Second-harmonic generation in multilayer hexagonal boron nitride flakes

TL;DR

This study demonstrates that thick multilayer hexagonal boron nitride flakes exhibit strong second-harmonic generation, making them suitable for nonlinear optical applications and layer characterization despite their increased thickness.

Contribution

It shows that thick hBN flakes can generate significant SHG, expanding their use in nonlinear optics and characterization beyond few-layer samples.

Findings

Thick hBN flakes produce comparable SHG to few-layer samples.

SHG mapping reveals layer structure in thick flakes.

Thick flakes are easier to exfoliate with large sizes.

Abstract

We report second-harmonic generation (SHG) from thick hexagonal boron nitride (hBN) flakes with approximately 109-111 layers. The resulting effective second-order susceptibility is similar to previously reported few-layer experiments. 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.