Nonlinear ionization of pure atomic and molecular gases by intense UV femtosecond laser pulses

Mechanisms of nonlinear absorption and ionization of pure atomic argon and molecular nitrogen gases by UV femtosecond laser pulses were studied using photogalvanic and photoacoustic techniques. The effect of the intermediate Rydberg resonance, its dynamic Stark perturbation and ponderomotive upshift of the first ionization potential of argon atoms and nitrogen molecules by the intense laser pulses has been revealed by observing an increase of a power slope of ion yield from three to four at increasing laser intensity.