Electron Beam Excitation of Metal Vapor Excimers

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There have been many studies of alkali dimer diffuse bands because of the excimer-type nature.In this work, aimed at understanding the characteristics of the electrical excitation of such diffuse bands and achieving new tunable and high power excimer lasers, we report on the investigation of the Na_2 violet, K_2 yellow and Rb_2 red band emissions and gain measurements by electron beam pumping. The e-beam facility used in the experiment had a peak current of 15kA,a pulse width of 50 ns, and an electron particle energy of 300 keV.A net gain coefficient of 4.5% of the K_2 yellow diffuse band was observed from e-beam-excited mixtures of K/K_2 vapor with argon or helium buffer gas. The continuum spectra centered at 574 nm were attributed to triplet-triplet K_2 2^3II_g*1^3SIGMA^+_u bound-free transitions. Also, an ASE of the Na_2 violet, K_2 yellow and Rb_2 red bands were observed when the excitation energy density exceeded 5 mJ/cm^3. Calculated spectra of the Na_2 and K_2 2^3II_g*1^3SIGMA^+_u by using ab initio potentials are in good agreement with the observed one. The high population density of the 2^3II_g state was proposed to be due to the dissociative recombination of alkali trimer ions (Na_3^+, K_3^+ or Rb_3^+) which are efficiently yielded by electron beam excitation.K_3^++e^-*K_3^* (unstable) *K+K_2 (2^3II_g),Because the reaction energy difference delta E is 0.03 eV for Na and 0.28 eV for K.The process is predicted to have large cross sections. Thus, the upper state of such specific excimer transition may be produced selectively by this reaction kinetics following a very nonselective ionization. For this reason, the potential alkali dimer 2^3II_g*1^3SIGMA^+_u laser might be very suitable for electrically pumping. It is quite conceivable that such dissociative recombination-based excimer lasers might also be presented in the other metal vapor mediums.