Optical Dephasing of Excitonic Polaritons in CuCl Studied by Time-Resolved, Nondegenerate Four-Wave Mixing

Abstract

Optical dephasing of excitonic polaritons in CuCl is directly measured for the first time in the picosecond time domain by means of time-resolved, nondegenerate four-wave mixing. Dephasing of the ${\ensuremath{\omega}}_{1}$ polariton pulse is probed by an interrogation ${\ensuremath{\omega}}_{2}$ polariton pulse whose group velocity is faster than that of the ${\ensuremath{\omega}}_{1}$ polariton pulse. It is found that the dephasing damping constant $\frac{\ensuremath{\Gamma}}{2}$ of excitonic polaritons is of order of 0.01 meV and increases as $\ensuremath{\hbar}{\ensuremath{\omega}}_{1}$ approaches the exciton resonance energy from below.