Proximity Effects in Radiative Transfer

Though the dependence of near-field radiative transfer on the gap between two planar objects is well understood, that between curved objects is still unclear. We show, based on the analysis of the surface polariton mediated radiative transfer between two spheres of equal radii $R$ and minimum gap $d$, that the near--field radiative transfer scales as $R/d$ as $d/R \rightarrow 0$ and as $\ln(R/d)$ for larger values of $d/R$ up to the far--field limit. We propose a modified form of the proximity approximation to predict near--field radiative transfer between curved objects from simulations of radiative transfer between planar surfaces.Comment: 5 journal pages, 4 figure

Spontaneous emission by rotating objects: A scattering approach

We study the quantum electrodynamics (QED) vacuum in the presence of a body rotating along its axis of symmetry and show that the object spontaneously emits energy if it is lossy. The radiated power is expressed as a general trace formula solely in terms of the scattering matrix, making an explicit connection to the conjecture of Zel'dovich [JETP Lett. 14, 180 (1971)] on rotating objects. We further show that a rotating body drags along nearby objects while making them spin parallel to its own rotation axis

A theory of electromagnetic fluctuations for metallic surfaces and van der Waals interactions between metallic bodies

A new general expression is derived for the fluctuating electromagnetic field outside a metal surface, in terms of its surface impedance. It provides a generalization to real metals of Lifshitz theory of molecular interactions between dielectric solids. The theory is used to compute the radiative heat transfer between two parallel metal surfaces at different temperatures. It is shown that a measurement of this quantity may provide an experimental resolution of a long-standing controversy about the effect of thermal corrections on the Casimir force between real metal plates.Comment: 4 pages, 2 figures; typos corrected, minor changes to match the published version in Physical Review Letter

Quantum field theory of the van der Waals friction

The van der Waals friction between two semi-infinite solids, and between a small neutral particle and semi-infinite solid is reconsidered on the basis of thermal quantum field theory in the Matsubara formulation. The calculation of the friction to linear order in the sliding velocity is reduced to the finding of the equilibrium Green functions. Thus this approach cab be extended for bodsies with complex geometry. The friction calculated in this approach agrees with the friction calculated using a dynamical modification of the Lifshitz theory, which is based on the fluctuation-dissipation therem. We show that the van der Waals fricxtion can be measured in non-contact friction experiment using state-of-the art equipment

Second-order calculation of the local density of states above a nanostructured surface

We have numerically implemented a perturbation series for the scattered electromagnetic fields above rough surfaces, due to Greffet, allowing us to evaluate the local density of states to second order in the surface profile function. We present typical results for thermal near fields of surfaces with regular nanostructures, investigating the relative magnitude of the contributions appearing in successive orders. The method is then employed for estimating the resolution limit of an idealized Near-Field Scanning Thermal Microscope (NSThM).Comment: 10 pages, 7 figure

Theory of friction: contribution from fluctuating electromagnetic field

We calculate the friction force between two semi-infinite solids in relative parallel motion (velocity $V$), and separated by a vacuum gap of width $d$. The friction force result from coupling via a fluctuating electromagnetic field, and can be considered as the dissipative part of the van der Waals interaction. We consider the dependence of the friction force on the temperature $T$, and present a detailed discussion of the limiting cases of small and large $V$ and $d$.Comment: 15 pages, No figure

Statistics of speckle patterns

We develop a general method for calculating statistical properties of the speckle pattern of coherent waves propagating in disordered media. In some aspects this method is similar to the Boltzmann-Langevin approach for the calculation of classical fluctuations. We apply the method to the case where the incident wave experiences many small angle scattering events during propagation, but the total angle change remains small. In many aspects our results for this case are different from results previously known in the literature. The correlation function of the wave intensity at two points separated by a distance $r$, has a long range character. It decays as a power of $r$ and changes sign. We also consider sensitivities of the speckles to changes of external parameters, such as the wave frequency and the incidence angle.Comment: 4 pages, 2 figure

Propagation of coherent waves in elastically scattering media

A general method for calculating statistical properties of speckle patterns of coherent waves propagating in disordered media is developed. It allows one to calculate speckle pattern correlations in space, as well as their sensitivity to external parameters. This method, which is similar to the Boltzmann-Langevin approach for the calculation of classical fluctuations, applies for a wide range of systems: From cases where the ray propagation is diffusive to the regime where the rays experience only small angle scattering. The latter case comprises the regime of directed waves where rays propagate ballistically in space while their directions diffuse. We demonstrate the applicability of the method by calculating the correlation function of the wave intensity and its sensitivity to the wave frequency and the angle of incidence of the incoming wave.Comment: 19 pages, 5 figure

Trace formulae for non-equilibrium Casimir interactions, heat radiation and heat transfer for arbitrary objects

We present a detailed derivation of heat radiation, heat transfer and (Casimir) interactions for N arbitrary objects in the framework of fluctuational electrodynamics in thermal non-equilibrium. The results can be expressed as basis-independent trace formulae in terms of the scattering operators of the individual objects. We prove that heat radiation of a single object is positive, and that heat transfer (for two arbitrary passive objects) is from the hotter to a colder body. The heat transferred is also symmetric, exactly reversed if the two temperatures are exchanged. Introducing partial wave-expansions, we transform the results for radiation, transfer and forces into traces of matrices that can be evaluated in any basis, analogous to the equilibrium Casimir force. The method is illustrated by (re)deriving the heat radiation of a plate, a sphere and a cylinder. We analyze the radiation of a sphere for different materials, emphasizing that a simplification often employed for metallic nano-spheres is typically invalid. We derive asymptotic formulae for heat transfer and non-equilibrium interactions for the cases of a sphere in front a plate and for two spheres, extending previous results. As an example, we show that a hot nano-sphere can levitate above a plate with the repulsive non-equilibrium force overcoming gravity -- an effect that is not due to radiation pressure.Comment: 29 pages, 6 figures (v2: Sentence added in Sec. 1

Scattering-matrix approach to Casimir-Lifshitz force and heat transfer out of thermal equilibrium between arbitrary bodies

We study the radiative heat transfer and the Casimir-Lifshitz force occurring between two bodies in a system out of thermal equilibrium. We consider bodies of arbitrary shape and dielectric properties, held at two different temperatures, and immersed in a environmental radiation at a third different temperature. We derive explicit closed-form analytic expressions for the correlations of the electromagnetic field, and for the heat transfer and Casimir-Lifshitz force, in terms of the bodies scattering matrices. We then consider some particular cases which we investigate in detail: the atom-surface and the slab-slab configurations