R. Carminati

Surface electromagnetic waves thermally excited: Radiative heat transfer, coherence properties and Casimir forces revisited in the near field

We review in this article the influence of surface waves on the thermally excited electromagnetic field. We study in particular the field emitted at subwalength distances of material surfaces. After reviewing the main properties of surface waves, we introduce the fluctuation-dissipation theorem that allows to model the fluctuating electromagnetic fields. We then analyse the contribution of these waves in a variety of phenomena. They give a leading contribution to the density of electromagnetic states, they produce both temporal coherence and spatial coherence in the near field of planar thermal sources. They can be used to modify radiative properties of surfaces and to design partially spatially coherent sources. Finally, we discuss the role of surface waves in the radiative heat transfer and the theory of dispersion forces at the subwavelength scale.

Definition and measurement of the local density of electromagnetic states close to an interface

We define unambiguously the local density of electromagnetics states (LDOS) close to an interface. We show that we can measure this LDOS by making a thermal emission spectrum with a near-field scanning optical microscope

Optical content and resolution of near-field optical images: Influence of the operating mode

Recent experimental work has shown that the contrast of near-field optical images depends on the path followed by the tip during the scan. This artifact may misguide the interpretation of the images and the estimation of the optical resolution. We provide a rigorous theoretical study of this effect based on three-dimensional perturbation theory and two-dimensional exact numerical calculations. We quantitatively study the dependence of the artifact on the illumination/detection conditions and on the scattering potential of the sample. This study should provide guidelines for future experimental work.

Optical resonances in one-dimensional dielectric nanorod arrays: field-induced fluorescence enhancement.

Arrays of transparent dielectric nanorods are shown to produce very large local field enhancements at specific resonant conditions. These structures would lead to enhancement of molecular fluorescence signals without quenching. The resonant angular width and field enhancements are analytically derived as a function of wavelength, grating period, rod radius, and dielectric constant.

Optical contrast, topographic contrast and artifacts in illumination-mode scanning near-field optical microscopy

We use a two-dimensional exact numerical simulation and a three-dimensional perturbative analysis to study the coupling between dielectric contrast and topography in the images obtained by illumination-mode scanning near-field optical microscopy. We use a model for the emitting tip, which describes the polarization and confinement effects of a real tip. We analyze the image formation, especially the coupling between topographic and dielectric contrast. In the case of weakly scattering samples, we introduce rigorously the concepts of impulse response and equivalent surface profile. This tool may be useful to describe and understand quantitatively experimental images. Finally, we study the presence of artifacts in the images, due to the coupling between optical scattering and the z motion of the tip in constant-distance operating mode. We put forward the difficulty of predicting the relative weight of the artifact and the purely optical contributions.

Contrast mechanisms in illumination-mode SNOM

We study theoretically and numerically the contrast mechanism in illumination-mode SNOM. We present a model, based on the Born approximation, which shows how the topographic and dielectric content of the sample is encoded in the measured signal. Under certain conditions, the image formation mechanism may be described by an impulse response that we define. Our model is in perfect agreement with numerical simulations of a two-dimensional model SNOM, under s-polarised illumination.

Nanoscale radiative heating of a sample with a probe

The purpose of this paper is to show that it is possible to transfer large amount of heat to a sample at a nanometer scale by approaching a probe such as those used in near-field microscopies. We evaluate the different heat exchange processes such as convective and radiative heat transfer. An application to local heating is discussed.

Thermal response of silicon crystal to pico-femtosecond heat pulse by molecular dynamics

We investigate the thermal response of a silicon crystal irradiated by a pico-femto heat pulse by using molecular dynamics technique and a linear response theory–based statistical analysis. The thermal susceptibility is first defined in terms of computed quantities and then convoluted with time Gaussian temperature pulses. The qualitative difference between the responses to various pulse durations is explained and the results are compared to those of classical Fourier model. Non-Fourier behaviors are emphasized and a mean phonon relaxation time is identified.

Resonant emission and transmission of infrared radiation by microstructured surfaces supporting surface phonon-polaritons

A new phenomenon has been demonstrated recently dealing with radiative properties of microstructured surfaces. It has been shown that light can be resonantly transmitted by a film with a periodic array of holes due to the excitation of surface plasmons. In this paper, we report similar results in the infrared due to the excitation of surface phonon-polaritons. Another striking property of microstructured surfaces supporting surface phonon-polaritons is their ability to emit light in very narrow solid angles. In this paper, we show that it is also possible to design a surface that allows to emit light isotropically with a 100% emissivity. Experimental results are reported.

Electromagnetic modes of a linear chain of nanoparticles

We study numerically the dispersion relation and the structure of the optical modes along a chain of metallic nanoparticles. Polariton modes exists in both the radiative and non-radiative regions. Applications to nanophotonics are discussed.