1,721,174 research outputs found
Numerical Methods for Computing Casimir Interactions
Full text linkWe review several different approaches for computing Casimir forces and related fluctuation-induced interactions between bodies of arbitrary shapes and materials. The relationships between this problem and well known computational techniques from classical electromagnetism are emphasized. We also review the basic principles of standard computational methods, categorizing them according to three criteria\-choice of problem, basis, and solution technique\-that can be used to classify proposals for the Casimir problem as well. In this way, mature classical methods can be exploited to model Casimir physics, with a few important modifications.Keywords:
Imaginary Frequency, Perfectly Match Layer, Casimir Force, Casimir Energy, Perfect Electric ConductorUnited States. Army Research Office (Contract W911NF-07-D-0004)Massachusetts Institute of Technology. Ferry FundUnited States. Defense Advanced Research Projects Agency (Contract N66001-09-1-2070-DOD
Fundamental Limits to Near-Field Optical Response over Any Bandwidth
Full text linkWe develop an analytical framework to derive upper bounds to light-matter interactions in the optical near field, where applications ranging from spontaneous-emission amplification to greater-than-blackbody heat transfer show transformative potential. Our framework connects the classic complex-analytic properties of causal fields with newly developed energy-conservation principles, resulting in a new class of power-bandwidth limits. These limits demonstrate the possibility of orders-of-magnitude enhancement in near-field optical response with the right combination of material and geometry. At specific frequency and bandwidth combinations, the bounds can be closely approached by canonical plasmonic geometries, with the opportunity for new designs to emerge away from those frequency ranges. Embedded in the bounds is a material “figure of merit,” which determines the maximum response of any material (metal, dielectric, bulk, 2D, etc.), for any frequency and bandwidth. Our bounds on local density of states represent maximal spontaneous-emission enhancements, our bounds on cross density of states limit electromagnetic-field correlations, and our bounds on radiative heat transfer (RHT) represent the first such analytical rule, revealing fundamental limits relative to the classical Stefan-Boltzmann law.United States. Army Research Office (Contract W911NF-18-2-0048)United States. Army Research Office (Contract W911NF-13-D-0001
Formulation for scalable optimization of microcavities via the frequency-averaged local density of states
No full textWe present a technique for large-scale optimization of optical microcavities based on the frequency-averaged local density of states (LDOS), which circumvents computational difficulties posed by previous eigenproblem-based formulations and allows us to perform full topology optimization of three-dimensional (3d) leaky cavity modes. We present theoretical results for both 2d and fully 3d computations in which every pixel of the design pattern is a degree of freedom (“topology optimization”), e.g. for lithographic patterning of dielectric slabs in 3d. More importantly, we argue that such optimization techniques can be applied to design cavities for which (unlike silicon-slab single-mode cavities) hand designs are difficult or unavailable, and in particular we design minimal-volume multi-mode cavities (e.g. for nonlinear frequency-conversion applications).United States. Air Force Office of Scientific Research. Multidisciplinary University Research Initiative (AFOSR MURI grant number FA9550-09-1-0704)United States. Army Research Office. Institute for Soldier Nanotechnologies (Contract W911NF-07-D0004
Optical Bernoulli forces
No full textBy Bernoulli's law, an increase in the relative speed of a fluid around a body is accompanied by a decrease in the pressure. Therefore, a rotating body in a fluid stream experiences a force perpendicular to the motion of the fluid because of the unequal relative speed of the fluid across its surface. It is well known that light has a constant speed irrespective of the relative motion. Does a rotating body immersed in a stream of photons experience a Bernoulli-like force? We show that, indeed, a rotating dielectric cylinder experiences such a lateral force from an electromagnetic wave. In fact, the sign of the lateral force is the same as that of the fluid-mechanical analog as long as the electric susceptibility is positive (ε>ε[subscript 0]), but for negative-susceptibility materials (e.g., metals) we show that the lateral force is in the opposite direction. Because these results are derived from a classical electromagnetic scattering problem, Mie-resonance enhancements that occur in other scattering phenomena also enhance the lateral force.United States. Army Research Office (Contract W911NF-13-D-0001
Is the electrostatic force between a point charge and a neutral metallic object always attractive?
