Coherent exciton dynamics: time-resolved polarimetry

摘要

When coherent optical radiation is incident on a material, the polarisation that is produced within the sample initially has a well defined spatial and temporal phase relationship (or coherence) that is determined by the phase of the exciting field. That coherence persists until it is destroyed by scattering processes within the material. For the excitation of carriers in bulk semiconductors and quantum-confined semiconductor structures (e.g., multiple quantum wells, MQWs), these dephasing times typically range from a few femtoseconds (at room temperature) to a few picoseconds (at liquid helium temperatures). For this reason, the study of elementary coherent processes in semiconductors had to await the relatively recent development of picosecond and femtosecond mode-locked lasers. By comparison, the coherent regimes in atoms and molecules have been studied extensively.