Theory of continuum-Raman spectroscopy with pulses

A uniform theory of Raman scattering and resonance fluorescence from an intermediate dissociative manifold for excitation with pulses is developed. It is shown that transient effects lead to the appearance of additional terms, not included in the Kramers–Heisenberg formula. The role of ‘‘true’’ Raman scattering vs ‘‘resonance fluorescence’’ in contributing to the observed signal is elucidated. It is shown that the relative importance of these two processes is strongly dependent on the pulse parameters and the spontaneous emission lifetimes. ‘‘True’’ Raman is shown to dominate at very short times, during the rise of the pulse. At longer times resonance fluorescence sets in and dominates the observed signal. The important implications of the above to the time-averaged excitation-emission spectrum (the emission signal as a function of the excitation wavelength), with real ns pulses is discussed. The present study explains recent experiments showing rich structure in the excitation emission spectrum of IBr [I. Levy et al., J. Chem. Phys. 96, 1858 (1992)].