Ultrashort pulse characterization in the mid-infrared.

We describe a second-harmonic-generation frequency-resolved optical gating measurement device optimized for the characterization of few-cycle pulses in the mid-IR spectral range. The system has a temporal range of 100 ps with resolution of 0.12 fs, and it is capable of measuring pulses as short as 1.5 cycles (15 fs) at 3 microm. Through interchangeable beam splitters and detectors it covers a wavelength range from 800 nm to 5 microm with up to 0.5 cm(-1) resolution. We demonstrate measurement of a richly featured 3.2 microm pulse with 9.6 cycle duration, recovering the main pulse of 96 fs, as well as low-intensity post-pulses with picosecond offset. We also characterize a 100 fs pulse after dispersion through a 1 cm sapphire plate, comparing the measured phase difference with the calculated one.