JPH01151279A - Gas laser equipment - Google Patents

Abstract

PURPOSE:To realize a laser resonator having a large aperture beyond the limit of Fresnel number and a short resonator, by specifying a value of configuration parameter and voltage parameter of a discharge tube of which inner wall cross section is circular and outer wall cross section is 2n-gon and by setting the current density at the center of the discharge tube larger than that of the other area. CONSTITUTION:A discharge tube 20 has a circular inner wall cross section and a 2n-gonal (n=2, 3...) outer wall cross section. The values of K and t0/di are set to obtain RP>=1.2, by making the current density at the center of the discharge tube 20 larger than that at the other area; where di is inner diameter of the discharge tube 20, t0 is the minimum wall thickness, K is the ratio of the applied voltage between electrodes 30, 40 to the discharge maintaining voltage at the discharge tube 20, and RP is the current density at the center of the discharge tube 20 to the average current density on a segment vertical to a central line of a pair of electrode 30, 40 through the center of the discharge tube 20. In this way, a laser oscillator can be provided, which has a large aperture beyond the limit of Fresnel number and a short resonator.

Description

[Detailed description of the invention] [Industrial application field] This invention induces oscillation of laser light by causing a discharge inside a dielectric discharge tube filled with a laser medium gas such as CO2, N2, He, etc. Related to gas laser equipment.

[Conventional technology]

Conventionally, there have been devices of this type as shown in FIGS. 9 and 10. FIG. 9 is a front view showing a conventional silent molding type gas laser device, and FIG. 10 is a sectional view taken along the line TV-IV' in FIG.

In the figure, 1 is a cylindrical discharge tube usually made of Pyrex glass, etc., with an inner diameter of 13II11 and a thickness of 1111.
It is about 1 meter long. 2 and 3 are a pair of electrodes that are in close contact with the outer wall of the discharge tube 1, and 4 is a high frequency power source, the output line of which is electrically connected to the electrodes 2 and 3. Furthermore, a total reflection mirror 5 and a partial reflection mirror 6 are attached to both axially opposing ends of the discharge tube 1, respectively. The discharge tube 1 is connected to air pipes 7 and 8, each of which has an air blower 19 and a heat exchanger 10 therein, and is cyclically communicated with the air pipes 7 and 8. Arrow 11 indicates laser light.

Next, the operation will be explained using a C02 gas laser device as an example.

Inside the discharge tube 1, a mixed gas of CO2, He, and N2 is present in several numbers.
It is filled with a pressure of 0-200 Torr.

In this discharge tube 1, a high frequency power source 4 is connected to electrodes 2 and 3.
For example, when a voltage of about 100kHz and 8kV is applied, a silent discharge occurs between the electrodes 2 and 3 as shown in FIG. Laser oscillation occurs within the optical resonator formed by the reflecting mirror 6. A portion of the laser light is extracted to the outside through partial reflection 16, as shown by arrow 11.

On the other hand, when the gas temperature increases due to discharge, the laser output decreases, so the gas is circulated by the blower 9 and cooled through the heat exchanger 10. As a result, the gas temperature within the discharge tube 1 is maintained below a predetermined value.

By the way, in such a conventional device, since the discharge tube 1 has a cylindrical shape, the distance between the electrodes 2 and 3 is long at the center, but becomes shorter as it approaches both ends. There is a problem that current flows in a concentrated manner. Therefore, this conventional gt[l! In this case, the discharge becomes hollow, which causes a decrease in the central intensity of the beam mode, a decrease in cutting performance during processing, and a transmission loss (diffraction loss) during beam transmission.

Therefore, Japanese Patent Application Publication No. 157277/1983, Japanese Patent Application Laid-open No. 61/1983
In Publication No. 295681, the discharge tube is constructed so that the thickness of the discharge tube is thin at the center of the electrode and becomes thicker as the distance from the center increases, thereby making the discharge space uniform and increasing the discharge current density. I try to make it even.

[Problem that the invention seeks to solve]

However, these conventional techniques attempt to make the discharge current density distribution uniform, so they have the problem of increasing the size of the laser discharge tube when trying to obtain single-mode laser oscillation suitable for cutting and drilling. have.

In other words, in a stable resonant system in which laser media with a uniform discharge distribution are sandwiched and faced to each other, the oscillation mode is a higher-order mode (
Since it is determined by the ratio of diffraction loss with TEMlo, TEM2o...), single mode (TEMMo) has good light focusing performance.

), the so-called Fresnel
) There is a restriction that the number N (=ab/Lλ) must be set small. Here, shi is the resonator length, a is the beam radius, and λ is the oscillation wavelength.

