Nonlinearities in semiconductor microcavities: a correlation spectroscopy study

Abstract

High-quality microresonator lasers can be realised using semiconductor microcavities containing nanostructures as optically active medium, e.g. quantum wells and quantum dots. These highly efficient lasers are of great importance for prospective applications, such as in optoelectronics. This dissertation thesis investigates two kinds of microcavity lasers. The first part of the thesis concerns quantum-dot micropillar lasers operating in the regime of weak light-matter coupling. The transition from dominating spontaneous emission to lasing operation is analysed in terms of the excitation-power dependent coherence properties and the degree of linear polarisation. To this end, we performed photoluminescence spectroscopy as well as correlation spectroscopy experiments, revealing clear nonlinearities around the lasing threshold. Hence, a full characterisation of the lasing transition of such micropillar lasers is given. In the second part, a quantum-well microcavity operating in the regime of strong coupling is studied. Due to the strength of the light-matter interaction, new eigenstates are created in the microcavity system: excitons-polaritons. These bosonic quasi-particles are known to undergo a phase transition similar to Bose-Einstein condensation, i.e. they accumulate in large numbers in the ground state at a certain particle density. As condensed polaritons are phase-locked, their emission is coherent as well. Combining experimental results obtained from angle-resolved spectroscopy with photon-correlation spectroscopy data, the present work demonstrates that coherent emission from such a condensate can be distinguished from conventional photon lasing by the analysis of two distinct nonlinearities at different particle densities.