Three-wave mixing and light diffraction by transient light induced gratings for the study of fast relaxation processes

The action of two successive intense ultrashort coherent light pulses with different wave vectors k(1) and k(2) on a nonlinear inhomogeneously broadened medium is considered. The resulting spatial and temporal polarization and saturation structure is calculated within a two level density matrix approach. Without use of perturbation theory, both the dynamic behavior of the nonlinear medium under hole burning conditions and the temporal behavior of the output pulse in the 2k(1)-k(2) direction generated by the polarization of the medium during and after the action of the second pulse are discussed. The diffraction of a third probe pulse by the saturation grating as well as by the polarization of the medium is calculated. Possibilities for measuring the longitudinal, transverse and inhomogeneous relaxation times are discussed.