Electromagnetic forces and torques in nanoparticles irradiated by a plane wave

Optical tweezers and optical lattices are making it possible to control small particles by means of electromagnetic forces and torques. In this context, a method is presented in this work to calculate electromagnetic forces and torques for arbitrarily-shaped objects in the presence of other objects illuminated by a plane wave. The method is based upon an expansion of the electromagnetic field in terms of multipoles around each object, which are in turn used to derive forces and torques analytically. The calculation of multipole coefficients are obtained numerically by means of the boundary element method. Results are presented for both spherical and non-spherical objects.Comment: 5 papges, 2 figure

Interaction of radiation and fast electrons with clusters of dielectrics: A multiple scattering approach

4 pages, 3 figures.-- PACS numbers: 73.20.Mf, 41.20.Jb, 61.16.Bg, 61.46.+wA fast, accurate, and general technique for solving Maxwell's equations in arbitrarily disposed clusters of dielectric objects is presented, based upon multiple scattering of electromagnetic multipole fields. Examples of application to the simulation of electron energy loss, radiation emission induced by fast electrons, and light scattering are offered. Large rates of Smith-Purcell radiation are predicted in the interaction of fast electrons with strings of Al and SiO2 spheres, suggesting its possible application in tunable soft UV light generation. Mutual electromagnetic interaction among objects in the different clusters under consideration is shown to be of primary importance.Help and support from the University of the Basque Country, the Spanish Ministerio de Educación y Cultura under Fulbright Grant No. FU-98-22726216, and the U.S. DOE under Contract No. DE-AC03-76SF00098 are gratefully acknowledged.Peer reviewe

Probing Quantum Optical Excitations with Fast Electrons

Probing optical excitations with nanometer resolution is important for understanding their dynamics and interactions down to the atomic scale. Electron microscopes currently offer the unparalleled ability of rendering spatially-resolved electron spectra with combined meV and sub-nm resolution, while the use of ultrafast optical pulses enables fs temporal resolution and exposure of the electrons to ultraintense confined optical fields. Here, we theoretically investigate fundamental aspects of the interaction of fast electrons with localized optical modes that are made possible by these advances. We use a quantum-optics description of the optical field to predict that the resulting electron spectra strongly depend on the statistics of the sample excitations (bosonic or fermionic) and their population (Fock, coherent, or thermal), whose autocorrelation functions are directly retrieved from the ratios of electron gain intensities. We further explore feasible experimental scenarios to probe the quantum characteristics of the sampled excitations and their populations.Comment: 13 pages, 6 figures, 56 reference

Nonlinear Plasmonic Sensing with Nanographene

Plasmons provide excellent sensitivity to detect analyte molecules through their strong interaction with the dielectric environment. Plasmonic sensors based on noble metals are, however, limited by the spectral broadening of these excitations. Here we identify a new mechanism that reveals the presence of individual molecules through the radical changes that they produce in the plasmons of graphene nanoislands. An elementary charge or a weak permanent dipole carried by the molecule are shown to be sufficient to trigger observable modifications in the linear absorption spectra and the nonlinear response of the nanoislands. In particular, a strong second-harmonic signal, forbidden by symmetry in the unexposed graphene nanostructure, emerges due to a redistribution of conduction electrons produced by interaction with the molecule. These results pave the way toward ultrasensitive nonlinear detection of dipolar molecules and molecular radicals that is made possible by the extraordinary optoelectronic properties of graphene.Peer ReviewedPostprint (published version