STRONG-FIELD THEORY OF NONLINEAR POLARIZATION SPECTROSCOPY - FUNDAMENTALS AND THE 2-LEVEL SYSTEM

To formulate a description of nonlinear polarization spectroscopy that is valid over a wide range of pump intensities, we present an approac h that considers any order of the external fields. The Liouville von N eumann equation governing the dynamics of a multilevel molecular syste m is made tractable by expansion of the particular density matrix into powers of the carrier waves of the external fields. For a two-level s ystem a solution of the resulting set of equations to first order of t he probe field but to all orders of pump field is demonstrated. A rema rkable change in the homogeneously broadened line shape is obtained at high pump intensities, caused by the optical Stark effect among other s. Improvements over results derived by other authors are discussed. ( C) 1997 Optical Society of America.