The alignment properties and distribution of flow speed during Poiseuille flow through a microchannel of a nematic liquid crystal in a cell with homeotropic surface alignment has been measured using a combination of conoscopy, fluorescence confocal polarizing microscopy, and time-lapse imaging. Two topologically distinct director profiles, with associated fluid velocity fields, are found to exist with the preferred state dictated by the volumetric flow rate of the liquid crystal. The results show excellent agreement with model data produced using the Ericksen-Leslie nematodynamics theory.

In this work the construction of a wavelength-tunable optical sensor with a fixed angle of incidence, incorporating an acousto-optic tunable filter (AOTF) is described. The AOTF is used to control the wavelength of a ppolarized light beam incident on a gold-coated diffraction grating. A surface plasmon resonance (SPR) is observed as a deep minimum in the intensity of the reflected beam as the incident wavelength is incremented. Slight modification of this arrangement allows measurement of the differential reflectivity profile with respect to wavelength. By locking to the zero differential corresponding to the SPR reflectivity minimum and monitoring the AOTF drive frequency (typically about 100 MHz) the SPR minimum position is then measured to within a precision of 0.0005 nm. The sensitivity of this system was found to be equal to a change in the refractive index of a gas of 1 x concentration of 0.01 ppm NO2 in N2 was detected.Furthermore, by adding a chemically active overlayer to the system a

The enhanced light scattering from microscopic latex spheres placed in the optical field associated with a surface-plasmon resonance is explored. Spheres of 200 nm diameter are placed on an optically thin gold film that supports the surface-plasmon and the scattered intensity is then measured as a function of scattering angle. This is compared to the scattering profiles obtained from spheres placed on a bare glass substrate. In both cases, the experimental data are compared to theory. This system is of interest in the field of optical biosensing.

Using a sensitive optical wavelength modulation technique the surface-plasmon excited on a gold grating surface immersed in sulphuric acid is studied at the same time as cyclic voltammetry is undertaken. Because of the optical sensitivity of the modulation technique significant optical effects are observed at potentials well below those at which any gross oxidation effects occur. PACS

In this work sinusoidal diffraction gratings with a range of pitches and amplitudes are used to align nematic liquid-crystal layers in a twisted homogeneous configuration. The grating profiles are accurately characterized using optical surface plasmon polariton spectroscopy, which then allows a calculation of the anchoring energy as predicted by the simple Berreman expression. The experimental Rapini–Papoular anchoring energy is also obtained by a measurement of the director twist away from the alignment direction (easy axis) at room temperature. A linear relationship is found between the two anchoring energies, except when it falls below 4×10−7 J m−2. Noticeably, the correlation between the two theories is not unity, if room-temperature elastic constants are used in the calculation. This apparent inconsistency is explained if the effect of surface memory on the system is considered. Indeed, if elastic constants, corresponding to a higher temperature at which surface memory effects are absent, are used in the Berreman expression, good agreement between the predicted and experimentally measured energies is found.

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In this work surface plasmon resonance studies have been used to characterize the response of a thin film of 18-crown-6 metal-free phthalocyanine upon exposure to NO2. The phthalocyanine was deposited by spin coating onto a gold film which supported the surface plasmon resonance. By fitting angle dependent reflectivity data to the Fresnel theory for a range of wavelengths it has been possible to obtain the real and imaginary parts of the optical permittivity of the material over the visible part of the spectrum. This procedure has been conducted both before and after exposure to the gas giving an accurate characterization of the changes brought about by the NO2. Thereby the wavelength at which the system's sensitivity to NO2 is an optimum has been calculated. As a secondary measure, the optical parameters derived from the surface plasmon resonance experiments have been compared to data obtained by ultraviolet-visible spectroscopy.

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