High-order harmonic generation from inhomogeneous fields

TL;DR

This paper investigates how inhomogeneous fields from plasmonic nanostructures influence high-order harmonic generation, revealing enhanced cutoff energies and even harmonic production through theoretical models.

Contribution

It introduces a comprehensive theoretical analysis combining TDSE and SFA approaches to understand HHG in non-homogeneous fields, highlighting the effects of field inhomogeneity and electron confinement.

Findings

Inhomogeneous fields produce even harmonics.

Cutoff energies are significantly increased.

Both TDSE and SFA predict similar HHG features.

Abstract

We present theoretical studies of high-order harmonic generation (HHG) produced by non-homogeneous fields as resulting from the illumination of plasmonic nanostructures with a short laser pulse. We show that both the inhomogeneity of the local fields and the confinement of the electron movement play an important role in the HHG process and lead to the generation of even harmonics and a significantly increased cutoff, more pronounced for the longer wavelengths cases studied. In order to understand and characterize the new HHG features we employ two different approaches: the numerical solution of the time dependent Schr\"odinger equation (TDSE) and the semiclassical approach known as Strong Field Approximation (SFA). Both approaches predict comparable results and show the new features, but using the semiclassical arguments behind the SFA and time-frequency analysis tools, we are able to fully understand the reasons of the cutoff extension.