FR2538610A1 - LASER CATHODE, METHOD OF FORMING A THERMAL JOINT BETWEEN A LASER ENCLOSURE AND A CATHODE, AND LASER - Google Patents

Abstract

An improved laser cathode is disclosed. It comprises a hemispherical hollow envelope 28 made of a material with a previously chosen thermal characteristic. The inner surface of this envelope has a layer 30, for example of aluminum. A thermal seal 32 is made between the body 12 of the laser, made of a material with a low coefficient of thermal expansion, and the cathode 22. Field of application: lasers. (CF DRAWING IN BOPI)

Description

253-8610

  The invention relates to improvements

  brought to the field of lasers It relates more particularly

  specifically to an improved laser cathode.

  A laser cathode is used to provide electrons to the process of forming a laser beam. Such a cathode is often of generally domed configuration, having an aluminum surface, and is placed near the end of a channel in a laser body and containing suitable gases such as helium and In operation, it is maintained at a negative potential and bombarded by

  positively charged helium and neon ions, which

  the electrons supplied to the oxidized surface of the cathode, due to its negative potential, to produce

  uncharged gas molecules.

  A classic laser has mirrors highly

  polished at opposite ends of the laser body.

  When such a laser is used as part of a set of instruments, only a relatively small variation in the distance between the mirrors is tolerable, as this distance is critical to the resulting output frequency of the laser. Maintaining a distance predetermined, within tolerances, poses a technical problem difficult to

  solve when the laser is used in an environ-

  In order to solve this problem, the body of the laser is commonly made of a material with an extremely low coefficient of thermal expansion, such as various glass-ceramics, for example those

  known under the trademarks "Zerodur" and "Cer-

  In addition, the cathode must include a metal to function as a source of electrons. As mentioned above, aluminum has often been used to

the cathode of a laser.

  Currently, aluminum or aluminum alloy laser cathodes are produced by a number of known methods including stamping and machining operations. These methods require extensive cleaning and preparation of the inner surface of the cathode. In some applications, however, the cathode must be sealed to the body of the laser. Therefore, a glass-on-metal seal is commonly made in accordance with the different compositions of the cathode and the body of the laser. Indium is commonly used as a coating agent. Such an indium seal is described

  in U.S. Patent No. 4,273,282.

  Although an aluminum or alloy cathode

  of aluminum provide electrons to the process of

  the degree of expansion that it undergoes under thermal stress, although it does not degrade the short-term operation of the laser, affects its long-term integrity The great disparity between the coefficients of dilation the heat of the aluminum or other metal cathode and the body of the glass-ceramic laser creates important constraints in such a system. The difference between the coefficients of thermal expansion of aluminum and the material of the "Zerodur" type, for example, limits the life expectancy of a joint made between such a cathode and such a laser body when subjected to cycles varying between -55 o C and 1250 o C, for example although there is

  interesting processes for making a hermetic

  These methods can not be used to seal a metal to glass. Therefore, the glass aluminum seal, commonly comprising indium, is limited to the melting temperature of the glass. indium which is 1560 C. The invention eliminates the aforementioned drawbacks affecting the prior art by proposing an improved manufacturing method and apparatus concerning the field of lasers The invention relates first of all to an improved cathode for laser This cathode comprises a substantially hemispherical hollow envelope,

  made of a material having a thermal characteristic

  previously chosen The envelope includes a

  inner surface layer of aluminum.

2 '538610

  The invention relates secondly to a laser

  invention comprising a body and a cathode

  it is a substantially hemispherical hollow envelope made of a previously selected thermal characteristic material. The cathode envelope has a superimposed layer.

inner string made of aluminum.

  Another aspect of the invention resides in a process for sealing a laser body, consisting of a material with a low thermal coefficient, to a cathode. The method consists in producing the cathode envelope made of a material with a low thermal coefficient, and then sealing

the cathode on the body of the laser.

  The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting example and in which the single figure is a section of a laser

according to the invention.

  The single figure shows a side section of a laser 10 according to the invention This laser 10 comprises a body 12 preferably made of glass ceramic such as "Cer-Vit" or "Zerodur" type The body 12 of the laser, has a cavity 14 of forming a cavity laser beam having highly polished mirrors 16 and 18 at its

  opposite ends An anode 20 and a cathode 22

  nicate with bores 24 and 26 facing upwards

and opening into the cavity 14.

