WO1991019336A1

WO1991019336A1 - Ion laser and manufacturing process

Info

Publication number: WO1991019336A1
Application number: PCT/EP1991/000851
Authority: WO
Inventors: Erich Weimel
Original assignee: Nwl Laser-Technologie Gmbh
Priority date: 1990-06-08
Filing date: 1991-05-06
Publication date: 1991-12-12

Abstract

An argon ion laser has a cathode (2) and an anode (3) at the two ends of its gas-tight discharge tube (1). The anode (3) is designed as a one-piece anode tube (11) made of sintered aluminium oxide powder which does not conduct electricity but is a good conductor of heat; the tube has an electrically conductive inner partial coating (10a). The conductive inner partial coating (10a) acts as an anode electrode and is connected by a solder joint to a flange (7) which serves as an anode lead. The two ends of the tube have a coating (10a, 12), preferably of nickel, which permits gas-tight soldering of the anode tube (11) to both the discharge tube (1) and the flange (7). The flange (7) and the discharge tube (1) are electrically insulated from each other by the anode tube (11). This anode tube (11) can be used to construct a simple and an extremely reliable argon laser; the heat is dissipated from the anode (3) of the laser of the invention much more efficiently than in known lasers because the heat generated at the anode (3) is absorbed directly by the cooling water.

Description

Ion laser and manufacturing process

The invention relates to an ion laser, in particular an argon ion laser according to the preamble of claim 1 and a method for producing the ion laser according to the preamble of claim 7.

A laser of this type is known from US Pat. No. 4,477,907. The known argon-ion laser has a glow cathode, an anode designed as a mirror holder, a discharge tube between the anode and cathode, and a gas reservoir. The discharge tube and gas reservoir were a ceramic tube made of beryllium oxide, at the ends of which the metallic, adjustable resonator mirror holder was soldered in a vacuum-tight manner.

Another argon ion laser of this type known from US Pat. No. 4,764,932 has a discharge tube constructed from individual beryllium tube segments. The ends of the pipe are made with a molybdenum-magnesium alloy metallized and connected to each other via a solder ring by brazing. At one end of the discharge tube is a bypass reflector with a hot cathode and at the other end a piece of metal tube is attached as an anode.

Both in the case of the anode used as a resonator mirror holder and in the case of the metal tube there were problems with tightness at the connection point to the discharge tube.

The object of the invention is to provide a laser of the type mentioned at the outset, the anode of which is easy to manufacture and remains gas-tightly connected to the discharge tube and an electrical anode connection during operation, even at high thermal loads .

The solution to the problem is the subject matter of patent claim 1 with respect to the laser and the subject matter of patent claim 7 with respect to the method for producing the laser. Subject matter of patent claims 2 to 6 Find preferred embodiments of the laser according to the invention and subject matter of patent claims 8 to 10 preferred methods for the production of the laser.

An example of the ion laser according to the invention is explained in more detail below with reference to drawings. Show it:

1 shows a longitudinal section through the anode-side end of the laser without a cooling device, the anode tube of the laser not yet being connected to its anode current connection flange and its discharge tube, and

2 shows a longitudinal section analogous to FIG. 1, but with cooling lung as well as with. the discharge tube and the anode: power connection flange connected anode tube.

The argon ion laser as the ion laser has a gas-tight discharge tube 1 filled with argon as the active gas at a pressure of 1 μPa, at one end a tubular anode 3 and at the other end, which is only shown schematically, an indicated glow cathode 2 is mounted in a gas reservoir, not shown. An electrical current flowing between cathode 2 and anode 3 through a channel 4 of the discharge tube 1 ionizes the argon contained therein, whose emitted radiation 6a, shown in broken lines in FIG. 1, on the axis of the channel 4, each on one of the discharge tubes 1 th side of the cathode 2 and the anode 3 arranged, schematically shown resonator mirrors 8a and 8b is reflected. A small percentage of the radiation 6a is coupled out as a laser beam 6b through the resonator mirror 8a. Because of its electrical charge, the ionized argon is transported through the channel 4 to the cathode 2, discharged there and then flows through three bypass tubes 5 parallel to one another and to the channel 4 in the discharge tube 1, only one of which is cut into the tube Figures is shown, back to the anode 3. At the end of the anode 3 facing away from the discharge tube 1, a metallic, centrally pierced flange 7 is attached as an anode current feed line, which is connected to the housing of the argon ion laser (not shown) and to which the resonator mirror 8b is attached.

