Femtosecond photon echo and virtual echo measurements of the vibronic and vibrational coherence relaxation times of iodine vapor

Femtosecond three-pulse four-wave mixing (FWM) techniques are used to sort and measure the processes that contribute to coherence relaxation. We compa re the observed relaxation times for vibronic coherence using photon echo ( PE) and reverse transient grating (RTG) measurements at different temperatu res to isolate inhomogeneous and homogeneous components. Different pulse se quences are used to select ground or excited state vibrational coherences. Measurements of ground and excited stale wave packet spreading times due to anharmonicity, a process that does not involve energy dissipation or phase relaxation, are also presented. (C) 2001 Elsevier Science B.V. All rights reserved.