Schmidt-like coherent mode decomposition and spatial intensity   correlations of thermal light
  We experimentally study the properties of coherent mode decomposition for intensity correlation function of quasi-thermal light. We use the technique of spatial mode selection developed for studying transverse entanglement of photon pairs, and show that it can be extended to characterize classical spatial correlations. Our results demonstrate the existence of a unique for a given thermal source basis of coherent modes, correlated in a way much resembling the Schmidt modes of spatially entangled photons. 
I.B.Bobrov, S.S.Straupe, E.V.Kovlakov and S.P.Kulik
quant-ph physics.optics