Continuous-wave backward frequency doubling in periodically poled   lithium niobate
  We report on backward second-harmonic-generation in bulk periodically poled congruent lithium niobate with a 3.2 microns period. A tunable continuous-wave Ti:sapphire laser allowed us exciting two resonant quasi-phase-matching orders in the backward configuration. The resonances were also resolved by temperature tuning and interpolated with standard theory to extract relevant information on the sample. 
Salvatore Stivala, Alessandro C. Busacca, Luciano Curcio, Roberto L.   Oliveri, Stefano Riva-Sanseverino and Gaetano Assanto
physics.optics