High-order harmonic generation by enhanced plasmonic near-fields in metal nanoparticules

TL;DR

This paper investigates how enhanced, spatially non-homogeneous plasmonic near-fields around metal nanoparticles influence high-order harmonic generation, leading to increased harmonic cut-off energies and potential new methods for coherent XUV light production.

Contribution

It introduces a theoretical framework incorporating non-homogeneous plasmonic fields into HHG modeling, revealing their significant impact on harmonic spectra extension and trajectory selection.

Findings

Non-homogeneous plasmonic fields extend harmonic cut-off energies.

Classical and quantum simulations show consistent HHG behavior.

Metal nanoparticles enable localized synthesis of laser fields for XUV generation.

Abstract

We present theoretical investigations of high-order harmonic generation (HHG) resulting from the interaction of noble gases with localized surface plasmons. These plasmonic fields are produced when a metal nanoparticle is subject to a few-cycle laser pulse. The enhanced field, which largely depends on the geometrical shape of the metallic structure, has a strong spatial dependency. We demonstrate that the strong non-homogeneity of this laser field plays an important role in the HHG process and leads to a significant increase of the harmonic cut-off energy. In order to understand and characterize this new feature, we include the functional form of the laser electric field obtained from recent attosecond streaking experiments [F. S{\"u}{\ss}mann and M. F. Kling, Proc. of SPIE, {\bf Vol. 8096}, 80961C (2011)] in the time dependent Schr\"odinger equation (TDSE). By performing classical simulations of the HHG process we show consistency between them and the quantum mechanical predictions. These allow us to understand the origin of the extended harmonic spectra as a selection of particular trajectory sets. The use of metal nanoparticles shall pave a completely new way of generating coherent XUV light with a laser field which characteristics can be synthesized locally.