FLUORESCENCE INTERFERENCE NOISE IN A 2-SITE SYSTEM - EXCITATION TRANSFER DYNAMICS FROM INTENSITY FLUCTUATIONS

The optical response of a two-site system driven by a pair of optical pulses in an interferometric set up has been studied theoretically by applying the density operator formalism. The one-exciton approach is t aken for modeling two coupled two-level systems (TLS), the external fi eld is presented semiclassically and bath-induced dissipative processe s are included. In the delta-pulse limit the population of the excited state has been formulated to the lowest order perturbation expansion in the external field. In the limit of slow luminescence the interfero gram of time-integrated total fluorescence has been calculated for pul ses with constant relative phase. For phase-randomized pulses the vari ance of the correlated fluorescence signal as a function of the pulse delay allows direct interrogation of coherent transients and dephasing processes. Our analysis follows the principle of coherence observatio n by interference noise, COIN [O. Kinrot, I. Sh. Averbukh, and Y. Prio r, Phys. Rev. Lett. 75, 3822 (1995)], but is a generalization of this concept to expand on electronically interacting TLS. The theoretical r esults demonstrate that analysis of fluorescence interference fluctuat ions may provide a powerful diagnostic tool for probing the initial qu antum coherence of energy transfer, i.e., excitation oscillations by e mploying fs-fluorescence correlation measurements in stable interferom etric configurations. (C) 1998 American Institute of Physics. [S0021-9 606(98)00740-5].