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 compare the observed relaxation times for vibronic coherence using photon echo (PE) and reverse transient grating (RTG) measurements at different temperatures to isolate inhomogeneous and homogeneous components. Different pulse sequences are used to select ground or excited state vibrational coherences. Measurements of ground and excited state wave packet spreading times due to anharmonicity, a process that does not involve energy dissipation or phase relaxation, are also presented.