Speaker
Description
The interaction of light with metasurfaces, two-dimensional arrays of subwavelength-spaced nanostructures, or "meta-atoms", paves the way for the advanced study of their optical properties. Metasurfaces can be meticulously designed to introduce desired localized and spatially varying electromagnetic responses, thereby collectively imparting arbitrary phase, amplitude, and polarization transformations upon an incident wavefront. The fundamental principle hinges on the resonant coupling of incident light with the meta-atoms, which can be precisely tailored by controlling their geometry, material composition, and arrangement. Consequently, by systematically measuring the far-field optical response—such as the intensity and polarization state of transmitted, reflected, or scattered light—one can retrieve the effective optical parameters of the metasurface. This characterization process enables the direct quantification of key performance metrics, including polarization conversion efficiency, phase modulation depth, and operational bandwidth, thereby providing critical insights into the underlying light-matter interactions that govern the metasurface's functionality. These interactions are often studied by conventional benchtop lasers, while the interaction of Free-Electron Lasers (FELs) with metasurfaces is a cutting-edge field driven by the unique properties of FELs (high intensity, ultrashort pulses, broad tunability, and spatial coherence) and the unprecedented light control offered by metasurfaces. However, the ability of FELs to probe metasurfaces is so far limited to pump-probe spectroscopies, which are informative but do not exploit their potential in full. In this presentation, the interaction of FELs with metasurfaces is revisited from a comparison point of view with their counterpart, conventional benchtop lasers. The extraordinary ability of FELs to study metasurfaces is discussed, which can be used as a guideline by researchers in the field of metamaterials and nanophotonics. Finally, some of our recent results on investigating the plasmonic metasurfaces using Free Electron Lasers for Infrared eXperiments (FELIX) are discussed. In this investigation, we studied how the geometrical features of plasmonic metasurfaces will affect the dynamic optical response using time-resolved pump-probe spectroscopy. The transient transmission change was measured for plasmonic metasurfaces with different plasmonic resonances, emphasizing the crucial role of resonance position.
