Ultrafast Metrology through Nonlinear Plasmonic Metasurfaces

Conventional ultrafast pulse characterization relies on bulk nonlinear crystals. While effective, these crystals are constrained by strict phase-matching conditions that restrict bandwidth, and their bulky sizes hinder on-chip integration. Here, we present a plasmonic metasurface platform that addresses these limitations by enabling second-harmonic generation over a subwavelength propagation. Our plasmonic nanoantennas with broken structural symmetry are designed to support a broadband electric-dipole resonance centered around 830 nm. For the first time, we introduce metasurfaces to ultrafast metrology by demonstrating both a metasurface-based interferometric autocorrelator for pulse intensity characterization and interferometric frequency-resolved optical gating for complete intensity-phase characterization. Furthermore, we characterize the device's photothermal resistance under extended pulsed excitation, establishing the operational fluence level for continuous metrology operation. This work paves the way for the development of broadband and chip-scale metrology systems.