Imaging the transverse component of optical near-fields in resonant photonic structures

TL;DR

This paper demonstrates imaging of the transverse optical near-fields in resonant photonic structures with nanometer resolution using ultrafast 4D STEM, revealing both longitudinal and transverse near-field components.

Contribution

First application of ultrafast 4D STEM to visualize transverse near-fields in resonant photonic structures, combining experimental imaging with numerical simulations.

Findings

Imaging of near-field transverse components in silicon nanostructures

Observation of efficient transverse electron streaking at optical frequencies

Consistency between measured near-field profiles and FDTD simulations

Abstract

We report on imaging the optical near-fields in resonant periodic photonic structures with nanometer resolution using ultrafast 4D scanning transmission electron microscopy (U4DSTEM). In particular, U4DSTEM is applied to visualize the transverse component of the Lorentz force of a synchronous near-field mode excited by an infrared femtosecond pulse in a periodic silicon nanostructure designed for photonic acceleration of electrons. Our results show that in addition to the accelerating/decelerating force acting on the electrons in the longitudinal direction along the electron propagation, the structures can be efficiently used for transverse electron streaking at optical frequencies when excited by light with polarization perpendicular to the electron trajectory. The measured spatial profile of the excited near-field mode intensity is consistent with the numerical simulations performed using finite-difference time domain technique.