COHERENT TRANSFER FROM FLUORESCENCE INTERFERENCE NOISE

The optical response of a finite-level system (FLS) to classical optic al field having two subsequent delta-pulses was studied by applying th e density operator formalism. The response of FLS has been developed f or spontaneous fluorescence for the case where the population relaxati on is much longer than the coherence relaxation. For a pair of time-de layed pulses with random relative phase the variance of the noisy corr elated fluorescence signal as a function of the pulse delay allows dir ect access to (coherent and incoherent) energy transfer rates. We show that the predicted COIN signal of some bichromophoric molecules (a) h as an undulatory pattern (direct evidence of intermoiety resonant tran sfer). (b) contains information on inter-site incoherent transfer. The COIN spectroscopy approach is a very stable and robust method which m ay provide a powerful diagnostic tool for 'visualizing' different tran sfer regimes present in FLS. (C) 1998 Elsevier Science B.V. All rights reserved.