Nanoscale Nonlinear Spectroscopy with Electron Beams

TL;DR

This paper theoretically shows that electron beams combined with optical pumping can probe the nonlinear optical response of materials at nanometer resolution, surpassing traditional optical methods.

Contribution

It introduces a method using stimulated electron-light interactions in PINEM to locally and quantitatively measure nonlinear optical responses at the nanoscale.

Findings

PINEM spectra depend on sample nonlinearity and can reveal second-harmonic responses.

PINEM can detect nonlinear signals with nanometer spatial resolution.

Spectral asymmetries indicate nonlinear optical effects in centrosymmetric structures.

Abstract

We theoretically demonstrate the ability of electron beams to probe the nonlinear photonic response with nanometer spatial resolution, well beyond the capabilities of existing optical techniques. Although the interaction of electron beams with photonic modes is generally weak, the use of optical pumping produces stimulated electron-light interactions that can reach order-unity probabilities in photon-induded near field electron microscopy (PINEM). Here, we demonstrate that PINEM can locally and quantitatively probe the nonlinear optical response. Specifically, we predict a dependence of PINEM electron spectra on the sample nonlinearity that can reveal the second-harmonic (SH) response of optical materials with nanometer resolution, observed through asymmetries between electron energy losses and gains. We illustrate this concept by showing that PINEM spectra are sensitive to the SH near field of centrosymmetric structures and by finding substantial spectral asymmetries in geometries for which the linear interaction is reduced.