We propose and analyze a k-filtering effect which gives rise to the drastic difference between the actual spatial coherence length of quasi-two-dimensional (quasi-2D) excitons or microcavity (MC) polaritons in planar nanostructures and that inferred from far-field optical measurements. The effect originates from the conservation of in-plane wavevector k in the optical decay of the particles in outgoing bulk photons. The k-filtering effect explains the large coherence lengths recently observed for indirect excitons in coupled quantum wells (QWs), but is less pronounced for MC polaritons at low temperatures, T<10K.
@article{arxiv.0802.4454,
title = {First-order spatial coherence of excitons in planar nanostructures: a k-filtering effect},
author = {L. Mouchliadis and A. L. Ivanov},
journal= {arXiv preprint arXiv:0802.4454},
year = {2009}
}