Ethanol Glass Dynamics: Logarithmic Line Broadening and Optically Induced Dephasing

The time and fluence dependence of the homogeneous line width of Zn-porphin in deuterated ethanol glass at 1.8 K is remeasured by stimulated photon echo. The observed spectral dynamics is interpreted in terms of the standard two-level system model and by using a commonly used modified version of it. It is shown, as was suggested recently, that time-dependent local heating is the cause of the plateau found in earlier echo experiments on this system. The anomalous intensity loss of the photon echo in the population dimension, however, is confirmed, as well as the existence of excess optical dephasing on a short time scale. The former effect is attributed to spontaneous frequency jumps outside the laser bandwidth, the latter to spectral diffusion induced by the change of electronic state of the chromophore. This phenomenon is not captured in existing theoretical models, which assume the probe molecule to be just a spectator of glass dynamics.