FR2595877A1 - HIGH PERFORMANCE LASER, PROCESS FOR MANUFACTURING THE SAME, AND GYROSCOPE USING THE SAME - Google Patents

Abstract

THE INVENTION RELATES TO A LASER WITH ADVANCED ELECTRODES. IT INCLUDES A DIELECTRIC BODY 12 ON WHICH ELECTRODES 20, 22 ARE FIXED IN A MATERIAL WHOSE THERMAL EXPANSION COEFFICIENT CORRESPONDS TO THAT OF THE BODY. THIN METAL FILMS 30 COVER THE INTERIOR SURFACE OF THE ELECTRODES, PROVIDING GOOD OPERATING CHARACTERISTICS AND SUPERIOR THERMAL QUALITIES TO THE DEVICE. FIELD OF APPLICATION: RING LASER GYROSCOPES.

Description

The present invention relates to improvements made to the field

  lasers. It relates more particularly to an improved laser comprising an improved electrode, as well as a method of attaching this electrode to a laser body. In the process of forming a laser beam, the laser electrodes, namely the anode and the cathode, interact to circulate a current in the laser beam forming gases, exciting these gases to the levels of the laser beam. higher energy requirements for beam formation. The electrodes are often arranged near channel ends formed within a body of the laser and containing

  appropriate gases such as helium and neon.

  The cathode is commonly of a generally domed metal configuration, whereas a functional metal anode can take various forms, including the shape of a dome or disk, although its operation is less sensitive to 20 form that of the cathode. In operation, the cathode is maintained at a negative potential and the anode is maintained at positively charged helium and neon ions in order to behave as an electron emitter.

  while the anode serves as an electron collector.

  A conventional laser application, such as a ring laser gyro, includes highly polished mirrors located 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 because this distance is critical for the output signal resulting from the laser. Maintaining a predetermined distance, within tolerances, poses a technical problem that is difficult to solve when the laser is used in a relative thermal environment.

  extreme situation. To solve this problem, the body of the laser is commonly made of an extremely low coefficient of thermal expansion material, including various glass ceramics such as those known under the trademarks "Zerodur" and "Cer-Vit". In addition, the cathode and the anode comprise a metal conductor for circulating a current

  through the formation gases of the laser beam.

  Currently, laser electrodes of metal or metal alloy are produced by a

  number of known methods including stamping and machining operations. These methods require extensive cleaning and preparation of the internal surfaces. In addition, in some applications, the electrodes must be sealed to the body of the laser.

  Thus, a glass-on-metal seal is commonly made in accordance with the different compositions of the electrodes and the body of the laser. Indium is commonly used as a sealant. Such an indium seal is described in the United States Patent

No. 4,273,282.

  Although metal or metal alloy electrodes make the necessary electrical contact from the outside to the inside of the laser and thus constitute a means of passing current for the laser beam forming process, the degree of expansion While undergoing thermal stress, although it does not degrade the short-term operation of the laser, it affects its long-term integrity. The great disparity between

  thermal expansion coefficients of the metal electrode and the glass-ceramic laser body introduce important constraints in such a system.

  The mismatch of the coefficients of thermal expansion of aluminum and "Zerodur" type material by

  For example, limits the life expectancy of a seal made between such an electrode and a laser body when they are subjected to cycles of, for example, between -55.degree. C. and 125.degree. 5 glass, commonly comprising indium, is limited by the melting temperature of indium 156 C.

  The stress introduced in a thermally stressed system, including a glass ceramic laser body connected to a metal electrode, may result in deformation, to a small degree, of the laser body. This deformation or bending can severely degrade the laser operating characteristics in applications such as, for example, the ring laser gyro. In addition to the physical deformation, the relative movement and cold flow of the indium sealant at the laser-electrode body interface leads to possible seal failures. Although "pure" glass joints exist, they are not suitable because of differential thermal expansions.

  caused by the constraints. These constraints may in fact cause a break in the body of the glass laser.