Figure 11 shows the relationship between Fresnel number and diffraction loss when the current density distribution is uniform, but when Fresnel number N is extremely small, TEMoo, TEMlo,
TEM2o...The total diffraction loss becomes large, and this loss exceeds the gain inside the resonator, so that laser oscillation cannot occur. When the Fresnel number N becomes a little larger, TEM
o. Only the diffraction loss of the mode is less than the internal gain of the resonator, and single mode laser oscillation is started. Furthermore, as the Fresnel number N increases, oscillations in higher-order modes gradually occur, and the proportion of components in higher-order modes increases.

As described above, in the uniform gain distribution method according to the prior art described above, TEMo. In order to obtain laser oscillation in this mode, there is an upper limit to the Fresnel number N that determines the design parameters of the resonator, and the Fresnel number needs to be set small.

The only way to decrease the Fresnel number N (=ab/Lλ) is to increase the resonator length or decrease the beam radius a, but in order to inject a certain amount of shaping power, it is necessary to decrease a. There is a practical lower limit, and for this reason, in conventional methods, in order to obtain the TEMo0 mode, the device length (resonator length) L is extended by making the resonator a folded structure. This has been an obstacle when downsizing.

This invention was made in view of these circumstances, and it allows the upper limit of the Fresnel number, which was a bottleneck in the conventional method of making the current density distribution uniform, to be set large, thereby reducing the size of the device. The present invention aims to provide a gas laser device that improves IFi elementization and beam mode.

[Means for Solving the Problems] Therefore, in this Komei, the discharge tube has an inner wall surface having a circular cross-sectional shape, and a peripheral outer wall surface having a cross-sectional shape of a 2n square (n=2.
3...), the inner diameter of the discharge tube is di, the thickness of the minimum thickness part of the discharge tube is to, and the ratio of the voltage applied between the electrodes to the discharge sustaining voltage in the discharge tube. is K, and when Rp is the current density at the center of the detonator relative to the average current density on a line passing through the center of the discharge tube and perpendicular to the center line of the pair of electrodes, R≧1.2.
By setting eight values of K and to/d· so that the current density at the center of the detonator is larger than that at other parts.

(Function) That is, according to the inventors' analytical experiments, the current density distribution in the discharge tube is determined by the to Z d i value that defines the cross-sectional shape of the discharge tube whose inner wall cross section is circular and the outer wall cross section is 2n square. It has been found that the applied voltage varies depending on the relative relationship with the value.Therefore, in the present invention, the above two t
By setting the o/d value and the value to the optimum value that satisfies Rp≧1.2, the current density in the center of the discharge tube is actively increased compared to other parts, and the beam mode is thereby changed. This makes it possible to set a Fresnel number that far exceeds the limits of the conventional uniform current density distribution method without any damage.

〔Example〕

First, the principle of this invention and a first embodiment of this invention will be explained with reference to FIGS. 1 to 6.

Fig. 2 shows a model of a discharge system with a non-uniform discharge gap, and Fig. 3 shows a uniform path of this model.According to the research of the inventors, Fig. Even in a high-frequency discharge with an uneven discharge gap as shown,
If we focus on the minute region defined by ΔS in FIG. 2, it has been confirmed that the well-known relational expression for parallel plate system glancing angle discharge holds true.

That is, the discharge current for a certain portion j divided into the minute regions ΔSl is i.times., and the discharge sustaining current 01)J. However, the following relationship holds true. Here, ■. , is the voltage applied between the electrodes, f is the power supply frequency, ε0 is the permittivity of vacuum, ε is the relative permittivity of the dielectric (the dotted part in Fig. 2: corresponds to the discharge tube), and t is the minute part j The thickness of the dielectric (discharge tube), k and op are constants, P is the gas pressure of the gas filled between the dielectric tubes (inside the discharge tube), and XJ is the discharge distance (fl, inner diameter of the tube) at the same microscopic portion j, respectively. show.

In this way, even if a discharge system has a non-uniform discharge gap, by miniaturizing it and considering it in the manner shown in Figure 2, the configuration can be determined by a discharge circuit corresponding to a parallel plate gap. It can be regarded as a parallel circuit connected in parallel as shown in FIG. 3 (each branch circuit corresponds to a minute region ΔS). And this means that the density of the current flowing between these non-uniform discharge gaps can also be calculated by calculating the discharge current i -1 in each of these minute parts separately.
Opening means that quantitative evaluation becomes possible.

Incidentally, if we rearrange the above equations (1), (2), and (3), we get...(;4) The distribution of the minute partial discharge current i is determined by the following equations: discharge OpJ tube thickness tj and discharge gap XJ can be changed by changing the distribution of .

