Abstract
Metasurfaces are subwavelength spatial variations in geometry and material where the structures are of negligible thickness compared to the wavelength of light and are optimized for far-field applications, such as controlling the wavefronts of electromagnetic waves. Here, we investigate the potential of the metasurface near-field profile, generated by an incident few-cycle pulse laser, to facilitate the generation of high-frequency light from free electrons. In particular, the metasurface near-field contains higher-order spatial harmonics that can be leveraged to generate multiple higher-harmonic X-ray frequency peaks. We show that the X-ray spectral profile can be arbitrarily shaped by controlling the metasurface geometry, the electron energy, and the incidence angle of the laser input. Using ab initio simulations, we predict bright and monoenergetic X-rays, achieving energies of 30 keV (with harmonics spaced by 3 keV) from 5-MeV electrons using 3.4-eV plasmon polaritons on a metasurface with a period of 85 nm. As an example, we present the design of a four-color X-ray source, a potential candidate for tabletop multicolor hard X-ray spectroscopy. Our developments could help pave the way for compact multi-harmonic sources of high-energy photons, which have potential applications in industry, medicine, and the fundamental sciences.
Highlights
The development of compact, tunable light sources is an extremely coveted goal: on-chip infrared and optical sources are sought after for photonic integration[1], while powerful tabletop UV to X-ray sources are potentially useful in applications ranging from medical therapy and diagnostics to industrial quality control, security scans, and the fundamental sciences[2,3,4,5]
We show that the metasurface geometry can be tailored to control and optimize the properties of the higher-order spatial harmonics, resulting in a tunable source of multi-harmonic radiation
We present a concept for a multiharmonic X-ray source, where electron energy and metasurface geometry can be used to directly tailor the spatiotemporal profile of the X-ray output
Summary
The development of compact, tunable light sources is an extremely coveted goal: on-chip infrared and optical sources are sought after for photonic integration[1], while powerful tabletop UV to X-ray sources are potentially useful in applications ranging from medical therapy and diagnostics to industrial quality control, security scans, and the fundamental sciences[2,3,4,5]. Active graphene plasmonbased light sources[13,14] have been considered, exploiting the strongly confined plasmonic field sustained by graphene to generate high-frequency radiation by scattering free electrons. These plasmon-based free-electron light sources have the potential to access extremely high photon energies (e.g., hard X-ray photons) without using highly relativistic electrons or high-intensity lasers. We leverage the presence of high-order spatial harmonics in metasurface-enhanced plasmon polaritons that are in turn excited by ultrashort laser pulses to generate multiple higher-order X-ray harmonics via electron–polariton scattering.
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call