Coexistence of local and nonlocal shock waves in nanomaterials

TL;DR

This paper demonstrates the formation and interaction of electronic and thermal dispersive shock waves in gold nanorod suspensions under laser illumination, revealing complex nonlinear phenomena relevant for advanced photonic applications.

Contribution

It uncovers the coexistence and interaction of two distinct dispersive shock waves in nanomaterials, a phenomenon not previously explored in this context.

Findings

Identification of electronic and thermal shock waves coexisting and interacting.

Observation of a double front of equal intensity resulting from shock wave interaction.

Confirmation of the nonlinear refractive index contributions from gold nanoparticles.

Abstract

High-performing nanomaterials are paramount for advanced photonic technologies, like sensing, lasing, imaging, data storage, processing, and medical and biological applications. Metal nanoparticles play a key role, because the localized surface plasmonic resonances enhance the linear and nonlinear optical properties of hosting materials, thus increasing the range of applications. The improved optical response results in an enriched and largely unexplored phenomenology. In the present work, we show the formation and interaction of two dispersive shock waves emerging by illuminating an aqueous suspension of gold nanorods with a pulsed laser beam. By analyzing the characteristic undular bores that regularize a shock front in a dispersive material, we were able to distinguish dispersive shock waves of different origins, i.e., electronic and thermal, first coexisting and then interacting to form a double front of equal intensity. The observed scenario agrees with existing literature reporting an electronic and thermal contribution to the nonlinear refractive index of material containing gold nanoparticles. Although a full comprehension of the reported results deserves an analytical description, they already pave the way to using materials containing metal nanoparticles as a platform for studying fundamental extreme nonlinear phenomena and developing novel solutions for sensing and control.