FEMTOSECOND HIGH-SENSITIVITY, CHIRP-FREE TRANSIENT ABSORPTION-SPECTROSCOPY USING KILOHERTZ LASERS

A simple method is demonstrated for high-sensitivity, chirp-free measu rements of femtosecond (fs) transient absorption over the entire bandw idth of a white-light continuum probe. This technique uses phase-sensi tive detection, with spectral scanning and simultaneous adjustment of the time delay between pump and probe pulses; it permits a direct meas urement of spectra undistorted by chirp at all time scales, limited on ly by the resolution of the fs source. The method is applied to study the ultrafast relaxation dynamics of rr-conjugated oligomers and semic onductor nanocrystals. (C) 1998 Optical Society of America.