9,550 research outputs found
Experimental observation of superscattering
Superscattering, induced by degenerate resonances, breaks the fundamental
single-channel limit of scattering cross section of subwavelength structures;
in principle, an arbitrarily large total cross section can be achieved via
superscattering. It thus provides a unique way to strengthen the light-matter
interaction at the subwavelength scale, and has many potential applications in
sensing, energy harvesting, bio-imaging (such as magnetic resonance imaging),
communication and optoelectronics. However, the experimental demonstration of
superscattering remains an open challenge due to its vulnerability to
structural imperfections and intrinsic material losses. Here we report the
first experimental evidence for superscattering, by demonstrating the
superscattering simultaneously in two different frequency regimes through both
the far-field and near-field measurements. The underlying mechanism for the
observed superscattering is the degenerate resonances of confined surface
waves, by utilizing a subwavelength metasurface-based multilayer structure. Our
work paves the way towards practical applications based on superscattering
General Metasurface Synthesis Based on Susceptibility Tensors
A general method, based on susceptibility tensors, is proposed for the
synthesis of metasurfaces transforming arbitrary incident waves into arbitrary
reflected and transmitted waves. The proposed method exhibits two advantages:
1)it is inherently vectorial, and therefore better suited for full vectorial
(beyond paraxial) electromagnetic problems, 2) it provides closed-form
solutions, and is therefore extremely fast. Incidentally, the method reveals
that a metasurface is fundamentally capable to transform up to four independent
wave triplets (incident, reflected and refracted waves). In addition, the paper
provides the closed-form expressions relating the synthesized susceptibilities
and the scattering parameters simulated within periodic boundary conditions,
which allows one to design the scattering particles realizing the desired
susceptibilities. The versatility of the method is illustrated by examples of
metasurfaces achieving the following transformations: generalized refraction,
reciprocal and non-reciprocal polarization rotation, Bessel vortex beam
generation, and orbital angular momentum multiplexing
Focusing and Compression of Ultrashort Pulses through Scattering Media
Light scattering in inhomogeneous media induces wavefront distortions which
pose an inherent limitation in many optical applications. Examples range from
microscopy and nanosurgery to astronomy. In recent years, ongoing efforts have
made the correction of spatial distortions possible by wavefront shaping
techniques. However, when ultrashort pulses are employed scattering induces
temporal distortions which hinder their use in nonlinear processes such as in
multiphoton microscopy and quantum control experiments. Here we show that
correction of both spatial and temporal distortions can be attained by
manipulating only the spatial degrees of freedom of the incident wavefront.
Moreover, by optimizing a nonlinear signal the refocused pulse can be shorter
than the input pulse. We demonstrate focusing of 100fs pulses through a 1mm
thick brain tissue, and 1000-fold enhancement of a localized two-photon
fluorescence signal. Our results open up new possibilities for optical
manipulation and nonlinear imaging in scattering media
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