12,169 research outputs found
Clocked Atom Delivery to a Photonic Crystal Waveguide
Experiments and numerical simulations are described that develop quantitative
understanding of atomic motion near the surfaces of nanoscopic photonic crystal
waveguides (PCWs). Ultracold atoms are delivered from a moving optical lattice
into the PCW. Synchronous with the moving lattice, transmission spectra for a
guided-mode probe field are recorded as functions of lattice transport time and
frequency detuning of the probe beam. By way of measurements such as these, we
have been able to validate quantitatively our numerical simulations, which are
based upon detailed understanding of atomic trajectories that pass around and
through nanoscopic regions of the PCW under the influence of optical and
surface forces. The resolution for mapping atomic motion is roughly 50 nm in
space and 100 ns in time. By introducing auxiliary guided mode (GM) fields that
provide spatially varying AC-Stark shifts, we have, to some degree, begun to
control atomic trajectories, such as to enhance the flux into to the central
vacuum gap of the PCW at predetermined times and with known AC-Stark shifts.
Applications of these capabilities include enabling high fractional filling of
optical trap sites within PCWs, calibration of optical fields within PCWs, and
utilization of the time-dependent, optically dense atomic medium for novel
nonlinear optical experiments
Wave propagation across interfaces induced by different interaction exponents in ordered and disordered Hertz-like granular chains
We study solitary wave propagation in 1D granular crystals with Hertz-like
interaction potentials. We consider interfaces between media with different
exponents in the interaction potential. For an interface with increasing
interaction potential exponent along the propagation direction we obtain mainly
transmission with delayed secondary transmitted and reflected pulses. For
interfaces with decreasing interaction potential exponent we observe both
significant reflection and transmission of the solitary wave, where the
transmitted part of the wave forms a multipulse structure. We also investigate
impurities consisting of beads with different interaction exponents compared to
the media they are embedded in, and we find that the impurities cause both
reflection and transmission, including the formation of multipulse structures,
independent of whether the exponent in the impurities is smaller than in the
surrounding media. We explain wave propagation effects at interfaces and
impurities in terms of quasi-particle collisions. Next we consider wave
propagation along Hertz-like granular chains of beads in the presence of
disorder and periodicity in the interaction exponents present in the Hertz-like
potential, modelling, for instance, inhomogeneity in the contact geometry
between beads in the granular chain. We find that solitary waves in media with
randomised interaction exponents (which models disorder in the contact
geometry) experience exponential decay, where the dependence of the decay rate
is similar to the case of randomised bead masses. In the periodic case of
chains with interaction exponents alternating between two fixed values, we find
qualitatively different propagation properties depending on the choice of the
two exponents. In particular, we find regimes with either exponential decay or
stable solitary wave propagation with pairwise collective behaviour.Comment: 33 pages, 28 figure
Application of multi-core and cluster computing to the Transmission Line Matrix method
The Transmission Line Matrix (TLM) method is an existing and established mathematical method for conducting computational electromagnetic (CEM) simulations. TLM models Maxwell s equations by discretising the contiguous nature of an environment and its contents into individual small-scale elements and it is a computationally intensive process. This thesis focusses on parallel processing optimisations to the TLM method when considering the opposing ends of the contemporary computing hardware spectrum, namely large-scale computing systems versus small-scale mobile computing devices.
Theoretical aspects covered in this thesis are:
The historical development and derivation of the TLM method.
A discrete random variable (DRV) for rain-drop diameter,allowing generation of a rain-field with raindrops adhering to a Gaussian size distribution, as a case study for a 3-D TLM implementation.
Investigations into parallel computing strategies for accelerating TLM on large and small-scale computing platforms.
Implementation aspects covered in this thesis are:
A script for modelling rain-fields using free-to-use modelling software.
The first known implementation of 2-D TLM on mobile computing devices.
A 3-D TLM implementation designed for simulating the effects of rain-fields on extremely high frequency (EHF) band signals.
