for the first time here, and there has been no research to date that provides a basis for knowing this dependence.

This is based on the fact that the inventors were the first to apply silent discharge to a C02 laser. As shown in Figure 3, silent discharge occurs when the voltage is applied
There is a discharge period and a non-discharge period during the cycle, and the temporally and spatially average discharge voltage during the discharge period is V*.

It has been revealed that during the discharge period, even more dispersed pulse-like minute discharges occur and disappear repeatedly for silent discharges in air and oxygen, and a similar phenomenon occurs in the sooty gas of a C02 laser. It is estimated to be. In other words, silent discharge itself includes all of the very different phenomena of ignition of discharge, maintenance of discharge, and extinction of discharge, so the absolute value of the voltage V* and its dependence on the type of gas are In either case, estimation from research fields such as spark discharge and glow discharge was impossible. The dependence of the gas constant A on the gas composition will be explained below based on experimental results.

In a C02-CO-N2-He mixed gas similar to that of the comparative example described above based on FIGS. 1 and 2, C02 was
%, and an example of the change in 2V* when the mole fraction of N2 is changed while keeping CO at 2% is shown in FIG.

FIG. 6 shows the resulting change in the gas constant A and the resulting change in the upper limit Wd of the discharge power. Furthermore, the minimum discharge power Wo and oscillation output W required for oscillation in each case are
Ratio between r and increment of discharge power Wd. (=△Wr/△Wd)
Figure 7 shows the changes in oscillation experiment results. Wo Tori o
If we use the upper limit W of oscillation output and the upper limit W of discharge power
What is dm fence? Wrm: (W is aX-Wo) ri o
…Connected by ■, the upper limit of oscillation efficiency is m pine beam m pine =
W Obigishi mini (・-W La group;)ri.

...'71. FIG. 8 shows the results of determining the upper limit maX of oscillation efficiency and the upper limit W{aX of oscillation output from the results shown in FIGS. 6 and 7.

As can be seen from Fig. 8, from the viewpoint of discharging power input, an effect more than twice that of the comparative example can be obtained when the molar fraction of N2 is 35% or more, and from the viewpoint of increasing oscillation efficiency, an effect of N2 from 60% to 70% is obtained.
% is optimal, and 80% of the optimal value can be achieved at N235-90%. For ease of understanding, as an example, an example with a N2 molar fraction of 60% and a comparative example of 15% are compared.
, Wr, and Vpp are shown in FIG.

In the N260% example, Vpp can be applied up to 2V, Wd is maximum 6.4KW, Wr is maximum 0.7W, and a silent discharge CQ laser with Ri = 11.2% is realized. was completed. As explained above, according to the above embodiment, by selecting the molar fraction of N2 to be 35 to 90%, it is possible to input a large amount of discharge power, and the silent discharge type has a large oscillation efficiency and oscillation output. It becomes possible to realize a C○2 laser. The optimization of the gas composition in the above-mentioned embodiments was carried out on the condition that no discharge breakdown occurred between the electrode la and the container 7 or other grounded metal parts in the apparatus shown in FIGS. 1 and 2. , Vppm Matsu's formula [41] was obtained as one of the starting points.

When the structure of the device is configured such that the distance L between the electrode la and the container 7 or other grounded metal part is sufficiently long,
VppmaX is a large value (mother 4 plates V) determined by the withstand voltage performance of the plates 2a and 2b. In this case, the above formula {1
} and assuming VppMX》2V*, it is clear that
Become WdmCritA・VppMX.

The effect of increasing the discharge power and obtaining a laser with high oscillation efficiency by using a gas composition with a large gas constant A can also be achieved in this case. Next, other embodiments of the invention will be described.

In the above-mentioned example, a case was described in which the mole fraction of N2 was changed at a constant mole fraction of C025% and C02%, but the component CO in the gas was originally caused by the dissociation of CO2 into CO and 02, which led to the laser This was used to prevent the oscillation efficiency from decreasing under conditions where the gas composition changes and the gas is shut off for a long time.

Therefore, when operating while replacing gas,
CO is not always necessary.

Further, if it is desired to perform efficient and stable operation for a long period of time without gas sealing, it is desirable to set the mole fraction of CO to an optimum value. The case where CO is not included and the case where CO is included will be described below.

First, FIG. 10 shows the relationship between the gas constant A and the composition of the C02-N2-He mixed gas.

In Figure 10, the value of the gas constant A is determined exclusively by N2, and the influence of the mole fraction of C02, He is 4.
Now, I understand. Therefore, the purpose of increasing WdMX can be achieved when the N2 mole fraction is 35% or more, as in the case of FIG. The effect of simultaneously increasing oscillation efficiency is
C02 can be achieved in the range of 1 to 10%. If the mole fraction of C02 is outside this range, o will be less than 10%,
This makes it less practical as a laser oscillator. Next, in the C02-CO-N2-He mixed gas, the 11th
As shown in the figure, the gas constant A increases rapidly when the mole fraction of CO is 0 to 5%.

On the other hand, RI is 10% when the mole fraction of CO exceeds 10%.
It becomes below. Comprehending the results with different C02 molar fractions, the following can be said. That is, if the mole fraction of CO is in the range of 0 to 2 times the mole fraction of CO2 and the mole fraction of N2 is in the range of 35 to 90%, the Wdm fence is made large and maX is made large. This results in a C02 laser with stable oscillation output for a long time even under gas-sealed operating conditions. Furthermore, some of He is A
The present invention is also effective even with a gas substituted with r.

