Time and frequency resolved femtosecond solvent dynamics

An optimized heterodyne method which recovers the electric held of four-wav e mixing signals as they exit the sample is used to probe femtosecond solva tion dynamics in methanol. A cyanine dye (IR144) which has a dipole moment change upon electronic excitation is used as a probe of solvent fluctuation s and reorganization. A single four-wave mixing field provides the spectrum and time resolved intensity of the signal, which reflect ensemble averaged solvent dynamics. The microscopic solvent dynamics can be revealed by doub le Fourier transformation of many four-wave mixing fields with respect to t he experimentally controlled initial dipole oscillation period and the fina l dipole emission time. (C) 2000 Elsevier Science B.V. All rights reserved.