Picosecond Time of Flight Measurements of Excitonic Polariton in CuCl

Abstract

The group velocity of excitonic polariton in CuCl has been measured at 4.2 K using picosecond light pulses. It is derived by measuring both the time delay of light pulses and the thickness of samples. Experimental results are well explained by the dispersion relation of excitonic polariton including spatial dispersion. In addition, the translational effective mass of exciton in CuCl is directly derived, i.e. M =(2.0 ±0.1) m 0 .