55 research outputs found
-operator bounds on angle-integrated absorption and thermal radiation for arbitrary objects
We derive fundamental per-channel bounds on angle-integrated absorption and
thermal radiation for arbitrary bodies---for any given material susceptibility
and bounding region---that simultaneously encode both the per-volume limit on
polarization set by passivity and geometric constraints on radiative
efficiencies set by finite object sizes through the scattering
-operator. We then analyze these bounds in two practical settings,
comparing against prior limits as well as near optimal structures discovered
through topology optimization. Principally, we show that the bounds properly
capture the physically observed transition from the volume scaling of
absorptivity seen in deeply subwavelength objects (nanoparticle radius or thin
film thickness) to the area scaling of absorptivity seen in ray optics
(blackbody limits).Comment: 9 pages including appendices, 2 figures, 1 tabl
Quantum nanophotonics using hyperbolic metamaterials
Engineering the optical properties using artificial nanostructured media
known as metamaterials has led to breakthrough devices with capabilities from
super-resolution imaging to invisibility. In this article, we review
metamaterials for quantum nanophotonic applications, a recent development in
the field. This seeks to address many challenges in the field of quantum optics
using recent advances in nanophotonics and nanofabrication. We focus on the
class of nanostructured media with hyperbolic dispersion that have emerged as
one of the most promising metamaterials with a multitude of practical
applications from subwavelength imaging, nanoscale waveguiding, biosensing to
nonlinear switching. We present the various design and characterization
principles of hyperbolic metamaterials and explain the most important property
of such media: a broadband enhancement in the electromagnetic density of
states. We review several recent experiments that have explored this phenomenon
using spontaneous emission from dye molecules and quantum dots. We finally
point to future applications of hyperbolic metamaterials of using the broadband
enhancement in the spontaneous emission to construct single photon sources.Comment: 25 pages, 12 figures, Review Articl
Fundamental limits to attractive and repulsive Casimir--Polder forces
We derive upper and lower bounds on the Casimir--Polder force between an
anisotropic dipolar body and a macroscopic body separated by vacuum via
algebraic properties of Maxwell's equations. These bounds require only a coarse
characterization of the system---the material composition of the macroscopic
object, the polarizability of the dipole, and any convenient partition between
the two objects---to encompass all structuring possibilities. We find that the
attractive Casimir--Polder force between a polarizable dipole and a uniform
planar semi-infinite bulk medium always comes within 10% of the lower bound,
implying that nanostructuring is of limited use for increasing attraction. In
contrast, the possibility of repulsion is observed even for isotropic dipoles,
and is routinely found to be several orders of magnitude larger than any known
design, including recently predicted geometries involving conductors with sharp
edges. Our results have ramifications for the design of surfaces to trap,
suspend, or adsorb ultracold gases.Comment: 6 pages, 3 figure
Fundamental limits to radiative heat transfer: theory
Near-field radiative heat transfer between bodies at the nanoscale can
surpass blackbody limits on thermal radiation by orders of magnitude due to
contributions from evanescent electromagnetic fields, which carry no energy to
the far-field. Thus far, principles guiding explorations of larger heat
transfer beyond planar structures have assumed utility in surface
nanostructuring, which can enhance the density of states, and further assumed
that such design paradigms can approach Landauer limits, in analogy to
conduction. We derive fundamental shape-independent limits to radiative heat
transfer, applicable in near- through far-field regimes, that incorporate
material and geometric constraints such as intrinsic dissipation and finite
object sizes, and show that these preclude reaching the Landauer limits in all
but a few restrictive scenarios. Additionally, we show that the interplay of
material response and electromagnetic scattering among proximate bodies means
that bodies which maximize radiative heat transfer actually maximize scattering
rather than absorption. Finally, we compare our new bounds to existing Landauer
limits, as well as limits involving bodies maximizing far-field absorption, and
show that these lead to overly optimistic predictions. Our results have
ramifications for the ultimate performance of thermophotovoltaics and nanoscale
cooling, as well as related incandescent and luminescent devices.Comment: 12 pages including appendices, 1 figure; SM and PSV contributed
equall
Channel-based algebraic limits to conductive heat transfer
Recent experimental advances probing coherent phonon and electron transport
in nanoscale devices at contact have motivated theoretical channel-based
analyses of conduction based on the nonequilibrium Green's function formalism.
The transmission through each channel has been known to be bounded above by
unity, yet actual transmissions in typical systems often fall far below these
limits. Building upon recently derived radiative heat transfer limits and a
unified formalism characterizing heat transport for arbitrary bosonic systems
in the linear regime, we propose new bounds on conductive heat transfer. In
particular, we demonstrate that our limits are typically far tighter than the
Landauer limits per channel and are close to actual transmission eigenvalues by
examining a model of phonon conduction in a 1-dimensional chain. Our limits
have ramifications for designing molecular junctions to optimize conduction.Comment: 10 pages, 2 figures, 2 appendice
B 12 -Mediated, Long Wavelength Photopolymerization of Hydrogels
Medical hydrogel applications have expanded rapidly over the past decade. Implantation in patients by non-invasive injection is preferred, but this requires hydrogel solidification from a low viscosity solution to occur in vivo via an applied stimuli. Transdermal photo-crosslinking of acrylated biopolymers with photoinitiators and lights offers a mild, spatiotemporally controlled solidification trigger. However, the current short wavelength initiators limit curing depth and efficacy because they do not absorb within the optical window of tissue (600 - 900 nm). As a solution to the current wavelength limitations, we report the development of a red light responsive initiator capable of polymerizing a range of acrylated monomers. Photo-activation occurs within a range of skin type models containing high biochromophore concentrations
Outlook for inverse design in nanophotonics
Recent advancements in computational inverse design have begun to reshape the
landscape of structures and techniques available to nanophotonics. Here, we
outline a cross section of key developments at the intersection of these two
fields: moving from a recap of foundational results to motivation of emerging
applications in nonlinear, topological, near-field and on-chip optics.Comment: 13 pages, 6 figure
Fundamental limits to radiative heat transfer: The limited role of nanostructuring in the near-field
In a complementary article, we exploited algebraic properties of Maxwell's
equations and fundamental principles such as electromagnetic reciprocity and
passivity, to derive fundamental limits to radiative heat transfer applicable
in near- through far-field regimes. The limits depend on the choice of material
susceptibilities and bounding surfaces enclosing arbitrarily shaped objects. In
this article, we apply these bounds to two different geometric configurations
of interest, namely dipolar particles or extended structures of infinite area
in the near field of one another, and compare these predictions to prior
limits. We find that while near-field radiative heat transfer between dipolar
particles can saturate purely geometric "Landauer" limits, bounds on extended
structures cannot, instead growing much more slowly with respect to a material
response figure of merit, an "inverse resistivity" for metals, due to the
deleterious effects of multiple scattering; nanostructuring is unable to
overcome these limits, which can be practically reached by planar media at the
surface polariton condition
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