255 research outputs found
Re-presenting Urban Aboriginal Identities: Self-Representation in Children of the Sun
lechingAboriginal studies to a diverse student cohort presents challenges in the pursuit of developing a critical pedagogy. In this paper, we present Children of the Sun (2006), a local film made by Indigenous youth in the Illawarra region south of Sydney, New South Wales. We outline the film's genesis and its utilisation in our praxis. The film is a useful resource in the teaching of urban Aboriginal identity to primarily non-indigenous students in the discipline of Aboriginal studies
Acoustic black holes in a two-dimensional "photon-fluid"
Optical field fluctuations in self-defocusing media can be described in terms
of sound waves in a 2D photon-fluid. It is shown that, while the background
fluid couples with the usual flat metric, sound-like waves experience an
effective curved spacetime determined by the physical properties of the flow.
In an optical cavity configuration, the background spacetime can be suitably
controlled by the driving beam allowing the formation of acoustic ergoregions
and event horizons. An experiment simulating the main features of the rotating
black hole geometry is proposed.Comment: revised versio
Recommended from our members
Structural changes in doctoral education in the UK: a review of graduate schools and the development of doctoral colleges
Recommended from our members
Structures and strategy in doctoral education in the UK and Ireland
This most recent report builds from previous UKCGE publications that have charted changes in structures that support doctoral education, to include a new focus on institutional strategies, priorities and commitments which shape the work of graduate schools across the UK and Ireland.
The 2022 report draws on the detailed responses from 74 higher education institutions, additional research on trends in national and international policy and practice in doctoral education and comparator data from the previous reports in this series, to offer readers an insight into the policy drivers, changing markets and the major challenges and opportunities which have driven decision-making in the doctoral space in the UK and Ireland in the last six years.
The important findings, outlined in the report, cover issues related to graduate school identity, leadership, access to resource, space, new ways of working, responses to the pandemic and the evolving policy agenda related to diversity and inclusion and health and well-being. It is an essential read for Deans and Directors of Graduate Schools or equivalent, research leaders, research policy-makers and funders and anyone with an interest in contributing to the urgent work required to ensure doctoral education can play a significant role in delivering both the kind of research that can drive post-pandemic recovery and the trained, highly skilled doctoral graduates who are happy and confident to lead it
Stable Mode Sorting by Two-Dimensional Parity of Photonic Transverse Spatial States
We describe a mode sorter for two-dimensional parity of transverse spatial
states of light based on an out-of-plane Sagnac interferometer. Both
Hermite-Gauss (HG) and Laguerre-Gauss (LG) modes can be guided into one of two
output ports according to the two-dimensional parity of the mode in question.
Our interferometer sorts HG_nm input modes depending upon whether they have
even or odd order n+m; it equivalently sorts LG modes depending upon whether
they have an even or odd value of their orbital angular momentum. It functions
efficiently at the single-photon level, and therefore can be used to sort
single-photon states. Due to the inherent phase stability of this type of
interferometer as compared to those of the Mach-Zehnder type, it provides a
promising tool for the manipulation and filtering of higher order transverse
spatial modes for the purposes of quantum information processing. For example,
several similar Sagnacs cascaded together may allow, for the first time, a
stable measurement of the orbital angular momentum of a true single-photon
state. Furthermore, as an alternative to well-known holographic techniques, one
can use the Sagnac in conjunction with a multi-mode fiber as a spatial mode
filter, which can be used to produce spatial-mode entangled Bell states and
heralded single photons in arbitrary first-order (n+m=1) spatial states,
covering the entire Poincare sphere of first-order transverse modes.Comment: 11 pages, 12 figures, 2 appendice
Single-Pixel Diffuser Camera
