Near-field thermophotovoltaic (NFTPV) devices have received great attention lately as attractive energy harvesting systems, whereby a heated thermal emitter exchanges super-Planckian near-field radiation with a photovoltaic (PV) cell to generate electricity. This work describes the advancement of NFTPV technology through both simulations of next-generation devices, and experimental research addressing the technical challenges faced by NFTVPs, including nanostructured material properties, and large-area near-field heat transfer. The first part of this work seeks to improve the performance of a possible NFTPV device by using a periodic tungsten grating as the thermal emission source. The effects on the electrical power generation and the conversion efficiency are investigated via simulations with different grating geometries. It is found that using the selected grating geometry the power output and efficiency could be increased by 40% and 6%, respectively, over a flat tungsten emitter. The reasoning behind the enhancement is attributed to a plasmonic resonance that shifts towards lower frequencies at large wavenumbers. Extensive experimental research is undertaken to investigate the technical challenges in NFTPVs. The optical properties of thin tungsten films, which may serve as an emitter material, are extracted through spectroscopic measurements, and are found to be significantly different from reported bulk values due to a wide range of crystal structures that are present in sputtered films. A heat transfer experiment is designed and built to measure near-field radiation between two doped-silicon slabs separated by a submicron vacuum gap. The details of this system and the sample fabrication show a robust and straightforward method of measuring large-area near-field radiative heat transfer at distances between 200 nm and 800 nm. The results of this experiment show the largest energy throughput of submicron near-field heat transfer to date, and serve to address technical challenges behind practical near-field thermophotovoltaic technology.

When any method of surface wave testing that involves Rayleigh waves is performed, one important assumption is that plane Rayleigh waves are being measured. In the forward modeling or inversion procedure that is used to analyze the field dispersion curve to determine the field V[subscript s] profile, the analysis is based on the wave field consisting of plane Rayleigh waves. Therefore, field dispersion curves that contain near-field data could adversely distort the field V[subscript s] profile. To minimize the influence of near-field effects, several criteria have been recommended in the past. However, most of the criteria were based on empirical equations that implicitly assumed zones of influence, or numerical simulations. There is a lack of experimental investigation, particularly full-scale field investigations. Even, the numerical solutions have been based on simple soil profiles without significant velocity contrasts between soil layers and/or varying thicknesses of soil layers which can significantly influence near-field effects. Data from full-scale field test using the Spectral-Analysis-of-Surface-Waves (SASW) method was used in this thesis research. SASW tests performed at two stages in the construction of a deep, 90-ft thick backfill were studied. The V[subscript s] profiles were normally dispersive, with a substantial increase in the velocity of the layer beneath the backfill. The study shows the adverse distortions that can occur in the field dispersion curve from near-field effects when the spacing of the receiver pair is: (1) above the zone of rapidly increasing V[subscript s] near the surface and (2) less than the depth to the stiffer layer in deeper measurements. Other factors that affect the results are discussed and recommendations are presented to minimize the introduction of near-field effects, at least in these relatively simple V[subscript s] profiles. / text

With the escalating demands for optical communication network system, the need for broadband gain medium in optical communication has increased. Among them, Cr4+:YAG crystal has shown an exceptionally successful broadband amplified spontaneous emission (ASE) light source that fully cover 1.2-1.6 £gm range (3-dB bandwidth up to 265 nm). More recently, we demonstrated the realization of a waveguiding, low-loss, and ultralow threshold Cr4+:YAG double-clad crystal fiber (DCF) based ultrabroadband ASE light source, optical amplifier, and laser grown by the codrawing laser-heated pedestal growth (LHPG) technique. These results demonstrate the potential of the Cr4+:YAG DCF for the replacement of the erbium doped fiber in future optical communications. In this thesis, we focus on the correlation between the nanospectroscopy and nanostructure of the Cr:YAG DCF in order to further improve its device performance. For nanospectroscopic and nanostructural characterizations, near-field scanning optical microscopy (NSOM) and high-resolution transmission electron microscopy (HRTEM) techniques have played key roles. In this thesis, we successfully prepared the HRTEM specimen of Cr:YAG DCF, which is heterostructure, ultrahard, but fragile. Here we show the first study on the nanospectroscopy and nanostructure of the nanocrystals in the inner cladding of Cr:YAG DCF by highly spatial resolved NSOM. The NSOM results were compared with those obtained by HRTEM. In addition, the difference in thermal expansion coefficients between a YAG core and an inner cladding creates a significant localized strain field beneath the core, which can result in optical confinement and provide the possibility to simultaneously control the Cr3+ and Cr4+ fluorescence with systematically varied growth parameters. This new class of strain-tunable Cr:YAG DCF opens up new opportunity to improve the performance of the Cr:YAG DCF based ultrabroadband light source, optical amplifier, and crystal fiber laser in all-optic fiber communications.

