ИСТИНА

In our work we develop a new consistent theoretical description of far-field spatial features and photon correlations in BSV radiated in high-gain parametric down-conversion. Instead of initial numerously correlated angular modes we introduce the collective angular Schmidt modes that are independent from each other. Such possibility is based on the known Schmidt decomposition procedure. In the frame of the Heisenberg representation we obtain the fully analytical solution for the spatial evolution of the photon-creation operators for these collective Schmidt modes. Using the obtained solution we calculate analytically the angular distribution of non-linear signal as well as different correlation characteristics such as covariance, second-order correlation function, etc in terms of both Schmidt modes and initial angular modes for signal and idler beams. We present the comparison of our theoretical results with the properties of bright squeezed vacuum observed in experiments performed in MPL and demonstrate a good agreement.