JPS5917986B2 - gas laser equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gas laser device, and particularly to a gas laser device using glow discharge as an excitation source.

Generally, gas laser devices that use a gaseous laser medium use glow discharge as the excitation source, but in order to achieve high output, a method is adopted in which the gaseous laser medium is forcibly circulated using a blower or the like to cool it. Although it has been
Gas laser devices are classified into several types depending on the direction of the laser optical axis, gas flow direction, or discharge direction.

Among these, the high-speed axial flow gas laser device generates a discharge in the direction of the laser optical axis and circulates a high-speed gas flow in the same direction, and has high efficiency, simple structure, and laser light. It has advantages such as an axially symmetrical intensity distribution, and is used as a laser for processing such as welding.
By the way, in order to realize high output of a gas laser device, the glow discharge injection power must be increased.

For this reason, in the past, the discharge area of the electrode was expanded to increase the glow discharge current, and as a result, the glow discharge injection power was increased. However, the current-voltage characteristics of glow discharge generally exhibit negative differential resistance characteristics, so as the current increases,
As a result, glow discharge becomes unstable and tends to shift to arc discharge.

In addition, the discharge path of glow discharge under a gas pressure of several tens of Torr in a high-speed gas flow tends to become narrower, and the glow becomes concentrated in a part, especially on the cathode discharge surface.As a result, the glow discharge becomes more It becomes unstable, tends to shift to arc discharge, and prevents an increase in glow discharge injection power. In order to solve the above problems, in the past, a wide cathode discharge surface was divided into a plurality of discharge areas to prevent the glow from concentrating in some areas. However, by dividing the discharge surface, the configuration of the gas laser device has become complicated. In addition, it became more susceptible to the influence of gas flow velocity distribution on the discharge surface. That is, because the gas flow velocity distribution on the cathode discharge surface is generally not completely uniform, the current density increases in the discharge area where the flow velocity is low, making it easier to transition to arc discharge. Therefore, the instability of the glow discharge still prevents an increase in the discharge injection power.
SUMMARY OF THE INVENTION An object of the present invention is to provide a gas laser device that can produce stable glow discharge even with large discharge injection power.

In order to achieve this objective, the gas laser device of the present invention includes:
The discharge surface of the cathode is composed of a cylindrical inner surface that is approximately coaxial with the laser tube axis, and the length of the discharge surface in the gas flow direction is 0.5 m.
7! L or more, 2m7! It is characterized by being less than or equal to L. The present invention will be further described below with reference to embodiments shown in the drawings.

FIG. 1 is an explanatory diagram showing an embodiment of a high-speed axial flow type gas laser device according to the present invention, and this embodiment is an example configured as a high-output carbon dioxide laser device.

In the figure, numeral 1 is a laser tube, and both laser tubes 1,
1, anodes 2, 2} and cathodes 3, 3 are installed, respectively.

The cathodes 3 and 3 are connected to one output end of a DC high voltage power supply 5 via stabilizing resistors 4, 4, respectively, and the DC high voltage power supply 5
The anodes 2, 2 are connected to the other terminal of the electrode to form a discharge circuit. As shown in Figure 2 and Figure 3,
Eight gas flow windows 6 are formed on the cathode 3 in order to increase the aperture ratio and increase the gas flow rate, and a discharge surface 7 consisting of a cylindrical inner surface coaxial with the laser optical axis is provided. It is being

t in Fig. 2 is the discharge surface 7 in the gas flow direction shown by the arrow.
Indicates the length of Inside the laser tubes 1, 1, CO2:N2:He=1:10:14 is used as a gaseous laser medium.
A mixed gas of (total pressure number + TOrr) is sealed, and this mixed gas is excited by plasmas 9, 9 by the discharge circuit.

Further, at each end of the laser tube 1, a concave reflecting mirror 10 and a flat output mirror 11, which constitute an optical resonator, are installed facing each other, and the light within this optical resonator is reflected back and forth between the two mirrors 10 and 11. As the light is amplified by stimulated emission, a part of it is transmitted through the plane output mirror 11 and emitted as laser output light 12.

In this embodiment, a forced gas circulation system is adopted to increase the output of the laser output light 12, and a blower 13 is provided for this purpose.

This blower 13 forces the mixed gas to flow at high speed in the tube axis direction from the joining side of the laser tubes 1, 1 toward both the cathode side and the anode side through the connecting pipe 14. After this mixed gas is heated by the plasmas 9, 9, it passes through connecting pipes 15, 15 connected near the ends of the laser tubes 1, 1, and then passes through the heat exchanger 1.
6 and 16, and is further returned to the blower 13 through both connecting pipes 17, 17 and 18, where it is forced to circulate as shown by the arrow. When using the gas laser device as described above to obtain laser light by exciting the mixed gas through the discharge circuit and causing an inverted density distribution in the energy level of carbon dioxide molecules, the glow discharge current in the laser tube 1 is As the discharge injection power increases, the discharge gradually becomes unstable and the fluctuation range of the discharge current also increases.

