Spectral and spatial shaping of Smith Purcell Radiation

The Smith Purcell effect, observed when an electron beam passes in the vicinity of a periodic structure, is a promising platform for the generation of electromagnetic radiation in previously-unreachable spectral ranges. However, most of the studies of this radiation were performed on simple periodic gratings, whose radiation spectrum exhibits a single peak and its higher harmonics predicted by a well-established dispersion relation. Here, we propose a method to shape the spatial and spectral far-field distribution of the radiation using complex periodic and aperiodic gratings. We show, theoretically and experimentally, that engineering multiple peak spectra with controlled widths located at desired wavelengths is achievable using Smith-Purcell radiation. Our method opens the way to free-electron driven sources with tailored angular and spectral response, and gives rise to focusing functionality for spectral ranges where lenses are unavailable or inefficient

Spherical aberration correction in a scanning transmission electron microscope using a sculpted foil

Nearly twenty years ago, following a sixty year struggle, scientists succeeded in correcting the bane of electron lenses, spherical aberration, using electromagnetic aberration correction. However, such correctors necessitate re-engineering of the electron column, additional space, a power supply, water cooling, and other requirements. Here, we show how modern nanofabrication techniques can be used to surpass the resolution of an uncorrected scanning transmission electron microscope more simply by sculpting a foil of material into a refractive corrector that negates spherical aberration. This corrector can be fabricated at low cost using a simple process and installed on existing electron microscopes without changing their hardware, thereby providing an immediate upgrade to spatial resolution. Using our corrector, we reveal features of Si and Cu samples that cannot be resolved in the uncorrected microscope.Comment: Roy Shiloh, Roei Remez, and Peng-Han Lu equally contributed to this wor

Roadmap on superoscillations

Superoscillations are band-limited functions with the counterintuitive property that they can vary arbitrarily faster than their fastest Fourier component, over arbitrarily long intervals. Modern studies originated in quantum theory, but there were anticipations in radar and optics. The mathematical understanding—still being explored—recognises that functions are extremely small where they superoscillate; this has implications for information theory. Applications to optical vortices, sub-wavelength microscopy and related areas of nanoscience are now moving from the theoretical and the demonstrative to the practical. This Roadmap surveys all these areas, providing background, current research, and anticipating future developments

Roadmap on Superoscillations

Superoscillations are band-limited functions with the counterintuitive property that they can vary arbitrarily faster than their fastest Fourier component, over arbitrarily long intervals. Modern studies originated in quantum theory, but there were anticipations in radar and optics. The mathematical understanding—still being explored—recognises that functions are extremely small where they superoscillate; this has implications for information theory. Applications to optical vortices, sub-wavelength microscopy and related areas of nanoscience are now moving from the theoretical and the demonstrative to the practical. This Roadmap surveys all these areas, providing background, current research, and anticipating future developments

Wavefront Shaping of Plasmonic Beams by Selective Coupling

Custom plasmonic beams are advantageous for numerous scientific and technological aspects. While plasmonic wavefront shaping had traditionally been a truly planar process, taking place on a single surface, here we explore a new method for plasmonic shaping by selectively coupling plasmonic waves between different surfaces of an insulator–metal–insulator structure. In contrast to most previous shaping techniques that rely on free-space illumination, here the plasmonic beam in the buried surface acts as the light source. We demonstrate, both experimentally and numerically, a way to tailor the amplitude and phase of the wavefront using this new technique. The proposed method can be used to efficiently shape the plasmonic beam, for potential applications in sensing, interferometry, and communications

Visualization 1: Measurement of acceleration and orbital angular momentum of Airy beam and Airy-vortex beam by astigmatic transformation

Propagation of Astigmatic transformed Airy-Vortex beam Originally published in Optics Letters on 15 November 2015 (ol-40-22-5411

Perspektiven fuer die Agrarreformpolitik Simbabwes im Lichte aethiopischer und kenianischer Erfahrungen

SIGLEBibliothek Weltwirtschaft Kiel C137341 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Generation of super-oscillatory electron beams beyond the diffraction limit

