LASER IONIZATION OF NOBLE-GASES BY COULOMB-BARRIER SUPPRESSION

Laser ionization of noble gases was studied with a 1.053-mu-m, 1-psec Nd:glass laser. A systematic scan of intensities from mid-10(13) W/cm2 to mid-10(16) W/cm2 was performed, resulting in the production of charge states as high as Xe12+. Ionization occurs exclusively in the tunneling regime. We compare experimental ion production rates with those predicted by several different theories. Agreement between experimental ion-production curves and theoretical predictions is good for two theoretical models: (1) an elaboration of the Keldysh tunneling model, developed by Ammosov et al. [Sov. Phys. JETP 64, 1191 (1986)] and (2) a much more primitive model, based on Coulomb-barrier suppression, in which tunneling and other quantum-mechanical effects are ignored completely. The success of the more primitive model suggests that a new term, barrier-suppression ionization, rather than tunneling or multiphoton ionization, may be the most appropriate at this wavelength and in this range of intensities.