Normalized E,k polariton-population (photoluminescence) images recorded using Fourier-space imaging, below, at 0.8Pth (a) and above condensation threshold, at 1.4Pth, (b). Dashed red curves show lower polariton branch dispersion in the linear regime. c Photoluminescence intensity at k|| ~ 0, integrated into the range over ±0.2 μm−1 (black squares) and full-width at half-maximum (FWHM, red squares) and d energy of the ground polariton state versus pump power. The superlinear increase and 10-fold linewidth narrowing together with high-energy shift of the polariton ground state observed above the threshold are commonly-recognised features of non-equilibrium polariton condensation. e Degree of linear polarization (blue squares) as a function of pump power, indicating that the condensate inherits the polarization of the pump beam. Solid curves in c–e represent numerical simulations of time-integrated photoluminescence, the ground state energy, and degree of linear polarization as functions of pump power, respectively. The red dashed curve in c is a guide for the eye. Error bars in c, d determined as standard deviations of the best-fit results of integrated photoluminescence intensity at different pump powers. Error bars in d are within the marker size. Error bars in e correspond to standard deviations of DLP obtained from photoluminescence intensities measured for orthogonal polarizations.