Apparatus for and method of operating a laser wherein a discharge is produced preferably in a high pressure lasing gaseous mixture comprising at least one suitable first gaseous species capable of providing an excited state which has a finite probability of being ionized and a molecular second gaseous species having a capability for attaching electrons to form negative ions. The gaseous mixture may, for example, comprise argon, neon, helium, xenon, krypton or a metal vapor such as mercury as the first species and, for example, hydrogen iodide, carbon tetrachloride, bromine, iodine or fluorine as the second species. A buffer gas such as, for example, argon, helium or neon may also be used. The discharge is produced by means of an electron beam and an electric field. The discharge resulting from the application of the electric field heats secondary electrons produced by the electron beam to an energy level sufficient to make excited states. Thus, for a mixture comprising argon, krypton and fluorine, for example, the heated secondary electrons pump at least some of the argon and the krypton to the metastable state. The excited argon transfers energy to the krypton to form additional excited krypton which, in turn, reacts with the fluorine to form excited krypton fluoride molecules. The krypton fluoride then dissociates or decays upon the emission of spontaneous or stimulated radiation. At power input levels where the electron density remains constant in time for a constant electric field, efficient discharge pumping of the excited states is provided when the fractional excited state population is kept small. Stable discharge operation is achieved when the lasing mixture contains an amount of the second species gas sufficient to provide an attachment rate n times the equilibrium ionization rate where n is the number of electron excitations which causes ionization of the first species.