Coherent interaction of resonance radiation with many-level systems

A study is made of the resonant interaction of monochromatic radiation with many-level weakly nonequidistant systems and also of the interaction of ultrashort radiation pulses with systems of the same kind when the carrier frequency of the pulses is near a resonance frequency. In both cases, equations are obtained that describe the interaction of the radiation with the many-level systems. Analytic solutions of the problem are obtained for a three-level equidistant system under certain additional assumptions. A way of reducing the problem to a set of homogeneous algebraic equations is indicated for the case of monochromatic radiation.