Fig. 3: Determination of the quasi-BIC.

a Two-photon-induced absorption (TPA) spectra (\(\frac{1}{V}\int {\left|E\right|}^{4}{{{{{\rm{dV}}}}}}\) spectra) calculated for Si/SiO2 cuboids with w = 360 nm and different lengths. ED, MD, MO represent electric dipole, magnetic dipole, and magnetic octupole, respectively. The TPA and scattering spectra calculated for Si/SiO2 cuboids with l = 740 and 780 nm are shown in b, c. The excitation spectra measured for Si/SiO2 cuboids with l = 740 and 780 nm are shown in d, e, respectively. In each case, the scattering spectrum is also provided for reference.