Linear and nonlinear optical properties of semiconductor microcavities exhibiting normal-mode coupling

Abstract

The work in this dissertation has focused on the optical properties of semiconductor microcavities containing one or more high-quality, narrow-linewidth quantum wells, and how the appropriate design and growth of such structures can result in a nonperturbative coupling of light and matter. We apply the term Normal-Mode Coupling to describe this interaction, as it can be ascribed to the dipole interaction lifting the degeneracy between field and emitter resonances, resulting in a strongly coupled two- (or more-) oscillator system. Linear reflection, transmission, and photoluminescence measurements for the two-oscillator systems show two dips or peaks near zero detuning, whereas samples with two nonidentical quantum wells coupled to the microcavity display a three-resonance behavior. It is demonstrated that the linewidths of these samples are not only functions of the uncoupled cavity and exciton lineshapes, but are also sensitive to the local variations of the index of refraction and optical absorption. To this end, absorption measurements of multiple-quantum-well samples lead to a phenomenological derivation of the optical susceptibility inclusive of the influence of structural disorder. Use of this susceptibility in a transfer-matrix calculation then gives good agreement with experiment. The ability to see well-resolved normal-mode coupling peaks at room temperature is also demonstrated. Here, the distributed Bragg reflector mirror layers are created through oxidation of the AlAs mirror layers, resulting in increased field confinement and larger splitting. The superlative splitting-to-linewidth ratios at resonance for these samples make them ideal candidates for nonlinear studies. Pump-probe transmission and photoluminescence studies utilizing both resonant and nonresonant pump excitation are presented. Nonlinear saturation of the quantum-well excitonic resonance leads to increased absorption at the normal-mode coupling transmission peaks, which reduces their amplitude. For relatively small positive cavity-exciton detunings, there is a good correspondence between photoluminescence crossover and the opening up of probe transmission at the uncoupled cavity-mode resonance. It is demonstrated that this occurs when the exciton absorption is bleached, and the coupling undergoes a transition from nonperturbative to weak. In this case, nonlinear absorption measurements on a cavityless multiple-quantum-well sample provide the nonlinear optical susceptibility for use in a transfer-matrix simulation for the off-resonant pumping experiments.