Preparation and decay of unstable molecular states undergoing memory effects: Excitation by coherent electromagnetic pulses of arbitrary strength

It is shown that the preparation and decay of non-markovian dissipative systems can be handled without any restriction on both excitation intensity and memory strength. Any perturbative approximation in the treatment of non-markovian interaction is avoided. The theory is explicity related to physical models relevant to the problem of molecular radiationless decay. In this respect, it is shown that a quantitative evaluation of the “radiative state” time evolution along the lines of the recent paper by Rhodes can easily be performed whatever the strength of external interaction. It is emphasized that no quantum beat phenomenon may be interpreted in an unambiguous way in the absence of any information on the dissipation coupling. As a new effect of coherent excitation on the nature of the excited state, it is shown that increasing light intensity may allow the molecule to be prepared in the “radiative state” without using 4 excitations. It is stressed, furthermore, that the excitation of a discrete set of states by long duration pulses has the effect of invalidating the replacement of a complex molecular system by a more simple one, which in turn is to be regarded as the basic idea of the theory. The above physical circumstance seems to be the unique one under which the present approach is no longer applicable. Evidence for this statement is provided by a quantitative simulation of hypothetical experiments of the same kind as the recent ones by Zewail et al.