Transient behavior in the optical bistability mediated by phonon-mode and virtual-exciton coupling is studied for an electron-phonon-coupling system, such as polydiacetylene toluene sulfonate. Numerical calculations are used to analyze the evolution between bistable states, and switching behavior and Rabi oscillations are found.
For a polymer inside an optical cavity, optical multistability mediated by phonon modes and virtual exciton coupling is investigated. The cavity field, excitons, and phonon modes are treated as damped oscillators, and the equations of motion for the dynamical variables are obtained by applying Dekker's theory for dissipative systems. Steady-state results are obtained numerically for polydiacetylene [bis(p-toluene sulfonate)] with the input field frequency on or off resonance with the cavity field. The variation of the cavity-field intensity follows a reversed hysteresis loop on resonance, while it may follow either a normal or a reversed hysteresis loop off resonance depending on the course of change of the driving-field intensity at the unstable turning point. The variation is inverted when the detuning changes its sign. It is also found that the virtual excitons, phonon modes, and feedback of the cavity are all indispensable to such tristability.
Propagation of a light pulse in the bulk and hole bleaching in the absorption spectrum from a film of polydiacetylene-toluene sulfonate are investigated in the transient regime. This polymer is treated as an example of an exciton-phonon coupling system with only two phonon modes dominating the coupling. For the propagation, we use the Maxwell wave equation to express the field in terms of the polarization density, which is found microscopically from a set of optical Bloch-like equations in the semiclassical approximation. Phonon-mediated phenomena predicted in this work include the photon echo in a solid and bistable behavior of both the absorption coefficient and refraction index. The absorption spectrum is calculated for a thin film of an exciton-phonon system under a strong pump field and a weak probe field from the optical Bloch-like equations only. Phonon-mediated bleaching of holes is obtained in good agreement with experiments.
Abstract Nonlinear optical responses of exciton-phonon coupling systems near a reflecting surface are investigated. For a polydiacetylene chain lying parallel to the surface, optical bistability induced by the surface is discovered. It is also found that the threshold and contrast of the bistability can be controlled by adjusting the distance of the system from the surface, and that vacuum fluctuations are reduced whenever the bistability occurs. The nature of the bistability and its origin are discussed.
Abstract A joint effect of exciton–phonon and exciton–exciton interactions on optical properties of semiconductors is studied. In these substances the exciton density is shown to be a multivalued function of incident light intensity and the frequency and temperature conditions under which the optical bistability arises are specified. Investigation of nonlinear optical properties of semiconductors with account for the indirect phototransitions exhibits that both multistable optical states and the bistable ones distinguished by a complicated dynamics of the switching may be observed in such systems.
An investigation is reported of static and dynamic optical bistability and optical switching in a system of coherent excitons and biexcitons in semiconductors subject to the exciton-photon interaction and optical conversion of excitons into biexcitons. The Heisenberg equations of motion for excitons and biexcitons and the wave equation for the field are used to derive a system of nonlinear differential equations describing the dynamic evolution of such a system. The equation of state for a theory of optical bistability is derived for the static case. A study is made of the stability of stationary optical bistability states. A computer experiment is used in an investigation of the switching times between the branches