All-dielectric metasurface with enhanced third-harmonic dichroism driven by quasi-BIC

Circular dichroism (CD), yielding a different response upon illumination with light having opposite spin angular momentum, is opening the way for many new applications from telecommunications to sensing [1]. Although this phenomenon is extremely weak in natural materials, metasurfaces (MS) considerably enhance CD [2]. In comparison to the linear regime, CD in the nonlinear regime (NLCD), e.g. higher harmonic-generation for one circular light polarization with respect to the opposite one, may exhibit much higher contrast. To date, NLCD demonstrations are still limited to plasmonic structures [3] ; however nonlinear MS based on dielectric materials have the potential to yield high NLCD with superior conversion efficiencies than their plasmonic counterpart