Localized surface plasmon resonances (LSPR) occur in certain metals where electrons confined to the metal surface oscillate with similar frequency as the perturbation source, giving rise to localized electromagnetic fields. In this study we employ experimental and theoretical analyses to characterize LSPR in Alcore(Al2O3)shell nanoparticles with controlled morphologies. We perform simulations of LSPR using Boundary Element Methods, where the electron beam is passing at a 2.5 nm distance from the surface of an icosahedron-shaped Alcore(Al2O3)shell nanoparticles. The energy loss probability spectra show that for the mode located at an energy around 7 eV, the LSPR energy and intensity have lower values compared to other modes, when the impact factor is placed near a facet, edge and corner of the nanoparticle respectively. This agrees with our experiment, where we collected electron energy-loss spectroscopy-LSPR measurements near the surface of the nanoparticles using a monochromated 80 KeV electron source with 100 meV energy resolution. The experimental spectra appertaining to the edge and corner of the nanoparticle display an energy shift as a function of position of the electron beam with respect to the nanoparticle. By applying a Non-Negative Matrix Factorization algorithm, we de-coupled convoluted LSPR signals and attribute them to the geometry of the nanoparticle. This allowed us to map the coupling coefficient of the electron beam with the LSPR revealing the energy transfer path from the excitation source to the plasmonic nanoparticles. This study paves the way for a better understanding of the localization of LSPR in nanocatalysts with nano-engineered morphologies.
Small-angle beam deviation has many applications and is conventionally performed by wedge prisms. The usual method
suffers from a disadvantage that the manufacturing tolerances limit the resolution to about an arc second. The paper
presents a new technique of using low frequency gratings to realize small-angle beam deviation with higher resolution.
By rotating a grating placed in the laser beam path, the deviation of the diffracted light beams can be controlled. Using
the proposed method, very small beam deviation angle can be achieved under large grating rotation angle, resulting in
high reduction ratio. Theoretical analysis shows that as long as the grating period is large enough, the reduction ratio can
be much higher than that given by a wedge prism. The theoretical result has been verified experimentally using a
holographic grating with 7.25 μm period placed in a Mach-Zehnder interferometer.
2-channel multiplexer/demultiplexer (Muxer/Demuxer) is a key component for bidirectional data traffics applied for
optical communication. Up to date various types of Muxer/Demuxer have been proposed and demonstrated. A grating
coupler diffracts light into substrates or waveguides, along which light beam propagates by total internal reflection. In
addition, one can exploit the dispersive and filtering characteristics of gratings, for dropping or separating one or several
wavelengths from one another. When a laser beam containing two wavelengths is striking the surface of the grating with
an incident angle within certain range, four diffracted beams will be generated. If two diffracted beams, corresponding to
different wavelengths, meet the condition of total internal reflection, they will propagate inside the glass substrate
(performs as a waveguide). While the third one cannot meet total reflection condition, and the last one should become
the evanescent wave. Therefore it can separate two signals and couple signals to different waveguides. These functions
are suited for WDM application and directional couplers. For convenience sake, the visible lights at 458nm and 633nm
were used as the incident laser beams. To give a simple sample for 1×2 demultiplexing system, a holographic grating
was recorded, with the period around 441nm which was chose discretionally within the certain range. The primary
experimental results indicate that the two-wavelength signal can be separated and coupled into the respective waveguide
as long as the grating is recorded and operated complying with the certain condition. The average insertion loss and
crosstalk of the device were presented in this paper.