14,749 research outputs found
An optimized ultrasound detector for photoacoustic breast tomography
Photoacoustic imaging has proven to be able to detect vascularization-driven
optical absorption contrast associated with tumors. In order to detect breast
tumors located a few centimeter deep in tissue, a sensitive ultrasound detector
is of crucial importance for photoacoustic mammography. Further, because the
expected photoacoustic frequency bandwidth (a few MHz to tens of kHz) is
inversely proportional to the dimensions of light absorbing structures (0.5 to
10+ mm), proper choices of materials and their geometries, and proper
considerations in design have to be made for optimal photoacoustic detectors.
In this study, we design and evaluate a specialized ultrasound detector for
photoacoustic mammography. Based on the required detector sensitivity and its
frequency response, a selection of active material and matching layers and
their geometries is made leading to a functional detector models. By iteration
between simulation of detector performances, fabrication and experimental
characterization of functional models an optimized implementation is made and
evaluated. The experimental results of the designed first and second functional
detectors matched with the simulations. In subsequent bare piezoelectric
samples the effect of lateral resonances was addressed and their influence
minimized by sub-dicing the samples. Consequently, using simulations, the final
optimized detector could be designed, with a center frequency of 1 MHz and a -6
dB bandwidth of ~80%. The minimum detectable pressure was measured to be 0.5
Pa, which will facilitate deeper imaging compared to the currrent systems. The
detector should be capable of detecting vascularized tumors with resolution of
1-2 mm. Further improvements by proper electrical grounding and shielding and
implementation of this design into an arrayed detector will pave the way for
clinical applications of photoacoustic mammography.Comment: Accepted for publication in Medical Physics (American Association of
Physicists in Medicine
The impact of lens galaxy environments on the image separation distribution
We study the impact of lens galaxy environments on the image separation
distribution of lensed quasars. We account for both environmental convergence
and shear, using a joint distribution derived from galaxy formation models
calibrated by galaxy-galaxy lensing data and number counts of massive
elliptical galaxies. We find that the external field enhances lensing
probabilities, particularly at large image separations; the increase is ~30% at
\theta=3'' and ~200% at \theta=5'', when we adopt a power-law source luminosity
function \Phi(L) \propto L^-2.1. The enhancement is mainly driven by
convergence, which boosts both the image separation and magnification bias (for
a fixed lens galaxy mass). These effects have been neglected in previous
studies of lens statistics. Turning the problem around, we derive the posterior
convergence and shear distributions and point out that they are strong
functions of image separation; lens systems with larger image separations are
more likely to lie in dense environments.Comment: 8 pages, 10 figures, accepted for publication in MNRA
Forcing Mutual Coherence in Diode Laser Stacks
This paper will discuss both theoretical and experimental attempts to improve the spatial beam quality of diode laser stacks using an external optical system. An overview and derivation of the mathematics of both the optical system and diode lasers will be discussed. The experimental setup will be presented, as well as the fundamental theoretical and experimental results that suggest the external optical system used for this thesis fails to improve the beam quality of a diode laser stack
Metallic nanorings for broadband, enhanced extraction of light from solid-state emitters
We report on the increased extraction of light emitted by solid-state sources
embedded within high refractive index materials. This is achieved by making use
of a local lensing effect by sub-micron metallic rings deposited on the sample
surface and centered around single emitters. We show enhancements in the
intensity of the light emitted by InAs/GaAs single quantum dot lines into free
space as high as a factor 20. Such a device is intrinsically broadband and
therefore compatible with any kind of solid-state light source. We foresee the
fabrication of metallic rings via scalable techniques, like nano-imprint, and
their implementation to improve the emission of classical and quantum light
from solid-state sources. Furthermore, while increasing the brightness of the
devices, the metallic rings can also act as top contacts for the local
application of electric fields for carrier injection or wavelength tuning.Comment: 10 pages, 3 figure
Super-resolution imaging of a low frequency levitated oscillator
We describe the measurement of the secular motion of a levitated nanoparticle
in a Paul trap with a CMOS camera. This simple method enables us to reach
signal-to-noise ratios as good as 10 with a displacement sensitivity
better than 10/Hz. This method can be used to extract trap
parameters as well as the properties of the levitated particles. We demonstrate
continuous monitoring of the particle dynamics on timescales of the order of
weeks. We show that by using the improvement given by super-resolution imaging,
a significant reduction in the noise floor can be attained, with an increase in
the bandwidth of the force sensitivity. This approach represents a competitive
alternative to standard optical detection for a range of low frequency
oscillators where low optical powers are require
A Compressive Multi-Mode Superresolution Display
Compressive displays are an emerging technology exploring the co-design of
new optical device configurations and compressive computation. Previously,
research has shown how to improve the dynamic range of displays and facilitate
high-quality light field or glasses-free 3D image synthesis. In this paper, we
introduce a new multi-mode compressive display architecture that supports
switching between 3D and high dynamic range (HDR) modes as well as a new
super-resolution mode. The proposed hardware consists of readily-available
components and is driven by a novel splitting algorithm that computes the pixel
states from a target high-resolution image. In effect, the display pixels
present a compressed representation of the target image that is perceived as a
single, high resolution image.Comment: Technical repor
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