We show that the resonant interaction between a field mode and a pair of vibronic levels is influenced by dynamical coupling to nonresonant states. The dependence of the occupation probability of vibronic states on dipole coupling, displacement, and resonance condition is discussed.
Taking into account the vibronic-level structure in a laser medium, we study the influence of electron-vibration interaction on the field dynamics. Different vibronic transitions are coupled in the medium through this interaction and contribute to the emission from excited states, thus coupling different field modes in the cavity and influencing the field dynamics. A general model is presented and solved in a simple example of four coupled transitions. In particular, the effect of degenerate transitions is stressed.
The resonance fluorescence from a vibronic system with displaced potential-energy surfaces is studied. Because of the equal vibrational frequencies in the two electronic quantum states, a large number of vibronic transitions can be excited by a strong laser field. Even in the case of weaker driving fields, nonperturbative effects may be observed provided that the vibrational relaxation is slow enough. If the vibronic coupling is not extremely strong, the Rabi oscillations will arise mainly from the excitation of the vibrationless transition. Furthermore, the damping of the Rabi oscillations may be accompanied by a substantial decrease in intensity.
Using the model of displaced potential energy surfaces, we studied the spectrum of the resonance fluorescence light from vibronic systems. In this model, equal vibrational frequencies in the two electronic quantum states allow many vibronic transitions to be in resonance with a monochromatic driving laser field tuned to the electronic transition frequency. Level splittings in the strong-field case give rise to a multiple-line spectrum of the scattered light. In particular, the Rayleigh component consists of a superimposed series of triplets, whereas the Raman part is built up by superimposed quadruplets.
The problem of resonant interaction between an electromagnetic radiation field and a vibronic system, such as a molecule or a localized electronphonon system, is considered. The vibronic coupling is assumed to result from displaced and distorted potential energy surfaces for the vibrational motion in the electronic quantum states involved in the resonant interaction with the radiation field. Furthermore, the vibrational energy relaxation is taken into account without assumptions about Markovian-type relaxation. In order to study correlation properties of higher than second order in the electric field strength of the light emitted a method of calculation of the expectation value of an arbitrary product combination of effective time evolution operators of the vibronic system is developed. The calculations are performed by utilizing Feynman's disentangling and operator ordering techniques and yield closed solutions in the low-temperature limit. The theory is used for studying the intensity and the normally ordered intensity correlation function of the resonance fluorescence light from a two-atom molecule excited by a relatively weak laser field, which undergoes phase fluctuations. It is shown that the vibronic coupling can give rise to an anticorrelation effect which is substantially stronger than in the case of resonance fluorescence from an atom. For the case of small vibrational damping a general formula which directly connects the asymptotic long-time behaviour of the normalized intensity correlation function with the vibrational relaxation in the molecule is deduced. It should be convenient for the determination of very small vibrational decay rates.