Classical and fluctuation‐induced electromagnetic interactions in micron‐scale systems: designer bonding, antibonding, and Casimir forces

Abstract

Whether 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 quantumfluctuation 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.

Fluctuating volume-current formulation of electromagnetic fluctuations in inhomogeneous media: Incandescence and luminescence in arbitrary geometries

“…Interest in complex designs is also fueled by our increasing ability to engineer selective and even dynamically tunable emitters and detectors at wavelengths for which there is currently a lack of coherent sources, 12,[45][46][47][48][49] in addition to solar-energy harvesting applications. [50][51][52][53][54][55] In addition to radiation, fluctuations can also mediate heat exchange 6,8,56 and interactions 7,15,21,57,58 (known as Casimir forces) between objects. Unlike heat exchange, Casimir interactions persist even at equilibrium and are known to arise primarily due to contributions of quantum rather than finite-temperature fluctuations.…”

“…One fundamental distinction between "near-field" effects (between objects at wavelength-scale separations or less) and the more familiar "far-field" phenomena (separations ≫ wavelength) is that the former can be significantly enhanced by the contributions of evanescent waves, 6,56,59,60 growing in a power-law fashion with decreasing object separations. As a result, the heat transfer between real materials can exceed the predictions of the Stefan-Boltzmann law by orders of magnitude 13 and quantum forces can reach atmospheric pressures at nanometric lengthscales, 21 motivating interest in complex designs that can be tailored for various applications, including thermophotovoltaic energy conversion, [61][62][63][64] nanoscale cooling, 65,66 and MEMS design. [67][68][69] Until very recently, however, calculations and experiments remained focused on planar structures and simple approximations thereof.…”

“…71,72 Naively, this involves repeated calculations of EM Green's functions throughout the bodies, which can prove prohibitive for complex objects where the latter must be computed numerically, especially due to the broad bandwidth associated with thermal fluctuations, but it turns out that more sophisticated formulations exist. 14,21 These include time-and frequency-domain methods where the power transfer or force on an object is obtained via integrals of the flux or Maxwell stress tensor, or equivalently EM Green's functions, along some arbitrary surface enclosing the body. 36,[73][74][75][76][77][78][79][80] Recent techniques forgo surface integrations altogether in favor of unfamiliar but more efficient expressions involving traces of either scattering 31,33,34,[37][38][39]81,82 or boundary-element 26,27,83 matrices.…”

Design Rules For a Nano-Opto-Mechanical Actuator Based on Suspended Slot Waveguides

“…The device performance was theoretically investigated under the condition of optical force uniformly distributed along the waveguide. However, in the nanometer-scale range, the Casimir force is not negligible between uncharged materials, which may cause problems such as stiction [13][14][15], possibly leading to collapse and adhesion between movable parts during the fabrication process. In this sense, the contribution presented by this work is a systematic study to outline the fundamental design rules for a nano-opto-mechanical actuator based on silicon-on-insulator (SOI) suspended slot waveguides, since the work cited in literature [6] only analyzes the actuator performances for a well-defined waveguide cross-section, and neglects the influence of the Casimir force.…”

Effect of shape in near-field thermal transfer for periodic structures

“…Geometries that are considered range from planar structures 1,12,13 to cases where a sphere [14][15][16] , a cone 16 , or a cylinder 16 is placed on top of a planar substrate. There are several reviews that summarize the results of this line of research 17,18 . In addition to a variety of exact numerical techniques, there also exists a set of approximation methods for thermal transfer calculations.…”