Third-Order Nonlinear Processes in Lossy Chalcogenide Metasurfaces Supporting Quasi-Bound States in the Continuum

Near-infrared to ultraviolet wavelength conversion can be achieved in a chalcogenide-based metasurfaces: the combination of high-field localization and phase-locking allows one to circumvent the high absorption typical of the ultra-violet frequency range. We investigate nonlinear third-order processes triggered in the near-infrared by the excitation of quasi-bound states in the continuum, and investigate them when the metasurface is illuminated by TM- and TE-polarized light. Our findings suggest that the resonance quality factor is not necessarily a good predictor of nonlinear processes' efficiencies.