Based on this background, we assume a discharge tube 20 with a circular hole in the center and a square external cross section as shown in Fig. 1, and evaluate the discharge current density of the silent discharge that occurs here. Let's try it.

In addition, in the same figure, 30 and 40 are this discharge tube 20.
A high frequency voltage is applied to these electrodes 30 and 40 from a high frequency power source 50.

Now, as shown in FIG. 1, the X-axis is taken in a direction passing through the center of the tube axis of the discharge tube 20 and perpendicular to the center line of the electrodes 30 and 40.
If the length of one side of the square is D and the hole inner diameter is di, then the point (
The discharge current density ρ at X, O). , (X) is the previous (4)
By the formula, ρo, (X)=πfε. ε””t(x)LD
It can be expressed as (X) = d 1 cos θ.

This equation (5) can be normalized as the number between the angles θ shown in FIG.

R+1-CO3θ where: Shape parameter Here, the above R is a parameter indicating the ratio of the minimum wall thickness to to the inner diameter di of the discharge tube 20, so hereinafter this will be referred to as the "shape parameter". Moreover, since the above is a parameter indicating the ratio of the voltage applied between the electrodes 30 and 40 to the sustaining voltage within the discharge tube 2, this will be referred to as the "If voltage parameter" hereinafter.

Regarding this equation (6), current density characteristics when the voltage parameter K is kept constant and the shape parameter R is varied are shown in FIGS. 4(a) to 4(d).

According to these FIGS. 4(a) to (d), the applied voltage between the electrodes is ■. , is equal to the discharge sustaining voltage for the discharge tube inner diameter di, that is, when the voltage parameter is = 1.0 (the fourth
In Figure (a)), no current flows in the center of the discharge tube, but xi flows intensively near the side wall of the discharge tube, and the applied voltage
. By further increasing , and increasing the value of the voltage parameter (see Figure 4 (b) to (d)), the shape parameter R
It can be seen that the smaller (=2 t o /d+), that is, the smaller the minimum wall thickness value to of the discharge tube 20, the more current flows through the center of the discharge tube. The effect shown as the central prominence is R<0
．． It is noticeable when 2. Furthermore, when R>0.5, even if the voltage parameter K is changed (increased), the current density distribution remains flat and no change occurs in the distribution.

Figure 5 (a>,
(b). FIGS. 5(a) and (b) show the above-mentioned (6)
Contrary to the above, the equation shows the current density characteristics when the shape parameter R is kept constant and the voltage parameter K is varied.

That is, in FIG. 5(a) showing an example of R<0.2, (R
= 0.1), as the applied voltage increases (as the voltage parameter K increases), the current density at the center of the discharge tube increases rapidly, and when K≧1.0, the current density is concentrated at the center. effect can be obtained. On the other hand, in FIG. 5(b) showing an example of R>0.5 (R=0.5>, even if the applied voltage is increased, the current density in the center does not increase much and remains flat throughout the area. You can see how it maintains its condition and rises.

In order to quantitatively examine the above effects regarding equation (6) above,
The ratio of the current density ρ' (0) at the center point of the discharge tube to the average current density ρt op of ρ' (X), p R (= ρ'(o)/ρ' op), and the shape parameter p
FIG. 6 shows the relationship between Op and R.

According to FIG. 6, as the voltage parameter K increases, the curves rise almost parallel to each other, but when K>1.6, the rise of the curves becomes extremely small, and as a result, one predetermined curve You can see how it approaches. Also, according to this figure, the smaller the shape parameter R, the larger Rp becomes, and the degree of concentration at the center of the discharge tube increases;
It can be seen that in the region where R>1.6 and R>1, R asymptotically approaches 1 (has a flat current density distribution).

According to research conducted by the inventors, it has been found that Rp, which serves as a barometer representing the degree of centrality, needs to satisfy the following conditions.

Rp≧1.2 Therefore, for example, an applied voltage of ≧1.1 ■. When using Laser II that applies p, the above R.

In order to satisfy the condition ≧1.2, n
=0.2. Further, when K is a relatively large value of about 1.6 or 2.0, the above condition of R≧1.2 can be satisfied even if R is about 0.6.

Thus, according to FIG. 6, when K is large, R can satisfy the condition of Rp≧1.2 even if it is a relatively large value, and when K is small to about 1605 or 1.1, R If set to a small value of 0.2 or less, Rp≧1
．． It can be seen that condition 2 can be satisfied. In fact, as a result of conducting experiments using a discharge tube with an R value that satisfies Rp≧1.2 and a value of In the resonator system, TEMo. We were able to successfully obtain this mode and confirm that the present invention is effective.

