Upcoming Lectures
This lecture series is sponsored by the Materials Research Institute, Chemistry, Physics, Engineering Science and Mechanics, and Nuclear Engineering Departments
February 10, 2026
12:20 p.m. - 1:20 p.m.
W-202 Millennium Science Complex
University Park, PA
Nanoscale spectroscopy of optical materials with combined free electrons and photons
Dr. Mathieu Kociak
Universite Paris Saclay
Senior Research Director
French National Centre for Scientific Research (CNRS)
ABSTRACT:
Hunting optical phenomena at the nanometer scale—performing nano-optics—is inherently paradoxical. On one hand, optical processes are governed by length scales comparable to the wavelength of visible light, typically a few hundred nanometers. On the other hand, the optical properties of nanostructures start to deviate from their bulk counterparts precisely when their size becomes smaller than this scale. Metallic nanoparticles, for instance, support plasmon resonances whose spectral features are extremely sensitive to subtle variations in size and shape. In other systems, such as quantum dots or quantum wells, atomic-scale structural details can become decisive. To probe these effects, a whole class of experimental approaches has emerged over the past two decades to circumvent the optical diffraction limit, enabling access to the optical response of individual nanostructures and to the new physics they reveal. In this talk, I will introduce a family of such techniques that use focused beams of free electrons—such as those available in a transmission electron microscope—to perform optical spectroscopy at the nanometer scale, sometimes in conjunction with laser beams. I will show how these methods can map plasmons, excitons, photonic modes, and even phonons with unmatched spatial resolution in a variety of materials, from metallic nanoparticles to heterostructures in 2D materials. Beyond the beauty of the resulting images, I will discuss how these experiments can now be interpreted quantitatively in purely optical terms—extinction and scattering cross-sections, or electromagnetic local density of states. Finally, I will illustrate how recent developments in this field open the way to new classes of free-electron experiments, from quantum optical measurements to nanoscale thermometry.
BIO:
Mathieu Kociak is a senior research director at the French National Centre for Scientific Research (CNRS), working within the STEM group at the Laboratory for Solid State Physics (LPS) in Orsay, France. He is also in charge of platforms and large instruments at Université Paris-Saclay. His research focuses on understanding the interplay between the structure and the optical and electronic properties of individual nano-objects. To this end, he combines advanced instrumentation development in electron microscopy, experimental investigations using scanning transmission electron microscopy (STEM), and theoretical modeling of electron–matter–photon interactions. He is the recipient of a prestigious ERC Advanced Grant (FreeQCC, 2025–2030). Kociak's honors include the quadrennial FEI-EM Award (2012) from the European Microscopy Society and the Agar Medal from the Royal Microscopical Society (2015).