Advanced dynamics of optically trapped nanowire waveguides

Abstract

In this thesis I describe a number of studies to examine some high order effects of advanced trapping dynamics beyond the standard single gradient force optical trap. Our interests lay primarily on low symmetry particles, specifically on high refractive index, high aspect ratio nanowires. We examine higher order dynamics due to coupling between rotational and translational degrees of freedom when a single high aspect ratio nanowire is trapped. We also study the coupling of the trapping laser into the waveguiding modes of the trapped nanowire, as well as the coupling interactions between multiple trapped nanowires.

On single optically trapped nanowires, we show calculations beyond the standard power spectral analysis to demonstrate the emergence of resonance behaviour in overdamped systems due to the coupling between rotational and translational degrees of freedom. We also experimentally demonstrate the effects of such coupling which shows up in the form of resonance peaks in the power spectrum when single nanowires are trapped in optical tweezers.

Next we examine the coupling of light into the waveguide modes of high refractive index nanowires by calculating the field profiles, dispersion and group velocity. We then investigate the optical coupling between multiple high refractive index nanowires in close proximity. In particular, we calculate the field profiles, dispersion and optical force of coupled nanowire waveguides with the Coupled Mode Theory and Perturbation Theory. The optical forces between coupled waveguides is also calculated and compared to results obtained from Maxwell’s Stress Tensor calculations.

In the final results chapter, we explore various experimental approaches to experimentally measure the coupled nanowire system that was calculated in the previous chapter. We propose time-shared optical tweezers with interferometric particle tracking as a means of physically measuring the coupling between nanowires and investigate the feasibility of this measurement technique for our system.

In summary, we conducted theoretical analysis and experiments that aid in the further understanding of the advanced dynamics of high refractive index, high aspect ratio nanowires within the optical trapping domain.