Quasi-BIC Resonant Enhancement of Second-Harmonic Generation in WS2Monolayers

Atomically thin monolayers of transition metal dichalcogenides (TMDs) have emerged as a promising class of novel materials for optoelectronics and nonlinear optics. However, the intrinsic nonlinearity of TMD monolayers is weak, limiting their functionalities for nonlinear optical processes such as frequency conversion. Here we boost the effective nonlinear susceptibility of a TMD monolayer by integrating it with a resonant dielectric metasurface that supports pronounced optical resonances with high quality factors: bound states in the continuum (BICs). We demonstrate that a WS2 monolayer combined with a silicon metasurface hosting BICs exhibits enhanced second-harmonic intensity by more than 3 orders of magnitude relative to a WS2 monolayer on top of a flat silicon film of the same thickness. Our work suggests a pathway to employ high-index dielectric metasurfaces as hybrid structures for enhancement of TMD nonlinearities with applications in nonlinear microscopy, optoelectronics, and signal processing.Financial support was provided by the Australian Research Council (DE180100070 and DP150102071), the University of Technology Sydney (Seed Funding Grant), the Strategic Fund of the Australian National University, and the Russian Foundation for Basic Research (19-02-00419 and 19-32- 90106). K.K. acknowledges support from the Foundation for the Advancement of Theoretical Physics and Mathematics “BASIS