Broadband frequency conversion of ultrashort pulses using high- Q metasurface resonators

Frequency conversion of light can be dramatically enhanced using high quality factor (Q-factor) resonator. Unfortunately, the achievable conversion efficiencies and conversion bandwidths are fundamentally limited by the time-bandwidth limit of the resonator, restricting their use in frequency conversion of ultrashort pulses. Here, we propose and numerically demonstrate sum-frequency generation based frequency conversion using a metasurface-based resonator configuration that could overcome this limitation. The proposed experimental configuration takes use of the spatially dispersive responses of periodic metasurfaces supporting collective surface lattice resonances (SLRs), and can be utilized for broadband frequency conversion of ultrashort pulses. We investigate a plasmonic metasurface, supporting a high-Q SLR (Q = 500, linewidth of 2 nm) centered near 1000 nm, and demonstrate 1/41000-fold enhancements of nonlinear signals. Furthermore, we demonstrate broadband frequency conversion with a pump conversion bandwidth reaching 75 nm, a value that greatly surpasses the linewidth of the studied resonator. Our work opens new avenues to utilize high-Q metasurfaces for broadband nonlinear frequency conversion.