Broadband enhancement of Cerenkov second harmonic generation in a sunflower spiral nonlinear photonic crystal

We present an experimental study on the Cerenkov second harmonic emission in a novel sunflower spiral array of ferroelectric domains in LiNbO3 crystal. The spiral patterns offer a diffusive, circularly symmetric distribution of reciprocal lattice vectors, thereby enabling enhanced emission of the Cerenkov beam in a broad spectral range. Instead of the traditional electric field poling, the sunflower spiral patterns are fabricated here by using our pioneering method of ferroelectric domain engineering with ultrafast light. This all-optical method gives access to high quality domain structures with short periods, which is beneficial for efficient Cerenkov harmonic generation. (c) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement