Coherent Plasmonic Absorption in the Femtosecond Regime

TL;DR

This paper investigates how plasmonic absorption in nanostructured metamaterials and gold films varies with femtosecond optical pulse durations, revealing a rapid relaxation time and implications for ultrafast optical switching.

Contribution

It demonstrates the transient behavior of plasmonic absorption and identifies a 11 fs relaxation time, highlighting the potential for ultrafast all-optical switching devices.

Findings

Plasmonic relaxation time of 11 fs identified.

Metamaterials switch from beam-splitter to absorber based on pulse duration.

Bandwidth limit of ~90 THz for coherently-controlled optical switching devices.

Abstract

Dissipation of electromagnetic energy through absorption is a fundamental process that underpins phenomena ranging from photovoltaics to photography, analytical spectroscopy, photosynthesis, and human vision. Absorption is also a dynamic process that depends on the duration of the optical illumination. Here we report on the resonant plasmonic absorption of a nanostructured metamaterial and the non-resonant absorption of an unstructured gold film at different optical pulse durations. By examining the absorption in travelling and standing waves, we observe a plasmonic relaxation time of 11 fs as the characteristic transition time. The metamaterial acts as a beam-splitter with low absorption for shorter pulses, while as a good absorber for longer pulses. The transient nature of the absorption puts a frequency limit of ~90 THz on the bandwidth of coherently-controlled, all-optical switching devices, which is still a thousand times faster than other leading switching technologies.