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Abstract

Optical trapping and optical tweezers have been used to confine and control micron and nano-sized objects based on light–matter interactions. When multiple particles are in a single optical trap, they interact with one another and form organized arrays referred to as optical matter. Optical matter is a unique formation of matter in that the interactions between particles are controlled by an external light source and its properties can be tuned with the properties of light, such as intensity, polarization, and phase. The persistent flux of the optical field that is inherent to optical matter provides novel dynamical properties, making optical matter systems inherently non-equilibrium and creating non-conservative forces and non-reciprocal interactions. As will be shown in this thesis, these properties can be utilized to build functional materials that do work at the nano-scale. The role of non-conservative forces acting on a single optically trapped particle has been studied, but less attention has been given to the role of non-conservative interactions present in optical matter. We demonstrate that non-conservative interactions give rise to a non-reciprocal net-force in an optically bound hetero-dimer. More generally, when there are many identical particles forming an array, a single non-identical intruder particle is expelled from the array due to non-reciprocal interactions. This principle is used to segregate mixtures of optically trapped nanoparticles by size and material. We also demonstrate that non-conservative interactions give rise to positive and negative orbital torques in optical matter arrays. These arrays convert the incident spin angular momentum of light into scattered outgoing orbital angular momentum. This conversion processes is used to design a stochastic optical matter machine that utilizes non-conservative driving forces and Brownian forces for its operation. A common theme that emerges is the importance of collective electrodynamic excitations in structured nanoparticle arrays. The selective excitation of different collective scattering modes is achieved using scalar and cylindrical vector beams. These principles are used to design and analyze a core-satellite meta-atom that has strong near-field coupling and can support magnetic modes at optical frequencies. Such meta-atoms are potential building blocks for meta-fluids and meta-materials. Optical matter and meta-atom systems are efficiently simulated using a developed generalized Mie theory software that can be coupled to a Langevin equation of motion.

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