Temporal dynamics of quasi-BIC near fields in plasmonic-dielectric metasurfaces

Controlling near-field in space and time is crucial to applications of high-Q nonlocal metasurfaces, for instance for their use in nonlinear frequency conversion. We discuss near-field interferometric autocorrelation (IAC) measurements that reveal the dynamics of optical fields of quasi-bound states in the continuum (quasi-BICs) in plasmonic-dielectric metasurfaces. Using two-photon excited luminescence (TPEL) from quantum dots as local probes, our IAC measurements probe resonant near-field enhancement. Femtosecond laser pulse excitation of quasi-BICs produces coherent oscillations visible in TPEL, offering insights into resonances and their temporal beating. We discuss application scenarios for frequency-converting nonlinear metasurfaces in XUV generation and wafer metrology, as well as strategies for achieving high metasurface Q factors in metallic and dielectric systems.