2,410 research outputs found
Plasmonic Superlens Imaging Enhanced by Incoherent Active Convolved Illumination
We introduce a loss compensation method to increase the resolution of
near-field imaging with a plasmonic superlens that relies on the convolution of
a high spatial frequency passband function with the object. Implementation with
incoherent light removes the need for phase information. The method is
described theoretically and numerical imaging results with artificial noise are
presented, which display enhanced resolution of a few tens of nanometers, or
around one-fifteenth of the free space wavelength. A physical implementation of
the method is designed and simulated to provide a proof-of-principle, and steps
toward experimental implementation are discussed
Theory of coherent active convolved illumination for superresolution enhancement
Recently an optical amplification process called the plasmon injection scheme
was introduced as an effective solution to overcoming losses in metamaterials.
Implementations with near-field imaging applications have indicated substantial
performance enhancements even in the presence of noise. This powerful and
versatile compensation technique, which has since been renamed to a more
generalized active convolved illumination, offers new possibilities of
improving the performance of many previously conceived metamaterial-based
devices and conventional imaging systems. In this work, we present the first
comprehensive mathematical breakdown of active convolved illumination for
coherent imaging. Our analysis highlights the distinctive features of active
convolved illumination, such as selective spectral amplification and
correlations, and provides a rigorous understanding of the loss compensation
process. These features are achieved by an auxiliary source coherently
superimposed with the object field. The auxiliary source is designed to have
three important properties. First, it is correlated with the object field.
Second, it is defined over a finite spectral bandwidth. Third, it is amplified
over that selected bandwidth. We derive the variance for the image spectrum and
show that utilizing the auxiliary source with the above properties can
significantly improve the spectral signal-to-noise ratio and resolution limit.
Besides enhanced superresolution imaging, the theory can be potentially
generalized to the compensation of information or photon loss in a wide variety
of coherent and incoherent linear systems including those, for example, in
atmospheric imaging, time-domain spectroscopy, symmetric
non-Hermitian photonics, and even quantum computing.Comment: revised, more details and references adde
Enhancing the Resolution of Imaging Systems by Spatial Spectrum Manipulation
Much research effort has been spent in the 21st century on superresolution imaging techniques, methods which can beat the diffraction limit. Subwavelength composite structures called ``metamaterials had initially shown great promise in superresolution imaging applications in the early 2000s, owing to their potential for nearly arbitrary capabilities in controlling light. However, for optical frequencies they are often plagued by absorption and scattering losses which can decay or destroy their interesting properties. Similar issues limit the application of other superresolution devices operating as effective media, or metal films that can transfer waves with large momentum by supporting surface plasmon polaritons. In this dissertation, new methods of mitigating the loss of object information in lossy and noisy optical imaging systems are presented. The result is an improvement in the upper bound on lateral spatial resolution. A concentration is placed on metamaterial and plasmonic imaging systems, and the same methods are subsequently adapted to more conventional far-field imaging systems. First, through numerical simulation it is shown that a lossy metamaterial lens has degraded imaging performance which can be partially compensated by deconvolution post-processing of the resultant image. This post-processing procedure is then shown to emulate a physical process called plasmon injection, which has been previously implemented to effectively remove the losses in a plasmonic metamaterial. Next, a more realistic scenario is considered; a thin film of silver acting as a near-field plasmonic ``superlens. In this case, methods are implemented to model incoherent light propagation so that the image can be reconstructed using only intensity data, removing the need for phase measurement. The same procedure from above is followed, and the resolution is enhanced. To push the resolution further, a spatial filtering method called active convolved illumination is developed to overcome the resolution limit set by the noise floor of the system. Finally, the spatial filtering methods are applied to more a more conventional far-field imaging system. Supported by experiment, the lateral resolution of a low numerical aperture imaging system is improved by blocking photons at the Fourier plane. For coherent light, a diffractive superlens is designed which uses the same principles from the above theory, except it encodes the high spatial frequency waves into propagating waves via a diffraction grating. The result is lateral resolution performance that surpasses similar previously published devices by 10 nm at a wavelength more than 80 nm longer
