JPS59132692A - Improved laser cathode - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to improvements in laser technology. More particularly, the present invention relates to an improved laser cathode.

Description of the Prior Art Laser cathodes serve to provide electrons to carry out the lasing process.

Often such a cathode is generally dome-like in shape with an aluminum surface and is located near the end of a channel within the laser body containing the appropriate gas, such as helium and neon. In operation, the cathode is maintained at a negative potential and bombarded with positively charged helium and neon ions. The ions combine with electrons supplied to the oxidized surface of the cathode by the cathode's negative potential to form uncharged gas molecules.

A typical laser has highly polished mirrors at both ends of the laser body. When such a laser is used as an element in an instrumentation system, only relatively small amounts of vibration can be tolerated with respect to the distance between the mirrors. This is because this distance is critical for determining the laser output frequency. Maintaining a preselected distance within an acceptable range presents a difficult technical problem when the laser is operating in a relatively extreme thermal environment. To address this problem, laser bodies are typically constructed from materials with extremely low coefficients of thermal expansion, including various glass-ceramics known under the registered trademarks "Zerodur" and "Cer=Vit." Manufactured. On the other hand, the cathode must contain metal to function as an electron source. As mentioned above, aluminum has often been used for laser cathodes.

Aluminum or aluminum alloy laser cathodes are generally manufactured by a number of recognized methods including stamping and machining. Such methods require lengthy cleaning and preparation of the internal surface of the cathode.

Additionally, in some applications, the cathode must be sealed to the body of the laser. Thus, the glass-to-metal seal is generally affected by the different materials of the cathode and laser body. Indium is commonly used as a sealant.

Such indium seals are known from the Nobel Prize for Glass or Ceramic-to-Metal Seals.
l l ) disclosed in other U.S. Pat. No. 4,273,282.

While the aluminum or aluminum alloy cathode donates electrons during the laser action process, the degree of expansion of the cathode appears under thermal stress. There is no degradation when the laser is operated for short periods of time, but long-term integrity is affected.

(7) The large difference in coefficient of thermal expansion between the aluminum or other metal cathode and the glass-ceramic laser body introduces large stress factors within such systems.

The thermal expansion coefficient mismatch between aluminum and zero duer is, for example, for cycles between -55°C and 125°C.
This limits the life expectancy of the seal between the cathode and the laser body. Although there are attractive sealing processes for glass-to-glass bonding, such as electric field-assisted bonding, these processes cannot be used to seal metal to glass. Therefore, aluminum-to-glass seals, which typically contain indium, are limited by indium's melting point of 156°C.

SUMMARY OF THE INVENTION The present invention overcomes the drawbacks of the prior art by providing an improved manufacturing method and apparatus for laser technology. In the first aspect, an improved laser cathode is provided (8). Such cathodes have a generally hemispherical hollow shell made of a material with preselected thermal properties. The shell has an inner surface layer containing aluminum.

In a second aspect, an improved laser is provided. The laser includes a laser body and a cathode that includes a generally hemispherical hollow shell made of a material with preselected thermal properties. The cathode shell includes an inner surface layer that includes aluminum.

Yet another aspect of the invention resides in a method of sealing a laser body formed of a low coefficient of thermal expansion material to a cathode. The method includes manufacturing a cathode shell of a low coefficient of thermal expansion material. The cathode is then sealed to the laser body.

The above and additional advantages and features of the present invention will become apparent from the detailed description below. In the detailed description, reference is made to the numerals characterizing the invention in the accompanying drawings.

Like numbers consistently refer to like parts.

DETAILED DESCRIPTION Referring now to the drawings, there is shown a side cross-sectional view of a laser 10 in accordance with the present invention. Laser 10 includes a laser body 12 . The laser body 12 is preferably made of ceramic glass such as Cerpit or Zerodure. A laser working cavity 14 is within the laser body 12;
It has highly polished mirrors 16°18 at each end. The anode 20 and cathode 22 communicate with vertical bores 24 and 26 that supply energy to the lasing cavity 14 .

Cathode 22 is generally hemispherical and has an outer shell 28 of glass, quartz, or glass ceramic. The shell 28 is
It has a thin film layer 30 of aluminum or aluminum alloy on its inside. Shell 28 may be formed by many methods well known in the glass and quartz molding arts, including glass blowing and molding techniques.