This thesis is in support of the Precision Personnel Locator (PPL) project being conducted by Worcester Polytechnic Institute (WPI). The overall goal of the PPL project is to locate firemen and other emergency personnel in buildings using Radio Frequency (RF) techniques. The aspiration is to prevent a tragedy similar to the Worcester Cold Storage fire of 1999. The Mantenna homing wand is a spinoff of the PPL system which uses the Near Field properties of Very Low Frequency (VLF band) waves. The Mantenna has been used to successfully demonstrate the ability to locate targets inside harsh RF environments and other radio opaque environments where normal radiation field based systems have degraded performance, such as commercial, industrial, and apartment buildings. This thesis builds upon the Mantenna rescue device by construction of a transmitter subsystem which is physically smaller than the previous version by redesign of the compact VLF antenna. Additionally, exploitation of the approach used by the Mantenna for homing purposes is explored for full location estimation. This work provides the theoretical background and proof of concept test of a Near Field based location system. Simulation and test results are compared for a minimal configuration involving a single receiver.

Tese de mestrado integrado. Engenharia Electrotécnica e de Computadores. Universidade do Porto. Faculdade de Engenharia. 2011

We present a novel concept to design apertureless plasmonic probes for near-field scanning optical microscopy (NSOM) with enhanced optical power throughput and near-field confinement. Specifically, we combine unidirectional surface plasmon polariton (SPP) generation along the tip lateral walls with nanofocusing of SPPs through adiabatic propagation towards an apertureless tip. Three probe designs are introduced with different light coupling mechanisms. Optimal design parameters are obtained with 2D analysis and realistic probe geometries with patterned plasmonic surfaces are proposed using the optimized designs. The electromagnetic properties of the designed probes are characterized in the near-field and compared to those of a conventional single-aperture probe with same pyramidal shape. The optimized probes feature enhanced light localization in near-field of tip apex and improved optical throughput. Our ideas effectively combine the resolution of apertureless probes with throughput levels much larger than those available even in aperture-based devices. / text

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Simulation techniques are developed for high NA polarized microscopy with Babinet's principle, partial coherence and vector diffraction for non-periodic geometries. A mathematical model for the Babinet approach is developed and interpreted. Simulation results of the Babinet's principle approach are compared with those of Rigorous Coupled Wave Theory (RCWT) for periodic structures to investigate the accuracy of this approach and its limitations.A microscope system using a special solid immersion lens (SIL) is introduced to image Blu-Ray (BD) optical disc samples without removing the protective cover layer.Aberration caused by the cover layer is minimized with a truncated SIL. Sub-surface imaging simulation is achieved by RCWT, partial coherence, vector diffraction and Babinet's Principle. Simulated results are compared with experimental images and atomic force microscopy (AFM) measurement.A technique for obtaining native and induced using a significant amount of evanescent energy is described for a solid immersion lens (SIL) microscope.Characteristics of native and induced polarization images for different object structures and materials are studied in detail. Experiments are conducted with a NA = 1.48 at wavelength550nm microscope. Near-field images are simulated and analyzed with an RCWT approach. Contrast curve versus object spatial frequency calculations are compared with experimental measurements. Dependencies of contrast versus source polarization angles and air gap for native and induced polarization image profiles are evaluated. By using the relationship between induced polarization and topographical structure, an induced polarization image of an alternating phase shift mask (PSM) is converted into a topographical image, which shows very good agreement with AFM measurement. Images of other material structures include a dielectric grating, chrome-on-glass grating, silicon CPU structure, BD-R and BD-ROM.

Metal nanostructures, with their extraordinary optical properties, have attracted great attention in recent years. Subwavelength-scaled metal elements, without involving array effects, have the unique ability to confine or route light at the nano-scale. In this thesis, we provide three topics relating to the manipulation of light using metal nanostructures. We first present a theory to solve the end-face reflection of a subwavelength metal stripe, which is beneficial to the design of optical resonator antennas. Subsequently, we take the advantage of the destructive interference among triple nano-slits to sharpen the focus beam in the near-field at near-infrared wavelengths, which is of interest to the study of near-field optical phase imaging and lithography. Lastly, we demonstrate a rectangular subwavelength aperture quad to convert linearly polarized radiation to a radially polarized beam, which is useful to create a deep-subwavelength focus and for optical trapping. / Graduate

Thesis (PhD) - Swinburne University of Technology, Faculty of Engineering and Industrial Sciences, Centre for Micro-Photonics, 2005. / A thesis submitted for the degree of Doctor of Philosophy, Centre for Micro-Photonics, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, 2005. Typescript. Bibliography: p. 129-142.