  Optically pumping high quality semiconductor microcavities allows for the
spontaneous formation of polariton condensates, which can propagate over
distances of many microns. Tightly focussed pump spots here are found to
produce expanding incoherent bottleneck polaritons which coherently amplify the
ballistic polaritons and lead to the formation of unusual ring condensates.
This quantum liquid is found to form a remarkable sunflower-like spatial ripple
pattern which arises from self interference with Rayleigh-scattered coherent
polariton waves in the Cerenkov regime.
