Frequency-selective terahertz wave amplification by a time-boundary-engineered Huygens metasurface

TL;DR

This paper demonstrates that a dielectric Huygens metasurface can achieve broadband near-unity transmission and wave amplification by employing femtosecond laser-induced time boundaries, enabling tunable terahertz wave amplification.

Contribution

It introduces a novel method of using time-boundaries in a Huygens metasurface for ultrafast wave amplification and tunable control of terahertz signals.

Findings

Transmittance exceeds unity, achieving over 20% intensity gain.

Wave amplification is tunable by adjusting the timing of the femtosecond laser excitation.

Numerical simulations confirm ultrafast Q-switching causes the observed amplification.

Abstract

Ultrafast manipulation of optical resonance can establish the time-boundary effect in time-variant media leading to a new degree of freedom for coherent control of electromagnetic waves. Here, we demonstrate that a free-standing all dielectric Huygens metasurface of degenerate electric and magnetic resonances can prompt the broadband near-unity transmission in its static state, whereas it enables wave amplification in the presence of time boundary. The time boundary is realized by femtosecond laser excitations that transiently inject free carriers into the constituent meta-atoms for dynamic removal of a pre-established two-fold degeneracy. We observe that the transmittance in the photo-excited Huygens metasurface can exceed unity transmittance, i.e., THz wave amplification, by a factor over 20% in intensity at frequencies tunable by varying the arrival of time boundary with respect to that of the seed terahertz pulse. By numerical simulations and analysis with time-dependent coupled mode theory, we show that the wave amplification results from the ultrafast Q-switching and shift in resonant frequencies. This work demonstrates a new approach to achieve tunable amplification in an optical microcavity by exploiting the concept of time-variant media and the unique electromagnetic properties of Huygens metasurface.