Observations of optical bistability are reported for a system composed of multiple atomic beams passing through a high-finesse optical cavity. Both the transmitted power and the intracavity fluorescent intensity have been recorded as functions of incident laser power for zero cavity and atomic detunings. A quantitative study has been made of the evolution of the steady-state switching intensities from well below the critical onset of bistability to well above this point. The results show reasonable agreement with a Gaussian-beam theory of optical bistability, but systematic departures are noted.
The steady-state bistability and the evolution of the field envelope of a ring-cavity optical-bistable system including the effect of the transverse radiation field and the effect of an inhomogeneously broadened atomic medium are studied by means of the mean-field approximation and dressed-mode theory in this paper. Our study shows that the bistable region enlarges with an increase of the ratio
r0/
w0 (
r0 is the radius of the cylindrical atomic sample and
w0 the beam waist of the Gaussian beam), and decreases with increasing width of the inhomogeneously broadened line. The transverse-field effect has more impact on the magnitude of the bistable region than the inhomogeneous broadening under certain conditions. In the case of two unstable modes, the evolution of the field envelope before reaching the stable oscillation regime differs remarkably from that in the case of the plane-wave approximation with a homogeneously broadened atomic medium.
The influence of transverse effects on optical bistability in Fabry-Perot cavity filled with saturable absorber was numerically investigated. A simple model of singlet absorption was used on numerically solving the relationships between the input and output light fields. The proposed model corresponds well to organic compounds considered as novel optical materials with third-order optical nonlinearities. The proposed optically bistable systems were demonstrated for two organic dyes of fluorescein and rhodamine 6G dispersed in transparent solid matrices. Their optically bistable behaviour was anticipated considering the homogeneous and Gaussian distribution of light energy in the radial direction. Most notable cases are discussed related to the changes of the Gaussian beam radii, positive feedback conditions in the Fabry-Perot cavity and considering linear and nonlinear absorption parameters of the organic media. The simulation results enabled us to establish numerically thresholds of Fabry-Perot mirror reflectance and Gaussian beam radius for both nonlinear organic materials, above which absorptive optical bistability can occur. The results can be helpful in design of optical switches for all-optical communication networks.