Backward second-harmonic generation in periodically poled bulk LiNbO_3

Abstract
We experimentally demonstrate backward second-harmonic generation in periodically poled LiNbO3 with a 3.3-µm domain period. We observed higher-order phase matching near 1490, 1600, and 1700 nm (fundamental) for the 19th, 18th, and 17th orders, respectively, with a maximum conversion efficiency of 0.02%.