JPS6239554B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rare gas ion laser tube with a plasma capillary made of graphite plates.

The rare gas ion laser tube utilizes laser transition at the ion level, so the plasma capillary can be heated from 10A to
Passes a discharge current of up to 50A. In order to achieve sufficient current density to obtain laser gain, the plasma capillary usually has an inner diameter of 2 to 5 mm, resulting in a large voltage drop, and most of the discharge power of a rare gas ion laser tube is consumed in the plasma capillary. . Therefore, it is necessary to use materials and structures for the plasma capillary that can withstand the generated heat of several kilowatts to several tens of kilowatts. One method of constructing a plasma capillary is to use one or several cascaded tubes of an insulator with good thermal conductivity, such as beryllia porcelain, to form a vacuum envelope and an outer surface. It is directly water cooled. but,
Beryllia porcelain thin tubes have the disadvantage that it is difficult to obtain materials and the structure of the laser tube becomes complicated.

Another method is to connect multiple disk-shaped conductive materials with excellent heat resistance and heat radiation properties such as graphite through an insulator to form a disk row, and then cover this disk row with a heat-resistant insulator such as quartz covered with cooling water. The disk is housed in a vacuum-tight container, discharges through a small hole provided in the center of the disk, and the heat generated by the discharge is radiated from the disk. However, the method using a graphite desk is easy to obtain materials and configure the laser tube, but due to the ion bombardment caused by large current discharge and the mechanical weakness of graphite itself, graphite tends to become finely powdered. The particles are carried to the end of the laser tube by the rare gas flow generated by diffusion and large current discharge and adhere to the inner surface of the Brewster window, causing loss in laser oscillation, causing a decrease in the oscillation laser output and disturbance of the oscillation mode. The problem is that the laser oscillation eventually stops and the end of its life is reached, and that fine powder that does not reach the Brewster window also accumulates in the tube, narrowing the laser oscillation area and reducing the laser output, or that it accumulates between the disks and causes damage between the disks. There are drawbacks such as poor insulation and eventually inability to discharge.

SUMMARY OF THE INVENTION An object of the present invention is to provide a long-life rare gas ion laser tube having a graphite disk plasma capillary that can withstand large current discharge and is less likely to generate fine powder.

That is, the present invention includes a plasma capillary made of a plurality of graphite plates arranged at regular intervals, each having a central discharge hole for generating laser light and small holes for gas return provided around the central hole, and The inner surface of the discharge hole in the plate is covered with silicon carbide to minimize the pulverization of graphite, thereby extending the life of the laser tube. Furthermore, silicon carbide may be provided so as to cover the surface of the graphite plate except for the outer peripheral surface.

The present invention will be explained below with reference to the drawings.

As shown in FIG. 1, a conventional rare gas ion laser tube having a graphite disk plasma capillary includes a cathode 1, a plurality of graphite disks constituting the plasma capillary, and an anode 3.
, a pair of Brewster windows 4, 4' and a transparent envelope 5
It consists of A rare gas 6 such as Ar or Kr is sealed inside the envelope 5 as a laser medium, and a laser optical axis 7 is set through the center hole of the disk. As shown in FIG. 2, the disk 2 made of high-purity graphite has a disk shape with a small hole 8 forming a discharge path in the center and a plurality of small holes 9 for gas return around the center. is provided. Small hole 9
In order to prevent the discharge path from being formed in this part,
Each has a smaller diameter than the small hole 8 and has a smaller conductance. The disks 2 are isolated for a certain period of time by an electric insulator (not shown), and a large number of disks 2 are lined up to form a plasma capillary.

The heat generated by the discharge causes the disk 2 to reach a high temperature, and this generated heat is transferred to the outer peripheral surface 1 of the disk 2.
0 is radiated through the transparent envelope 5 into cooling water (not shown) provided around the transparent envelope 5. The temperature T(〓) of the disk 2 is mainly determined by the thermal emissivity ε of the outer peripheral surface 10 of the disk.
It is determined by the Shuttejuan-Boltzmann law as follows.

