title: Simulation of four-wave mixing signals by a perturbative approach: application to ultrafast two-dimensional infrared spectroscopy.
abstract: We propose an alternative method for the calculation of the phase-matched contributions, which are responsible for the third-order optical signals measured in four-wave mixing experiments. In particular, we extend the strong field dissipation theory of Meier and Tannor [J. Chem. Phys. 111, 3365 (1999)] to the case of a perturbative treatment with respect to the exciting laser fields. Our approach is based on an analytical expression of the third-order density matrix and hence it does not require to verify numerically the irrelevance of higher order terms or the calculation of a spatial Fourier transform. In order to illustrate this method, we simulate the experimental signal measured in femtosecond two-dimensional infrared (2D-IR) vibrational spectroscopy. We consider an intramolecular anharmonic vibrational mode modeled by a Morse potential and coupled to a dissipative bath of harmonic oscillators. We calculate the 2D-IR correlation spectrum and we discuss the influence of the population decay on the line shapes. In particular, we compare two situations, one where only pure dephasing processes are considered, and another one where phase losses due to population relaxation are also taken into account. We show that the shape of the peaks observed in a 2D-IR correlation spectrum differs in these two cases, and therefore this difference appears as a signature of population decay and gives information on the importance of pure dephasing processes in phase loss mechanisms.
authors.affiliation: Département d'Optique ultra-rapide et de Nanophotonique, Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504 ULP-CNRS, 23 Rue du Loess, B.P. 43, 67034 Strasbourg Cedex 2, France. jean-pascal.lavoine@ipcms.u-strasbg.fr
authors.forename: J P
authors.initials: JP
authors.lastname: Lavoine