Smith-Purcell Metasurface Lens

Abstract

We demonstrate focused emission of visible and near-infrared Smith-Purcell radiation by a free-electron-driven metasurface lens emitter. Our findings pave the way for free-electron light sources focusing at wavelengths lacking efficient optics.

Boosting the Efficiency of Smith–Purcell Radiators Using Nanophotonic Inverse Design

“…More generally, the versatility of the optimization technique allows to design the spectrum (ω), spatial distribution ( r ), and polarization ( e ) of radiation by favoring one kind | e · E ( r , ω)| and penalizing others, −| e ′· E ( r ′, ω′)|, with possibly orthogonal polarization e ′. Lifting the periodicity constraint opens the space to complex metasurfaces, which would for example enable designs for focusing or holograms. ,− , …”

“…The latter are generally limited by the chosen method of fabrication. Typical gratings for the generation of near-infrared, visible, or ultraviolet light are fabricated by reactive-ion etching or focused-ion-beam milling of silicon or fused silica. − , Coating the grating with a metal such as gold, silver, or aluminum can lead to plasmonic enhancement. − …”

“…While a simple rectangular grating has been the most common choice in Smith–Purcell experiments, other designs have been investigated, such as metasurfaces and aperiodic structures. ,− Here, we explored the optimization technique of nanophotonic inverse design − to generate SPR much more efficiently. In contrast to other photonic designs created manually and optimized for a small set of parameters, inverse design finds an optimal design without any prior knowledge of its shape, purely based on the desired performance.…”