S=εσT ^4where , S is the radiant energy per unit time and unit peripheral surface area from the disk, and σ is the Schutefan-Boltzmann constant. In a typical argon ion laser, T is set at about 1000°C. However, graphite material has a hardness of 1 to 2 and is mechanically brittle and easily crumbles. Due to ion bombardment caused by large current discharge and high temperature operation, the inner wall of the discharge area 8 of disk 2 in particular collapses due to long-term operation, and graphite becomes fine powder. become As a result, fine powder accumulates on the inner wall of the small discharge hole 8, and the small discharge hole 8 gradually narrows, the oscillation mode volume of the laser decreases, and the laser output decreases.

Furthermore, the fine powder coming out of the small discharge holes 8 accumulates between the graphite disks and adheres to the insulator that insulates the disks, deteriorating the insulation and eventually making it impossible to discharge.

Further, a part of the finely powdered graphite moves within the laser tube due to the argon gas flow during discharge, reducing the laser oscillation output or deteriorating the oscillation mode. Graphite disk rare gas ion lasers often reached the end of their service life due to such pulverization of graphite.

FIG. 3 is a cross-sectional structure of a graphite disk for a plasma capillary of a rare gas ion laser tube according to an embodiment of the present invention. The disk 2 based on the present invention is made of high-purity graphite 11 similar to the conventional one, and the inner surface of the small discharge hole is covered with silicon carbide 12. Silicon carbide has long been known as a material with high heat resistance (can be used up to 1500℃) and high hardness (hardness 9.5), and compared to graphite, thin films ranging from several tens of micrometers to several mm can be produced using the deposit method or conversion method. can be formed on the surface of

When a disk with this structure is used as a plasma capillary in a rare gas ion laser tube, discharge occurs through the small hole 8 in the center, and the temperature of the entire disk rises, but because the inner surface of the discharge hole is covered with silicon carbide. , the generation of fine powder is kept to a minimum. Further, heat is radiated from the disk mainly through the outer circumferential surface 13, but there is no problem since there is no silicon carbide film in this area and the graphite itself is exposed. The thermal emissivity of silicon carbide is approximately 0.75, and compared to graphite's thermal emissivity of 0.9, in order to achieve the same disk temperature, if the entire surface is made of silicon carbide, the outer peripheral area, that is, the disk diameter, must be reduced by 20%. By leaving graphite in areas other than the inner surface of the small discharge holes, it is possible to prevent a decrease in heat radiation and make the temperature rise of the disk almost the same as that of a conventional graphite disk of the same size.

In the above example, silicon carbide was provided only on the inner surface of the discharge hole of the graphite plate, but
It may be provided on the entire surface of the graphite plate except for the outer peripheral surface 10.

Therefore, according to the present invention, it is possible to obtain a rare gas ion laser tube that has a completely conventional structure, generates less fine powder, and has a long life.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing a rare gas ion laser tube using a graphite disk, Fig. 2 is a cross-sectional view showing the structure of a conventional graphite disk, and Fig. 3 is a graphite disk showing an embodiment of the present invention. FIG. 3 is a cross-sectional view showing the structure of the disk. 1... Cathode, 2... Graphite disk, 3... Anode, 4, 4'... Brewster window, 5... Envelope, 6... Rare gas, 7... Laser optical axis, 8... Small hole for discharge, 9... Small hole for gas return, 10... Outer peripheral surface, 11... Graphite,
12...Silicon carbide film.

Claims (1)

[Scope of Claims] 1. A plasma tube comprising a plurality of graphite plates arranged at regular intervals, each having a central hole for discharge that generates laser light and small holes for gas return provided around the center hole, A rare gas ion laser tube characterized in that at least the inner surface of a central discharge hole, excluding the outer peripheral surface of a graphite plate, is covered with silicon carbide. 2. The rare gas ion laser tube according to claim 1, wherein the entire surface of the graphite plate other than the outer peripheral surface is covered with silicon carbide.