Calculated femtosecond optical response for trans-polyacetylene

Abstract

Summary form only given. A strong optical pump pulse applied to a polymer chain leads to vibrations of the electron energies and by electron phonon interaction to vibrating distortions of the chain. Besides soliton-like excitations, which are reflected by the chain ends there are breather-like oscillations of the chain. Using the SSH-Hamiltonian interacting with the external electric field in dipole approximation as a model for polyacetylene the time dependence of the coupled electron phonon system is solved numerically. Treating the dynamics of the chain classically the induced response to the electric field is calculated exactly. Particularly the energy absorption of a probe pulse is determined. The oscillating nature of the electron-phonon system results in a nearly periodic dependence of the absorption on the delay time between pump and probe pulse at pulse durations less than 100 fs. The delay time between pump and probe pulse is chosen to be less than 1 ps. One of the unexpected results is that the frequency of change in the absorption is much lower than the breather frequency. Since the chain is highly polarizable local field corrections are essential and are, therefore, included in the calculation of the absorption.