Generation of polarization entangled photon pairs by a single crystal   interferometric source pumped by femtosecond laser pulses
  Photon pairs, highly entangled in polarization have been generated under femtosecond laser pulse excitation by a type I crystal source, operating in a single arm interferometric scheme. The relevant effects of temporal walk-off existing in these conditions between the ordinary and extraordinary photons were experimentally investigated. By introducing a suitable temporal compensation between the two orthogonal polarization components highly entangled pulsed states were obtained. 
M. Barbieri, C. Cinelli, F. De Martini, P. Mataloni