Description
Complex-frequency excitation provides a powerful tool for controlling resonant scattering by tailoring not only the carrier frequency but also the temporal growth or decay rate of the incident waveform. In this work, we investigate complex-frequency excitations in dielectric metasurfaces that support quasi-bound states in the continuum (quasi-BIC). Instead of relying solely on conventional frequency-domain S-matrix calculations, we develop a time-domain inverse-modeling framework that directly retrieves the intrinsic pole-zero parameters of a metasurface from its transient port signals. The method uses known incident pulses and the corresponding scattered time-domain fields to construct a rational state-space representation of the metasurface response, from which resonant poles, residues, and scattering zeros can be extracted.
Using a silicon dielectric metasurface as a representative platform, we show that the retrieved pole-zero model accurately reproduces the transient and spectral scattering response and enables the synthesis of complex-frequency waveforms for coherent virtual absorption. In particular, by exciting the metasurface near a scattering zero with an exponentially tailored coherent input, the outgoing fields can be strongly suppressed without introducing material loss. This establishes a direct link between time-domain measurements, resonant eigenmode dynamics, and complex-frequency scattering control.
The proposed framework provides a general tool for analyzing and programming resonant nanophotonic systems from transient data and can be extended to time-varying, nonlinear, or chiral metasurfaces for which conventional steady-state frequency-domain descriptions are insufficient.
| I am the presenting author | Yes |
|---|