Thermally induced absorptive optical bistability in GaAs/(Al,Ga)As multiple quantum wells
The temperature distribution in a GaAs/(Al,Ga)As multiple quantum well structure was measured with high lateral and temporal resolution while passing through the characteristic hysteresis loop of a thermally induced absorptive optical bistability. In a pump and probe beam experiment, the local transmission spectra of the quantum well structure were recorded and the temperature distribution in the sample was deduced from the spectral positions of characteristic exciton resonances. These resonances remain sufficiently sharp even far above room temperature to guarantee an accuracy of better than 3 K The experiment was conducted under both steady-state and dynamical conditions. The steady-state results were compared with numerical calculations, showing good agreement. The dependence of the relative width of the characteristic hysteresis on the environmental temperature of the bistable sample was investigated. A simple relaxation-time model of the bistability was shown to describe nicely the observed behaviour if the bleaching of the lowest exciton resonance due to high laser intensities is considered. Based on this dependence, a miniature temperature-sensing device using an optical fibre to guide the laser beam is presented.