Ultrafast Dynamics of Gold Nanorods: Tuning between Photo-Bleaching and Photo-Induced Absorption

TL;DR

This study investigates ultrafast electron dynamics in gold nanorods, revealing how their optical responses switch between photo-bleaching and photo-induced absorption depending on the surface plasmon resonance relative to the laser photon energy.

Contribution

It provides new insights into the ultrafast optical behavior of gold nanorods and how their dynamics can be tuned by adjusting their surface plasmon resonance.

Findings

Photo-induced absorption occurs when ELSP>EL.

Photo-bleaching with biexponential decay occurs when ELSP<EL.

Decay times increase linearly with pump intensity.

Abstract

We report ultrafast electron dynamics in gold nanorods investigated using 80 fs laser pulses centered at 1.57 eV. Five types of nanorod colloidal suspensions in water having their longitudinal surface plasmon peak (ELSP) on either side of the laser photon energy (EL) have been studied. For ELSP>EL, photo-induced absorption with single decay time constant is observed. On the other hand, for ELSP<EL, photo-bleaching is observed having biexponential decay dynamics; the faster one between 1-3 ps and slower one between 7ps to 22ps both of them increasing almost linearly with the difference |EL-ELSP|. These time constants increase linearly with the pump intensity. Simulations have been carried out to understand the interplay between photo-bleaching and photoinduced absorption.