Redshift of few-cycle infrared pulses in the filamentation regime

By focusing infrared (IR) pulses of low energy (∼0.4 mJ) into an argon cell at a pressure of a few bars, a supercontinuum is generated with a longwavelength tail that can exceed 1500 nm for initial pulse durations of ∼5 fs in the single-filamentation regime. Numerical calculations simulating the propagation of single- or few-cycle IR pulses show that this red-shift is enhanced by a sharp leading edge appearing in the pulse temporal profile, as the pulse undergoes break-up due to the interplay between Kerr self-focusing, strong dispersion and plasma generation. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.