Two- and three-photon processes in atomic krypton and their use in laser guiding of electron beams

Abstract

Neutral krypton atoms were excited from the ground state 4p6 1S0 to the 4p5 6p[3/2]2 state by two-photon absorption from a line-narrowed ArF excimer laser operating at 193.41 nm. A third photon, absorbed while the atom is in the excited state, ionizes it. Excited state and ion densities were theoretically computed using a standard rate equation analysis. The irradiance levels used (1–5 × 108 W/cm2) were too low for significant ground and excited state ac Stark and Rabi effects. The photon detection system was calibrated with a standard tungsten lamp. Ion signals were measured with known electrical components. The resulting ion and excited state densities, corrected for collisional losses, agreed with the theoretical analysis to within 20% on the average. These results have been used with a modified electron beam propagation code to model such propagation in a low-pressure laser-excited krypton channel. The modifications included the effects of field ionization and enhanced collisional ionization of the excited krypton atoms.