Resonant Brillouin Scattering of Excitonic Polaritons in Gallium Arsenide

We report the first experimental observation of resonant Brillouin scattering of excitonic polaritons in a semiconductor. The usual symmetric Brillouin doublet becomes an asymmetric multiplet when the incident light energy is scanned through the $n=1\mathrm{}$ exciton resonance and allows a direct measurement of the polariton dispersion curve. In GaAs we determine a longitudinal-transverse splitting of 0.08 ± 0.02 meV and a translational mass $M_{\mathrm{ex}}=(0.6\mathrm{}\pm 0.1)m_0$ for the [100] heavy exciton. The excitions couple preferentially to LA phonons.