Second harmonic generation from multilayer hexagonal boron nitride

Abstract

We report second harmonic generation (SHG) from thick hexagonal boron nitride (hBN) flakes with approximately 109 layers. Surprisingly, the resulting signal is stronger when compared to previously reported few-layer experiments that showed the SHG efficiency gradually decreasing with the increasing thickness. This confirms that thick hBN flakes can serve as a platform for nonlinear optics, which is useful because thick flakes are easy to exfoliate while retaining a large flake size. We also show spatial second harmonic maps revealing that SHG remains a useful tool for the characterization of the layer structure even in the case of a large number of layers.