165 research outputs found
Reconstructing Fine Details of Small Objects by Using Plasmonic Spectroscopic Data
This paper is concerned with the inverse problem of reconstructing a small
object from far field measurements. The inverse problem is severally ill-posed
because of the diffraction limit and low signal to noise ratio. We propose a
novel methodology to solve this type of inverse problems based on an idea from
plasmonic sensing. By using the field interaction with a known plasmonic
particle, the fine detail information of the small object can be encoded into
the shift of the resonant frequencies of the two particle system in the far
field. In the intermediate interaction regime, we show that this information is
exactly the generalized polarization tensors associated with the small object,
from which one can perform the reconstruction. Our theoretical findings are
supplemented by a variety of numerical results. The results in the paper also
provide a mathematical foundation for plasmonic sensing
Reconstructing fine details of small objects by using plasmonic spectroscopic data. Part II: The strong interaction regime
This paper is concerned with the inverse problem of reconstructing a small
object from far field measurements by using the field interaction with a
plasmonic particle which can be viewed as a passive sensor. It is a follow-up
of the work [H. Ammari et al., Reconstructing fine details of small objects by
using plasmonic spectroscopic data, SIAM J. Imag. Sci., to appear], where the
intermediate interaction regime was considered. In that regime, it was shown
that the presence of the target object induces small shifts to the resonant
frequencies of the plasmonic particle. These shifts, which can be determined
from the far field data, encodes the contracted generalized polarization
tensors of the target object, from which one can perform reconstruction beyond
the usual resolution limit. The main argument is based on perturbation theory.
However, the same argument is no longer applicable in the strong interaction
regime as considered in this paper due to the large shift induced by strong
field interaction between the particles. We develop a novel technique based on
conformal mapping theory to overcome this difficulty. The key is to design a
conformal mapping which transforms the two particle system into a shell-core
structure, in which the inner dielectric core corresponds to the target object.
We show that a perturbation argument can be used to analyze the shift in the
resonant frequencies due to the presence of the inner dielectric core. This
shift also encodes information of the contracted polarization tensors of the
core, from which one can reconstruct its shape, and hence the target object.
Our theoretical findings are supplemented by a variety of numerical results
based on an efficient optimal control algorithm. The results of this paper make
the mathematical foundation for plasmonic sensing complete.Comment: 24 pages, 4 figure
Reconstruction of domains with algebraic boundaries from generalized polarization tensors
This paper aims at showing the stability of the recovery of a smooth planar
domain with a real algebraic boundary from a finite number of its generalized
polarization tensors. It is a follow-up of the work [H. Ammari et al., Math.
Annalen, 2018], where it is proved that the minimal polynomial with real
coefficients vanishing on the boundary can be identified as the generator of a
one dimensional kernel of a matrix whose entries are obtained from a finite
number of generalized polarization tensors. The recovery procedure is
implemented without any assumption on the regularity of the domain to be
reconstructed and its performance and limitations are illustrated
Plasmonic photoconductive terahertz focal-plane array with pixel super-resolution
Imaging systems operating in the terahertz part of the electromagnetic
spectrum are in great demand because of the distinct characteristics of
terahertz waves in penetrating many optically-opaque materials and providing
unique spectral signatures of various chemicals. However, the use of terahertz
imagers in real-world applications has been limited by the slow speed, large
size, high cost, and complexity of the existing imaging systems. These
limitations are mainly imposed due to the lack of terahertz focal-plane arrays
(THz-FPAs) that can directly provide the frequency-resolved and/or
time-resolved spatial information of the imaged objects. Here, we report the
first THz-FPA that can directly provide the spatial amplitude and phase
distributions, along with the ultrafast temporal and spectral information of an
imaged object. It consists of a two-dimensional array of ~0.3 million plasmonic
photoconductive nanoantennas optimized to rapidly detect broadband terahertz
radiation with a high signal-to-noise ratio. As the first proof-of-concept, we
utilized the multispectral nature of the amplitude and phase data captured by
these plasmonic nanoantennas to realize pixel super-resolution imaging of
objects. We successfully imaged and super-resolved etched patterns in a silicon
substrate and reconstructed both the shape and depth of these structures with
an effective number of pixels that exceeds 1-kilo pixels. By eliminating the
need for raster scanning and spatial terahertz modulation, our THz-FPA offers
more than a 1000-fold increase in the imaging speed compared to the
state-of-the-art. Beyond this proof-of-concept super-resolution demonstration,
the unique capabilities enabled by our plasmonic photoconductive THz-FPA offer
transformative advances in a broad range of applications that use hyperspectral
and three-dimensional terahertz images of objects for a wide range of
applications.Comment: 62 page
Far-field Super-resolution Chemical Microscopy
Far-field chemical microscopy providing molecular electronic or vibrational
fingerprint information opens a new window for the study of three-dimensional
biological, material, and chemical systems. Chemical microscopy provides a
nondestructive way of chemical identification without exterior labels. However,
the diffraction limit of optics hindered it from discovering more details under
the resolution limit. Recent development of super-resolution techniques gives
enlightenment to open this door behind far-field chemical microscopy. Here, we
review recent advances that have pushed the boundary of far-field chemical
microscopy in terms of spatial resolution. We further highlight applications in
biomedical research, material characterization, environmental study, cultural
heritage conservation, and integrated chip inspection.Comment: 34 pages, 8 figures,1 tabl
Shape reconstructions by using plasmon resonances
We study the shape reconstruction of a dielectric inclusion from the faraway
measurement of the associated electric field. This is an inverse problem of
practical importance in biomedical imaging and is known to be notoriously
ill-posed. By incorporating Drude's model of the dielectric parameter, we
propose a novel reconstruction scheme by using the plasmon resonance with a
significantly enhanced resonant field. We conduct a delicate sensitivity
analysis to establish a sharp relationship between the sensitivity of the
reconstruction and the plasmon resonance. It is shown that when plasmon
resonance occurs, the sensitivity functional blows up and hence ensures a more
robust and effective construction. Then we combine the Tikhonov regularization
with the Laplace approximation to solve the inverse problem, which is an
organic hybridization of the deterministic and stochastic methods and can
quickly calculate the minimizer while capture the uncertainty of the solution.
We conduct extensive numerical experiments to illustrate the promising features
of the proposed reconstruction scheme
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