Effects of multiple ionization in atomic gases irradiated by one- and two-color ultrashort pulses.

The dynamics of femtosecond light pulses ionizing noble gases from single or multiple ionization schemes are numerically compared, with the emphasis on two-color pulses. We discuss the influence of multiply-charged ions on the excitation of harmonics in focused propagation and on the supercontinuum and clamping intensity of laser filaments. Depending on the atom’s first binding energy, multiple ionization based on Ammosov–Delone–Krainov (ADK) tunneling rates can increase the peak intensities, the number of harmonics or the spectral blueshifts, compared with quasistatic hydrogen-like rates. With two-color pulses, noticeable differences occur in the frequency domain corresponding to broadband terahertz pulses. [ABSTRACT FROM AUTHOR]