Sensitivity improvement of spectral phase interferometry for direct electric-field reconstruction for the characterization of low-intensity femtosecond pulses

A modified-SPIDER (spectral phase interferometry for direct electric-field reconstruction) technique where external powerful optical pulses are employed as a light source of chirped reference pulses for sum-frequency generation is proposed and is demonstrated experimentally. It provides great improvements in sensitivity and signal-to-noise ratio, and will enable a single-shot measurement for a weak pulse, such as 1 nJ/THz-bandwidth. The technique demonstrates high accuracy for determining the delay-time, t, for weak pulse characterization, which greatly affects the group-delay dispersion of the reconstructed spectral phase.