Phase retrieval and time-frequency methods in the measurement of ultrasnort laser pulses

Abstract

The recovery of an optical field with respect to position when only the intensity can be measured is an important problem in image science. In this case a priori information in the form of constraints can be applied and advantage can be taken of the inherently two-dimensional nature of the problem in order to reconstruct the full complex field from the available information. A similar recovery problem also arises with temporally varying data. One such case is the measurement of the complete time-dependent intensity and phase of an ultrashort laser pulse. This problem is particularly difficult for two reasons. First, it is inherently one-dimensional, so phase-retrieval methods, so successful for the spatial problem, do not directly apply. Second, such pulses are shorter than all possible measuring devices, so even the intensity cannot be measured. Traditionally, optical scientists working with ultrashort laser pulses have had only partial diagnostics, typically the intensity autocorrelation and the spectral intensity of the pulse. These diagnostics are not enough to completely characterize the laser pulse.