Third-Order Optical Nonlinearity of Hexagonal Boron Nitride Atomic Layer

The third-order optical nonlinearity of hexagonal boron nitride (hBN) nanosheet was characterized by z-scan, I-scan, and spatial self-phase modulation (SSPM). The hBN nanosheets exhibited a positive nonlinear absorption or reverse saturable absorption (RSA) and its coefficient was estimated to be ~ 7.1 x 10-10 m/W via the open z-scan. The I-scan technique further verified the polarity of nonlinear absorption and the prospective application for laser safety (optical limiting) of the optical sensors from high-power lasers. It is found that the given hBN atomic layers could absorb up to ~22 % of incoming laser beam. In addition, the absence of a nonlinear refraction effect was observed using the closed z-scan and SSPM for a given excitation peak intensity. It implies that the free carrier-induced nonlinear absorption that diminishes the NLR signal via free-carrier dispersion. Acknowledgment: This work at HU is supported by ARO W911NF-15-1-0535 and NASA NNX15AQ03A.