Theoretical study of ultrafast dephasing by four-wave mixing
Abstract
Microscopic dynamics. of materials can be studied by time delayed four-wave mixing spectroscopy. Dephasing constants can be measured by such experiments. Experimental results are easily analysed when the correlation time tau_c of the exciting electric field is much shorter than the dephasing time T2 However when these quantities are on the same time scale numerical fits are necessary. In the present work we analysed theoretically a time delayed four-wave mixing experiment. The material is described by an ensemble of two-level systems and a large inhomogeneous broadening is assumed. Using the third order term of the density matrix we establish a relation between T2, tau_c and tau_m the time delay for which the maximum of the diffracted light intensity is observed. The conditions to obtain an estimate of T2 from the measurement of tau_m are discussed.