Determination of diffusion coefficients of an exciton and excitonic molecule in CuCl by picosecond transient grating spectroscopy

We have made the first successful direct observation of the diffusion coefficients of an exciton and excitonic molecule in CuCl by tunable picosecond transient grating spectroscopy under the resonant two-photon excitation of the excitonic molecule. The diffusion coefficients of the exciton and the excitonic molecule are 330 ± 200 and 45 ± 10 ${\mathrm{cm}}^2$/sec at 1.8 K, respectively. The main part of this difference between the diffusion coefficients of the exciton and excitonic molecule is explained by the difference of the size of the exciton and excitonic molecule.