  The problems described above, by interacting, limit the efficiency and appropriate laser manufacturing processes for applications such as ring laser gyroscopes, in which the exclusion of contaminating substances is essential for optimum quality of the laser. production and optimal performance of the instrument. In the manufacture of such a precision apparatus, heat is commonly used to release volatile materials (such as

  only water, alcohols and plastics).

  When assembling a ring laser gyroscope apparatus, comprising a laser body, mirrors and electrodes, the instrument is placed on a charging rack and the assembly is cooked so that the substances unwanted contaminants are released. This firing step and the resulting purity of the laser have their effectiveness limited by the 156 C melting point of the indium seal (otherwise, the assembly could be fired at a higher temperature of about 100 C, limited by the capacity of the mirrors of the whole). Therefore, in addition to the adverse effects of the difference in thermal stresses, the efficiency of operation and the ease

  The fabrication of the conventional laser assembly, which comprises a metal electrode and a dielectric ceramic laser body, having different thermal expansion coefficients and connected by an indium seal, are limited.

  The present invention eliminates the above-mentioned drawbacks affecting the prior art by proposing to perfect a laser of the type comprising a dielectric material body having a previously selected thermal expansion characteristic, and at least one electrode attached thereto. , the improvement being that the electrode consists of a previously selected dielectric material having a thermal expansion characteristic which corresponds closely to that of the laser body, this electrode being bonded, with the assistance of a field, to the body dielectric

of the laser.

  In accordance with another aspect, the invention provides an improved method of manufacturing a ring laser gyroscope. The improved method comprises the steps of fabricating a laser electrode in part from a previously selected dielectric material having a thermal expansion characteristic which closely matches that of the laser body. The electrode is then bonded under the assistance of a field to the body of the laser. The body

  is finally cooked, the electrode being fixed thereto, at a temperature greater than 156 ° C.

  The invention will be described in more detail with reference to the accompanying drawing by way of non-limiting example and in which the single FIGURE is a sectional view.

  cross section of a laser according to the invention.

  The single figure is a lateral section of a laser 10 according to the invention. The laser 10 comprises a body 12, preferably made of a glass ceramic 10 such as "Cer-Vit" or "Zerodur" type. A cavity 14 for forming a laser beam is delimited inside the body 12 of the laser and has highly polished mirrors 16, 18 at its opposite ends. An anode 20 and a cathode 22 communicate with upwardly facing bores 24 and 26 supplying the cavity 14. The cathode 22 is generally hemispherical, comprising an outer shell 28 of glass, fused silica or glass ceramic, of which The interior 20 is coated with a thin film of aluminum or an aluminum alloy. Envelope 28 may be made by any of a number of methods well known in the art 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 "Zerodur" type, "Cer-Vit" or doped glass known under the trademark "ULE". Suitable techniques for coating the inner surface of the envelope 28 to form the layer 30 include the deposition

  under vacuum, spray coating and ion sputtering of aluminum or aluminum alloys.

  A sectional view of the anode 20 would show a substantially identical configuration. In the case of the anode, the thin film may be formed of copper or a copper alloy. Many other metals may be suitable, including nickel, chromium, iron,

  titanium, tungsten, aluminum and gold.

  It has been found that by using electrodes having an envelope having a coefficient of thermal expansion which closely corresponds to that of the laser body 12, the stresses exerted on the joints which fix the electrodes to the body of the laser are significantly reduced and, by therefore, the performance and life of the laser are improved. It has furthermore been found that thin, suitable metal foils do not have sufficient mass to impose significant stresses on the joint; therefore, as long as the metal layer is sufficiently thick to make the electrode uniformly conductive, the performance of the electrode is quite suitable and equates to that of a fully metal electrode

or metal alloy.

