Broadband frequency conversion of ultrashort pulses using high-$Q$ metasurface cavities

TL;DR

This paper introduces a novel metasurface-based cavity design that enables broadband frequency conversion of ultrashort pulses, overcoming traditional limitations of high-$Q$ cavities through collective surface lattice resonances.

Contribution

It proposes and numerically demonstrates a metasurface cavity configuration supporting broadband frequency conversion, surpassing the bandwidth limitations of conventional high-$Q$ cavities.

Findings

Achieved ~1000-fold enhancement of nonlinear signals.

Demonstrated a pump conversion bandwidth of 75 nm.

Supported a high-$Q$ SLR with Q=500 near 1000 nm.

Abstract

Frequency conversion of light can be dramatically enhanced using high quality factor ($Q$-factor) cavities. Unfortunately, the achievable conversion efficiencies and conversion bandwidths are fundamentally limited by the time-bandwidth limit of the cavity, 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 cavity 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) centred near 1000 nm, and demonstrate ~1000-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 cavity. Our work opens new avenues to utilize high-$Q$ metasurfaces also for broadband frequency conversion of light.