Wavelength tuning of a few-cycle laser pulse by molecular alignment in femtosecond filamentation wake

We show by means of numerical simulations that the quantum wake of impulsive molecular alignment provides a simple system to achieve frequency tuning of the broadband spectrum of a few-cycle pulse. A femtosecond pump pulse serves both to form a filament in a molecular gas and to align the molecules. A delayed few-cycle pulse probing the quantum wake is shown to experience a guiding mechanism. Its spectrum is red- or blueshifted while its duration remains comparable to the duration of the incident pulse, resulting in a controllable process to tune the frequency of a few-cycle laser pulse.