Observation of Saturable and Reverse Saturable Absorption at Longitudinal Surface Plasmon Resonance in Gold Nanorods

TL;DR

This study observes both saturable and reverse saturable absorption in gold nanorods at their surface plasmon resonance using femtosecond laser pulses, revealing potential for optical limiting.

Contribution

It reports the first detailed observation of both saturable and reverse saturable absorption in gold nanorods at SPR, with insights into their mechanisms and potential applications.

Findings

Saturable absorption occurs near the SPR wavelength with a recovery time of tens of picoseconds.

Reverse saturable absorption dominates at higher excitation irradiances.

Gold nanorods are promising for optical limiting applications.

Abstract

Saturable and reverse saturable absorption at longitudinal surface plasmon resonance (SPR) in gold nanorods (Au NRs) have been observed using Z-scan and transient absorption techniques with femtosecond laser pulses. At lower excitation irradiances, the wavelength dispersion of saturable absorption has been determined near the longitudinal mode of SPR with a recovery time determined to be a few ten picoseconds on the SPR resonance. With higher excitation irradiances, reverse saturable absorption occurs and becomes dominant. The underlying mechanisms are discussed. Such reversible saturable absorption makes Au NRs an ideal candidate for optical limiting applications.