Characteristics of femtosecond laser pulses propagating in multiply ionized rare gases

A three-dimensional non-adiabatic model in combination with a rate equation model is used to characterize high-intensity (>1016 W/cm2) femtosecond laser pulse propagation in atomic gas medium. In these conditions the atoms in the target gas will become multiply charged ions, while the laser pulse will propagate in a medium with high electron concentration created by itself. We obtain pulse characteristics in time, frequency and space domain for two representative cases: 800 nm and 267 nm (third harmonic) multi-cycle pulses which are both of practical importance. We show that the spatial-temporal variation of the refractive index in the macroscopic medium is the primary reason for pulse temporal/spectral and spatial shaping during propagation.