The anode 3 is a tubular anode carrier 11, on the inner surface of which an electrically conductive coating is applied as the anode electrode 10a. The anode tube 11 is made of approximately 97.5% pure aluminum oxide powder with a Grain size sintered between about five and twenty micrometers. The grain size of the ceramic powder and the firing temperature are selected so that the completely burned anode tube 11 has a maximum leak rate between the interior and exterior of the tube of less than 1 mPa / cm ^* - * - s.

The part of the anode tube 11 facing away from the discharge tube 1 has a vertical end face 9 and is provided on its tube inside with a coating 10 extending beyond the tube center, which extends around the tube end onto the tube outer jacket. The part 10a of the coating 10 lying in the tube interior consists of a galvanically applied copper layer 10a and serves as an anode electrode. It lies on an adhesive layer made of molybdenum-manganese, applied by means of screen printing. Depending on the anode current to be used, the thickness of the copper layer 10a is between fifty and two hundred micrometers. At z. For example, a laser output power of 6, a two-hundred micron thick copper layer is applied to derive an anode current of 35 A. The coating part of the outer tube jacket, denoted by 10b, which extends around the end face 9 and immediately adjoins it, the coating 10, and a coating 12 on the end of the anode tube 11 lying against the discharge tube 1, the end face 14 of which is chamfered, consists of a electroplated solderable nickel layer, which also lies on a molybdenum-manganese layer applied by screen printing as an adhesive layer on the ceramic material The nickel coatings 10b and 12 serve as a soldering surface for the gas-tight connection of the anode tube 11 to the flange 7 and to the discharge tube 1, as described below. The copper and nickel coating 10a and 10b are connected to one another in an electrically conductive manner. The nickel coating 10b extends from the end face 9 only so far on the outer tube jacket that as described below, no electrical contact with the cooling water is possible. The nickel coating 12 is electrically insulated on the inside of the tube by an uncoated ring area 16 from the copper coating 10a and on the outside of the tube by an uncoated ring area 17 from the nickel coating 10b in order to establish an electrical connection between the discharge tube 1 and that via the flange 7 to prevent electrically connected copper coating 10a as an anode electrode, as described below. The position and width of the uncoated ring region 16 is selected so that when the anode tube 11 is connected to the discharge tube 1, the coating 12 is set back by one to two millimeters with respect to the end face of the discharge tube 1.

The discharge tube 1 has at its left end, shown in the figures, a stepped shoulder 19 provided with a solderable connection; the solderable connection extends only up to a distance of one to two millimeters to the front of paragraph 19. The outer diameter of the shoulder 19 is adapted to the inner diameter of the anode tube 11 at its end carrying the beveled end face 14. The angled end of the anode tube 11 is pushed onto this shoulder 19 up to the stop on the shoulder edge 21. The end face 9 of the anode tube 11 is pushed into an annular groove 23 of the flange 7, the dimensions of which are adapted to the inside and outside diameter of the anode tube 11 on the end face 9, until it stops at the bottom of the annular groove. The annular groove 23 is chamfered on each of its upper edges. A brazing ring 27a and 27b made of hard solder is applied to each of these chamfers 25a and 25b; there is also a brazing ring 29 in a gap 30, formed with the inclined end face 14 of the anode tube 11 and the shoulder edge 21. In the case of laser operation, the anode 3 is cooled by cooling water. As shown in FIG. 2, the cooling water enters through a cooling water inlet 33 into a metallic cooling tube 35 which encloses the anode 3, the discharge tube 1 and the cathode 2; the cooling water outlet, not shown, is located in the cooling tube 35 in the vicinity of the cathode 2. The part of the cooling tube 35 on the anode side has an annular end face 36 which is matched to the outer diameter of the anode tube 11 and is made of Teflon through a sealing and insulating disk 37 electrically isolated from flange 7. The end face 36 and the sealing and insulation disk 37 are chamfered on their mutually adjacent edges of the openings receiving the anode tube 11. The two bevels 39a and 39b receive a sealing ring 41 which prevents the cooling water from escaping to the flange 7.

A magnetic coil 43 is attached to the inside of the cooling tube 35 over the entire length of the discharge tube 1. The coil 43 generates a magnetic field strength of approximately 1600 Gauss in the channel 4 in order to protect the walls of the channel 4 as much as possible from the spiral erosion of the plasma discharge. The cooling water thus not only cools the anode tube 11, the discharge tube 1 and the cathode 2, but also the coil 43, which is charged with approximately 1000 W.

To assemble the laser, the cooling tube 35 and the sealing and insulation ring 37 are pushed over the discharge tube 1, the discharge tube 1, anode tube 11 and flange 7 are plugged together and heated, the material lying on the bevels 25a and 25b and in the gap 30 Brazing rings 27a, 27b and 29 due to capillary action in the gaps between anode tube 11 and discharge tube l or flange 7 runs. The anode tube 11, the discharge tube 1 and the flange 7 are now connected to one another in a mechanically fixed and vacuum-tight manner; likewise the copper coating 10a is connected as an anode electrode to the flange 7, which acts as an electrical anode connection.