In 1873, Ernst Abbe discovered that the imaging resolution of conventional lenses is fundamentally limited by diffraction, which, since then, has been overcome using a variety of different approaches in optical microscopy. In electron microscopy, thanks to remarkable developments in aberration corrected electron optics, the resolution of transmission electron microscopes (TEMs) and scanning TEMs (STEMs) has reached the sub-Ångström regime. However, it is still limited by instrumental stability, residual higher-order aberrations and the diffraction limit of the electron-optical system. Recently, a concept termed super-oscillation, which is analogous to the idea of super-directive antennas in the microwave community [1], was proposed [2, 3] and applied in light optics for far field imaging of sub-wavelength, barely-resolved objects beyond the diffraction limit [4]. A super-oscillating function is a band-limited function that is able to oscillate faster locally than its highest Fourier component and thereby produce an arbitrarily small spot in the far field.Here, we demonstrate experimentally for the first time a super-oscillatory electron beam whose characteristic probe size is much smaller than the Abbe diffraction limit. Figure 1(a) shows scanning electron microscopy (SEM) images of a conventional grating mask (left) and a super-oscillation off-axis hologram (right) that have the same outer diameters (10 µm). The masks were fabricated by focused ion beam milling 200-nm-thick SiN membranes coated with 150 nm Au. The masks were inserted into the C2 aperture plane of a probe-corrected FEI Titan 80-300 (S)TEM. Owing to the probe aberration corrector and relatively small numerical aperture (convergence semi-angle), diffraction-limited spots could be easily obtained from the conventional grating (Fig. 1, left), while a super-oscillatory electron probe, which was generated at the first diffraction order (Fig. 1, right), produced a much smaller hot-spot in the center. The size of the super oscillation hot-spot is approximately one third of that of the diffraction-limited spot. It could theoretically be decreased further, even below the de-Broglie wavelength of the electrons, by varying the ratio between the inner and outer radii.Further applications of such super-oscillatory electron wave functions, e.g. enhanced STEM imaging, will be presented

Generation of super-oscillatory beams beyond the diffraction limit

In 1873, Ernst Abbe discovered that the imaging resolution of conventional lenses is fundamentally limited by diffraction, which, since then, has been overcome using a variety of different approaches in optical microscopy. In electron microscopy, thanks to remarkable developments in aberration corrected electron optics, the resolution of transmission electron microscopes (TEMs) and scanning TEMs (STEMs) has reached the sub-Ångström regime. However, it is still limited by instrumental stability, residual higher-order aberrations and the diffraction limit of the electron-optical system. Recently, a concept termed super-oscillation, which is analogous to the idea of super-directive antennas in the microwave community [1], was proposed [2, 3] and applied in light optics for far field imaging of sub-wavelength, barely-resolved objects beyond the diffraction limit [4]. A super-oscillating function is a band-limited function that is able to oscillate faster locally than its highest Fourier component and thereby produce an arbitrarily small spot in the far field.Here, we demonstrate experimentally for the first time a super-oscillatory electron beam whose characteristic probe size is much smaller than the Abbe diffraction limit. Figure 1(a) shows scanning electron microscopy (SEM) images of a conventional grating mask (left) and a super-oscillation off-axis hologram (right) that have the same outer diameters (10 µm). The masks were fabricated by focused ion beam milling 200-nm-thick SiN membranes coated with 150 nm Au. The masks were inserted into the C2 aperture plane of a probe-corrected FEI Titan 80-300 (S)TEM. Owing to the probe aberration corrector and relatively small numerical aperture (convergence semi-angle), diffraction-limited spots could be easily obtained from the conventional grating (Fig. 1, left), while a super-oscillatory electron probe, which was generated at the first diffraction order (Fig. 1, right), produced a much smaller hot-spot in the center. The size of the super oscillation hot-spot is approximately one third of that of the diffraction-limited spot. It could theoretically be decreased further, even below the de-Broglie wavelength of the electrons, by varying the ratio between the inner and outer radii.Further applications of such super-oscillatory electron wave functions, e.g. enhanced STEM imaging, will be presented

Nanostructuring of electron beams

The remarkable technological advancements that culminated in today's powerful electron microscope have enabled scientists to traverse into new regimes of the nanoworld. However, the versatility of this complicated optical beamline allows for more than just inspecting atoms: by shaping the electron beam, new and interesting phenomena are sought after by the interaction of shaped beams with matter. Here, we review the recent newly-emerged field of electron beam shaping by thin-film interaction of nanostructures and by interaction with shaped electrostatic fields