Alignment of fluorescent molecules vapour-deposited on to highly oriented PTFE substrates

The alignment of six fluorescent materials (p-terphenyl, p-quaterphenyl, p-quinquephenyl, diphenylstilbene, 1,4-bis(2-methylstyryl)benzene, and 1,4-bis-2-(5-phenyloxazolyl)benzene) grown from the vapour phase on to friction-deposited, highly oriented poly(tetrafluoroethylene) (PTFE) films was studied. The dichroic ratio of the fluorescent films produced was determined by polarized spectroscopic fluorescence measurements, and the crystallographic orientation of these materials was determined by transmission electron microscopy. The measured dichroic ratios ranged from 1.7 for diphenylstilbene to 5.0 for the p-quaterphenyl film. Electron diffraction patterns revealed that five of the fluorescent materials grew epitaxially on the single crystal-like PTFE films, the fluorescent crystals adopting particular orientations with respect to the crystallographic planes of PTFE. On the other hand, crystals of 1,4-bis-2-(5-phenyloxazolyl) benzene aligned in a fibre pattern, apparently by a grapho-epitaxial mechanism.     

Applications of ultrashort pulse propagation in Bragg gratings forwavelength-division multiplexing and code-division multiple access

We discuss theoretical and experimental studies on the propagation of ultrashort pulses through fiber Bragg gratings. We also consider several applications in optical communications to be found by combining ultrashort pulses and fiber Bragg gratings: a multiwavelength source for wavelength-division-multiplexed systems and a means for implementing optical code-division multiple access     

Optical characterization of low-temperature-grown GaAs forultrafast all-optical switching devices

Low-temperature-grown GaAs (LT-GaAs) is a promising material for all-optical switching devices due to its outstanding optical characteristics. In this paper, we outline a simplified model we have developed to describe the dynamics of the carriers in this material. We also report the results of a series of measurements that we have performed to characterize the optical properties of the material. Specifically, we present the first measurements of the two-photon absorption coefficient and the refractive index changes as a function of the growth and annealing temperatures in LT-GaAs. Finally, we show how our model can be used to optimize the material for applications in all-optical switching     

Investigation of solar selective and microstructural properties of molybdenum black immersion coatings on cobalt substrates

Molybdenum black solar selective coatings have been produced on cobalt by immersion in a solution of ammonium paramolybdate and nickel sulphate. The cobalt was electroplated on nickel-plated copper prior to immersion in the paramolybdate solution. The maximum solar absorptance of the resulting molybdenum black coating was about 0.91. The minimum emittance was about 0.1 for coatings on cobalt deposited with an addition agent and about 0.23 for coatings on cobalt deposited without addition agent in the 60 °C plating solution. These differences have been related to the coating morphology determined by scanning electron microscopy. The emittance of coatings on cobalt deposited without addition agent decreases (or remains unchanged) during short-term heat treatment while that of coatings deposited on cobalt plated with addition agent increases somewhat. Reduction of the cobalt plating bath temperature to 45 °C can also lead to good initial coating properties but without the requirement for an addition agent in the cobalt plating bath. XPS studies show that the oxidation state of molybdenum in the coatings is approximately + 5 corresponding to Mo₄O₁₁. This reduces to + 4 after argon ion bombardment. Some cobalt may be present in the coatings in the form of CoO.     

Sky blue,but what blue? A new evaluation of the colors of the sky for artists and designers

This study describes a process of relating the perceptual analysis of the colors of the terrestrial atmosphere to currently available pigments used in artists' painting systems. This process sought to discover how the colors of the sky could be defined and simulated by these pigments. The author also describes how confusion over the bewildering choice of suitable pigments on offer in the market place can be clarified. © 2006 Wiley Periodicals, Inc. Col Res Appl, 32, 249–255, 2007