We present a compact, diffuser assisted, single-pixel computational camera. A rotating ground glass diffuser is adopted, in preference to a commonly used digital micro-mirror device (DMD), to encode a two-dimensional (2D) image into single-pixel signals. We retrieve images with an 8.8% sampling ratio after the calibration of the pseudo-random pattern of the diffuser under light-emitting diode (LED) illumination. Furthermore, we demonstrate hyperspectral imaging with line array detection by adding a diffraction grating. As the random and fixed patterns of a rotating diffuser placed in the image plane can serve as 2D modulation patterns in single-pixel imaging, we do not need further calibration for spectral imaging case since we use a parallel recovery strategy for images at all wavelengths. The implementation results in a cost-effective single-pixel camera for high-dimensional imaging, with potential for imaging in non-visible wavebands
Pump induced Autler-Townes effect and A-T mixing in a four level atoms
It is shown by theoretical simulation that tuning of the pump power can
induce mixing and crossing of Autler-Townes(A-T)components of closely spaced
transitions in atoms. Pump radiation also leads to small shifts of the central
hole of A-T doublet. Off-resonance pumping gives an asymmetry in the A-T
components and by controlling pump frequency detuning it is also possible to
mix the A-T components.Comment: 10 Pages, 3 figur
Optically bound microscopic particles in one dimension
Counter-propagating light fields have the ability to create self-organized
one-dimensional optically bound arrays of microscopic particles, where the
light fields adapt to the particle locations and vice versa. We develop a
theoretical model to describe this situation and show good agreement with
recent experimental data (Phys. Rev. Lett. 89, 128301 (2002)) for two and three
particles, if the scattering force is assumed to dominate the axial trapping of
the particles. The extension of these ideas to two and three dimensional
optically bound states is also discussed.Comment: 12 pages, incl. 5 figures, accepted by Phys. Rev.
Self-evolving ghost imaging
Ghost imaging captures 2D images with a point detector instead of an array sensor. It could therefore solve the challenge of building cameras in wave bands where sensors are difficult and expensive to produce and could open up more routine THz, near-infrared, lifetime, and hyperspectral imaging simply by using single-pixel detectors. Traditionally, ghost imaging retrieves the image of an object offline by correlating measured light intensities with pre-designed illuminating patterns. Here we present a "self-evolving"ghost imaging (SEGI) strategy for imaging objects bypassing offline postprocessing. It also offers the capability to image objects in turbid media. By inspecting the optical feedback, we evaluate the illumination patterns by a cost function and generate offspring illumination patterns that mimic the object's image, bypassing the reconstruction process. At the initial evolving state, the object's "genetic information"is stored in the patterns. At the following imaging stage, the object's image (48Ă48 pixels) can be updated at a 40 Hz imaging rate. We numerically and experimentally demonstrate this concept for static and moving objects. The frame-memory effect between the self-evolving illumination patterns provided by the genetic algorithm enables SEGI imaging through turbid media.We further demonstrate this capability by imaging an object placed in a container filled with water and sand. SEGI shows robust and superior imaging power compared with traditional computational ghost imaging. This strategy could enhance ghost imaging in applications such as remote sensing, imaging through scattering media, and low-irradiative biological imaging
Optical parametric oscillation with distributed feedback in cold atoms
There is currently a strong interest in mirrorless lasing systems, in which
the electromagnetic feedback is provided either by disorder (multiple
scattering in the gain medium) or by order (multiple Bragg reflection). These
mechanisms correspond, respectively, to random lasers and photonic crystal
lasers. The crossover regime between order and disorder, or correlated
disorder, has also been investigated with some success. Here, we report
one-dimensional photonic-crystal lasing (that is, distributed feedback lasing)
with a cold atom cloud that simultaneously provides both gain and feedback. The
atoms are trapped in a one-dimensional lattice, producing a density modulation
that creates a strong Bragg reflection with a small angle of incidence. Pumping
the atoms with auxiliary beams induces four-wave mixing, which provides
parametric gain. The combination of both ingredients generates a mirrorless
parametric oscillation with a conical output emission, the apex angle of which
is tunable with the lattice periodicity
- âŠ