Highly sensitive direct characterization of femtosecond pulses by electro-optic spectral shearing interferometry

We report what is to our knowledge the first experimental demonstration of spectral shearing interferometry by use of an electro-optic temporal phase modulator to generate the spectral shear. This approach achieves far better sensitivity than nonlinear optical pulse characterization techniques, including other versions of spectral shearing interferometry. Temporal phase modulation is conceptually simple and is implemented easily with telecommunication components. The technique is versatile, and a wide range of pulse durations can be measured with minimal changes in the setup. We demonstrate the accurate characterization of a 156-MHz train of 1540-nm pulses with durations ranging from 750 fs to more than 30 ps after various amounts of chirping, at average powers below 1 microW.