Full text linkWe give an example of a geometry in which the electrostatic force between a point charge and a neutral metallic object is repulsive. The example consists of a point charge centered above a thin metallic hemisphere, positioned concave up. We show that this geometry has a repulsive regime using both a simple analytical argument and an exact calculation for an analogous two-dimensional geometry. Analogues of this geometry-induced repulsion appear in many other contexts, including Casimir systems.Harvard University. Society of FellowsUnited States. Defense Advanced Research Projects Agency (contract N66001-09-1-2070-DOD)Massachusetts Institute of Technology (Ferry Fund for Innovation in Research Education
Efficient Computation of Power, Force, and Torque in BEM Scattering Calculations
No full textWe present concise, computationally efficient formulas for several quantities of interest-including absorbed and scattered power, optical force (radiation pressure), and torque-in scattering calculations performed using the boundary-element method (BEM) [also known as the method of moments (MoM)]. Our formulas compute the quantities of interest directly from the BEM surface currents with no need ever to compute the scattered electromagnetic fields. We derive our new formulas and demonstrate their effectiveness by computing power, force, and torque (PFT) in a number of example geometries. Free, open-source software implementations of our formulas are available for download online.United States. Defense Advanced Research Projects Agency (Grant N66001-09-1-2070-DOD)Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Grant W911NF-07-D-0004)United States. Air Force. Office of Scientific Research. Multidisciplinary University Research Initiative (Grant FA9550-09-1-0704
Quantitative test of general theories of the intrinsic laser linewidth
Full text linkWe perform a first-principles calculation of the quantum-limited laser
linewidth, testing the predictions of recently developed theories of the laser
linewidth based on fluctuations about the known steady-state laser solutions
against traditional forms of the Schawlow-Townes linewidth. The numerical study
is based on finite-difference time-domain simulations of the semiclassical
Maxwell-Bloch lasing equations, augmented with Langevin force terms, and thus
includes the effects of dispersion, losses due to the open boundary of the
laser cavity, and non-linear coupling between the amplitude and phase
fluctuations ( factor). We find quantitative agreement between the
numerical results and the predictions of the noisy steady-state ab initio laser
theory (N-SALT), both in the variation of the linewidth with output power, as
well as the emergence of side-peaks due to relaxation oscillations.Comment: 24 pages, 10 figure
Speed-of-light limitations in passive linear media
Full text linkWe prove that well-known speed-of-light restrictions on electromagnetic energy velocity can be extended to a new level of generality, encompassing even nonlocal chiral media in periodic geometries, while at the same time weakening the underlying assumptions to only passivity and linearity of the medium (either with a transparency window or with dissipation). As was also shown by other authors under more limiting assumptions, passivity alone is sufficient to guarantee causality and positivity of the energy density (with no thermodynamic assumptions). Our proof is general enough to include a very broad range of material properties, including anisotropy, bianisotropy (chirality), nonlocality, dispersion, periodicity, and even delta functions or similar generalized functions. We also show that the “dynamical energy density” used by some previous authors in dissipative media reduces to the standard Brillouin formula for dispersive energy density in a transparency window. The results in this paper are proved by exploiting deep results from linear-response theory, harmonic analysis, and functional analysis that had previously not been brought together in the context of electrodynamics.Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Grant W911NF-07-D0004
Classical and fluctuation-induced electromagnetic interactions in micron-scale systems: designer bonding, antibonding, and Casimir forces
No full textWhether intentionally introduced to exert control over particles and macroscopic objects, such as for trapping or cooling, or whether arising from the quantum and thermal fluctuations of charges in otherwise neutral bodies, leading to unwanted stiction between nearby mechanical parts, electromagnetic interactions play a fundamental role in many naturally occurring processes and technologies. In this review, we survey recent progress in the understanding and experimental observation of optomechanical and quantum-fluctuation forces. Although both of these effects arise from exchange of electromagnetic momentum, their dramatically different origins, involving either real or virtual photons, lead to different physical manifestations and design principles. Specifically, we describe recent predictions and measurements of attractive and repulsive optomechanical forces, based on the bonding and antibonding interactions of evanescent waves, as well as predictions of modified and even repulsive Casimir forces between nanostructured bodies. Finally, we discuss the potential impact and interplay of these forces in emerging experimental regimes of micromechanical devices
- …
