Abstract

We present a simple calculation of the frequency sweep imposed on femtosecond duration laser pulses interacting with a saturable absorber, including the effect of self-phase modulation (SPM) due to the nonlinear refractive index of the solvent. According to the intensity of the propagating pulse the contributions to the frequency sweep, due to absorber saturation and due to SPM in the solvent, can combine to produce a chirp that is positive or negative through the main part of the pulse. We have not included in our simplified model the effect of the nonzero phase memory time of the absorbing dye and have also disregarded the effect of group velocity dispersion in propagation of the pulse through the very thin (50-μm) dye jet.

© 1986 Optical Society of America