Nanoóptica: controlando la luz en la nanoescala

La localización de la luz en diversas nanoestructuras ha permitido superar los límites de la óptica convencional, posibilitando un control sin precedentes de diversos procesos optoelectrónicos. La comprensión de la interacción entre la luz y la materia en la nanoescala sienta las bases de la generación, control, y manipulación de haces de luz en espacios ínfimos, abriendo un nuevo abanico de posibilidades tecnológicas. Entre otras, la nanoóptica permite obtener imagenes nanoscópicas de nanopartículas y sustancias biológicas, transmitir señal óptica de alta densidad en dispositivos, realizar termoterapia contra células cancerígenas o mejorar las prestaciones de células solares.Peer Reviewe

Probing the electromagnetic response of dielectric antennas by vortex electron beams

Focused beams of electrons, which act as both sources, and sensors of electric fields, can be used to characterise the electric response of complex photonic systems, by locally probing the induced optical near fields. This functionality can be complemented by embracing the recently developed vortex electron beams (VEBs), made up of electrons with orbital angular momentum, which could in addition probe induced magnetic near fields. In this work we revisit the theoretical description of this technique, dubbed vortex Electron Energy-Loss Spectroscopy (v-EELS). We map the fundamental, quantum-mechanical picture of the scattering of the VEB electrons, to the intuitive classical models which treat the electron beams as superposition of linear electric and magnetic currents. We then apply this formalism to characterise the optical response of dielectric nanoantennas with v-EELS. Our calculations reveal that VEB electrons probe electric or magnetic modes with different efficiency, which can be adjusted by changing either beam vorticity or acceleration voltage, to determine the nature of the probed excitations. We also study a chirally-arranged nanostructure, which in the interaction with electron vortices produces dichroism in electron energy loss spectra. Our theoretical work establishes VEBs as versatile probes that could provide information on optical excitations otherwise inaccessible with conventional electron beams

Nanoscale Optical Tomography using Volume-scanning Near-field Microscopy

The relationship between sample structure and data in volume-scanning backscattering mode near-field optical microscopy is investigated. It is shown that the three-dimensional structure of a dielectric sample is encoded in the phase and amplitude of the scattered field and that an approximate reconstruction of the sample structure may be obtained

Substrate-enhanced infrared near-field spectroscopy

17 pages, 8 figures.-- OCIS codes: 240.6490, 300.6340, 180.4243, 290.5825.-- © 2008 Optical Society of America.We study the amplitude and phase signals detected in infrared scattering-type near field optical microscopy (s-SNOM) when probing a thin sample layer on a substrate. We theoretically describe this situation by solving the electromagnetic scattering of a dipole near a planar sample consisting of a substrate covered by thin layers. We perform calculations to describe the effect of both weakly (Si and SiO2) and strongly (Au) reflecting substrates on the spectral s-SNOM signal of a thin PMMA layer. We theoretically predict, and experimentally confirm an enhancement effect in the polymer vibrational spectrum when placed on strongly reflecting substrates. We also calculate the scattered fields for a resonant tip-substrate interaction, obtaining a dramatic enhancement of the signal amplitude and spectroscopic contrast of the sample layer, together with a change of the spectral line shape. The enhanced contrast opens the possibility to perform ultra-sensitive near field infrared spectroscopy of monolayers and biomolecules.We wish to acknowledge financial support from the Department of Industry of the Basque Country (ETORTEK project NANOTRON), from Gipuzkoa Foru Aldundia (nanoGUNE), from the Spanish MEC (NAN2004-08843-C05- 05 and MAT2007-66050), from BMBF grant no. 03N8705, and from the Bavarian California Technology Center (BaCaTec). T.T. was supported by a fellowship within the Postdoc-Programme of the German Academic Exchange Service (DAAD).Peer reviewe