In this paper, we report the microscopic excitation and imaging of dielectric Mie resonators. The interaction of tightly focused vector beams with dielectric nanoparticles leads to exotic phenomena including multipolar excitation by displacement resonances, directional scattering, as well as superresolution imaging
We study the scattering behavior of silicon nanoblocks in various displacements with respect to the optical axis of a tightly focused linearly polarized Gaussian beam. Experimentally, the laser scanning image of a single nanoblock deviates significantly from coherent image convolution. Theoretically, with exact Cartesian multipole decomposition, the results are explained through generation of high-order multipoles at large focus displacement and multipole interference. Surprisingly, due to the high-order multipoles, the efficiency of photothermal nonlinearity and Raman scattering are better with displaced focus. Our result extends Mie theory with displaced tight focus, opening up new opportunities in nanoscale light-matter interactions.
The phase of an optical system being a circularly variable becomes undefined when the intensity vanishes, which is generally referred to as optical singularity. At the intensity vanishing point, singular phase or topological phase appears. In fact, optical singularity is pervasive in many physical phenomena such as vortex beams, reflection at Brewster’s angle, and perfect absorption and so on. Associated with the singularity point, the optical systems exhibit many nontrivial behaviors which could underpin tremendous nanophotonic applications. In this talk, I will present the utilization of such singular optics for metasurfaces as well as for far-field superresolution imaging. In the first part, we show that the losses of atomic thin layered materials can be used to create points of darkness (zero reflection). The singular phase behavior of the optical systems crossing the darkness point can lead to an abrupt phase jump of pi. Harnessing the Heaviside phase jump, we demonstrate atomic thin metasurface for light field manipulations. In the second part, we show that high-index dielectric nanostructures can support radiationless anapole state allowing vanishing far-field scattering accompanying with strong near fields. The unique feature can be utilized for giant photothermal nonlinear scattering modulations as well as application in far-field superresolution localization microscopy with an accuracy up to 40 nm.
Even though optical storage has been well heralded as green techniques, the conventional optical memories have been constantly challenged as they reached theirs physical limits imposed by nonlinear effects. Recently, nanophotonics harnesses light’s interaction with materials at the nanoscale including the generation of nanoscale optical probes and the interaction with nanocomposite materials, offering bottom-up new approaches far superior to the conventional technology. In this regard, nanophotonics has emerged as a major propellant for the next generation of ultra-high capacity optical memories for big data. In this talk, we present the recent development of ultra-high capacity optical memories multiplexing information in the physical domain of the writing beams through tailoring the interaction between a tightly focused pulsed laser beam and plasmonic materials [1]. To circumvent the diffraction limit of light discovered by Ernst Abbe, tremendous research approaches have been developed including stimulated emission depletion (STED) microscopy [2]. Through coherently manipulating the distribution of excitons in the fluorophore molecules by a dual-beam approach, where one Gaussian shaped beam can pump the molecules into the excited state while the second doughnut shaped beam can inhibit the subsequent emission through stimulated emission processes, STED microscopy enables superresolved imaging as well as laser lithography [3, 4]. Based on this principle, superresolution optical memories enabled by the dual-beam approach has been demonstrated with an ultra-high equivalent capacity [5].
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