Spectroscopy of exciton polaritons in Cu2O and GaAs-based microcavities

Abstract

Exciton-polaritons are light-matter quasi-particles, the theoretical concept of which was developed in the 1950s, and intensely studied in the following decades in bulk material. The observation of strong coupling between photons and excitons in semiconductor microcavities in 1992 paved the way for promising concepts for applications such as quantum simulators, optical logic circuits and novel light emitting devices. However, the realization of devices based on exciton-polaritons is still in the proof of principle stage. In this thesis, new insights into the fundamental optical properties of exciton-polaritons as well as a contribution towards the realization of polariton-based lasing devices and logic circuits are provided. Here, exciton-polaritons in Cu2O bulk semiconductor material and in GaAs-based microcavities are examined. In Cu2O the up to now hardly investigated blue exciton-polariton series is studied by means of a novel spectroscopic approach involving two single-frequency lasers, which gives evidence for a coherent propagation of polaritons in a spectral region of large absorption. Furthermore, the feasibility of different concepts of polariton laser operation in GaAs-based microcavities is evaluated, in which the regime of polariton lasing in the visible spectral range up to temperatures of 70 K is identified, whereas no indication for terahertz lasing is observed. Finally, the interactions between polariton condensates and background carriers are investigated. Here, a pronounced decrease of the polariton condensate coherence is observed due to the presence of background carriers. Beyond that, an all-optical approach for steering the polariton condensate flow by tailoring potential landscapes by means of injection of background carriers is presented, which is appealing for the realization of all-optical logic circuits.