Spatially single-mode source of bright squeezed vacuum
  Bright squeezed vacuum, a macroscopic nonclassical state of light, can be obtained at the output of a strongly pumped non-seeded traveling-wave optical parametric amplifier (OPA). By constructing the OPA of two consecutive crystals separated by a large distance we make the squeezed vacuum spatially single-mode without a significant decrease in the brightness or squeezing. 
A. M. P\'erez, T. Sh. Iskhakov, P. Sharapova, S. Lemieux, O. V.   Tikhonova, M. V. Chekhova, G. Leuchs
quant-ph