Spectrally and Spatially Resolved Smith-Purcell Radiation in Plasmonic Crystals with Short-Range Disorder

Abstract

Electrons interacting with plasmonic structures can give rise to resonant excitations in localized plasmonic cavities and to collective excitations in periodic structures. We investigate the presence of resonant features and disorder in the conventional Smith-Purcell effect (electrons interacting with periodic structures) and observe the simultaneous excitation of both the plasmonic resonances and the collective excitations. For this purpose, we introduce a new scanning-electron-microscope-based setup that allows us to probe and directly image new features of electron-photon interactions in nanophotonic structures like plasmonic crystals with strong disorder. Our work creates new possibilities for probing nanostructures with free electrons, with potential applications that include tunable sources of short-wavelength radiation and plasmonic-based particle accelerators.

Maximal spontaneous photon emission and energy loss from free electrons

“…Consider an electron at velocity β = v/c traversing a structure with periodicity a; it generates far-field radiation at wavelength λ and polar angle θ, dictated by where m is the integer diffraction order. The absence of a minimum velocity in equation (1) offers prospects for threshold-free and spectrally tunable light sources, spanning from microwave and terahertz [14][15][16] , across visible [17][18][19] , and towards X-ray 20 frequencies. In stark contrast to the simple momentum-conservation determination of wavelength and angle, there is no unified yet simple analytical equation for the radiation intensity.…”

Controlling Cherenkov Angles with Resonance Transition Radiation

“…These are characteristic features of the effective backward Cherenkov radiation, which originates only from the constructive interference of resonance transition radiation in the backward direction. This new mechanism for the generation of Cherenkov radiation is different from that of conventional Cherenkov radiation described by the theory developed by Frank and Tamm [2,34] and that of Smith-Purcell radiation [37,38]. For the latter two cases, the generated fields are directly emitted into the air region without the intermediate modulation by a periodic dielectric environment, and the charged particle moves only within one material without crossing interfaces between different materials.…”

“…Therefore, transition radiation from a periodic structure is called the resonance transition radiation [38,39,48].…”

Near-field resonances in photon emission via interaction of electrons with coupled nanoparticles

“…Today we observe the burst of interest in the collective effects in the radiation processes of different nature and in different spectral ranges, from submillimeter (terahertz) to infrared, optical, UV, and x-ray ranges. Local field effects [1][2][3][4][5], including giant enhanced surface phenomena [1,6], excitation of plasmons in surface nanostructures [1,[7][8][9], new applications and ways of realization of the Smith-Purcell effect [5,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22], and many other interesting ideas including the strange, at first glance, ones like search for the new physics with atoms and molecules [23] rather than with collisions of superhighenergy charged particle beams at modern colliders--all these appeal to the attention of researchers all over the world. In a way, it is fair to say that today the interest in collective effects in radiation from complex systems, essentially dependent on the effects of coupling between their constituent elements, takes the lead over the existing theoretical background.…”