Abstract:
A laser discharge tube is provide having a ceramic rod of rectangular cross section through which extends a discharge channel and at least one gas return channel, and cooling plates affixed at the larger outside surfaces of the rectangular ceramic rod.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a gas laser having a discharge channel in a discharge tube. 
     2. Description of the Related Art 
     A gas laser is disclosed in U.S. Pat. No. 3,753,144, showing examples of formats of gas lasers. In a first exemplary embodiment, a thin discharge tube and a separate gas return tube are provided. The first embodiment is not suitable for mounting mirrors on the discharge tube since differences in thermal expansion between the laser tube and the gas return line can cause misalignment of the mirror. On the other hand, another example shows the laser discharge capillary and the gas return channels accommodated in a relatively wide ceramic tube. Such arrangement generally exhibits a poor heat transfer characteristic from the capillary to the outside wall. Therefore, complex measures must be undertaken for heat dissipation. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an improved heat transfer characteristic in a gas laser while also providing adequate mechanical strength and stability with respect to temperature fluctuations, and at little costs. 
     This and other objects are achieved in a gas laser having a discharge channel and at least one gas return channel formed within an elongated ceramic rod having a substantially rectangular cross section. The rectangular cross section of the ceramic rod provides adequate mechanical stability to the gas laser along with extremely good thermal stability. The improved thermal stability is aided by an appropriate arrangement of the discharge channels and the gas return channels. It is possible to integrate the gas return channels into the ceramic rod of the present invention. Particularly low thermal stresses result during operation of the gas laser when the laser discharge channel lies along an axis of symmetry of the ceramic rod and two of the gas return channels, each of circular cross section and the same diameter, are provided symmetrically spaced on either side of the discharge channel. 
     A plurality of cooling devices, such as cooling plates, are affixed to the outside of the ceramic rod for heat dissipation. The wall thickness of the ceramic rod between the discharge channel and the cooling plates is kept very thin so that heat is quickly eliminated by the cooling plates, thereby preventing thermic warping. The cooling plates for the present gas laser are affixed to at least the two opposed elongated surfaces of the ceramic body, and are preferably attached only at the two wider outside surfaces of the rectangular ceramic rod, since the majority of the heat generated by the operation of the gas laser is present there. In one preferred embodiment, the cooling plates have the same width as the ceramic rod. In this embodiment, manipulation of the ceramic rod results in relatively little loading with mechanical stresses. Furthermore, even during temperature fluctuations, the cooling plates provide extremely favorable temperature distribution. 
     In order to further improve the distribution of stresses due to temperature fluctuations and to provide particularly accurate mirror positions for the resonator mirrors, an embodiment of the ceramic rod is provided having 2n gas return channels that are uniformly distributed at both sides of the discharge channel, and symmetrically spaced therefrom. The 2n gas return channels are provided where n is a positive whole number. Preferably, n is equal to either one or two. 
     Thus, the present invention provides a gas laser which is relatively simple to manufacture and has a particularly favorable temperature distribution characteristic within the ceramic rod. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a gas laser incorporating a laser discharge tube according to the principles of the present invention; and 
     FIG. 2 is an enlarged cross section along the line II--II of FIG. 1 showing the discharge tube of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A gas laser is provided having a discharge tube 1 carrying resonator mirrors 5 at its respective opposite end faces to produce an optical resonator for laser light. The discharge tube 1 is also connected to electrode parts 3 and 4. A middle portion, or rod, 2 of the discharge tube 1 extending between the electrode parts 3 and 4 is of generally rectangular cross section and is provided with cooling plates 7. 
     As can be seen in FIG. 2, the cooling plates 7 are secured to an outside surface 6 of the rectangular midportion 2 of the discharge tube 1. As can be seen, the cooling plates 7 have the same width as, and are secured to, the two wider surfaces of the outside surface 6 of the rectangular midportion 2. 
     A discharge channel, or capillary, 8 extends concentrically along an axis of symmetry 10 of the discharge tube or rod 2. Gas return channels 9 are also provided arranged at identical distances from the axis of symmetry 10 and lying opposite one another. 
     The discharge tube, or rod, 1 is of a ceramic material. In a preferred embodiment, the ceramic tube or rod 2 is composed of Al 2  O 3  ceramic; and the cooling plates 7 are preferably of copper. 
     Due to its rectangular shape, the ceramic rod 2 has a very small wall thickness between the discharge channel 8 and the cooling plates 7 so that heat generated in the discharge channel 8 is quickly dissipated to the cooling plates 7. The cooling plates 7 distribute the heat over the width of the ceramic tube 2, among other things, so that the ceramic tube 2 is heated uniformly, or respectively, cooled uniformly over its width. A relatively small, highly loadable embodiment of a laser discharge tube which is insensitive to thermal stresses is thereby provided. 
     The width of the ceramic rod 2 provides physical strength to withstand handling and to ensure that accurate alignment of the mirrors 5 is maintained. The symmetrical arrangement of discharge and gas return channels provides stability during thermal expansion and contraction. 
     Thus, a laser discharge tube 2 as disclosed herein has relatively great mechanical strength and high temperature transfer capabilities. The laser beam precision is high since misalignment of the resonator mirrors 5 is less likely with the present discharge tube. An example of a laser in which the present discharge tube can be used is an argon laser having a power output in the milliwatt range. 
     Although other modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.