My major research subjects center on electron correlation effects in low dimensional systems, optical instabilities, enhancement mechanisms, excited state nonlinear optics, and ultrafast nonlinear optical processes. When an open atomic system is driven far from equilibrium by an external source, it may jump from an initial stationary state of independent atomic motion to a macroscopic ordered state of cooperative motion due to nonlinear coupling between the atoms and the external field. A major physical realization of such instability phenomena is optical bistable transmission in which an external coherent optical field resonantly drives a nonlinear optical material contained in an optical cavity to new nonequilibrium stationary states of broken symmetry. The nonlinear electronic excitations in random glassy media comprised of low dimensional polymers, or quantum confined semiconductor structures, can provide the large nonlinearity essential to the direct onset of bistability at fast and ultrafast timescales. In nonresonant nonlinear optical processes in electronic systems, the real population for the virtual optical excitations can be either the usual singlet ground state or an optically pumped excited state.
Similar phenomena can occur at ultrafast femtosecond timescales as well.
Rev. A, 1990.