  The seal 32 is advantageously formed in a field-assisted bonding process, such as the method known as the "Mallory" process. In such a method, the send electrode and the laser body are brought to a temperature of 300 to 400 ° C, while a potential difference is applied between the electrode and the laser body. When the assembly is heated, its electrical conductivity increases, allowing an electric current to pass through the electrode-body interface of the laser. The current causes diffusion of the metal of the thin film into the glass. This results in the formation of a permanent and solid bond

  which is insensitive to certain deterioration modes characterizing conventional glass-on-metal bonds and including, for example, those resulting from the melting temperature of indium.

  The tightly coupled thermal characteristics of the laser body 12, the anode 20 and the cathode 22 allow the use of field-assisted linkage methods. Such methods give bonds of considerably increased strength (several thousand kPa, unlike the strength of the indium seal which is a few hundred kPa). As mentioned above, the very strength of this connection allows the transmission of destructive thermal stresses between a laser body and a thermally different electrode.

  When the closely tuned laser body and electrode are connected by a field-assisted bonding method, the resulting assembly, in the case of a ring laser gyroscope, can be subject to highly-efficient manufacturing processes. advantageous that significantly improve the quality and performance of the resulting instrument. Elimination of the stresses due to the differences in thermal expansion and the relatively low melting point of the indium seal allows the assembly (including the electrodes welded thereto) to be cooked in a low pressure medium at a temperature greater than about 100 C at the melting point of indium (in the case of a ring laser gyroscope, the cooking of the instrument on the charging medium would be limited, by the mirrors of the assembly, at about 250 C, whereas the point of

  melting of indium is about 150 C).

  A highly desirable consequence of the higher firing temperature is its effect on the vacuum medium. Increasing the cooking temperature by 100 ° C raises the vapor pressures of the material by more than two decades, which is a factor increase of more than 100. Since the cleaning of the assembly depends on the difference between the vapor pressure and that of the ambient environment, it follows that it takes a pumping time 100 times shorter to reach a given level of cleanliness. Consequently, the manufacture of a laser according to the invention is less expensive and the quality of the performance and the useful life of

this laser are increased.

  It therefore appears that the invention provides an improved method and apparatus for the manufacture of a laser. Using the teachings of the invention, a longer life laser apparatus can be produced which can be used in thermal media which would otherwise significantly degrade the possible performance. In addition, using the teachings of the invention, binding processes that are not applicable to the prior art can be advantageously used to obtain the results indicated above. These bonding processes together with the configuration of the laser electrodes result in a higher quality laser assembly at a lower cost.

manufacture lowered.

  It goes without saying that many modifications can be made to the laser described and shown without departing from the scope of the invention.

Claims (8)

  1. A laser of the type comprising a dielectric body (12) made of a material having a previously chosen thermal expansion characteristic, and at least one electrode (20 or 22) fixed to this body, characterized in that said electrode consists of a dielectric material (28) previously selected having a thermal expansion characteristic which closely matches that of the body, and in that said electrode is bonded, under field assistance, to the dielectric body.   2. Laser according to claim 1, characterized in that the electrode further comprises a metal coating (30).   3. Laser according to claim 2, characterized in that the electrode has a substantially hemispherical and hollow shape inside which   the metal coating is located.   4. Laser according to claim 3, charac20 terized in that said electrode is a cathode (22).   Laser according to claim 4, characterized in that said electrode further comprises at least one anode (20).   6. A method of manufacturing a ring laser gyroscope comprising the steps of: preparing a laser body of a previously selected thermal feature material and attaching at least one electrode. to this body, the method being characterized in that it consists in manufacturing the electrode, in part, in a previously selected dielectric material having a thermal expansion characteristic which closely corresponds to that of the body, and then binding, under assistance of a field, said electrode   to the body, and then to cook the body, on which the electrode is fixed, at a temperature higher than 156 C.   7. Method according to claim 6, characterized in that it further comprises coating the electrode with a metal.   A ring laser gyroscope produced by the method of claim 7.