Showing papers by "Viktor A. Podolskiy published in 2014"

Nonlocal optics of plasmonic nanowire metamaterials

Abstract: We present an analytical description of the nonlocal optical response of plasmonic nanowire metamaterials that enable negative refraction, subwavelength light manipulation, and emission lifetime engineering. We show that dispersion of optical waves propagating in nanowire media results from coupling of transverse and longitudinal electromagnetic modes supported by the nanowires and derive the nonlocal effective medium approximation for this dispersion. We derive the profiles of electric field across the unit cell, and use these expressions to solve the long-standing problem of additional boundary conditions in calculations of transmission and reflection of waves by nonlocal nanowire media. We verify our analytical results with numerical solutions of Maxwell's equations and discuss generalization of the developed formalism to other uniaxial metamaterials.

Looking into meta-atoms of plasmonic nanowire metamaterial.

Abstract: Nanowire-based plasmonic metamaterials exhibit many intriguing properties related to the hyperbolic dispersion, negative refraction, epsilon-near-zero behavior, strong Purcell effect, and nonlinearities. We have experimentally and numerically studied the electromagnetic modes of individual nanowires (meta-atoms) forming the metamaterial. High-resolution, scattering-type near-field optical microscopy has been used to visualize the intensity and phase of the modes. Numerical and analytical modeling of the mode structure is in agreement with the experimental observations and indicates the presence of the nonlocal response associated with cylindrical surface plasmons of nanowires.

All-Semiconductor Negative-Index Plasmonic Absorbers

Abstract: We demonstrate epitaxially grown all-semiconductor thin-film midinfrared plasmonic absorbers and show that absorption in these structures is linked to the excitation of highly confined negative-index surface plasmon polaritons. Strong (>98%) absorption is experimentally observed, and the spectral position and intensity of the absorption resonances are studied by reflection and transmission spectroscopy. Numerical models as well as an analytical description of the excited guided modes in our structures are presented, showing agreement with experiment. The structures investigated demonstrate a wavelength-flexible, all-semiconductor, plasmonic architecture with potential for both sensing applications and enhanced interaction of midinfrared radiation with integrated semiconductor optoelectronic elements.

Engineering absorption and blackbody radiation in the far-infrared with surface phonon polaritons on gallium phosphide

Abstract: We demonstrate excitation of surface phonon polaritons on patterned gallium phosphide surfaces. Control over the light-polariton coupling frequencies is demonstrated by changing the pattern periodicity and used to experimentally determine the gallium phosphide surface phonon polariton dispersion curve. Selective emission via out-coupling of thermally excited surface phonon polaritons is experimentally demonstrated. Samples are characterized experimentally by Fourier transform infrared reflection and emission spectroscopy, and modeled using finite element techniques and rigorous coupled wave analysis. The use of phonon resonances for control of emissivity and excitation of bound surface waves offers a potential tool for the exploration of long-wavelength Reststrahlen band frequencies.

ε -near-zero enhanced light transmission through a subwavelength slit

Abstract: We present a comprehensive analysis of the role of $\ensuremath{\epsilon}$-near-zero (ENZ) materials with realistic losses in enhanced light transmission through subwavelength channels. In this work, we utilize a bulk ENZ material consisting of heavily doped semiconductor, operating at the semiconductor's plasma frequency (in mid-infrared regime). Resonant transmission peaks for transverse magnetic polarized light have been experimentally observed when such material is used as a coupling layer and/or inside the subwavelength slit. In the process, we developed a generalized mode-matching-based approach to calculate and analyze light propagation through slits and waveguides embedded inside planar layer stacks and applied this approach to the particular case of ENZ-filled subwavelength slit. The developed formalism inherently provides the individual amplitudes of the guided modes inside the slit and their coupling efficiencies to the surrounding media. Using the calculated coupling efficiencies, we were successful in explaining the resonant transmission behavior of these structures and also were able to track the origin of enhancements. Our analysis demonstrates that in the presence of losses, the transmission efficiency is dominated by the bulk plasma resonances of the ENZ coupling layer and minimal advantage is gained by filling the slit with ENZ material. The enhancements were also observed to be dependent on the thickness of the substrate layer. Further analysis of the calculated amplitudes using the numerical algorithm developed an approximate analytical model for systems with deep subwavelength slits.

Toward parametric amplification in plasmonic systems: second harmonic generation enhanced by surface plasmon polaritons.

Abstract: Having in mind parametric amplification of surface plasmon polaritons (SPPs) as the final goal, we took the first step and studied in the Kretschmann geometry a simpler nonlinear optical process - second harmonic generation (SHG) enhanced by SPPs propagating at the interface between gold film and 2-methyl-4-nitroaniline (MNA). The experimentally demonstrated SHG efficiency was nearly 10(6) times larger than the one reported previously in the SPP system with different nonlinear optical material. The experimentally measured nonlinear conversion efficiency is estimated to be sufficient for parametric amplification of surface plasmon polaritons at ultra-short laser pumping.