Enhancing the resolution of hyperlens by the compensation of losses without gain media
We present a method to improve the resolution of available hyperlenses in the
literature. In this method, we combine the operation of hyperlens with the
recently proposed plasmon injection scheme for loss compensation in
metamaterials. Image of an object, which is otherwise not resolvable by the
hyperlens alone, was reconstructed up to the minimum feature size of one
seventh of the free-space wavelength.Comment: 4 pages, 5 figure
Hyperbolic metamaterial as a tunable near-field spatial filter for the implementation of the active plasmon injection loss compensation scheme
We present how to physically realize the auxiliary source described in the
recently introduced active plasmon injection loss compensation scheme for
enhanced near-field superlensing. Particularly, we show that the
characteristics of the auxiliary source described in the active plasmon
injection scheme including tunable narrow-band and selective amplification via
convolution can be realized by using a hyperbolic metamaterial functioning as a
near-field spatial filter. Besides loss compensation, the proposed near-field
spatial filter can be useful for real-time high resolution edge detection.Comment: 8 pages, 8 figure
Active plasmon injection scheme for subdiffraction imaging with imperfect negative index flat lens
We present an active physical implementation of the recently introduced
plasmon injection loss compensation scheme for Pendry's non-ideal negative
index flat lens in the presence of realistic material losses and
signal-dependent noise. In this active implementation, we propose to use a
physically convolved external auxiliary source for signal amplification and
suppression of the noise in the imaging system. In comparison with the previous
passive implementations of the plasmon injection scheme for sub-diffraction
limited imaging, where an inverse filter post-processing is used, the active
implementation proposed here allows for deeper subwavelength imaging far beyond
the passive post-processing scheme by extending the loss compensation to even
higher spatial frequencies.Comment: 13 pages, 15 figure
A general model of resonance capture in planetary systems: First and second order resonances
Mean motion resonances are a common feature of both our own Solar System and
of extrasolar planetary systems. Bodies can be trapped in resonance when their
orbital semi-major axes change, for instance when they migrate through a
protoplanetary disc. We use a Hamiltonian model to thoroughly investigate the
capture behaviour for first and second order resonances. Using this method, all
resonances of the same order can be described by one equation, with
applications to specific resonances by appropriate scaling. We focus on the
limit where one body is a massless test particle and the other a massive
planet. We quantify how the the probability of capture into a resonance depends
on the relative migration rate of the planet and particle, and the particle's
eccentricity. Resonant capture fails for high migration rates, and has
decreasing probability for higher eccentricities. More massive planets can
capture particles at higher eccentricities and migration rates. We also
calculate libration amplitudes and the offset of the libration centres for
captured particles, and the change in eccentricity if capture does not occur.
Libration amplitudes are higher for larger initial eccentricity. The model
allows for a complete description of a particle's behaviour as it successively
encounters several resonances. We discuss implications for several scenarios:
(i) Planet migration through gas discs trapping other planets or planetesimals
in resonances. (ii) Planet migration through a debris disc. (iii) Dust
migration through PR drag. The Hamiltonian model will allow quick
interpretation of the resonant properties of extrasolar planets and Kuiper Belt
Objects, and will allow synthetic images of debris disc structures to be
quickly generated, which will be useful for predicting and interpreting disc
images made with ALMA, Darwin/TPF or similar missions. [Abridged]Comment: 19 pages, 14 figures; accepted to MNRA
Enhanced superlens imaging with loss-compensating hyperbolic near-field spatial filter
Recently a coherent optical process called plasmon injection () scheme,
which employs an auxiliary source, has been introduced as a new technique to
compensate losses in metamaterials. In this work, a physical implementation of
the scheme on a thin silver film is proposed for enhanced superlens
imaging. The efficacy of the scheme is illustrated by enhancing near-field
imaging deeper beyond the diffraction limit in the presence of absorption
losses and noise. The auxiliary source is constructed by a high-intensity
illumination of the superlens integrated with a near-field spatial filter. The
integrated system enables reconstruction of an object previously unresolvable
with the superlens alone. This work elevates the viability of the scheme
as a strong candidate for loss compensation in near-field imaging systems
without requiring non-linear effects or gain medium.Comment: 5 pages, 5 figure
Expression of Ki-67 and Bcl-2 in gastric epithelial cells: role of antralization in gastric carcinogenesis
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