Low-energy photoelectron transmission through aerosol overlayers

The transmission of low-energy (<1.8eV) photoelectrons through the shell of core-shell aerosol particles is studied for liquid squalane, squalene, and DEHS shells. The photoelectrons are exclusively formed in the core of the particles by two-photon ionization. The total photoelectron yield recorded as a function of shell thickness (1-80nm) shows a bi-exponential attenuation. For all substances, the damping parameter for shell thicknesses below 15nm lies between 8 and 9nm, and is tentatively assigned to the electron attenuation length at electron kinetic energies of ~0.5-1eV. The significantly larger damping parameters for thick shells (> 20nm) are presumably a consequence of distorted core-shell structures. A first comparison of aerosol and traditional thin film overlayer methods is provided

Strategy for designing broadband epsilon-near-zero metamaterial with loss compensation by gain media

A strategy is proposed to design the broadband gain-doped epsilon-near-zero (GENZ) metamaterial. Based on the Milton representation of effective permittivity, the strategy starts in a dimensionless spectral space, where the effective permittivity of GENZ metamaterial is simply determined by a pole-zero structure corresponding to the operating frequency range. The physical structure of GENZ metamaterial is retrieved from the pole-zero structure via a tractable inverse problem. The strategy is of great advantage in practical applications and also theoretically reveals the cancellation mechanism dominating the broadband near-zero permittivity phenomenon in the spectral space

Ab initio theory of Fano resonances in plasmonic nanostructures and metamaterials

An ab initio theory for Fano resonances in plasmonic nanostructures and metamaterials is developed using Feshbach formalism. It reveals the role played by the electromagnetic modes and material losses in the system, and enables the engineering of Fano resonances in arbitrary geometries. A general formula for the asymmetric resonance in a non-conservative system is derived. The influence of the electromagnetic interactions on the resonance line shape is discussed and it is shown that intrinsic losses drive the resonance contrast, while its width is mostly determined by the coupling strength between the non-radiative mode and the continuum. The analytical model is in perfect agreement with numerical simulations.Comment: 13 pages, 5 figure

Varying the effective refractive index to measure optical transport in random media

We introduce a new approach for measuring both the effective medium and the transport properties of light propagation in heterogeneous media. Our method utilizes the conceptual equivalence of frequency variation with a change in the effective index of refraction. Experimentally, we measure intensity correlations via spectrally resolved refractive index tuning, controlling the latter via changes in the ambient pressure. Our experimental results perfectly match a generalized transport theory that incorporates the effective medium and predicts a precise value for the diffusion constant. Thus, we directly confirm the applicability of the effective medium concept in strongly scattering materials.Comment: 5 pages, 5 figure

Millimeter Wave Scattering from Neutral and Charged Water Droplets

We investigated 94GHz millimeter wave (MMW) scattering from neutral and charged water mist produced in the laboratory with an ultrasonic atomizer. Diffusion charging of the mist was accomplished with a negative ion generator (NIG). We observed increased forward and backscattering of MMW from charged mist, as compared to MMW scattering from an uncharged mist. In order to interpret the experimental results, we developed a model based on classical electrodynamics theory of scattering from a dielectric sphere with diffusion-deposited mobile surface charge. In this approach, scattering and extinction cross-sections are calculated for a charged Rayleigh particle with effective dielectric constant consisting of the volume dielectric function of the neutral sphere and surface dielectric function due to the oscillation of the surface charge in the presence of applied electric field. For small droplets with (radius smaller than 100nm), this model predicts increased MMW scattering from charged mist, which is qualitatively consistent with the experimental observations. The objective of this work is to develop indirect remote sensing of radioactive gases via their charging action on atmospheric humid air.Comment: 18 pages, 8 figure

Multidimensional optical fractionation with holographic verification

The trajectories of colloidal particles driven through a periodic potential energy landscape can become kinetically locked in to directions dictated by the landscape's symmetries. When the landscape is realized with forces exerted by a structured light field, the path a given particle follows has been predicted to depend exquisitely sensitively on such properties as the particle's size and refractive index These predictions, however, have not been tested experimentally. Here, we describe measurements of colloidal silica spheres' transport through arrays of holographic optical traps that use holographic video microscopy to track individual spheres' motions in three dimensions and simultaneously to measure each sphere's radius and refractive index with part-per-thousand resolution. These measurements confirm previously untested predictions for the threshold of kinetically locked-in transport, and demonstrate the ability of optical fractionation to sort colloidal spheres with part-per-thousand resolution on multiple characteristics simultaneously.Comment: 4 pages, 2 figures. Accepted for publication in Physical Review Letter

Near-field enhancement and sub-wavelength imaging in the optical region using a pair of two-dimensional arrays of metal nanospheres

Near-field enhancement and sub-wavelength imaging properties of a system comprising a coupled pair of two-dimensional arrays of resonant nanospheres are studied. The concept of using two coupled material sheets possessing surface mode resonances for evanescent field enhancement is already well established in the microwave region. This paper shows that the same principles can be applied also in the optical region, where the performance of the resonant sheets can be realized with the use of metallic nanoparticles. In this paper we present design of such structures and study the electric field distributions in the image plane of such superlens.Comment: 15 pages, 9 figure