Abstract

Spectrally broadband, temporally ’’incoherent” light has been employed to obtain femtosecond time resolution in various nonlinear optical experiments by exploiting the fact that in many such processes it is the coherence time of the light source, not the duration of its pulse intensity envelope, that dictates the temporal resolution of the experiment.¹-⁴ One such process is the photon echo configuration of time-resolved four-wave mixing,⁵-⁹ which can distinguish the contributions to molecular electronic spectral linewidths from "homogeneous” and ’’inhomogeneous” broadening if the latter is static on the time scale of the entire matter-radiation interaction sequence. In liquids, spectral difiusion--the interconversion of spectroscopically different local environments for different chromophores--is usually fast relative to the actual pulse durations of most incoherent light sources, complicating efforts to study electronic dephasing with such sources. When femtosecond pulses are used, the overall time scale of the experiment can be made subpicosecond if desired, or it can be made arbitrarily long by employing the three-pulse technique. No such tunability is possible when the light source has a temporally long intensity envelope, however short its correlation time.

© 1994 Optical Society of America