As described above, in this embodiment, the inner wall of the discharge tube has a circular cross-sectional shape, the outer wall has a square cross-sectional shape, and the voltage parameter and the shape parameter R satisfy Rp≧1.2. By setting this, the gain distribution at the center of the discharge tube is actively increased, thereby making it possible to realize a laser device with a large diameter and short resonator length that exceeds the limit of the conventional Fresnel number.

FIG. 7 shows another embodiment of the present invention, in which the cross-sectional shape of the outer wall of the discharge tube is a regular hexagon, and electrodes 60 are sequentially arranged in pairs on opposing outer surfaces. ing. In other words, in the above embodiment, the discharge direction is fixed in one direction, so the current density at the center of the discharge tube increases only in the cross section perpendicular to the discharge direction, and in the cross section parallel to the discharge direction. The current density distribution becomes uniform in the cross section. Therefore, in this embodiment, the counter electrode 60 is arranged in a rotational manner so that the deviation of the beam due to the discharge direction is alleviated to a practically acceptable level.

Furthermore, in FIG. 8, a discharge tube with a square outer surface and a circular inner surface is made into a continuously twisted outer shape, and electrodes 70 are arranged facing each other on the outer surface of the discharge tube, thereby further improving the symmetry of the beam mode. There is.

In these embodiments shown in FIGS. 7 and 8,
The voltage parameter and the shape parameter R are set so as to satisfy Rp≧1.2 as in the previous embodiment, thereby increasing the current density distribution at the center of the discharge tube.

Note that the present invention can make appropriate changes to the above embodiments, and the cross-sectional shape of the outer wall of the discharge tube may be a regular octagon, a regular 10
Square, etc., 2n polygon (n=2
．． 3.4...) is sufficient.

(Effects of the Invention) As explained above, according to the present invention, by setting the shape parameters and voltage parameters of a discharge tube having a circular inner wall cross section and a 2n square outer wall cross section to appropriate values, the central part of the discharge tube Since the current density is actively increased compared to other parts, it is possible to realize a laser resonator with a large diameter and short resonator length that exceeds the Fresnel number limit of the conventional uniform current density distribution method. That is, single-mode laser light can be obtained with a small and simple device without complicating the structure such as the folding structure that has conventionally been adopted.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram showing a discharge tube corresponding to the cross section of the discharge tube and its calculation model in an embodiment of the gas laser oscillation device according to the present invention, and Fig. 2 is a schematic diagram showing a discharge system model having an uneven discharge gap. , Fig. 3 shows the equidiscretion path of the model in Fig. 2, Fig. 4 shows the influence of the shape parameter R on the discharge current density distribution, and Fig. 5 shows the influence of the voltage parameter K on the discharge current density distribution. 6 is a graph showing the relationship between the shape parameters R and R using the voltage parameter K as a parameter. FIGS. 7 and 8 are perspective views showing other embodiments of the present invention, and FIG. 10 is a schematic front view showing the general configuration of the gas laser oscillation device;
The figure is a cross-sectional view showing the cross-sectional structure along the line IV-IV' in Figure 9, and Figure 11 is the Fresnel number N in the uniform discharge distribution.
It is a graph which shows the relationship between and diffraction loss. 1.20. ...discharge tube, 2.3.30,40°60.
70... Electrode, 4.50... High frequency power supply, 5...
Total reflection mirror, 6... Partial reflection mirror, 7, 8... Air pipe,
9...Blower, 10...Heat exchanger. Figure 4 (α) C1 Figure 4 (C) Figure 4 (d) 7j- Figure 5 (Q) Figure 5 (b) Figure 6 Figure 8 Figure 9 Figure 10 - N=a2 /L Hitomi-sama: Joint j! ! A Wang Tong Q Quan: Plane Confucian vs. Figure 11

Claims (1)

[Scope of Claims] A discharge tube filled with a laser medium gas and made of a dielectric material, and a discharge tube disposed oppositely in close contact with the outer surface of the discharge tube.
In the gas laser device, the discharge tube has a pair of electrodes, and applies a predetermined alternating current voltage to the pair of electrodes to generate a discharge in the discharge tube to excite a laser medium gas and generate laser light. , the cross-sectional shape of the inner wall surface is circular, and the cross-sectional shape of the outer wall surface is 2n square (n = 2, 3...
), the inner diameter of the discharge tube is d_i, the thickness of the minimum thickness part of the discharge tube is t_o, the ratio of the voltage applied between the electrodes to the discharge sustaining voltage in the discharge tube is K, Further, when R_p is the current density at the center of the discharge tube relative to the average current density on a line passing through the center of the discharge tube and perpendicular to the center line of the pair of electrodes, K and t_o/ A gas laser device characterized in that by setting each value of d_i, the current density at the center of the discharge tube is made larger than at other parts.