1,164 research outputs found
Superpixel-based spatial amplitude and phase modulation using a digital micromirror device
We present a superpixel method for full spatial phase and amplitude control
of a light beam using a digital micromirror device (DMD) combined with a
spatial filter. We combine square regions of nearby micromirrors into
superpixels by low pass filtering in a Fourier plane of the DMD. At each
superpixel we are able to independently modulate the phase and the amplitude of
light, while retaining a high resolution and the very high speed of a DMD. The
method achieves a measured fidelity for a target field with fully
independent phase and amplitude at a resolution of pixels per
diffraction limited spot. For the LG orbital angular momentum mode the
calculated fidelity is , using DMD pixels. The
superpixel method reduces the errors when compared to the state of the art Lee
holography method for these test fields by and , with a comparable
light efficiency of around . Our control software is publicly available.Comment: 9 pages, 6 figure
Properties of entangled photon pairs generated in one-dimensional nonlinear photonic-band-gap structures
We have developed a rigorous quantum model of spontaneous parametric
down-conversion in a nonlinear 1D photonic-band-gap structure based upon
expansion of the field into monochromatic plane waves. The model provides a
two-photon amplitude of a created photon pair. The spectra of the signal and
idler fields, their intensity profiles in the time domain, as well as the
coincidence-count interference pattern in a Hong-Ou-Mandel interferometer are
determined both for cw and pulsed pumping regimes in terms of the two-photon
amplitude. A broad range of parameters characterizing the emitted
down-converted fields can be used. As an example, a structure composed of 49
layers of GaN/AlN is analyzed as a suitable source of photon pairs having high
efficiency.Comment: 14 pages, 23 figure
Exploiting speckle correlations to improve the resolution of wide-field fluorescence microscopy
Fluorescence microscopy is indispensable in nanoscience and biological
sciences. The versatility of labeling target structures with fluorescent dyes
permits to visualize structure and function at a subcellular resolution with a
wide field of view. Due to the diffraction limit, conventional optical
microscopes are limited to resolving structures larger than 200 nm. The
resolution can be enhanced by near-field and far-field super-resolution
microscopy methods. Near-field methods typically have a limited field of view
and far-field methods are limited by the involved conventional optics. Here, we
introduce a combined high-resolution and wide-field fluorescence microscopy
method that improves the resolution of a conventional optical microscope by
exploiting correlations in speckle illumination through a randomly scattering
high-index medium: Speckle correlation resolution enhancement (SCORE). As a
test, we collect two-dimensional fluorescence images of 100-nm diameter
dye-doped nanospheres. We demonstrate a deconvolved resolution of 130 nm with a
field of view of 10 x 10 \text{\mu m}^2
Scattering Lens Resolves sub-100 nm Structures with Visible Light
The smallest structures that conventional lenses are able to optically
resolve are of the order of 200 nm. We introduce a new type of lens that
exploits multiple scattering of light to generate a scanning nano-sized optical
focus. With an experimental realization of this lens in gallium phosphide we
have succeeded to image gold nanoparticles at 97 nm optical resolution. Our
work is the first lens that provides a resolution in the nanometer regime at
visible wavelengths.Comment: 4 pages, 3 figure
Influence of Thermal Turbulence in a Convective Ascending Stream on Phase Fluctuations of a Laser Beam
The effects of thermal turbulence on the phase fluctuations of a laser beam are investigated in laboratory. The turbulent region created by means of a horizontal heated Nichrome grid is made to shift upwards owing to the convective motion. A Mach-Zehnder interference experiment is performed in which two beams from a laser source are superimposed after crossing the turbulent region. The displacements of the fringe pattern allow one to study the temporal decay of the mean square refractive index fluctuation. An interpretation of the results is given on the basis of the theory of an isotropic turbulent scalar field
Bleeding jejunal varices and portal thrombosis in a splenectomized patient with hereditary spherocytosis
Bleeding from varices located in the small bowel is a
very uncommon finding; nonetheless, such events accompany
with a high mortality rate (1– 4). Moreover,
early diagnosis of jejunal or ileal varices cannot usually
be accomplished with standard diagnostic tools
(ie, esophagogastroduodenoscopy, colonoscopy).
Most reports in the literature relate to subjects with
liver cirrhosis, often with hepatocarcinoma; in unusual
anatomical situations, varices may develop beyond
the ligament of Treitz in adjunct to the far more
common location in the esophageal and gastric wall.
Thrombosis of the portal vein is a common feature in
such conditions. Portal thrombosis has also been described
in association with overt or latent myeloproliferative
diseases (5); its occurrence in nonneoplastic
hematological conditions in subjects with normal liver
function is quite uncommon.
This report describes the observation of jejunal
varices, with repeated episodes of “melena of unknown
origin,” some of which quite severe, as their
clinical presentation in a patient with portal thrombosis
and with otherwise absolutely normal liver function,
who had undergone splenectomy for hereditary
spherocytosis in early adolescence
Cavity Quantum Electrodynamics with Anderson-localized Modes
A major challenge in quantum optics and quantum information technology is to
enhance the interaction between single photons and single quantum emitters.
Highly engineered optical cavities are generally implemented requiring
nanoscale fabrication precision. We demonstrate a fundamentally different
approach in which disorder is used as a resource rather than a nuisance. We
generate strongly confined Anderson-localized cavity modes by deliberately
adding disorder to photonic crystal waveguides. The emission rate of a
semiconductor quantum dot embedded in the waveguide is enhanced by a factor of
15 on resonance with the Anderson-localized mode and 94 % of the emitted
single-photons couple to the mode. Disordered photonic media thus provide an
efficient platform for quantum electrodynamics offering an approach to
inherently disorder-robust quantum information devices
On the Noise Generated by Shear-Layer Instabilities in Turbulent Jets
Solutions to the linearized equations of motion are used to study sound radiation by convected disturbances in the jet core. The spectrum of eigenmodes reveals the presence of modes that represent convected vortical and entropic motions in the potential core of the jet. We investigate the near-field acoustics produced by these core modes using the Parabolozied Stability Equations. At the conditions of commercial jet engines during take-off, the core modes radiate sound effectively along Mach lines due to the jet centerline velocity being supersonic relative to the fee-stream speed of sound. Summing three of these modes to create two distinct disturbances - one that is velocity dominated, and another that is entropy dominated - one observes that entropy variations radiate sound more effectively than vortical variations.
The results yield a first insight into the impact of large-scale mixing inhomogeneities on the acoustic field. Such disturbances are created by devices in the jet engine itself, such as flow mixers, turbine exit vanes, and combustion-chamber (i.e. pattern factors)
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