NONRESONANT DIELECTRIC HOLE-BURNING SPECTROSCOPY OF SUPERCOOLED LIQUIDS

The nonexponential response of propylene carbonate and glycerol near t heir glass transitions could be selectively altered using nonresonant spectral hole burning (NSHB) experiments. This observation provides ev idence of the existence of a distribution of relaxation times in these supercooled liquids. NSHB is based an a pump, wait, and probe scheme and uses low-frequency large amplitude electrical fields to modify the dielectric relaxation. The temporal evolution of the polarization of the sample is then measured subsequent to a small voltage step. By var iation of a recovery time inserted between pump and probe, the refilli ng of the spectral features could be monitored and was found to rake p lace on the time scale set by the peak in the distribution. The recove ry time and pump frequency dependences of the spectral modifications w ere successfully simulated using a set of coupled rate equations. (C) 1997 American Institute of Physics.