Interference of surface plasmons and Smith-Purcell emission probed by angle-resolved cathodoluminescence spectroscopy

Abstract

We investigate the interplay between geometrical lattice resonances and surface plasmons mediating the emission of Smith-Purcell visible light via angle-resolved cathodoluminescence spectroscopy. We observe strong modulations in the dispersion curves of Smith-Purcell radiation (SPR) when they intersect the surface plasmons of silver gratings using a 200-kV transmission electron microscope. The decay of the plasmons away from the grating is directly probed by controlling the electron-beam position relative to the sample surface with nanometer precision. Our measurements are in excellent agreement with numerical simulations, clearly revealing the presence of characteristic Fano profiles resulting from the interference of the light continuum and the discrete plasmon states for each direction of emission. The intensity anomaly in the SPR emission pattern can be well explained from the geometrical consideration of the intersections between the dispersion planes of the SPR and surface plasmon polariton (SPP). A strong and directional SPR beam can be realized under the condition that the SPR dispersion plane comes in contact with the band edge of the SPP dispersion plane.

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.…”

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

“…The Smith-Purcell effect critically depends on precise fabrication of such a periodic structure, which is why the substantial progress in nanofabrication techniques in recent years has revealed a large variety of new applications (e.g., Refs. [14][15][16][17][18][19][20]) based on the SmithPurcell effect. Interestingly, the inverse Smith-Purcell effect has also shown exciting possibilities [21,22], which consequently led to more advanced photonic crystal structures being used as promising platforms for particle acceleration by light excitation of a periodic structure [23][24][25].…”

The role of transition radiation in cathodoluminescence imaging and spectroscopy of thin-foils

“…If angle resolved CL can be performed by imaging the light collected from a mirror using a 2D CCD camera then the coherent and incoherent contributions can be further separated as described in [36] for SEM-CL. Angle resolved CL has been carried out in the TEM by Yamamoto et al [37] using a larger mirror than ours in a 15 mm pole piece gap microscope.…”