Nanoparticles of different compositions, sizes, and shapes are elaborated and trapped in a reproducible and stable manner using our optical fiber tip tweezers. Here we report trapping of spherical YAG : Ce3 + particles of 300 and 60 nm diameters and of NaYF4 : Er3 + , Yb3 + nanorods of lengths from 640 nm to 1.9 μm. The properties of the tweezers are analyzed by video observations using Boltzmann statistics and power spectra analysis. Efficient trapping is found for the spherical particles and the small nanorods, whereas the large nanorods are efficiently trapped with only one fiber tip. The optical emission of a trapped nanorod completes the experimental results. Force calculations using the exact Maxwell stress tensor formalism are conducted to explain the experimental observations.
The coupling between thick-shell CdSe/CdS colloidal nanocrystals with the hot spots of a semicontinuous gold film is characterized by measuring simultaneously the photoluminescence decay rate and the linear polarization ratio. The absence of correlations between the two quantities is demonstrated. In contrast with the results obtained with continuous gold films, polarization ratios higher than 80% are achieved for the smallest nanocrystals. This ratio decreases quickly when the nanocrystals size is increased.
NaYF4:(Er,Yb,Gd) nanorods of different size were trapped using our original optical tweezers consisting of two fiber tips facing each other. Trapping properties were found to depended drastically on the actual particle size. Small rods were efficiently trapped whereas long rods were strongly attracted by the fiber tips and their stable trapping position was situated at the apex of one single fiber tip. In the case of the long particles the trapped particle modified the fiber tip emission properties and trapping of a second nanorod at distances of some microns from the first one is observed. These experimental results will be explained by numerical simulations using the exact Maxwell Stress Tensor approach.
The optical transmission between two metalized optical fiber tips with sub-wavelength open apertures was studied
for tip-to-tip distances down to ten nanometers. Transverse transmission maps with sub-wavelength structures
clearly indicated optical near-field coupling. Depending on light polarization in the emission fiber tips one or
two transmission peaks were observed. All these results were explained by a straightforward analytical model.
We present the stable trapping of luminescent 300-nm cerium-doped YAG particles in aqueous suspension using a dual fiber tip optical tweezers. The particles were elaborated using a specific glycothermal synthesis route together with an original protected annealing step. We obtained harmonic trap potentials in the direction transverse to the optical fiber axes. In the longitudinal direction, the potential shows some sub-structure revealed by two peaks in the distribution statistics with a distance of about half the wavelength of the trapping laser. We calculated intensity normalized trapping stiffness of 36 pN•μm-1W-1. These results are compared to previous work of microparticle trapping and discussed thanks to numerical simulations based on finite element method.
This work summarizes how plasmonic phenomena can enhance the fluorescence of lanthanides (Ln3+) coupled to metallic nanoparticles (MNP). Lanthanide-ions emission lines, based on 4f-4f transitions, are weak due to Laporte selection rules for optical transitions. This effect results in low absorption cross sections for excitation and long lifetimes for emission processes. We propose to use metallic nanoparticles in order to determine how plasmonic nanoparticles can enhance absorption and emission of two emblematic lanthanides ions used for bio-labeling and energy conversion, i.e., Eu3+ and Er3+. This work quantifies the average enhancement factor (AEF) is expected for different geometries of nanoparticle structures and compares it to previous studies. Then, we theoretically and numerically investigate metal-enhanced fluorescence of plasmonic core–shell nanoparticles doped with lanthanides ions. The shape and size of the particles are engineered to maximize the average enhancement factor of the overall doped shell. We show with theoretical considerations and numerical studies that the highest enhancement (11 in the visible and 7 in the near-infrared) is achieved by tuning either the dipolar or the quadrupolar particle resonance to the rare-earth ion’s excitation wavelength. Additionally, the calculated AEFs are compared to experimental data reported in the literature, obtained under similar conditions (plasmon-mediated enhancement) or when a metal–Ln3+ energy-transfer mechanism is involved.
Waveguiding by dielectric-loaded surface plasmon-polaritons (DLSPP) structures are numerically and experimentally investigated. We used the effective index model to understand the influence of basic waveguide parameters such as width and thickness on the properties of the surface plasmon guided modes. A waveguide was fabricated
and experimentally studied. The effective indices of the modes supported by the waveguide and their propagation length are evaluated by leakage radiation microscopy in both the Fourier and imaging planes. Several excitation schemes were tested including surface plasmon coupling by diascopic or episcopic illumination as well as defectmediated excitation of guided modes. We found good agreement between theoretical values predicted by the effective index model and experimental values deduced from leakage radiation images.
In this paper we present an experimental apparatus capable of measuring the differential scattering cross sections of individual nanoparticles and arrangement of nanoparticles. We show that the mapping a partial differential scattering cross section, qualitative information about the electromagnetic local density of states dominated by evanescent modes scattered by the structure can be obtained.