548 research outputs found
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Improving the stability of organosiloxane smectic A liquid crystal random lasers using redox dopants
This report is focus on the development of liquid crystal (LC) vis
ible
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light scattering devices
for random lasers. These light
-
scattering devices are based upon binary mixtures that consist of an
organosiloxane smectic A LC and a wide temperature range nematogen LC. Both the temperature range
of the smectic A phase and t
he dielectric anisotropy of the binary mixture are increased compared with
that of the neat organosiloxane compound. In the latter case, the increase in the dielectric anisotropy
results in a reduction of the magnitude of the electric field required to ind
uce a clear state.
Furthermore, it is found that the electric field threshold continues to decrease with increasing
concentration of the nematic compound. For the random laser devices, the pyrromethene 597 laser
dye was added to a mixture that was optimize
d for scattering and it was found that the absorption
properties of the dye becomes unstable in the presence of the electro
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hydrodynamic instabilities that
are required to generate scattering in the LC cells. This is believed to be due to electro
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chemical
reactions that occur at the electrodes. To avoid dye degradation and ensure repeatable electro
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optic
behaviour, a reduction
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oxidation (redox) couple is dispersed within the dye
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doped binary mixture. It is
shown that the addition of redox dopants helps to s
tabilize the dye in the scattering mixtures, and also
increases the long
-
term repeatability of the scattering behaviour. Finally, we conclude by
characterizing the random laser emission of the dye
-
doped binary mixture and demonstrate improved
stability.This is the author accepted manuscript. The final published version is available at http://www.sciencedirect.com/science/article/pii/S0925346715000816
Optical properties of planar chiral meta-materials
The polarization state of visible light is found to be altered upon reflection from artificial two-dimensional chiral media. Arrays of metallic planar chiral structures were fabricated by electron beam lithography and ion beam milling. The characteristic dimensions on the chiral elements correspond to wavelengths in the near-IR. Our chiral media are found to induce strong polarization effects, with the handedness of individual elements having a direct effect on the sense and magnitude of rotation of the diffracted light
Chiral gratings-a new class of polarization sensitive metamaterials
Summary form only given. Metallic bilayered structures with chirality and inductive coupling are predicted to show huge optical polarization rotatory power resembling that of liquid crystals. The semi-chiral planar gratings described here belong to a distinctively different class of 2D structures known as planar chiral structures
Stretchable liquid-crystal blue-phase gels
Liquid crystalline polymers are materials of considerable scientific interest
and technological value to society [1-3]. An important subset of such materials
exhibit rubber-like elasticity; these can combine the remarkable optical
properties of liquid crystals with the favourable mechanical properties of
rubber and, further, exhibit behaviour not seen in either type of material
independently [2]. Many of their properties depend crucially on the particular
mesophase employed. Stretchable liquid crystalline polymers have previously
been demonstrated in the nematic, chiral nematic, and smectic mesophases [2,4].
Here were report the fabrication of a stretchable gel of blue phase I, which
forms a self-assembled, three-dimensional photonic crystal that may have its
optical properties manipulated by an applied strain and, further, remains
electro-optically switchable under a moderate applied voltage. We find that,
unlike its undistorted counterpart, a mechanically deformed blue phase exhibits
a Pockels electro-optic effect, which sets out new theoretical challenges and
new possibilities for low-voltage electro-optic devices.Comment: 15 pages, 6 figures, additional data and discussion included.
Supplementary videos available from F. Castles on reques
Measuring our universe from galaxy redshift surveys
Galaxy redshift surveys have achieved significant progress over the last
couple of decades. Those surveys tell us in the most straightforward way what
our local universe looks like. While the galaxy distribution traces the bright
side of the universe, detailed quantitative analyses of the data have even
revealed the dark side of the universe dominated by non-baryonic dark matter as
well as more mysterious dark energy (or Einstein's cosmological constant). We
describe several methodologies of using galaxy redshift surveys as cosmological
probes, and then summarize the recent results from the existing surveys.
Finally we present our views on the future of redshift surveys in the era of
Precision Cosmology.Comment: 82 pages, 31 figures, invited review article published in Living
Reviews in Relativity, http://www.livingreviews.org/lrr-2004-
Blue-phase templated fabrication of three-dimensional nanostructures for photonic applications
A promising approach to the fabrication of materials with nanoscale features is the transfer of liquid-crystalline structure to polymers. However, this has not been achieved in systems with full three-dimensional periodicity. Here we demonstrate the fabrication of self-assembled three-dimensional nanostructures by polymer templating blue phase I, a chiral liquid crystal with cubic symmetry. Blue phase I was photopolymerized and the remaining liquid crystal removed to create a porous free-standing cast, which retains the chiral three-dimensional structure of the blue phase, yet contains no chiral additive molecules. The cast may in turn be used as a hard template for the fabrication of new materials. By refilling the cast with an achiral nematic liquid crystal, we created templated blue phases that have unprecedented thermal stability in the range -125 to 125 °C, and that act as both mirrorless lasers and switchable electro-optic devices. Blue-phase templated materials will facilitate advances in device architectures for photonics applications in particular
Spin-photon interface and spin-controlled photon switching in a nanobeam waveguide
Access to the electron spin is at the heart of many protocols for integrated
and distributed quantum-information processing [1-4]. For instance, interfacing
the spin-state of an electron and a photon can be utilized to perform quantum
gates between photons [2,5] or to entangle remote spin states [6-9].
