102 research outputs found
Efficient Microparticle Trapping with Plasmonic Annular Apertures Arrays
In this work, we demonstrate trapping of microparticles using a plasmonic
tweezers based on arrays of annular apertures. The transmission spectra and the
E- field distribution are simulated to calibrate the arrays. Theoretically, we
observe sharp peaks in the transmission spectra for dipole resonance modes and
these are redshifted as the size of the annular aperture is reduced. We also
expect an absorption peak at approximately 1,115 um for the localised plasmon
resonance. Using a laser frequency between the two resonances, multiple
plasmonic hotspots are created and used to trap and transport micron and
submicron particles. Experimentally, we demonstrate trapping of individual 0.5
um and 1 um polystyrene particles and particle transportation over the surface
of the annular apertures using less than 1.5 mW/um2 incident laser intensity at
980 nm
Optical nanofiber-based cavity induced by periodic air-nanohole arrays
We experimentally realized an optical nanofiber-based cavity by combining a
1-D photonic crystal and Bragg grating structures. The cavity morphology
comprises a periodic, triplex air-cube introduced at the waist of the
nanofiber. The cavity has been theoretically characterized using FDTD
simulations to obtain the reflection and transmission spectra. We have also
experimentally measured the transmission spectra and a Q-factor of ~784(87) for
a very short periodic structure has been observed. The structure provides
strong confinement of the cavity field and its potential for optical network
integration makes it an ideal candidate for use in nanophotonic and quantum
information systems
Efficient microparticle trapping with plasmonic annular apertures arrays
In this work, we demonstrate trapping of microparticles using plasmonic tweezers based on arrays of annular apertures. The transmission spectra and the electric-field distribution are simulated to calibrate the arrays. Theoretically, we observe sharp peaks in the transmission spectra for dipole resonance modes and these are red-shifted as the size of the annular aperture is reduced. We also expect an absorption peak at approximately 1115 m for the localised plasmon resonance. Using a laser frequency between the two resonances, multiple plasmonic hot spots are created and used to trap and transport micron and submicron particles. Experimentally, we demonstrate trapping of individual 0.5 μm and 1 μm polystyrene particles and the feasibility of particle transportation over the surface of the annular apertures using less than 1.5 mW μm⁻² incident laser intensity at 980 nm
Fano-Resonant, Asymmetric, Metamaterial-Assisted Tweezers for Single Nanoparticle Trapping
Plasmonic nanostructures can overcome Abbe's diffraction limit to generate
strong gradient fields, enabling efficient optical trapping of nano-sized
particles. However, it remains challenging to achieve stable trapping with low
incident laser intensity. Here, we demonstrate a Fano resonance-assisted
plasmonic optical tweezers (FAPOT), for single nanoparticle trapping in an
array of asymmetrical split nano-apertures, milled on a 50 nm gold thin film.
Stable trapping is achieved by tuning the trapping wavelength and varying the
incident trapping laser intensity. A very large normalized trap stiffness of
8.65 fN/nm/mW for 20 nm polystyrene particles at a near-resonance trapping
wavelength of 930 nm was achieved. We show that trap stiffness on resonance is
enhanced by a factor of 63 compared to off-resonance conditions. This can be
attributed to the ultra-small mode volume, which enables large near-field
strengths and a cavity Purcell effect contribution. These results should
facilitate strong trapping with low incident trapping laser intensity, thereby
providing new options for studying transition paths of single molecules, such
as proteins, DNA, or viruses.Comment: 28 pages, 7 figure
Chiral force of guided light on an atom
We calculate the force of a near-resonant guided light field of an ultrathin
optical fiber on a two-level atom. We show that, if the atomic dipole rotates
in the meridional plane, the magnitude of the force of the guided light depends
on the field propagation direction. The chirality of the force arises as a
consequence of the directional dependencies of the Rabi frequency of the guided
driving field and the spontaneous emission from the atom. This provides a
unique method for controlling atomic motion in the vicinity of an ultrathin
fiber.Comment: text and figures were revised, and a new discussion was adde
Asymmetric split-ring plasmonic nanostructures for optical sensing of Escherichia coli
Strategies for in-liquid micro-organism detection are crucial for the
clinical and pharmaceutical industries. While Raman spectroscopy is a promising
label-free technique for micro-organism detection, it remains challenging due
to the weak bacterial Raman signals. In this work, we exploit the unique
electromagnetic properties of metamaterials to identify bacterial components in
liquid using an array of Fano-resonant metamolecules. This Fano-enhanced Raman
scattering (FERS) platform is designed to exhibit a Fano resonance close to the
protein amide group fingerprint around 6030 nm. Raman signatures of Escherichia
coli were recorded at several locations on the metamaterial under off-resonance
laser excitation at 530 nm, where the photodamage effect is minimized. As the
sizes of the Escherichia coli are comparable to the micro-gaps, i.e 0.41
{\mu}m, of the metamaterials, its local immobilisation leads to an increase in
the Raman sensitivity. We also observed that the time-dependent FERS signal
related to bacterial amide peaks increased during the bacteria's
mid-exponential phase while it decreased during the stationary phase. This work
provides a new set of opportunities for developing ultrasensitive FERS
platforms suitable for large-scale applications and could be particularly
useful for diagnostics and environmental studies at off-resonance excitation.Comment: 15 pages, 5 figure
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