117 research outputs found
Characteristic Functions Describing the Power Absorption Response of Periodic Structures to Partially Coherent Fields
Many new types of sensing or imaging surfaces are based on periodic thin
films. It is explained how the response of those surfaces to partially coherent
fields can be fully characterized by a set of functions in the wavenumber
spectrum domain. The theory is developed here for the case of 2D absorbers with
TE illumination and arbitrary material properties in the plane of the problem,
except for the resistivity which is assumed isotropic. Sum and difference
coordinates in both spatial and spectral domains are conveniently used to
represent the characteristic functions, which are specialized here to the case
of periodic structures. Those functions can be either computed or obtained
experimentally. Simulations rely on solvers based on periodic-boundary
conditions, while experiments correspond to Energy Absorption Interferometry
(EAI), already described in the literature. We derive rules for the convergence
of the representation versus the number of characteristic functions used, as
well as for the sampling to be considered in EAI experiments. Numerical
examples are given for the case of absorbing strips printed on a semi-infinite
substrate.Comment: Submitted to JOSA
Simulations of astronomical imaging phased arrays
We describe a theoretical procedure for analyzing astronomical phased arrays
with overlapping beams, and apply the procedure to simulate a simple example.
We demonstrate the effect of overlapping beams on the number of degrees of
freedom of the array, and on the ability of the array to recover a source. We
show that the best images are obtained using overlapping beams, contrary to
common practise, and show how the dynamic range of a phased array directly
affects the image quality.Comment: 16 pages, 26 figures, submitted to Journal of the Optical Society of
America
Optical Physics of Imaging and Interferometric Phased Arrays
Microwave, submillimetre-wave, and far-infrared phased arrays are of
considerable importance for astronomy. We consider the behaviour imaging phased
arrays and interferometric phased arrays from a functional perspective. It is
shown that the average powers, field correlations, power fluctuations, and
correlations between power fluctuations at the output ports of an imaging or
interferometric phased array can be found once the synthesised reception
patterns are known. The reception patterns do not have to be orthogonal or even
linearly independent. It is shown that the operation of phased arrays is
intimately related to the mathematical theory of frames, and that the theory of
frames can be used to determine the degree to which any class of intensity or
field distribution can be reconstructed unambiguously from the complex
amplitudes of the travelling waves at the output ports. The theory can be used
to set up a likelihood function that can, through Fisher information, be used
to determine the degree to which a phased array can be used to recover the
parameters of a parameterised source. For example, it would be possible to
explore the way in which a system, perhaps interferometric, might observe two
widely separated regions of the sky simultaneously
Characterization of Power Absorption Response of Periodic 3D Structures to Partially Coherent Fields
In many applications of absorbing structures it is important to understand
their spatial response to incident fields, for example in thermal solar panels,
bolometric imaging and controlling radiative heat transfer. In practice, the
illuminating field often originates from thermal sources and is only spatially
partially coherent when reaching the absorbing device. In this paper, we
present a method to fully characterize the way a structure can absorb such
partially coherent fields. The method is presented for any 3D material and
accounts for the partial coherence and partial polarization of the incident
light. This characterization can be achieved numerically using simulation
results or experimentally using the Energy Absorption Interferometry (EAI) that
has been described previously in the literature. The absorbing structure is
characterized through a set of absorbing functions, onto which any partially
coherent field can be projected. This set is compact for any structure of
finite extent and the absorbing function discrete for periodic structures
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