Nanooptics in the electron microscope

Date: 10th February 2022
Time: 10:00 am - 11:00 am
Location: Online, AEDT

Presented by Prof. Mathieu Kociak​ of The University of Paris

Hunting optical phenomena at the nanometer scale, namely performing nanooptics, is paradoxical. On the one hand, the typical length-scale relevant for optics is of the order of a visible radiation wavelength: few hundred of nanometers. On the other hand, optical properties of nano-objects become to depart from bulk properties when the nano-objects become smaller than a few hundred of nanometers. In this case, the optical properties depend on minute variations of the size and shape of the nano-objects, and sometimes the morphology or structure of nano-objects have to be known with atomic resolution. Therefore, techniques that are not limited by the optical diffraction limit have been developed in the last 15 years to make possible to study novel optical nanomaterials and the novel physics they brought.

In this talk, I will present the use of free electron beams – such as delivered in a transmission electron microscope – to perform optical spectroscopy at the nanometer scale. I will show how they can be used to map phonons, plasmons and excitons with unbeatable spatial resolution, and even in 3D. Beyond their impressive success in generating nice images, I will show how it is now possible to quantitatively understand such experiments in pure optical terms, such as extinction and scattering cross-sections or electromagnetic local density of states. I will also emphasize recent developments in ultra-high spectral resolution that makes it possible to tackle new field of nanooptics, such as the study of strong coupling between plasmons and excitons or phonons.