| abstract |
Preionization is achieved in transverse-discharge gaseous lasers by means of the Malter effect. In two embodiments, the preionization is achieved either with a metal electrode which is the cathode during preionization and then is the anode during the subsequent pumping phase, or by means of a separate set of preionization electrodes. These preionization cathodes are metal electrodes, such as aluminum or tantalum electrodes, exhibiting high secondary electron emission by the Malter effect. High-field electron emission from these preionization cathodes is inherently possible because of a thin insulating layer on the surface. This layer separates positive ions attracted to the surface from the conducting metal and thereby creates a very high field gradient over a very short distance. In a preferred embodiment, uniform initial ionization is created during the preionization phase of operation; and the excitation is supplied by an electric field which is lower than that required to sustain the discharge; and the active medium is enclosed in an optical waveguide free of interfering structure. |