Polarition Dynamics in Semiconductor Microcavities

Savvidis, Pavlos G (2001) Polarition Dynamics in Semiconductor Microcavities. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

This thesis presents experimental analysis of polariton dynamics in semiconductor microcavities, by means of ultrafast laser spectroscopy. Polaritons resulting from strong mixing of quantum well excitons with photons trapped inside a cavity, possess integer spin and are expected to obey Bose-Einstein statistics at low densities. It is shown here how the new modified dispersion relation for these quasiparticles gives rise to entirely new properties.

By constructing a prototype femtosecond goniometer we directly probe these quasiparticles and examine the angular properties of their dispersion relation. We identify ultrafast stimulated scattering of polaritons that results in huge amplification of the incident probe beam which relies on the bosonic property of polaritons to accumulate in a single quantum state. A microcavity working as an amplifier is the first of its kind to amplify massive quasiparticles in solid state system in contrast to amplification of light.

A full theoretical analysis of the parametric scattering of polaritons above the amplification threshold when one or more modes on the dispersion are macroscopically and coherently occupied is developed explaining peculiar microcavity emission.

Continuous wave excitation experiments reveal the formation from noise of a macroscopically coherent state, which has a well-defined phase. Strong nonlinear increase of the final state population with the increasing excitation density corresponds to condensation into a single polariton mode with macroscopic occupancy. This phenomenon possesses a number of similarities to Bose-Einstein condensation of atoms, but now realized in solids attracting much recent interest.

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