Investigation of blueshift of supercontinuum from femtosecond filament plasma grating

A blueshift in frequency spectrum is observed in the supercontinuum radiation from a plasma grating, which is formed by the laser field interference in the overlap region of two noncollinear femtosecond plasma filaments. These two pump laser pulses show different profiles in their supercontinuum radiation. Both the energy exchange between two pump laser pulses and the blueshift are caused by the plasma grating within a 200-fs relative time delay between the pump laser pulses. Thus, these two processes are induced by the propagation of the laser pulses in the plasma. In addition, this blueshift of the supercontinuum from one filament is enhanced when the other filament increases its pump laser energy. The possible mechanism of this blueshift is also discussed. This offers a method of broadening and tailoring the supercontinuum radiation from the femtosecond plasma filament.