Dark blue Cerenkov second harmonic generation in the two layer stacked hexagonal

We report the dark blue nonlinear Cerenkov radiation by the second harmonic generation (SHG) in a two-layer-stacked hexagonal periodically-poled-MgO: LiNbO3s (PPMgOLNs). Based on the direct wafer bonding of two target PPMgOLNs rotating around the axis perpendicular to the plane with an angle of 30o,