Size-scaling in optical trapping of silicon nanowires.

We investigate size-scaling in optical trapping of ultrathin silicon nanowires showing how length regulates their Brownian dynamics, optical forces, and torques. Force and torque constants are measured on nanowires of different lengths through correlation function analysis of their tracking signals. Results are compared with a full electromagnetic theory of optical trapping developed in the transition matrix framework, finding good agreement.

Plasmon-enhanced optical trapping of gold nanoaggregates with selected optical properties.

We show how light forces can be used to trap gold nanoaggregates of selected structure and optical properties obtained by laser ablation in liquid. We measure the optical trapping forces on nanoaggregates with an average size range 20-750 nm, revealing how the plasmon-enhanced fields play a crucial role in the trapping of metal clusters featuring different extinction properties. Force constants of the order of 10 pN/nmW are detected, the highest measured on a metal nanostructure.

Brownian motion of graphene.

Brownian motion is a manifestation of the fluctuation-dissipation theorem of statistical mechanics. It regulates systems in physics, biology, chemistry, and finance. We use graphene as prototype material to unravel the consequences of the fluctuation-dissipation theorem in two dimensions, by studying the Brownian motion of optically trapped graphene flakes.

Nanopolaritons: vacuum Rabi splitting with a single quantum dot in the center of a dimer nanoantenna.

We demonstrate with accurate scattering calculations that a system constituted by a single quantum emitter (a semiconductor quantum dot) placed in the gap between two metallic nanoparticles can display the vacuum Rabi splitting. The largest dimension of the investigated system is only 36 nm. This nonperturbative regime is highly desirable for many possible applications in quantum information processing or schemes for controlling individual photons.

Rotational dynamics of optically trapped nanofibers.

We report on the experimental evidence of tilted polymer nanofiber rotation, using a highly focused linear polarized Gaussian beam. Torque is controlled by varying trapping power or fiber tilt angle. This suggests an alternative strategy to previously reported approaches for the rotation of nano-objects, to test fundamental theoretical aspects.

Optical trapping calculations for metal nanoparticles. Comparison with experimental data for Au and Ag spheres.

We calculate the optical forces on Au and Ag nanospheres through a procedure based on the Maxwell stress tensor. We compare the theoretical and experimental force constants obtained for gold and silver nanospheres finding good agreement for all particles with r < 80 nm. The trapping of the larger particles recently demonstrated in experiments is not foreseen by our purely electromagnetic theory based on fixed dielectric properties.

Optical trapping of nonspherical particles in the T-matrix formalism: erratum.

An erratum is presented to correct the errors in two equations in Sect. 2 of [Opt. Express 15, 11984-11998 (2007)].

Optical trapping of nonspherical particles in the T-matrix formalism.

The theory of the trapping of nonspherical particles in the focal region of a high-numerical-aperture optical system is formulated in the framework of the transition matrix approach. Both the case of an unaberrated lens and the case of an aberrated one are considered. The theory is applied to single latex spheres of various sizes and, when the results are compared with the available experimental data, a fair agreement is attained.

On the rotational stability of nonspherical particles driven by the radiation torque.

We calculate the radiation torque exerted by a monochromatic plane wave, either unpolarized or linearly polarized, on aggregates of spheres and investigate the stability of the resulting rotational motion. In fact, neglecting any braking momenta we calculate the component of the electromagnetic torque orthogonal to the principal axis of maximum moment of inertia through the center of mass (transverse torque), as a function of the direction of propagation of the incident field. The aggregates we study are composed of homogeneous spheres, possibly of different materials.

Radiation torque on nonspherical particles in the transition matrix formalism: erratum.

An erratum is presented to correct the errors in two equations in Sect. 3 of [Opt. Express 14, 9508--9521 (2006)].

Radiation torque on nonspherical particles in the transition matrix formalism: erratum.

An erratum is presented to correct the errors in two equations in Sect. 3 of [Opt. Express 14, 9508--9521 (2006)].

Radiation torque on nonspherical particles in the transition matrix formalism.

The torque exerted by radiation on small particles is recognized to have a considerable relevance, e.g., on the dynamics of cosmic dust grains and for the manipulation of micro and nanoparticles under controlled conditions.

Optical scattering by biological aerosols: experimental and computational results on spore simulants.

We present both a computational and an experimental approach to the problem of biological aerosol characterization, joining the expertises reached in the field of theoretical optical scattering by complex, arbitrary shaped particles (multipole expansion of the electromagnetic fields and Transition Matrix), and a novel experimental technique based on two-dimensional angular optical scattering (TAOS). The good agreement between experimental and computational results, together with the possibility for a laboratory single-particle angle-resolved investigation, opens a new scenario in biological particle modelling, and might have major implications for a rapid discrimination of airborne particles.

Optical properties of high-density dispersions of particles: application to intralipid solutions.

We propose to study the scattering properties of dense distributions of spherical scatterers by resorting to an iterative solution of the Foldy-Twersky equation for the propagation of the coherent field. As a result of the first step of the iterative procedure, the host medium is substituted by an effective medium of complex refractive index to account for the multiple-scattering processes that occur among the particles. Although we truncate the above-mentioned iterative procedure to the second step, the results of our calculations are in excellent agreement with previous experimental results of Zaccanti et al.

Efficient light-scattering calculations for aggregates of large spheres.

Calculation of the scattering pattern from aggregates of spheres through the T-matrix approach yields high-precision results but at a high-computational cost, especially when the aggregate concerned is large or is composed of large-size spheres. With reference to a specific but representative aggregate, we discuss how and to what extent the computational effort can be reduced but still preserve the qualitative features of the signature of the aggregate concerned.