Ultimately, a quantum network of entangled spins constitutes a new paradigm in
quantum optics [1]. Towards this goal, an integrated spin-photon interface
would be a major leap forward. Here we demonstrate an efficient and optically
programmable interface between the spin of an electron in a quantum dot and
photons in a nanophotonic waveguide. The spin can be deterministically prepared
with a fidelity of 96\%. Subsequently the system is used to implement a
"single-spin photonic switch", where the spin state of the electron directs the
flow of photons through the waveguide. The spin-photon interface may enable
on-chip photon-photon gates [2], single-photon transistors [10], and efficient
photonic cluster state generation [11]
Tinnitus referral pathways within the National Health Service in England: a survey of their perceived effectiveness among audiology staff
<p>Abstract</p> <p>Background</p> <p>In the UK, audiology services deliver the majority of tinnitus patient care, but not all patients experience the same level of service. In 2009, the Department of Health released a Good Practice Guide to inform commissioners about key aspects of a quality tinnitus service in order to promote equity of tinnitus patient care in UK primary care, audiology, and in specialist multi-disciplinary centres. The purpose of the present research was to evaluate utilisation and opinions on pathways for the referral of tinnitus patients to and from English Audiology Departments.</p> <p>Methods</p> <p>We surveyed all audiology staff engaged in providing tinnitus services across England. A 36-item questionnaire was mailed to 351 clinicians in all 163 National Health Service (NHS) Trusts identified as having a tinnitus service. 138 clinicians responded. The results presented here describe experiences and opinions of the current patient pathways to and from the audiology tinnitus service.</p> <p>Results</p> <p>The most common referral pathway was from general practice to a hospital-based Ear, Nose & Throat department and from there to a hospital-based audiology department (64%). Respondents considered the NHS tinnitus referral process to be generally effective (67%), but expressed needs for improving GP referral and patients' access to services. 'Open access' to the audiology clinic was rarely an option for patients (9%), nor was the opportunity to access specialist counselling provided by clinical psychology (35%). To decrease the number of inappropriate referrals, 40% of respondents called for greater awareness by referrers about the audiology tinnitus service.</p> <p>Conclusions</p> <p>Respondents in the present survey were generally satisfied with the tinnitus referral system. However, they highlighted some potential targets for service improvement including 1] faster and more appropriate referral from GPs, to be achieved through education on tinnitus referral criteria, 2] improved access to psychological services through audiologist training, and 3] ongoing support from tinnitus support groups, national charities, or open access to the tinnitus clinic for existing patients.</p
Understanding Galaxy Formation and Evolution
The old dream of integrating into one the study of micro and macrocosmos is
now a reality. Cosmology, astrophysics, and particle physics intersect in a
scenario (but still not a theory) of cosmic structure formation and evolution
called Lambda Cold Dark Matter (LCDM) model. This scenario emerged mainly to
explain the origin of galaxies. In these lecture notes, I first present a
review of the main galaxy properties, highlighting the questions that any
theory of galaxy formation should explain. Then, the cosmological framework and
the main aspects of primordial perturbation generation and evolution are
pedagogically detached. Next, I focus on the ``dark side'' of galaxy formation,
presenting a review on LCDM halo assembling and properties, and on the main
candidates for non-baryonic dark matter. It is shown how the nature of
elemental particles can influence on the features of galaxies and their
systems. Finally, the complex processes of baryon dissipation inside the
non-linearly evolving CDM halos, formation of disks and spheroids, and
transformation of gas into stars are briefly described, remarking on the
possibility of a few driving factors and parameters able to explain the main
body of galaxy properties. A summary and a discussion of some of the issues and
open problems of the LCDM paradigm are given in the final part of these notes.Comment: 50 pages, 10 low-resolution figures (for normal-resolution, DOWNLOAD
THE PAPER (PDF, 1.9 Mb) FROM http://www.astroscu.unam.mx/~avila/avila.pdf).
Lectures given at the IV Mexican School of Astrophysics, July 18-25, 2005
(submitted to the Editors on March 15, 2006
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