Therefore, this fluctuation range can be used as a measure of the stability of glow discharge. Figure 4 shows the discharge injection power P per laser tube that increases when the fluctuation width of the glow discharge current becomes 4 mA.

is shown for the case where the gas pressure inside the laser tube is 20T0rr and 25T0rr. As is clear from the figure, when the length t (expressed on a logarithmic scale) in the gas flow direction of the discharge surface 7 of the cathode 3 is greater than 2 mm, there is no noticeable difference in the magnitude of the discharge pourer power. But like this, t
If it exceeds 2 mm, the discharge injection power tends to decrease.

The reason for such a decrease in the discharge injection power is that the glow discharge does not spread over the entire discharge surface 7. However, t
The magnitude of the discharge injection power increases rapidly as the value of becomes less than 2 mm. Such an increase in the discharge injection power is due to the fact that the smaller the discharge surface 7 is, the less it is affected by adverse effects such as non-uniformity of gas flow velocity distribution. That is, according to the present invention, by reducing the area of the discharge surface 7, that is, by reducing the value of t, it has become possible to stabilize the glow discharge and increase the discharge injection power. However, as is clear from FIG. 4, if the area of the discharge surface 7 becomes too small, the current density at the discharge surface 7 increases, and as a result, the temperature of the discharge surface 7 rises and glows. There was a tendency for discharge to become impossible.

That is, as shown in FIG. 4, the discharge injection power reaches its maximum when t=0.9 mm, and it is clear that this value of t is the optimum value.

1 On the other hand, when t becomes smaller than 0.9 mm, the discharge injection power begins to decrease, and when t becomes less than 0.5 mm, the discharge injection power becomes lower than the discharge injection power when t exceeds 2.0 mm, and the discharge If the injection power is lower than this, it is not preferable from a practical point of view. That is, when t is less than 0.5 m77!1, not only does the discharge injection power decrease as described above, but also the glow discharge becomes unstable and tends to shift to arc discharge. As mentioned above, the value of t is 0.
It has become clear that when the diameter is 5 mm or more and 2 m71 L or less, the discharge injection power can be increased (2) and it is possible to maintain the glow discharge in a stable state. The reason why a stable glow discharge can be obtained by limiting the length t of the discharge surface in the gas flow direction is due to the turbulence component in the gas flow generated near the discharge surface as follows. considered to be a thing.

Generally, in a high-speed axial flow type gas laser device, the gas flow velocity v near the discharge surface ranges from several m/Sec to more than 100 m/Sec. It is known from a hydrodynamic viewpoint that when such a high-speed gas flow collides with the cathode 3, turbulence is generated near the discharge surface 7S of the cathode 3. On the other hand, the turbulent flow component near the discharge surface is, for example, U.S. Pat.
rlessElectrOdeCONstructi
It has also been recognized that it is an important factor in stabilizing the glow discharge, as seen in OnfOrGasTranspOrtLaserj. A high-speed axial flow gas laser device to which the present invention is applied (generally gas conditions are pressure number + TOrr
, flow velocity number + m/s to about 200 m/s), the turbulent component near the discharge surface 7 occurs in a region with a length of about 0.5 Lm to 271 Lm in the gas flow direction, which is the same as above. It has become clear that it is compatible with general gas conditions.

Therefore, it is considered that by making the length t of the discharge surface approximately equal to the length of the turbulent flow generation region, a stable glow discharge can be obtained as shown in FIG. 4. As explained above, according to the present invention, by setting the length of the discharge surface of the cathode in the gas flow direction to 0.5 m 1 L or more and 2 mm or less, it is possible to increase the discharge injection power, and to increase the It becomes possible to obtain a stable glow discharge even if the discharge injection power is insufficient, and it is possible to realize a high output gas laser device.

[Brief explanation of the drawing]

Fig. 1 is a schematic overall configuration diagram showing an embodiment of a high-speed axial flow gas laser device according to the present invention, and Fig. 2 is a cross-section of the laser tube used in the gas laser device of Fig. 1 along the - line in Fig. 3. FIG. 3 is an enlarged detailed sectional view, FIG. 3 is a front view of the cathode, and FIG. 4 is a diagram showing changes in discharge injection power depending on the length of the cathode discharge surface in the gas flow direction. 1... Laser tube, 2... Anode, 3...
・Cathode, 5... High voltage DC power supply, 7... Discharge surface, 9.
...Plasma, 10...Concave reflecting mirror, 11...Plane output mirror, 13...Blower.

Claims (1)

[Claims] 1. A laser tube enclosing a gaseous laser medium, an anode and a cathode provided in the laser tube, a DC high-voltage power supply for maintaining glow discharge between the anode and the cathode, and a laser including the glow discharge section inside. It has an output mirror and a reflecting mirror that are arranged to face each other to form a resonator, and a blower for circulating the gaseous laser medium in the laser tube, and the discharge surface of the cathode is aligned approximately with the laser tube axis. A gas laser device of a high-speed axial flow type configured with coaxial cylindrical inner surfaces, characterized in that the length of the discharge surface of the cathode in the gas flow direction is 0.5 mm or more and 2 mm or less.