Metamaterials-based Salisbury screens with reduced angular sensitivity

Abstract: We demonstrate that the incorporation of nonlocal nanowire metamaterials into Salisbury screens allows for a substantial reduction of the dependence of incident angle on the absorption maximum. Realizations of angle-independent Salisbury screens for the near-IR, mid-IR, and GHz frequencies are proposed and their performances are analyzed analytically and numerically. It is shown that nonlocal effective medium theory adequately describes the angular dependence of nanowire-based Salisbury screens.

All semiconductor negative-index plasmonic absorbers

Abstract: We demonstrate all-semiconductor thin-film plasmonic absorbers, where strong absorption in these structures is linked to the excitation of highly-confined negative-index surface plasmon polaritons. We present numerical and analytical descriptions of guided modes of the system.

Interscale Mixing Microscopy: numerically stable imaging of wavelength- scale objects with sub- wavelength resolution and far field measurements

Abstract: We present an imaging technique that allows the recovery of the transparency profile of wavelength-scale objects with deep subwavelength resolution based on far-field intensity measurements. The approach, interscale mixing microscopy (IMM), relies on diffractive element positioned in the near-field proximity to the object, to scatter information carried by evanescent waves into propagating part of the spectrum. A combination of numerical solutions of Maxwell equations and nonlinear fitting is then used to recover the information about the object based on far-field intensity measurements. The potential of the developed formalism to recover wavelength/20 features of wavelength-scale objects in presence of up to 10% noise is demonstrated.

Making the Mid-IR nano with epitaxial plasmonic devices

Abstract: We have extensively investigated heavily doped semiconductors as potential plasmonic metals at long wavelengths. The ability to control the doping level in a semiconductor material, both III-V's (InAs/InSb) and Silicon, allows for control of the metal's optical properties, and adds an intriguing additional controllable parameter to the design of plasmonic structures. These materials can be quite accurately modeled using the Drude formalism, even for energies larger than the band gap, and have a number of attractive qualities, including control of carrier concentration (and thus plasma frequency, ωρ), as well as single-crystal material quality, atomic-layer control of thicknesses, and the potential for integration with epitaxially-grown mid-IR optoelectronic devices. In this presentation, I will discuss recent developments in epitaxial plasmonic devices for mid-IR applications. First, the growth and characterization of our materials will be discussed, as well as the material limitations. Subsequently, I will demonstrate the doped semiconductors potential as epsilon-near-zero (ENZ) materials. At ENZ frequencies, we have demonstrated enhanced coupling to sub-wavelength waveguides, offering a potential route towards overcoming the mismatch between the micron-scale light of the mid-IR and the nano-scale. In addition, we have shown that near ENZ, these materials thin (d ≪ λo) loss-less dielectric films to serve as perfect absorbing layers, by controlling the metal/dielectric interface phase shift in thin film interference structures.

Mid-IR Plasmonics with Engineered Semiconductor Metals

Abstract: We investigate the utility of heavily doped semiconductors as plasmonic materials for mid-IR applications. The wavelength flexibility and design-ability of these materials allow for the demonstration of nanophotonic structures and devices for long-wavelength IR light.

Angle-independent Salisbury screens based on nonlocal nanowire metamaterials

Abstract: We demonstrate that nonlocal nanowire metamaterials can help to alleviate one of the main limitations of Salisbury screens, their dependence on the incident angle.

Diffractive Interface Theory: Nonlocal polarizability approach to the optics of metasurfaces

Abstract: We present a formalism for understanding the elecromagnetism of metasurfaces, optically thin composite films with engineered diffraction. The technique, diffractive interface theory (DIT), takes explicit advantage of the small optical thickness of a metasurface, eliminating the need for solving for light propagation inside the film and providing a direct link between the spatial profile of a metasurface and its diffractive properties. Predictions of DIT are compared with full-wave numerical solutions of Maxwell's equations, demonstrating DIT's validity and computational advantages for optically thin structures. Applications of the DIT range from understanding of fundamentals of light-matter interaction in metasurfaces to efficient analysis of generalized refraction to metasurface optimization.

Additional Waves in Nonlocal Nanowire Metamaterials

Abstract: We analyze, analytically and numerically, optical properties of plasmonic nanowire composites that form a promising platform for nanophotonics, present description of nonlocal electromagnetism in this media, and discuss implications of nonlocal response for different applications.

Numerically Stable Reconstruction of Wavelength-Scale Objects with Sub-Wavelength Resolution

Abstract: We present numerically stable expansion basis for diffraction-based far-field computational imaging systems and demonstrate the capabilities of reconstructing wavelength-scale objects with wavelength/20 resolution.