Experimental and theoretical investigation of a multicolor filament

Generation of ultrashort ultraviolet (uv) pulses by using nonlinear frequency conversion through filamentation was experimentally and theoretically investigated. By gently focusing second harmonic and fundamental Ti:sapphire laser pulses into gases, ultrashort uv pulses were efficiently generated by four-wave mixing processes through filamentation. The pressure dependence of the conversion efficiency cannot be explained by a one-dimensional model, but calculation of multicolor filament by a three-dimensional model was successful. The simulation result indicates a broad scalability of the scheme for frequency conversion of ultrashort pulses. The generated two-color uv pulses (200 and 260 nm) were successfully compressed down to similar to 15 fs.