Spin-Orbit Angular-Momentum Transfer from a Nanogap Surface Plasmon to a Trapped Nanodiamond.

The ability to control the motion of single nanoparticles or molecules is currently one of the major scientific and technological challenges. Despite tremendous progress in the field of plasmonic nanotweezers, controlled nanoscale manipulation of nanoparticles trapped by a plasmonic nanogap antenna has not been reported yet. Here, we demonstrate the controlled orbital rotation of a single fluorescent nanodiamond trapped by a gold trimer nanoantenna irradiated by a rotating linearly polarized light or circularly polarized light. Remarkably, the rotation direction is opposite to the light's polarization rotation. We numerically show that this inversion comes from sequential excitation of individual nanotriangles in the reverse order when the linear polarization is rotated, whereas using a circular polarization, light-nanoparticle angular momentum transfer occurs via the generation of a Poynting vector vortex of reversed handedness. This work provides a new path for the control of light-matter angular momentum transfer using plasmonic nanogap antennas.

Plasmonic Manipulation-Controlled Chiral Crystallization of Sodium Chlorate.

Plasmonic manipulation using well-designed triangular trimeric gold nanostructures achieves a giant (greater than 50%) crystal enantiomeric excess (CEE) of sodium chlorate (NaClO3). Stronger asymmetric interactions between molecule and light are pursued to reach high enantiomeric excess. The well-designed gold nanostructures immersed in a saturated NaClO3 D2O solution were irradiated with linear, left-hand, and right-hand circular polarizations of a 1064 nm continuous-wave laser. Within seconds of the start of the irradiation, an achiral metastable crystal was formed at the laser focus, and further irradiation induced a subsequent polymorphic transition to the chiral crystal. The crystal chirality is sensitive to the handedness of circular polarization, allowing for efficient enantioselectivity. The mechanisms to achieve this giant CEE are proposed based on the results of electromagnetic field analysis generated near the nanostructure by the finite element method.

Trapping and Deposition of Dye-Molecule Nanoparticles in the Nanogap of a Plasmonic Antenna.

Plasmonic nanostructures, which allow light focusing at the deep subwavelength scale, and colloidal nanoparticles with unique optoelectronic properties are nowadays fabricated with nanometer precision. However, to fully control and exploit nanoscale light-matter interactions in hybrid plasmonic-nanophotonic devices, both materials must be assembled in heterostructures with similar precision. Near-field optical forces have recently attracted much attention, as they can precisely trap and position nanoparticles at plasmonic hotspots. However, long-range attraction and the surface bonding of nanoparticles usually require other specific techniques, such as electrothermal heating and surface chemical treatments. This Letter reports on the optical trapping and deposition of dye-molecule nanoparticles in the nanogap of a gold antenna. The nanoparticles are captured by focusing a near-infrared laser beam on a targeted plasmonic antenna. This single-step deposition process requires only a few seconds under 1.4-1.8 MW·cm-2 continuous-wave illumination and shows a polarization dependence smaller than expected. Fluorescence and electronic microscopy observations suggest that nanoparticle deposition arises from a trade-off between optical and thermal effects.

Quantitative comparison of contrast and imaging depth of ultrahigh-resolution optical coherence tomography images in 800-1700 nm wavelength region.

We investigated the wavelength dependence of imaging depth and clearness of structure in ultrahigh-resolution optical coherence tomography over a wide wavelength range. We quantitatively compared the optical properties of samples using supercontinuum sources at five wavelengths, 800 nm, 1060 nm, 1300 nm, 1550 nm, and 1700 nm, with the same system architecture. For samples of industrially used homogeneous materials with low water absorption, the attenuation coefficients of the samples were fitted using Rayleigh scattering theory. We confirmed that the systems with the longer-wavelength sources had lower scattering coefficients and less dependence on the sample materials. For a biomedical sample, we observed wavelength dependence of the attenuation coefficient, which can be explained by absorption by water and hemoglobin.

Three-dimensional, non-invasive, cross-sectional imaging of protein crystals using ultrahigh resolution optical coherence tomography.

Micro-scale, non-invasive, three-dimensional cross-sectional imaging of protein crystals was successfully accomplished using ultra-high resolution optical coherence tomography (UHR-OCT) with low noise, Gaussian like supercontinuum. This technique facilitated visualization of protein crystals even those in medium that also contained substantial amounts of precipitates. We found the enhancement of the scattered signal from protein crystal by inclusion of agarose gel in the crystallization medium. Crystals of a protein and a salt in the same sample when visualized by UHR-OCT showed distinct physical characteristics, suggesting that protein and salt crystals may, in general, be distinguishable by UHR-OCT. UHR-OCT is a nondestructive and rapid method, which should therefore find use in automated systems designed to visualize crystals.