Ultrashort-pulse characterization from dynamic spectrograms by iterative phase retrieval

We develop a modified version of the dynamic spectrogram that permits complete characterization of an ultrashort optical pulse with fewer approximations than do other schemes. The experimental procedure for such a measurement uses a second-order optical nonlinearity and yet yields an intuitive spectrogram with no inherent symmetry constraints or ambiguity. We describe and demonstrate pulse-shape reconstruction from this type of spectrogram. Phase retrieval is performed by means of an iterative algorithm.