Phase retrieval of complex ultrashort pulses using multiple-shearing spectral interferometry

A novel method for improving the precision of spectral shearing interferometry by using multiple shears is presented. Spectral shearing interferometry is a class of techniques which includes SPIDER, 2DSI and SPIRIT, in which the unknown pulse is interfered with a spectrally shifted replica. The pulse duration is limited by the inverse of the spectral shear and the spectrometer resolution. However, decreasing the spectral shear degrades the reconstructed phase signal-to-noise ratio because the reconstruction algorithm accumulates random phase noise at every sampling point. Here, this problem is solved by using multiple shears and combining the information in an optimal fashion. Intuitively, this algorithm resolves fine spectral features using a small shear measurement whilst using the finite differences from a large shear measurement to correct the accumulated error. This dramatically improves the precision of the retrieval in the presence of detector shot noise.