| dc.description.abstract | Nanostructures that exhibit high quality factors, strongly enhanced and tightly confined electromagnetic fields down to subwavelength scales, and accessible hotspots are of paramount importance for photonic devices. Plasmonic nanostructures can generate highly enhanced and tightly confined electromagnetic hotspots but suffer from inherent metal losses that limit their quality factors. Dielectric Mie resonators using high-index dielectric materials have emerged as alternatives due to their negligible intrinsic losses; however, they typically exhibit lower quality factor values and larger mode volumes compared to plasmonic counterparts.
In this dissertation, two novel platforms are investigated: bowtie photonic crystal nanobeams (BPCNs) and metasurfaces driven by quasi-bound states in the continuum (quasi-BICs). Both can achieve high quality factors, strong field enhancement, subwavelength field confinement, flexible tunability, and accessible “hotspots” simultaneously. Based on these properties, new physical concepts and mechanisms that were unattainable in traditional plasmonic and Mie nanostructures are demonstrated.
In Chapter 2, a dielectric quasi-BIC metasurface composed of elliptical silicon resonators is used to demonstrate massive optical trapping of nanoparticles with low-intensity illumination. In Chapter 3, a BPCN nanotweezer system overcomes the limitations of previous photonic-crystal-based optical trapping techniques by utilizing strong electric field confinement to absorb light coupled into the bowtie defect and induce localized heating effects, initiating rapid microscale fluid motion and particle transport at velocities of tens of micrometers per second. In Chapter 4, when illumination power is increased and the chamber height is large, heating effects dominate nanoparticle movements, inducing positive thermophoresis and fluid convection to rapidly transport and aggregate nanoparticles within millimeter scale to the center of the laser spot. This demonstration opens new frontiers in harnessing non-plasmonic nanophotonics for manipulating microfluidic dynamics. In Chapter 5, by introducing slots, enhanced Q and field enhancements are observed in mid-infrared, with benefits for detecting coated proteins shown. Then a plasmonic metasurface, comprising gold elliptical resonators, is introduced as a thermal emitter, achieving a measured Q of approximately 50 with more than 0.6 emissivity. By incorporating slots, the Q can be further enhanced. This was unattainable in earlier metal emitter designs, where the Q was limited to below 10. | |
