Low-threshold lasing action driven by chiral quasi-bound state in the continuum in planar metasurface

We numerically study a resonant planar chiral dielectric metasurface that can be constructed to realize low-threshold lasing. The designed metasurface is made of a periodic array of a square lattice of a slanted ring formed by two half-rings staggered from each other placed on a glass substrate and supports chiral quasi-bound states in the continuum dominated by the magnetic quadrupole. Exploiting the chiral quasi-bound states in the continuum (BIC) response with high Q-factor and strongly localized fields inside the ring, we study the lasing action of the slanted ring. The results reveal that the chiral quasi-BIC exhibits the polarization-dependent threshold. We theoretically demonstrate that the threshold can be reduced to 6.72 and 8.11 μJ/cm2 for left and right circularly polarized pumping, respectively. These results promise various practical applications including chiral emission and lasing applications.