Plasmonic nanofocusing – grey holes for light

Abstract

Improving the resolution and sensitivity in all-optical microscopy and spectroscopy is inevitably one of the most important challenges in contemporary optical and nanoscience. Here, we discuss a novel approach, plasmonic nanofocusing, towards broadband, coherent all-optical microscopy with ultrahigh temporal and spatial resolution. The conceptual idea is to launch radially symmetric surface plasmon polariton modes onto the shaft of a sharp, conical metal taper. While propagating towards the apex of the pointed taper, the spatial extent of the plasmonic mode gradually shrinks, from several microns in diameter to a spot size of less than 10 nm at the pointed apex of the conical taper. Concomitantly, the local field amplitude of the plasmon mode gradually increases, resulting in a pronounced field enhancement at the apex and -thus -a bright and spatially isolated coherent light source with dimensions far below the diffraction limit. In this review, we characterize the optical properties of such three-dimensional conical metal tapers and demonstrate nanofocusing of radially symmetric plasmon modes. We use this nanolight source for coherent light scattering spectroscopy and demonstrate the sensitivity enhancement resulting from the pronounced spatial field confinement. It is shown that such off-resonant plasmonic nanoantennas facilitate the creation of nanofocused light spots with few-cycle time resolution. As a first application of this ability to nanolocalize ultrashort plasmon wavepackets, we demonstrate remotely-triggered multiphoton-induced photoemission from the very apex of the taper and implement this novel ultrafast electron gun in a point-projection electron microscope. Our results not only indicate the favourable optical properties of this plasmonic nanolens but also suggest that it may find interesting applications in ultrafast scanning optical spectroscopy and might enable new types of ultrafast electron holography and scanning tunnelling microscopy.

Schrödinger electrons interacting with optical gratings: quantum mechanical study of the inverse Smith–Purcell effect

“…In order to boost the interaction and facilitate the necessary momentum and energy transfer, the near-field distribution of the optical modes is usually considered as the interaction medium [10]. In particular, the evanescent field in the vicinity of discontinuities such as an interface [22][23][24], plasmonic nanostructures [25][26][27][28][29][30][31][32][33][34][35], photonic crystals [36,37], and gratings [38,39] has been so far considered. Interestingly, a classical treatment of the electron-photon interaction demonstrates the necessity of the momentum conservation criterion to be met as w = ⋅ k V e ph ph   (w ph is the angular momentum of the photon, k ph  is the wave vector of the photon, V e  is the velocity of the electron) which agrees perfectly well with the first principles of quantum mechanics [10].…”

Шаблонный Синтез Микроструктур Железа На Основе Трековых Мембран

“…46346.17262 Получение ориентированных металлических острийных микрострук-тур представляет интерес для создания систем управления излучением оптического и рентгеновского диапазонов, элементов устройств хране-ния информации и т. д. [1][2][3][4]. Если такая двумерная микроструктура состоит из магнитного материала (железа, никеля, кобальта или их сплавов), то благодаря сильной анизотропии формы она приобретает одноосную магнитную анизотропию, что обусловливает возможность ее использования в качестве элемента памяти [5].…”

Probing plasmonic excitation mechanisms and far-field radiation of single-crystalline gold tapers with electrons

“…One of the most established and widely used nanostructures are conically shaped metallic tapers, due to their practical application as waveguides or nanoantennas in scanning near-field optical microscopy (SNOM) [7,[15][16][17][18][19][20][21][22][23] or as an ultrafast photoemission source in point-projection microscopes [24][25][26][27][28][29][30][31][32][33].…”

“…To investigate the underlying physical principles of these technologically important nanophotonic devices, several characterization techniques and numerical simulation methods have been employed to further understand excitation and propagation processes and the mechanism of focusing electromagnetic energy to the nanoscale (figure 1c) [7,19,32,[34][35][36][37][38].…”