Zusammenfassung

A weak Fano-type structure one LO phonon energy above the fundamental exciton in bulk GaAs is investigated via highly sensitive femtosecond transmission spectroscopy. It is identified as the response of an exciton-LO phonon quasiparticle. The low-density dephasing time of this excitation is directly determined to be 300 fs. Temperature and carrier density dependent measurements elucidate the properties of this resonance which is inaccessible in linear spectroscopy.