Obituary

By the use of the quantum regression theorem the two-time dipole correlation function is calculated for a system characterized by the well-known phenomenological two-level density matrix. Calculation of the scattered light spectrum in the weak signal limit yields a lineshape containing a sharp component following the exciting light frequency and also a broad component characterized by the dephasing width. When no dephasing is present the result is the same as the isolated molecule result. The calculations indicate that broad fluorescence type emission is due to the presence of ensemble correlations which are important oly if the exciting field is present and if real dephasing processes occur. The relationship between these results and the semiclassical results is also discussed.