Nonlocality and Bose Einstein condensation of light

In arXiv:1406.6250, Marcello Calvanese Strinati and Claudio Conti consider a microcavity made by a graded-index (GRIN) glass, doped by dye molecules, placed within two planar mirrors and study Bose-Einstein condensation (BEC) of photons. The presence of the mirrors leads to an effective photon mass, and the index grading provides an effective trapping frequency; the photon gas becomes formally equivalent to a two dimensional Bose gas trapped in an isotropic harmonic potential. The inclusion of nonlinear effects provides an effective interaction between photons.Thermal lensing effects and the resulting nonlocal nonlinearity are considered, and quantitatively compared with the reported experimental data (courtesy of Jan Klaers and Martin Weitz)