By optimising both TLM solver implementations for their respective platforms, new opportunities present themselves. Rain-field simulations containing individual rain-drop geometry can be simulated, which was previously impractical due to the lengthy computation times required. Also, computationally time-intensive methods such as TLM were previously impractical on mobile computing devices. Contemporary hardware features on these devices now provide the opportunity for CEM simulations at speeds that are acceptable to end users, as well as providing a new avenue for educating relevant user cohorts via dynamic presentations of EM phenomena
Modeling of octave-spanning Kerr frequency combs using a generalized mean-field Lugiato-Lefever model
A generalized Lugiato-Lefever equation is numerically solved with a
Newton-Raphson method to model Kerr frequency combs. We obtain excellent
agreement with past experiments, even for an octave-spanning comb. Simulations
are much faster than with any other technique despite including more modes than
ever before. Our study reveals that Kerr combs are associated with temporal
cavity solitons and dispersive waves, and opens up new avenues for the
understanding of Kerr comb formation.Comment: 3 pages, 3 figures. Submitted to Optics Letters on 31 October 2012,
accepted with minor/optional revisions. This version is the revised
manuscrip
Demonstration of an Integrated Terahertz Band-Stop Filter Using an Apodized Bragg Grating
This paper presents the demonstration of an on-chip integrated Terahertz
(THz) Apodized Bragg grating (TABG) which functions as band-stop filter with a
center frequency of 0.8 THz and a bandwidth of 200 GHz. For experimentation, we
integrate the TABG into our THz System-on-Chip to enable wideband (DC - 1.5
THz) device characterization. Using this methodology, we measure the signal
transmission through the TABG and find the experimental results align with
simulation and theory provides a rejection of approximately 20 dB across the
stop-band.Comment: 9 pages, 8 figure
A Narrow-wall Complementary-split-ring Slotted Waveguide Antenna for High-power-microwave Applications
A narrow-band, rugged, complementary-split-ring (CSR) slotted waveguide antenna (SWA) with significant size reduction is presented. The antenna is to be vertically front mounted on a land vehicle, with a horizontally polarized fan-beam radiation pattern. The radiation characteristics of a CSR slot in the narrow-wall of a rectangular waveguide are studied for the first time in this work. Both simulation and experimental results show that the complementary-split-ring slot radiates a linearly polarized wave with a total efficiency and gain close to those of conventional longitudinal slots, while the proposed CSR slots have a maximal outer diameter of 0.23λ0, much smaller compared to conventional half-wavelength longitudinal slots. The CSR slotted waveguide antenna provides, approximately, 55% size reduction, with high directivity, low return loss, and very high power handling capability for S-band applications. A set of periodic air-filled corrugations is added to the other narrow-wall of the rectangular waveguide to improve the overall gain of the antenna. Experimental data is presented to further validate simulation results
Wave Propagation in Materials for Modern Applications
In the recent decades, there has been a growing interest in micro- and nanotechnology. The advances in nanotechnology give rise to new applications and new types of materials with unique electromagnetic and mechanical properties. This book is devoted to the modern methods in electrodynamics and acoustics, which have been developed to describe wave propagation in these modern materials and nanodevices. The book consists of original works of leading scientists in the field of wave propagation who produced new theoretical and experimental methods in the research field and obtained new and important results. The first part of the book consists of chapters with general mathematical methods and approaches to the problem of wave propagation. A special attention is attracted to the advanced numerical methods fruitfully applied in the field of wave propagation. The second part of the book is devoted to the problems of wave propagation in newly developed metamaterials, micro- and nanostructures and porous media. In this part the interested reader will find important and fundamental results on electromagnetic wave propagation in media with negative refraction index and electromagnetic imaging in devices based on the materials. The third part of the book is devoted to the problems of wave propagation in elastic and piezoelectric media. In the fourth part, the works on the problems of wave propagation in plasma are collected. The fifth, sixth and seventh parts are devoted to the problems of wave propagation in media with chemical reactions, in nonlinear and disperse media, respectively. And finally, in the eighth part of the book some experimental methods in wave propagations are considered. It is necessary to emphasize that this book is not a textbook. It is important that the results combined in it are taken “from the desks of researchers“. Therefore, I am sure that in this book the interested and actively working readers (scientists, engineers and students) will find many interesting results and new ideas
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