RU2191452C2 - Discharge tube for metal vapor laser - Google Patents

Abstract

FIELD: laser engineering. SUBSTANCE: discharge tube includes envelope surrounded by screening member and provided with blind annular slots on its inner side which are coaxial with envelope and are filled with envelope active material. Abutting against inner surface of each slot is substrate wetted by active material and covered with molten active material. Inner diameter of substrate is greater than that of envelope. The latter is assembled of cylindrical tubes spaced apart and joined over outer diameter by means of bushings mounted in metal holders which are tightly abutting against bushing surfaces. EFFECT: simplified design and enhanced mechanical endurance of tube. 6 dwg

Description

 The invention relates to laser technology, namely to discharge tubes of metal vapor lasers, and can be used in their design in order to increase reliability and durability without complicating the design.

A distinctive feature of this class of lasers is the presence of vapors of the active substance (copper, gold, lead, barium) in a gas-discharge plasma at a temperature of the order of 3000 ^° C and a shell not wetted by the active substance (for example, made of ceramic). A known discharge tube of a copper vapor laser with a shell not wetted by the active substance, in which the active substance (copper) is introduced into the laser discharge tube in the form of individual rings of small thickness [1]. When the discharge is switched on, the active substance heats up before melting, part of it, determined by the temperature in the region of the discharge, passes into steam and then participates in the processes of laser energy generation. The remaining part, due to the non-wettability of the ceramic shell by the active substance, takes the form of spheres, partially overlapping the aperture of the radiation beam and reducing its power.

 The closest technical solution, the prototype of the invention, is the design of the discharge tube of a metal vapor laser, including a shell (1), shielding elements (2) and active substance blocks containing a substrate of material wetted by the active substance (3a) with the active substance melt deposited on it (3b) (Fig. 1) [2]. The active substance in the design is copper, but there may be another metal from the above. The substrate for the active substance has the form of a hollow cylinder. The blocks of the active substance are supported by molybdenum supports (4) in the area adjacent to the high-temperature column of the gas discharge in front of the shielding elements located along the inner contour of the shell and are separated by ceramic insulators (5). Shielding elements act as heat insulators reflecting thermal radiation, helping to achieve the required operating temperature.

 When the discharge is switched on, the active substance melts and evaporates metal atoms, which during diffusion fill the entire free space of the gas discharge tube. The mass of the substance, due to the wettability of molybdenum, is held by the surface of molybdenum, does not change shape and does not overlap the aperture of the radiation beam.

 The design drawback is the presence of molybdenum supports in the high-temperature plasma region, which simultaneously perform the role of thermal isolation. At a high operating temperature, structural restructuring of metal structural elements occurs with the formation of dendrites [3], their embrittlement, destruction, and, as a result, the overlap of the aperture of the radiation beam, which limits the durability of the structure.

 Another disadvantage of the prototype is the presence in this design of a relatively cold shell. In the process, under the influence of a temperature gradient, the atoms of the evaporated metal diffuse towards the shell and condense on its surface. Over time, the block of active substance is completely depleted, and the metal accumulates on the shell surfaces adjacent to the block, located further from the discharge axis and having a lower temperature. A "cooled" metal can no longer form an amount of steam whose density is optimal for obtaining the same radiation power. This leads to a decrease in the power and, consequently, the durability of the laser.

 In addition, the design of the tube is much more complicated.

 The purpose of this technical solution is to increase the durability of the discharge tube on metal vapors without complicating the design.

 This goal is achieved by the fact that in the discharge tube on metal vapor, including the shell (1), the shielding elements (2) and blocks of the active substance containing a substrate of a material wetted by the active substance (3a) with the active substance melt deposited on it (3b) ( figure 2, 3), in the wall of the shell in the plane of its cross section from the inside there are blind grooves of a ring shape, the axes of which coincide with the axis of the shell, blocks of active substance are installed in the grooves of the shell so that their surface is adjacent to the surface of the groove, and the inner diameter of the block of active substance is not less than the diameter of the adjacent parts of the shell, the shielding elements are installed continuously around the entire shell and axially its surface.

 The essence of the proposed technical solution is as follows.

 Condensation of metal vapor on the shell can be eliminated if, in the operating mode, the temperature of the inner surfaces of the shell is not less than the temperature of the molten metal of the active substance block. Since the temperature of the internal surfaces of the discharge tube is determined by their distance from the axis of the discharge, this can be achieved if deaf ring-shaped grooves with axes coinciding with the axis of the shell are pierced from the inside of the wall of the shell in the plane of its cross section, and the active substance blocks are installed in the grooves of the shell so that their surface is adjacent to the surface of the groove, the inner diameter is not less than the diameter of the adjacent parts of the shell, and the shielding element is placed continuously around the entire surface shell and axially with its surface to create the same conditions for thermal insulation of all parts of the shell.

