We report the first observation of cavityless optical bistability in ZnSe. A shift in the band edge and self-focusing occurs due to the temperature rise of the material as the laser irradiance is increased. These two mechanisms are believed to provide the feedback necessary for bistable operation.
First reports of absorptive all-optical bistabilities in reflectance and luminescence of a Fabry-Perot cavity consisting of thin (0.70 ,cem) ZnSe film are presented. We demonstrate that the observation of bistability in the reflected beam does not require necessarily the appearance of bistability in the transmitted beam. Luminescence bistabilities, however, are observed both in the light captured Lrom the incident side 0L the film and in the light emitted from the transmission side. The bistabilities in reflection and luminescence are explained quite satisfactorily by the principle of increasing absorption due to photo-irradiation and the dependence of the luminescence intensity on a photo-thermally induced temperature change, respectively. A11 experiments were carried out at room temperature with the 488 nm line of an argon laser.
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.