Optical polarization

About: Optical polarization is a research topic. Over the lifetime, 13992 publications have been published within this topic receiving 244284 citations.

AlGaN-GaN double-channel HEMTs

Abstract: We present the design, fabrication, and characterization of AlGaN-GaN double-channel HEMTs. Two carrier channels are formed in an AlGaN-GaN-AlGaN-GaN multilayer structure grown on a sapphire substrate. Polarization field in the lower AlGaN layer fosters formation of a second carrier channel at the lower AlGaN-GaN interface, without creating any parasitic conduction path in the AlGaN barrier layer. Unambiguous double-channel behaviors are observed at both dc and RF. Bias dependent RF small-signal characterization and parameter extraction were performed. Gain compression at a high current level was attributed to electron velocity degradation induced by interface scattering. Dynamic IV measurement was carried out to analyze large-signal behaviors of the double-channel high-electron mobility transistors. It was found that current collapse mainly occurs in the channel closer to device surface, while the lower channel suffers minimal current collapse, suggesting that trapping/detrapping of surface states is mainly responsible for current collapse. This argument is supported by RF large-signal measurement results.

Polarization properties of extragalactic radio sources

Abstract: Differentes techniques permettant la mesure de la polarisation des rayonnements emis par les radiosources extragalactiques sont exposees. L'etude de la polarisation observee est un moyen d'investigation des structures du champ magnetique et de l'environnement physique des sources considerees

Forward and reverse product decompositions of depolarizing Mueller matrices.

Abstract: Because of the noncommutativity of the matrix product, the three factors into which a depolarizing Mueller matrix is decomposed, i.e., the diattenuator, the retarder, and the depolarizer, form six possible products grouped into two families, as already pointed out [J. Opt. Soc. Am. A13, 1106 (1996); Opt. Lett.29, 2234 (2004)]. We show that, apart from the generalized polar decomposition generating the first family of products, there exists a dual decomposition belonging to the second family. The mathematical procedure for this dual decomposition is given, and the symmetry existing between the two decompositions is pointed out. The choice of the most appropriate decomposition for a given practical optical arrangement is likewise discussed and illustrated by simple examples.

Surface plasmon resonance biosensing

Abstract: Optical affinity biosensors are devices that incorporate a biomolecular recognition element (e.g. antibody) which specifically recognizes a particular analyte and an optical transduction system which allows quantification of the interaction between the analyte and the biomolecular recognition element. In the last decade we have witnessed development of numerous optical transduction methods, including both label-based methods such as fluorescence spectroscopy and label-free methods such as optical interferometry, spectroscopy of guided modes of optical waveguides, and surface plasmon resonance. Label-free optical biosensors present unique technology that enables direct observation of molecular interaction in real-time and offer benefits of rapid, sensitive and label-free detection of chemical and biological species with potential applications in numerous important areas including proteomics, medical diagnostics, environmental monitoring, food analysis, agriculture, and security.

Physical Properties of Cometary Dust

Abstract: Prior to the 1986 apparition of comet Halley, all attempts to determine the physical properties of cometary dust were limited to remote observations and the analysis of various particles captured by the Earth’s atmosphere. The in situ measurements made by the three spacecraft that passed within 10,000 km of the nucleus provided the first opportunity to investigate both the full size-range of particles and the complete process of dust production. Information on composition is derived through mass spectra and the scattering and emission of light from the grains, whilst the dynamics of the dust coma can be modeled from the three separate sets of measurements made over a period of eight days.