Spatial Einstein-Podolsky-Rosen aspects in the optical parametric oscillator below thresholdA. Gatti, L. A. Lugiato, K. I. Petsas and I. MarzoliEurophys. Lett., 46 4 (1999) 461-466DOI: https://doi.org/10.1209/epl/i1999-00285-3