 In this case, even if the inner diameters of the blocks and interblock parts of the shell are equal, the surface temperature of the active substance of the block will be lower than the surface temperature of the adjacent part of the shell, because the thickness of the shell having certain heat-insulating properties behind the blocks of the active substance will be less than the thickness of the shell between the blocks.

 The grooves may have a closed shape (ring) (figure 2) or open (part of the ring) (Fig. 3). The type of groove depends on the requirement for the readiness time of the laser emitter, since with an increase in the total mass of the active metal, the time for its heating up and, consequently, the readiness time of the emitter increases.

 This design will also eliminate the use of support molybdenum discs. The shell itself will serve as a support, which will greatly simplify the design.

 In order to simplify the manufacturing technology of the tube and the disposal of its constituent elements, the tube shell can be assembled from several ceramic tubes separated by a gap (6), connected along the outer perimeter by ceramic bushings (7) (Fig. 4). However, due to the fact that the grooves of the discharge tube are filled with metal, the thermal conductivity of which is significantly higher than that of ceramics, the central parts of the bushings are heated faster than their ends in contact with ceramic tubes. This can lead to thermal stresses in the contact zone and to the destruction of the bushings. To equalize the temperature on the surface of the sleeve, it is proposed to install the latter in a metal cage (8) (since the metal has good thermal conductivity), the inner surface of which is tightly adjacent to the outer surface of the sleeve (Fig. 4).

 To increase the reliability of the shell, its design can be made of a long main pipe (9), into which short segments of insulating tubes (10) are introduced with an interval, and the outer diameter of the short tubes is equal to the inner diameter of the long pipe (Fig. 5).

 The gaps between the tubes in both shell options serve as grooves for the blocks of active substance.

 The invention is illustrated by drawings.

Figure 1 shows the design of the prototype, figure 2 - the design of the proposed solution, figure 3 - the design of the proposed solution with a variant form of the groove, in fig. 4, 5 - options for the design of the shell, Fig.6 is a photograph of a discharge tube and a molybdenum ring. In FIG. 1-6:
1 - the shell of the discharge tube,
2 - shielding elements,
3 - block active substance,
4 - support of molybdenum,
5 - insulator,
6 - tube
7 - sleeve
8 - metal clip,
9 - pipe
10 - insulating tube,
11 is a view of the tube from the side of the anode,
12 is a tube view from the cathode side,
13 - molybdenum ring after 200 hours of discharge. Formations of dendrites are visible.

 The device operates as follows. The metal heated in the discharge (3b) of the block of the active substance turns into a liquid that evaporates atoms. An equilibrium vapor concentration occurs above the metal surface. The inner wall of the shell (1) of the tube adjacent to the block of active substance is heated to a temperature no lower than the block itself. As a result of diffusion, metal atoms fill the entire space of the discharge tube without condensing on the shell (figure 2).

 The effectiveness of the invention is verified experimentally by the example of a tube on copper vapor (Fig.6). The molybdenum ring inserted inside the discharge tube instead of one of the blocks of the active substance was covered by dendrites during the first 200 hours of operation, blocking the channel aperture, which led to the loss of 50% of the laser radiation power. The negative effect of vapor condensation on the shell manifested itself in a longer time and depended on the amount of metal in the block of active substance. The exclusion of both reasons allowed to increase the durability of the discharge tube of the laser compared to the prototype 7-10 times. The obtained durability was 1500-2000 hours and was already associated with the dusting of the tube windows. The design of the tube has been greatly simplified.

 The effectiveness of the invention will be no less high if gold, lead or barium is used as the active substance, since the melting temperature of these substances is lower than that of copper, and therefore the tube shell will experience a lower temperature load than in the case of copper.

Sources of information
1. H 01 S 3/02, GB 2 126 413 "Laser vapor of a metal and a mixture of helium and cadmium gases", prior. from 1982

 2. H 01 S 3/03, GB 2 176 335. A. Maitland "Discharge tube of chemical vapor lasers", prior. from 1985

 3. N. A. Levina, E.N. Marner "Service conditions of high refractory oxide ceramics in vacuum furnaces with molybdenum, tungsten, niobium heaters." Refractories, 11, November 1968

Claims (1)

 A discharge tube of a metal vapor laser, including a shell surrounded by a shielding element, containing ring grooves with the active substance coaxial with the shell, made on the inner side of the shell, characterized in that the grooves are made in the form of blind grooves, the substrate is tightly adjacent to the inner surface of each of the material wetted by the active substance with a melt of this active substance deposited on it, the inner diameter of the substrate is larger than the inner diameter of the shell, while the shell is made of divided spaced cylindrical tubes connected to the external diameter of the sleeve mounted in metal holder, close fitting to the surfaces of the sleeves.

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