The anode tube 11 is, as already mentioned above, pressed from aluminum oxide powder and then fired at about 1800 ° C. A molybdenum-manganese layer is printed as an adhesive layer on the re-cooled anode tube 11 by means of a screen printing method at the locations at which the copper or nickel coating 10a, 10b and 12 is to be applied later. Copper or nickel is then electrolytically deposited on this molybdenum-manganese layer.

Instead of applying the molybdenum-manganese layer by means of screen printing, it can also be applied with a brush or by means of other customary methods. The copper or nickel coatings 10a, 10b and 12 can also be applied by means of a CVD process (chemical vapor deposition) or a sputtering process.

The nickel coatings 10b and 12 are only intended to ensure a good gas-tight solder connection between anode tube 11 and flange 7. Good electrical conductivity is not necessary, not even between the nickel layer 10b and the flange 7, since the anode current conduction takes place directly from the copper layer 10a to the flange 7. All coatings which ensure a good solder connection are therefore suitable as replacements for the nickel coatings 10b and 12.

The molybdenum-manganese adhesive layer is only intended to ensure good adhesion of the copper or nickel coating 10a, 10b and Allow 12 on the ceramic surface. An electrical conductivity of the adhesive layer is not necessary. It is therefore also possible to use other adhesive layer materials which are stable up to approximately 200.degree.

Instead of aluminum oxide, it is also possible to use other, electrically insulating, highly heat-conducting ceramic materials which have a sufficiently low leakage rate, as mentioned above. Beryllium oxide can also preferably be used.

The arrangement of the anode tube 11 can be used not only with the argon laser, but also with other ion and gas lasers.

The leak rate can be influenced not only by the firing process and the grain size of the ceramic powder, but also by the coatings applied. To lower the leak rate, the anode tube 11 can additionally be provided with an electrically insulating coating or a glaze directly on the ceramic body. The adhesive layer is then applied to this coating.

The advantage of the argon laser according to the invention lies in particular in its easy-to-manufacture anode tube 11, which is easy to connect both to the discharge tube 1 and to the flange 7 serving as the anode current feed line, the anode electrode 10a also simultaneously being connected to the flange in the case of gas-tight connection 7 is electrically connected. Since the anode electrode surface 10a is integrated in the anode tube 11, there is a robust and reliable construction, since slipping of the anode, such as. B. with other argon lasers, which one in an ano- use the inserted wire helix, is no longer possible.

Thermal tension between the anode tube 11 and the subsequent components 1 and 7 no longer occur, since the ceramic anode tube 11 is an excellent heat conductor which dissipates the heat generated at the anode electrode 10a for radiation to the entire anode tube surface. Due to the good heat dissipation, the thin copper coating 10a of the anode surface, whose mechanical forces are also low, does not become thermally stressed.

Since the anode electrode 10a is applied directly to the ceramic anode tube 11, in the laser according to the invention the heat dissipation from the anode electrode 10a to the cooling water flowing around the anode tube 11 is increased considerably compared to the heat dissipation of the anode in the known lasers. There are no electrical potential problems with the cooling water.

Claims

1. Ion laser, in particular argon laser, with a gas-tight discharge tube (1), at one end of which one

Anode (3) and at the other end a cathode (2) is arranged in order to generate an electrically ionized gas in the discharge tube (1), the emitted radiation of which on the axis of the discharge tube (1), outside of the cathode (2 ) and anode (3) arranged resonator mirrors (8a, 8b) is at least partially reflectable, characterized by a tubular anode support (11) made of electrically non-conductive material, the inner jacket of which is at least partially coated with an electrically conductive coating forming the anode electrode (10a) is provided.

2. Ion laser according to claim 1, characterized in that the tubular anode carrier (11) is formed in one piece from a ceramic material, preferably essentially from aluminum oxide or beryllium oxide.

3. Ion laser according to claim 1 or 2, characterized gekenn¬ characterized in that the tubular anode carrier (11) is formed so that the leakage rate between the tube interior and the exterior is less than 1 mPa / cm ³ * s.

4. Ion laser according to one of claims 1 to 3, gekenn¬ characterized by a second and third coating (10b, 12) on the discharge tube (1) facing or towards the end of the anode carrier (11), preferably substantially Nickel, which are connected in a vacuum-tight manner by a soldered connection to an anode current feed line (7) or the discharge tube (1) which is connected to the first coating (10a).