Programmable amplitude- and phase-modulated femtosecond laser pulses in the mid-infrared

We present a scheme to produce programmable phase- and amplitude-modulated femtosecond laser pulses in the mid-infrared regime of 3-10 mum by difference frequency mixing. The 80-fs signal output of an optical parametric amplifier is shaped with a liquid-crystal mask and mixed in an AgGaS2 crystal with a temporally stretched idler pulse. Without changing the mechanical alignment, we produce programmable amplitude modulations and chirped pulses at lambda = 3 mum with energy as high has thas 1 muJ. This scheme, further, allows the generation of controllable pulse sequences. The results are in good agreement with theoretical simulations. (C) 2002 Optical Society of America.