Controlled shaping of ultrafast electric field transients in the mid-infrared spectral range

We experimentally demonstrate amplitude and phase shaping of femtosecond mid-infrared pulses in a range centered about $14 \mathit{\mu }\mathrm{m}$. Single pulses with a tailored optical phase and phase-locked double pulses are generated by phase-matched difference-frequency mixing in a GaSe crystal of near-infrared pulses shaped with a liquid-crystal modulator. The electric field transients are directly measured by free-space electro-optic sampling, yielding pulse durations of 200–300 fs. Our data are in good agreement with a model that describes phase-matched optical rectification.