Furthermore, the shell 2B can be machined from a glass ceramic such as Zerodure, Cellpit, or a doped glass known by the trademark ULE. Suitable methods of coating the inner surface of shell 28 to form layer 30 include vacuum deposition of aluminum or aluminum alloys, sputter coating, and ion plating.

Applicants have discovered that by using the cathode shell 2B of a material with a coefficient of thermal expansion that closely matches that of the laser body 12, the application of acting on the seal holding the cathode to the laser body is significantly reduced, and The lifetime of the laser is therefore improved. Applicants have further discovered that there may not be enough aluminum or aluminum alloy to place significant stress on the seal. Therefore, layer 30
As long as the cathode 22 is thick enough to render the cathode 22 opaque, the performance of the cathode will be adequate and comparable to that of a cathode made solely of aluminum or aluminum alloys (11).

Seal 32 may be formed using a variety of materials by conventional processes including, but not limited to, forming an indium seal with heat and/or pressure. Furthermore,
Due to the fact that both the laser body 12 and the shell 28 of the cathode 22 are formed of a non-metallic, glassy material, the seal 32 is manufactured using the Mallory process.
88) can be formed by an electric field-assisted bonding process such as 88). In such a process, the glass cathode and laser body are heated to a temperature of 300°C to 400°C;
On the other hand, a potential voltage is applied between the cathode and the laser body. As the device is heated, its conductivity increases and current flows through the cathode-laser body interface. The current causes diffusion of aluminum atoms from layer 30 into the glass. As a result, a strong and permanent bond is formed. The bond is not subject to the damage modes characteristic of conventional glass-to-metal bonding, including bonding that utilizes the melting point of indium, for example.

Thus, it can be seen that the present invention provides an improved method and apparatus for the laser manufacturing art. By using the present technique, a laser device with improved durability for use in thermal environments is provided. That thermal environment significantly degrades operational performance without the present invention. Moreover, by using the technique of the present invention, advantageous bonding steps not applicable to the prior art may be used to achieve the aforementioned results.

[Brief explanation of the drawing]

The drawing shows a cross-sectional view of a laser according to the invention. [Explanation of symbols of main parts] Overall hemispherical shell...28 Layer made of aluminum...30

Claims (1)

Claims: 1. (a) A generally hemispherical hollow shell made of a material having preselected thermal properties. (b) An improved racer cathode characterized in that said layer has a layer comprising aluminum on its inner surface. 2. The improved laser cathode of claim 1, wherein said layer comprises glass. 34. An improved laser cathode according to claim 1, characterized in that the layer comprises quartz.
cathode. 4. The improved laser cathode of claim 1, wherein said layer comprises a preselected glass ceramic. 5. An improved laser cathode according to claim 1, 2, 3 or 4, characterized in that said layer is aluminum. 6. An improved laser cathode according to claim 1, 2, 3 or 4, wherein said layer comprises a preselected aluminum alloy. 7. A method of forming a thermal seal between a laser shell of a low thermal coefficient material and a cathode, comprising: (a) forming a shell of the cathode of a low thermal coefficient material; 1. A method of forming a thermal seal, the method comprising the step of sealing. 8. The method of claim 7, wherein the cathode shell comprises glass. 9. The method of claim 7, wherein the cathode shell is quartz. 10. The method of claim 7, wherein the cathode shell comprises a preselected glass ceramic. 11.Claim 7, 8, 9 or 1
The method of claim 0, comprising forming a layer containing aluminum on the inside of the cathode. 12. The method of claim 11, wherein the layer is aluminum. 13. The method of claim 11, wherein the layer is an alloy of aluminum. 14. The method of claim 7, wherein the cathode is pressure sealed to the laser body. 15. A method according to claim 7, characterized in that the cathode is sealed to the laser body with the aid of an electric field. 16. A generally hemispherical body comprising: (a) a laser body; and (b) a laser cathode sealed to said body, said cathode being formed from a material having preselected (3) characteristics. 1. A laser device characterized in that it has a hollow shell (i) in the form of an aluminum alloy, and (ii) the layer has a layer containing aluminum on its inner surface. 17. The laser device according to claim 16, wherein the layer includes glass. 18. The laser device according to claim 16, wherein the layer includes quartz. 19. Laser device according to claim 16, characterized in that said layer comprises a preselected glass-ceramic. 2. A laser device according to claim 16, characterized in that the laser cathode is sealed to the laser body with the aid of an electric field (4).