1,729 research outputs found
Cloaking of Arbitrarily-Shaped Objects with Homogeneous Coatings
We present a theory for the cloaking of arbitrarily-shaped objects and
demonstrate electromagnetic scattering-cancellation through designed
homogeneous coatings. First, in the small-particle limit, we expand the dipole
moment of a coated object in terms of its resonant modes. By zeroing the
numerator of the resulting rational function, we accurately predict the
permittivity values of the coating layer that abates the total scattered power.
Then, we extend the applicability of the method beyond the small-particle
limit, deriving the radiation corrections of the scattering-cancellation
permittivity within a perturbation approach. Our method permits the design of
invisibility cloaks for irregularly-shaped devices such as complex sensors and
detectors
Full-wave analytical solution of second-harmonic generation in metal nanospheres
We present a full-wave analytical solution for the problem of second-harmonic
generation from spherical nanoparticles. The sources of the second-harmonic
radiation are represented through an effective nonlinear polarization. The
solution is derived in the framework of the Mie theory by expanding the pump
field, the nonlinear sources and the second-harmonic fields in series of
spherical vector wave functions. We use the proposed solution for studying the
second-harmonic radiation generated from gold nanospheres as function of the
pump wavelength and the particle size, in the framework of the Rudnick-Stern
model. We demonstrate the importance of high-order multipolar contributions to
the second-harmonic radiated power. Moreover, we investigate the p- and s-
components of the SH radiation as the Rudnick-Stern parameters change, finding
a strong variation. This approach provides a rigorous methodology to understand
second-order optical processes in metal nanoparticles, and to design novel
nanoplasmonic devices in the nonlinear regime.Comment: 16 pages, 10 figure
Analysis of the Performance of Two Component Back-filling Grout in Tunnel Boring Machines Operating under Face Pressure
Design of ultracompact broadband focusing spectrometers based on deep diffractive neural networks
We propose the inverse design of ultracompact, broadband focusing
spectrometers based on adaptive deep diffractive neural networks (a-DNNs).
Specifically, we introduce and characterize two-layer diffractive devices with
engineered angular dispersion that focus and steer broadband incident radiation
along predefined focal trajectories with desired bandwidth and nm spectral
resolution. Moreover, we systematically study the focusing efficiency of
two-layer devices with side length and focal length
across the visible spectrum and we demonstrate accurate
reconstruction of the emission spectrum from a commercial superluminescent
diode. The proposed a-DNNs design method extends the capabilities of
efficient multi-focal diffractive optical devices to include single-shot
focusing spectrometers with customized focal trajectories for applications to
ultracompact multispectral imaging and lensless microscopy
Design of infrared microspectrometers based on phase-modulated axilenses
We design and characterize a novel axilens-based diffractive optics platform
that flexibly combines efficient point focusing and grating selectivity and is
compatible with scalable top-down fabrication based on a 4-level phase mask
configuration. This is achieved using phase-modulated compact axilens devices
that simultaneously focus incident radiation of selected wavelengths at
predefined locations with larger focal depths compared to traditional Fresnel
lenses. In addition, the proposed devices are polarization insensitive and
maintain a large focusing efficiency over a broad spectral band. Specifically,
here we discuss and characterize modulated axilens configurations designed for
long-wavelength infrared (LWIR) in the m--12~m wavelength range and
in the m--6~m mid-wavelength infrared (MWIR) range. These devices
are ideally suited for monolithic integration atop the substrate layers of
infrared focal plane arrays (IR-FPAs) and for use as compact
microspectrometers. We systematically study their focusing efficiency, spectral
response, and cross talk ratio, and we demonstrate linear control of
multi-wavelength focusing on a single plane. Our design method leverages
Rayleigh-Sommerfeld (RS) diffraction theory and is validated numerically using
the Finite Element Method (FEM). Finally, we demonstrate the application of
spatially modulated axilenses to the realization of compact, single-lens
spectrometer. By optimizing our devices, we achieve a minimum distinguishable
wavelength interval of at and
at . The proposed devices add
fundamental spectroscopic capabilities to compact imaging devices for a number
of applications ranging from spectral sorting to LWIR and MWIR phase contrast
imaging and detection
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