FIG. 1. (a) Photoluminescence intensity emitted by the confined polariton states in a trap of 10 µm in diameter, under non-resonant pumping (at 1.57 eV, in the first minimum of reflection of the DBR), in a logarithmic scale. Confined lower (upper) polariton states are visible below (above) 1.484 eV. Solid, dashed and dotted arrows indicate the lower polariton ground, first and second excited states respectively. (b) Interferogram resulting from the interference of the coherent emission of the lower polariton ground state ( n = 1 , m = 0) with the reference laser. (c),(d) and (e) are respectively the interferogram, the wavefunction amplitude and wavefunction phase of the lower polariton first excited doublet state ( n = 1 , m = ± 1). 9