Longitudinal spatial inhomogeneities in optical bistability due to induced absorption

Ian C. McMichael, Pochi Yeh, M. Khoshnevisan

Greg R. Olbright, H. M. Gibbs, Nasser N. Peyghambarian +3 more

Charles M. Bowden, Chi C. Sung, Joseph W. Haus +1 more

Longitudinal spatial effects in the nonlinear medium are analyzed in a model for mirrorless optical bistability due to induced absorption that treats heat conduction, electromagnetic field propagation, and temperature-dependent absorption. We consider two specific cases: the temperature-induced shift of the absorption peak of bound I2 excitons in CdS single crystals and the temperature-induced shrinkage of the band gap in GaAs/GaAlAs quantum-well material. For both cases it is shown that the inhomogeneous spatial distribution of the nonlinear absorption profile along the direction of propagation of the electric field undergoes a first-order-like phase transition commensurate with the transition of the output intensity from one value to another for fixed input intensity. Stability conditions are presented for the steady states of the output intensity as a function of the input intensity for the cases treated. There is a multiplicity of bistability curves, and the stability analysis produced the expected branches of stable solutions.

H. I. Carmichael, J.A. Hermann

Joseph W. Haus, Li Wang, Michael Scalora +1 more

Using the nonlinear oscillator model as a prototype medium exhibiting intrinsic optical bistability, we investigate the inhomogeneous absorption of the electromagnetic field. The forward- and backward-field amplitudes and diffraction effects are retained in the mathematical description. Analytic results are given in the limit of plane-wave propagation under steady-state conditions. The transmitted and reflected intensity exhibit a structure that is determined by the spatial inhomogeneity of the absorption in the longitudinal direction. The transmitted intensity has a structure that is dependent on the length of the medium. The reflected intensity has an interference structure from light reflected at the front surface and the internal boundary separating a high-polarization from a low-polarization branch. A degenerate-four-wave-mixing experiment is predicted to be a very sensitive probe of the internal boundary and the interference between the forward and backward field. The phase-conjugate signal develops large oscillations as the input field is varied. Numerical results for diffraction effects are also given, and we find that the plane-wave results for the center of the beam remain reliable down to Fresnel numbers of order unity and in media that are smaller than the linear absorption length.

W. D. St. John, James P. Wicksted, Gene Cantwell

Absorptive switching and transverse structures in resonatorless optical bistability in bulk ZnSe is observed upon exciting the sample at the Urbach edge. The switching is due to nonlinear absorption induced by a temperature tuning of the band gap. We have modeled such behavior by numerically solving for the intensity, carrier density, and temperature, including both longitudinal and transverse fluctuations. Simulations show that both longitudinal and transverse heat diffusion are necessary in producing specific structures, as well as in determining the time of switching. During switching, the experiment and theory illustrate for the intensity profile the formation of a local minima on axis (hole) followed by a local maxima on axis and local minima off axis (rings). Such beam distortions and bistable switching are the result of the spatial and temporal dynamics and positive feedback existing among the absorption and heating.