Optical bistability is a quantum optical realization of a first order phase transition far from equilibrium. A nonlinear optical material contained in an optical cavity driven resonantly by an external coherent optical field undergoes a first order phase transition to a new nonequilibrium stationary state of broken symmetry. Resonant and nonresonant nonlinear optical response of
pi-electron excitations in conjugated electronic structure provides the nonlinearity essential to the onset of bistability. Electronic correlation effects in reduced dimensions are responsible for nonresonant nonlinear optical responses. Saturable absorption studies of glassy polymer films consisting of quasi-two dimensional conjugated disc-like structure of silicon naphthalocyanine demonstrate that on-resonance the system behaves as an optical Bloch system with an intensity dependent refractive index of 1
times 10
sp−4 cm
sp2/kW. Based on the results of these studies, electronic absorptive optical bistability is observed on a nanosecond time scale in a nonlinear Fabry-Perot interferometer employing the saturable absorbing silicon naphthalocyanine film as the nonlinear optical medium.
We study quantum interference and nonlinear optical processes in the conduction band of an n-doped quantum well driven by one or two infrared fields. The fields couple a broad upper subband to a lower energy subband and the ground subband, forming a \ensuremath{\Lambda} configuration. We show, including the effect of electron-electron scattering and dynamic screening, that this configuration can lead to coherent control of the intersubband transitions, such as coherent population trapping. We also study quantum interference processes, such as laser-induced transparency and dark-line effects in the linear absorption and gain spectra of the system. The effects on these processes of differing field intensities and of electron-electron scattering are also discussed.
We study theoretically the Kerr nonlinearity of a probe field in the presence of a near resonant pump field in a two-subband system in a semiconductor quantum well structure. In our study we take into account the effects of electron–electron interactions and consider the interaction of the two-subband system with rectangular electromagnetic fields. For the description of the system dynamics we use the nonlinear differential equations of the density matrix elements for the several nonlinear optical processes, under the rotating wave approximation. These equations are solved numerically for a GaAs/AlGaAs quantum well structure. We show that the Kerr nonlinearity of a driven two-subband system can be significantly dependent on the frequency and the intensity of the pump field and on electron sheet density.