Direct Schmidt number measurement of high-gain parametric down   conversion
  In this work we estimate the transverse Schmidt number for the bipartite bright squeezed vacuum state by means of second-order intensity correlation function measurement. Assuming that the number of modes is equal in both beams we determine the Schmidt number considering only one of the subsystems. The obtained results demonstrate that this approach is equally efficient over the whole propagation of the state from the near field to the far field regions of its emitter. 
I. V. Dyakonov, P. R. Sharapova, T. Sh. Iskhakov, G. Leuchs
quant-ph