Nonperturbative calculations of the indices of refraction of multilevel systems

It is pointed out that the past few years have seen a revival of interest in theoretical calculations of coherent pulse-propagation phenomena, especially in multilevel systems, as the result of suggestions that coherent propagation phenomena may affect the interpretation of experiments on molecular multiple-photon excitation (MPE). The present investigation is concerned with the propagation of a plane, nearly (but not exactly) resonant, quasi-monochromatic laser pulse through a general multilevel quasi-monochromatic electromagnetic field through a medium is described by using Maxwell's equations in the slowly varying amplitude and phase approximation and the Schroedinger equation in the rotating-wave approximation.