Exciton-polariton dynamics in semiconduct

This thesis reports an experimental investigation of the nonlinear optical properties of bound electron-hole pairs (excitons) in quantum wells embedded in semiconductor microcavities. A microcavity is a monolithic resonator composed of two Bragg mirrors with cavity length comparable to the wavelength of light. The embedded quantum wells serve as the optically active medium which also confines the electronic excitations. Strong interaction between the cavity photons and the quantum well excitons results in new eigenstates of the system, the so called microactivity exciton-polaritons. Continuous wave excitation, and time-, spectral-, and angular-resolved ultrafast spectroscopy were employed in order to analyze the dynamics of this system. Microactivity exciton-polaritons exhibit a very steep dispersion around the ground polariton state resulting in a much longer polariton de Broglie wavelength compared to that of bare excitons. Therefore, quantum degeneracy of a polariton gas is achievable at much lower densities than for an exciton gas. Recently, observations of parametric polariton scattering under stimulation of the final state provided conclusive proof of the bosonic behaviour of polaritons. In this thesis a comprehensive analysis of the spin dynamics in the stimulated polariton scattering is presented. Due to the effect known as relaxation bottleneck, which prevents excitons from relaxing into the ground polariton state, Bose condensation of polaritons has not yet been observed from an initially incoherent population of excitons. However, experimental evidence is presented of the potential of electron-polariton scattering as an efficient process, which can drive polaritons from the bottleneck region to the ground state.