  The cathode 22 is substantially hemispherical in shape

  and comprises an outer casing 28 made of glass, quartz or glass ceramic, the inside of which is coated with a thin film of aluminum or an aluminum alloy. The casing 28 can be made by one any of a number of processes well known in the field of shaping glass and quartz, including glass molding and blowing techniques In addition, the casing 28 can be made by machining a glass ceramic such as Only "Zerodur" "Cer -Vit" or doped glass known under the trade mark "ULE". Suitable techniques for coating the inner surface of the casing 28 to form the diaper 30 include vacuum deposition. spray coating and ion sputtering of aluminum or

of aluminum alloys.

  It has been found that by using a cathode casing 28 made of a material having a coefficient of thermal expansion corresponding closely to that of the laser body 12, the stresses exerted on a seal 32, which fixes the cathode to the body of the laser, are significantly reduced and the life of the laser is

  thus increased It has also become apparent that a thin film

  The aluminum or aluminum alloy pipe 30 does not have a mass sufficient to impose significant stresses on the joint; therefore, as long as the layer is thick enough to render the cathode 22 opaque,

  the behavior of the latter is entirely appropriate.

  nable and it equals that of a cathode constituted

  only aluminum or aluminum alloy.

  The seal 32 may be formed of a number of materials and by conventional methods including, by no means limitation, those who make a seal

  indium by use of heat and / or pressure.

  In addition, since the body 12 of the laser and the enve-

  28 of the cathode 22 are made of glass-like non-metallic materials, the seal 32 can be formed by a field-assisted bonding method, such as

  as the process known as the "Mallory" process.

  In such a process, the glass cathode and the laser body are brought to a temperature of 300 to 400 ° C while a potential difference is applied between the cathode and the body of the laser. When the assembly is heated, its electrical conductivity increases, allowing the passage of an electric current through the cathode-body interface of the laser The current causes diffusion of the aluminum atoms of the layer 30 in the glass It results in the formation of a permanent bond and robust which is insensitive to certain deterioration modes characterizing the conventional links glass on metal,

  for example those resulting from the melting temperature of indium.

  It therefore appears that the process and the

  According to the invention, improvements in the field of laser manufacturing can be made. Using the invention, a longevity laser can be manufactured.

  increased, which can be used in thermal environments

  which would otherwise seriously affect the possi-

  In addition, by using the invention, advantageous bonding methods which are not applicable to the art can be used.

  previous, to obtain the results indicated previously.

  It goes without saying that many modifications can be made to the laser described and represented without

depart from the scope of the invention.

Claims (10)

  1 Laser cathode, characterized in that   has a hollow envelope (28) substantially hemispherical   made of a thermal characteristic material-   previously chosen, the inner surface of this   envelope having a layer (30) of aluminum.   2 cathode according to claim 1, characterized in that the casing is made of quartz glass   or in a previously chosen glass ceramic.   3 cathode according to one of claims 1 and   2, characterized in that said layer is made   aluminum or aluminum alloy previously chosen.   4 A method for producing a heat seal (32) between a laser body (12) made of a material with a low coefficient of thermal expansion, and a cathode (22), characterized in that it consists in producing the envelope (28). ) of the cathode in a material with a low coefficient of thermal expansion, and to seal the envelope of the cathode to the body.   Process according to Claim 4, characterized in that the cathode casing is made of glass,   in quartz or in a previously chosen glass ceramic.   6 Method according to one of claims 4 and 5,   characterized in that it further comprises forming a   layer (30) of aluminum inside the cathode.   Method according to claim 6, characterized in that said layer is made of aluminum or an aluminum alloy.   Method according to claim 4, characterized in that the cathode is pressure-sealed on the body of the laser, or sealed to the body of the laser by a method assisted by field.   9 Laser characterized in that it comprises a body (12), a cathode (22) sealed on the body and   comprising a substantially hemispherical shell (28)   phérique, made of a characteristic material   previously chosen, the inner surface of this enve-   loppe having a layer (30) of aluminum.   Laser according to Claim 9, characterized in that the casing is made of quartz glass   or in a previously chosen glass ceramic.   Laser according to claim 9, characterized in that the cathode is sealed to the body of the laser by a field-assisted method.