Generating highly squeezed Hybrid Laguerre-Gauss modes in   large-Fresnel-number Degenerate Optical Parametric Oscillators
  We theoretically describe the quantum properties of a large Fresnel number degenerate optical parametric oscillator with spherical mirrors that is pumped by a Gaussian beam. The resonator is tuned so that the resonance frequency of a given transverse mode family coincides with the down-converted frequency. After demonstrating that only the lower orbital angular momentum (OAM) Laguerre-Gauss modes are amplified above threshold, we focus on the quantum properties of the rest of (classically empty) modes. We find that combinations of opposite OAM (Hybrid Laguerre-Gauss modes) can exhibit arbitrary large quadrature squeezing for the lower OAM non amplified modes. 
Carlos Navarrete-Benlloch, Germ\'an J. de Valc\'arcel, and Eugenio   Rold\'an