Efficient amplification and tunable frequency conversion of femtosecond pulses

A two-stage femtosecond pulse amplification scheme is reported that is based on a pulse stretching-recompression procedure. Starting with 30 fs pulses of 10 nJ of a non-cw dye laser system, pulses of 50 fs duration are obtained with 60 μJ energy at 565 nm. An energy conversion efficiency of 2% is accomplished for the dye amplifier using pump pulses of 2 ns and a highly viscous solvent. Tunable femtosecond pulses are demonstrated by continuum generation of the amplified fs pulse in a 2 mm quartz plate and subsequent filtering in a graded interference filter in a spectral range larger than 200 nm. Cross correlation measurements indicate a duration of the converted pulses as short as 50 fs, close to the Fourier transformation limit.