Mapping local optical densities of states in silicon photonic structures with nanoscale electron spectroscopy

TL;DR

This paper demonstrates nanoscale electron spectroscopy to map local optical densities of states in silicon photonic structures, revealing spatial distributions of optical modes across a broad spectral range.

Contribution

It introduces a method to visualize optical mode distributions in photonic structures using electron energy loss spectroscopy at nanometer resolution.

Findings

Spatial maps of optical modes in silicon waveguides obtained

Optical mode distributions characterized from near-infrared to ultraviolet

Method enables detailed study of photonic density of states

Abstract

Relativistic electrons in a structured medium generate radiative losses such as Cherenkov and transition radiation that act as a virtual light source, coupling to the photonic densities of states. The effect is most pronounced when the imaginary part of the dielectric function is zero, a regime where in a non-retarded treatment no loss or coupling can occur. Maps of the resultant energy losses as a sub-5nm electron probe scans across finite waveguide structures reveal spatial distributions of optical modes in a spectral domain ranging from near-infrared to far ultraviolet.