That is, an example of the influence of the molar fraction of ~ on the gas constant A in the C02-CO-N2-He-An mixed gas is shown in the 12th example.
As shown in the figure. It can be seen from FIG. 12 that the mole fraction of Ar has little effect on the value of the gas constant A, and therefore on Wdm pine. On the other hand, when the mole fraction of ~ exceeds 17%, that is, exceeds the mole fraction of He, Ri. is less than 10%, and the effect of raising Katana Matsu becomes 4. And C0
The conditions were almost the same for both the ranges in which the mole fraction of CO2 was 1 to 10% and the mole fraction of CO was 0 to 2 times that of CO2. That is, when the mole fraction of CO2 is 1 to 10%, CO
W satisfies 0 to 2 times that of C02, the molar fraction of N2 satisfies all of 35 to 90%, and ~ is 0 to 1 times that of He.
A gas composition that increases aX and increases ma1 can be obtained. And replacing He with ~ means He
Since gas is expensive, it has a great practical effect of reducing the operating cost of Caesar. In the above-mentioned embodiments, a silent discharge type C02 laser is shown in which the gas flow and the optical axis are perpendicular to each other in all directions, but even in the case of a spiral configuration, the object of the distance L that determines the Vppm value is The present invention can be applied and the effects are the same, with the only difference being that .

FIG. 13 is a diagram showing the principle of construction of a spiral silent discharge laser, in which the portions of the insulating tube 15 covered with the electrodes la and lb act as the conveyors 2a and 2b, and the electrodes la and lb are covered with an insulating layer. It is wrapped in 14. In addition, a total reflection mirror 9, a partial reflection mirror 1
A heat exchanger and a blower (not shown) are connected to the gas guide 4, which is held by a metal mirror holder 13 that is grounded at 0' and is made of an insulator. In this example, the electrode l
The shortest distance between a and the mirror holder 13 is the distance L that determines VppmaX. As explained above, according to the present invention, the gas soot of a silent discharge laser contains at least three types of gas components, C02-N2-He, and the mole fraction of C02 is 1 to 10% and N2 The mole fraction of is 3
By using a mixed gas in the range of 5 to 90%, a large amount of discharge power can be input, and the oscillation efficiency is high, that is,
This has the effect of realizing a high-output laser.

In addition, in this invention, by adding CO to the C02-N2-He mixed gas as a gas soot and making the mole fraction of CO less than twice the mole fraction of CQ, it is possible to achieve the conditions under gas shut-off conditions. It is possible to provide a stable high-output laser over a long period of time.

In addition, by partially replacing He in the C02-N2-He or C02-CO-N2-He mixed gas as a gas medium with Ar, and making the molar fraction of ~ less than 1 times that of He, large output power can be achieved. It is possible to provide inexpensive gas for silent discharge type C02 lasers.

[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 taken along the D-0 line in Figure 1, - Figure 3 is an explanatory diagram of the current and voltage of the laser shown in Figures 1 and 2, and Figure 4
The figure shows the peak values of discharge power, oscillation output, and applied voltage for the gas composition of the comparative example. Figure 5 shows the relationship between the discharge sustaining voltage V*, the gas pressure p, and the product pd of the discharge gap length d. Figure 6 shows the relationship between the mole fraction of N2 in the gas, the maximum discharge power Wdm, and the gas constant A, and Figure 7 shows the relationship between the mole fraction of N2 in the gas and the discharge power. . FIG. 8 shows the relationship between the minimum discharge power Wo required for oscillation, and
The figure shows the relationship between the molar fraction of N2 in the gas and the maximum oscillation efficiency order X. Figure 9 shows the discharge power Wd, oscillation output Wr, and peak value Vpp of the applied voltage in the gas according to an embodiment of the present invention. Figure 10 is a diagram showing the influence of the mole fraction of C02 on the gas constant A for a C02-N2-He mixed gas, and Figure 11 is a diagram showing the relationship between C02 and the gas of a comparative example. Figure 12 shows the influence of the mole fraction of CO on the gas constant A for C02-CO-N2-He gas. Figures 13a and 13b, which show the mixed gas, are a side sectional view and a cross sectional view showing an example in which the present invention is applied to a Fuji-style silent discharge type C02 laser. la, lb... electrode, 2a, 2b...
...Electric body, 3...Discharge space, 4...
...Gas guide, 5...Heat exchanger, 6...
Blower, 7... Container, 8... AC power supply, 9
......Total reflection mirror, 10...Partial reflection mirror, 13
...Mirror holder, 15...Insulation tube. Note that the same reference numerals in the figures indicate the same or corresponding parts. 1st
Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 13 Figure 9 Figure 12 Figure 10 Figure 11

Claims (1)

[Claims] 1. A silent discharge in which an alternating current voltage is applied between a pair of electrodes, at least one of which is covered with a dielectric material, and a discharge surface is coated with a dielectric material to generate a silent discharge in a discharge space sandwiched between the two electrodes. type laser, the gas medium is at least CO_2-N_2-H
Contains three types of gas components e, and the mole fraction of CO_2 is 1
~10%, and the mole fraction of N_2 is in the range of 35 to 90%. 2 The gas in the discharge space is at least CO_2-CO-N_
The silent discharge laser according to claim 1, characterized in that it contains four types of gas components, 2-He, and the mole fraction of CO is within twice the mole fraction of CO_2. 3 The gas in the discharge space is at least CO_2-N_2-H
The silent discharge laser according to claim 1 or 2, characterized in that it contains four types of gas components: e-Ar, and the mole fraction of Ar is one times or less that of He.