Infra-Red Surface-Plasmon-Resonance technique for biological studies

We report on a Surface-Plasmon-Resonance (SPR) technique based on Fourier -Transform - Infra - Red (FTIR) spectrometer. In contrast to the conventional surface plasmon technique, operating at a fixed wavelength and a variable angle of incidence, our setup allows the wavelength and the angle of incidence to be varied simultaneously. We explored the potential of the SPR technique in the infrared for biological studies involving aqueous solutions. Using computer simulations, we found the optimal combination of parameters (incident angle, wavelength) for performing this task. Our experiments with physiologically important glucose concentrations in water and in human plasma verified our computer simulations. Importantly, we demonstrated that the sensitivity of the SPR technique in the infrared range is not lower and in fact is even higher than that for visible light. We emphasize the advantages of infra red SPR for studying glucose and other biological molecules in living cells.Comment: 8 pages,8 figure

Dynamical excitonic effects in metals and semiconductors

The dynamics of an electron--hole pair induced by the time--dependent screened Coulomb interaction is discussed. In contrast to the case where the static electron--hole interaction is considered we demonstrate the occurrence of important dynamical excitonic effects in the solution of the Bethe--Salpeter equation.This is illustrated in the calculated absorption spectra of noble metals (copper and silver) and silicon. Dynamical corrections strongly affect the spectra, partially canceling dynamical self--energy effects and leading to good agreement with experiment.Comment: Accepted for publication on Phys. Rev. Let

Optical anisotropic metamaterials: Negative refraction and focusing

We design three-dimensional (3D) metallic nanowire media with different structures and numerically demonstrate that they can be homogeneous effective indefinite anisotropic media by showing that their dispersion relations are hyperbolic. For a finite slab, a nice fitting procedure is exploited to obtain the dispersion relations from which we retrieve the effective permittivities. The pseudo focusing for the real 3D wire medium agrees very well with the homogeneous medium having the effective permittivity tensor of the wire medium. Studies also show that in the long-wavelength limit, the hyperbolic dispersion relation of the 3D wire medium can be valid even for evanescent modes.Comment: 7 pages, 9 figure

Material dependence of Casimir forces: gradient expansion beyond proximity

A widely used method for estimating Casimir interactions [H. B. G. Casimir, Proc. K. Ned. Akad. Wet. 51, 793 (1948)] between gently curved material surfaces at short distances is the proximity force approximation (PFA). While this approximation is asymptotically exact at vanishing separations, quantifying corrections to PFA has been notoriously difficult. Here we use a derivative expansion to compute the leading curvature correction to PFA for metals (gold) and insulators (SiO$_2$) at room temperature. We derive an explicit expression for the amplitude $\hat\theta_1$ of the PFA correction to the force gradient for axially symmetric surfaces. In the non-retarded limit, the corrections to the Casimir free energy are found to scale logarithmically with distance. For gold, $\hat\theta_1$ has an unusually large temperature dependence.Comment: 4 pages, 2 figure

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

Quantum and thermal Casimir interaction between a sphere and a plate: Comparison of Drude and plasma models

We calculate the Casimir interaction between a sphere and a plate, both described by the plasma model, the Drude model, or generalizations of the two models. We compare the results at both zero and finite temperatures. At asymptotically large separations we obtain analytical results for the interaction that reveal a non-universal, i.e., material dependent interaction for the plasma model. The latter result contains the asymptotic interaction for Drude metals and perfect reflectors as different but universal limiting cases. This observation is related to the screening of a static magnetic field by a London superconductor. For small separations we find corrections to the proximity force approximation (PFA) that support correlations between geometry and material properties that are not captured by the Lifshitz theory. Our results at finite temperatures reveal for Drude metals a non-monotonic temperature dependence of the Casimir free energy and a negative entropy over a sizeable range of separations.Comment: 11 pages, 5 figure

Giant Modal Gain, Amplified Surface Plasmon Polariton Propagation, and Slowing Down of Energy Velocity in a Metal-Semiconductor-Metal Structure

We investigated surface plasmon polariton (SPP) propagation in a metal-semiconductor-metal structure where semiconductor is highly excited to have optical gain. We show that near the SPP resonance, the imaginary part of the propagation wavevector changes from positive to hugely negative, corresponding to an amplified SPP propagation. The SPP experiences a giant gain that is 1000 times of material gain in the excited semiconductor. We show that such a giant gain is related to the slowing down of average energy propagation in the structur

Highly Confined Optical Modes in Nanoscale Metal-Dielectric Multilayers

We show that a stack of metal-dielectric nanolayers, in addition to the long- and short-range plasmons, guides also an entire family of modes strongly confined within the multilayer - the bulk plasmon modes. We propose the classification scheme that reflects specific properties of these modes. We report experimental verification of the bulk plasmon modes by measuring modal indices in a structure made of three pairs of silica(29nm)/gold(25nm) layers.Comment: 4 pages, 4 figure

Comparison between experiment and theory for the thermal Casimir force

We analyze recent experiments on measuring the thermal Casimir force with account of possible background effects. Special attention is paid to the validity of the proximity force approximation (PFA) used in the comparison between the experimental data and computational results in experiments employing a sphere-plate geometry. The PFA results are compared with the exact results where they are available. The possibility to use fitting procedures in theory-experiment comparison is discussed. On this basis we reconsider experiments exploiting spherical lenses of centimeter-size radii.Comment: Plenary talk at the 10th International Conference "Quantum Field Theory Under the Influence of External Conditions" (Benasque, Spain, 2011); 16 pages, 5 figure

Dependences of the Casimir-Polder interaction between an atom and a cavity wall on atomic and material properties

The Casimir-Polder and van der Waals interactions between an atom and a flat cavity wall are investigated under the influence of real conditions including the dynamic polarizability of the atom, actual conductivity of the wall material and nonzero temperature of the wall. The cases of different atoms near metal and dielectric walls are considered. It is shown that to obtain accurate results for the atom-wall interaction at short separations, one should use the complete tabulated optical data for the complex refractive index of the wall material and the accurate dynamic polarizability of an atom. At relatively large separations in the case of a metal wall, one may use the plasma model dielectric function to describe the dielectric properties of wall material. The obtained results are important for the theoretical interpretation of experiments on quantum reflection and Bose-Einstein condensation.Comment: 5 pages, 1 figure, iopart.cls is used, to appear in J. Phys. A (special issue: Proceedings of QFEXT05, Barcelona, Sept. 5-9, 2005