Response-theory for nonresonant hole burning: Stochastic dynamics

The time signals relevant for nonresonant spectral hole burning, a pump-wait-probe method designed to investigate slow relaxation, are calculated. The step-response function following the application of a high amplitude ac field (pump) and an intermediate waiting period is shown to be the sum of the equilibrium integrated response and a modification due to the preparation via ac irradiation. Both components are calculated for a class of stochastic dipole reorientation models. The results indicate that the method can be used for a clearcut distinction of homogeneously and heterogeneously broadened susceptibilities as they occur in the slow primary relaxation of supercooled liquids and other disordered materials. This is because only in the heterogeneous case is a frequency selective modification of the response possible.