Non-classical behavior in multimode and disordered transverse structures   in OPO. Use of the Q representation
  We employ the Q representation to study the non-classical correlations that are present from below to above-threshold in the degenerate optical parametric oscillator. Our study shows that such correlations are present just above threshold, in the regime in which stripe patterns are formed, but that they also persist further above threshold in the presence of spatially disordered structures. 
Roberta Zambrini, Stephen M. Barnett, Pere Colet, Maxi San Miguel