Random quasi-phase-matched second-harmonic generation in periodically   poled lithium tantalate
  We observe second harmonic generation via random quasi-phase-matching in a 2.0 \mu m periodically poled, 1-cm-long, z-cut lithium tantalate. Away from resonance, the harmonic output profiles exhibit a characteristic pattern stemming from a stochastic domain distribution and a quadratic growth with the fundamental excitation, as well as a broadband spectral response. The results are in good agreement with a simple model and numerical simulations in the undepleted regime, assuming an anisotropic spread of the random nonlinear component. 
Salvatore Stivala, Alessandro C. Busacca, Alessia Pasquazi, Roberto L.   Oliveri, Roberto Morandotti and Gaetano Assanto
physics.optics