Direct Observation of Optical Field Phase Carving in the Vicinity of Plasmonic Metasurfaces.

Plasmonic surfaces are mainly used for their optical intensity concentration properties that allow for enhancement of physical interaction like in nonlinear optics, optical sensors, or tweezers. Phase response in plasmonic resonances can also play a major role, especially in a periodic assembly of plasmonic resonators like metasurfaces. Here we show that localized surface plasmons collectively excited by a guided mode in a metallic nanostructure periodic chain present nonmonotonous phase variation along the 1D metasurface, resulting from both selective Bloch mode coupling and dipolar coupling. As shown by near-field measurements, the phase profile of the highly concentrated optical field is carved out in the vicinity of the metallic metasurface, paving the way to unusual local optical functions.

Observation of near-field dipolar interactions involved in a metal nanoparticle chain waveguide.

We present near-field measurements of transverse plasmonic wave propagation in a chain of gold elliptical nanocylinders fed by a silicon refractive waveguide at optical telecommunication wavelengths. Eigenmode amplitude and phase imaging by apertureless scanning near-field optical microscopy allows us to measure the local out-of-plane electric field components and to reveal the exact nature of the excited localized surface plasmon resonances. Furthermore, the coupling mechanism between subsequent metal nanoparticles along the chain is experimentally analyzed by spatial Fourier transformation on the complex near-field cartography, giving a direct experimental proof of plasmonic Bloch mode propagation along array of localized surface plasmons. Our work demonstrates the possibility to characterize multielement plasmonic nanostructures coupled to a photonic waveguide with a spatial resolution of less than 30 nm. This experimental work constitutes a prerequisite for the development of integrated nanophotonic devices.

Promoting Health Research among Underrepresented Students through the HUI SRC.

The Hawai'i Pacific University Undergraduate Infrastructure Student Research Center (HUI SRC) is focused on increasing participation of historically underrepresented populations, such as Native Hawaiians, other Pacific Islanders (NHPI), and Filipinos, in tomorrow's biomedical and health research workforce. This is achieved by promoting engagement and competency in entrepreneurial biomedical and health research among undergraduate students. The HUI SRC was modeled after the Morgan State University ASCEND SRC funded by the National Institute of General Medical Sciences. The HUI SRC is rooted in the Hawaiian cultural values of ho'oku'i, hui pu'ana, and lokahi, referring to the physical gathering space of the Student Research Center and the joining of people together around a unifying theme, in this case the pursuit of science. It is committed to intentionally engaging Indigenous knowledge and ways of doing in decolonizing research. This article describes the project and presents evaluation findings of the first year of implementation of the HUI SRC. The center was effective in increasing undergraduate students' science identity, academic self-concept, social self-concept, social support, peer support, and self-efficacy. These HUI SRC findings highlight the potential impact of undergraduate SRCs in expanding the pipeline of biomedical and health researchers from underrepresented populations, particularly among NHPI and Filipinos.

Enhanced light coupling in sub-wavelength single-mode silicon on insulator waveguides.

We report on NIR efficient end-coupling in single-mode silicon on insulator waveguides. Efficient coupling has been achieved using Polymer-Tipped Optical Fibers (PTOF) of adaptable radius of curvature (ROC). When compared with commercial micro lenses, systematic studies as a function of PTOF ROC, lead for subwavelength PTOF to a coupling factor enhancement as high as 2.5. This experimental behavior is clearly corroborated by radial FDTD simulations and an absolute coupling efficiency of about 50% is also estimated.

Field localization and enhanced Second-Harmonic Generation in silicon-based microcavities.

High-quality amorphous Silicon Nitride (a-Si(1-x)N(x):H) Fabry-Pérot microcavities can show resonant surface Second Harmonic Generation (SHG) effect. We consider two different layouts of planar microcavities with almost identical linear reflectance and show how the structure geometry can strongly affect SHG yield. In particular, a difference of more than one order of magnitude in the SHG intensity is observed when the fundamental beam is tuned at the cavity resonance frequency. We explain this finding on the basis of a theoretical model taking into account the spatial distribution of the electric fields of the pump and harmonic frequencies inside the structure. A satisfactory matching of experimental data with the theoretical model is obtained by considering the source of second-order nonlinearity as limited to surface contributions.

Enlarged atomic force microscopy scanning scope: novel sample-holder device with millimeter range.

We propose a homemade sample-holder unit used for nanopositionning in two dimensions with a millimeter traveling range. For each displacement axis, the system includes a long range traveling stage and a piezoelectric actuator for accurate positioning. Specific electronics is integrated according to metrological considerations, enhancing the repeatability performances. The aim of this work is to demonstrate that near-field microscopy at the scale of a chip is possible. For this we chose to characterize highly integrated optical structures. For this purpose, the sample holder was integrated into an atomic force microscope. A millimeter scale topographical image demonstrates the overall performances of the combined system.

Note: Multiscale scanning probe microscopy.

Combining the nanoscopic and macroscopic worlds is a serious challenge common to numerous scientific fields, from physics to biology. In this paper, we demonstrate nanometric resolution over a millimeter range by means of atomic-force microscopy using metrological stage. Nanometric repeatability and millimeter range open up the possibility of probing components and materials combining multiscale properties i.e., engineered nanomaterials. Multiscale probing is not limited to atomic-force microscopy and can be extended to any type of scanning probe technique in nanotechnology, including piezoforce microscopy, electrostatic-force microscopy, and scanning near-field optical microscopy.

Apertureless scanning near-field optical microscopy for ion exchange channel waveguide characterization.

We report the characterization of an integrated Ag+/Na+ ion exchange waveguide realized in a silicate glass substrate using apertureless scanning near-field optical microscopy. Our experimental set-up is based on the combination of a commercial atomic force microscope with an optical confocal detection system. Thanks to this system, the topography and evanescent optical field at the waveguide top surface are mapped simultaneously. Also, the process of apertureless scanning near-field optical microscopy image formation is analysed. In particular, fringe patterns appearing in the image reveal the intrinsic interferometric nature of the collected signal, due to interference between the field scattered by the tip end and background fields related to guide losses. We give a quantitative interpretation of these fringes. Evanescent intensity mapping on the sample surface allowed us to extract physical waveguide parameters. In particular, it shows an unambiguous multimode beat along the waveguide propagation axis. Furthermore, we show that analysis of this intensity profile reveals back-reflection effects from the waveguide exit facet. The resulting standing waves pattern allows us to evaluate the eigenmode propagation constants.