Abstract

A convenient technique to estimate the duration of femtosecond pulses is the measurement of second-order intensity-autocorrelations. However, a disadvantage of this method is that it delivers no information about asymmetry of the pulses measured. Higher order autocorrelation functions could principally overcome these problems, but they usually are difficult to perform with low-repetition-rate systems. The method proposed by us utilizes the fact that self-phase modulation in an n₂-medium is sensitive against pulse asymmetries and allows us to determine an integral asymmetry parameter. The quantities that are necessary are the spectrum of the original pulse and the spectrum after suitable self-phase modulation. By moving the sample along the focused beam, this spectrum can be adjusted to show a characteristic modulation. The features of this modulation contain information concerning the pulse asymmetry, which can be derived by a fitting procedure. Several pulse shapes and asymmetries as well as the influence of chirp for the applicability of this method are discussed.

© 1992 Optical Society of America