VLT FORS2 optical imaging and spectroscopy of nine luminous type 2 AGN at 0.3 < z < 0.6-I. Ionized gas nebulae

We present optical imaging and long slit spectroscopic observations of nine luminous type 2 active galactic nuclei (AGN) within the redshift range 0.3 <z< 0.6 based on Very Large Telescope Focal Reducer and Low Dispersion Spectrograph (VLT FORS2) data. Most objects (6/9) are high luminosity Seyfert 2, and three are type 2 quasars (QSO2), with our sample extending to lower luminosity than previous works. Seven out of nine objects (78 per cent) show morphological evidence for interactions or mergers in the form of disturbed morphologies and/or peculiar features such as tidal tails, amorphous haloes, or compact emission line knots. The detection rate of morphological evidence for interaction is consistent with those found during previous studies of QSO2 at similar z, suggesting that the merger rate is independent of AGN power at the high end of the AGN luminosity function. We find the emission line flux spatial profiles are often dominated by the often spatially unresolved central source. In addition, all but one of our samples is associated with much fainter, extended line emission. We find these extended emission line structures have a variety of origins and ionization mechanisms: star-forming companions, tidal features, or extended ionized nebulae. AGN related processes dominate the excitation of the nuclear gas. Stellar photoionization sometimes plays a role in extended structures often related to mergers/interactions

Optical probing of thin liquid-crystal layers using the prism-coupling technique

Prism-coupling work in polymer aligned liquid crystal layers is presented with special emphasis being placed on the ferroelectric chiral smectic C phase, of interest to electro-optic device fabrication. Experimental results as a function of temperature, wavelength and DC applied voltage are presented, together with a study of sp mixing which may have potential device applications as well as being an elegant technique with which to establish the optical dielectric tensor configuration in thin, aligned liquid crystal layers

The theoretical design and fabrication of a prism-coupled polarization conversion ferroelectric liquid-crystal light-modulator

It is possible to probe directly the optical dielectric tensor configuration within thin smectic layers (less than 6 µm thick) of ferroelectric liquid crystals (FLCs) by the propagation of optical prism-coupled leaky Fabry-Pérot modes. Incident polarized monochromatic light couples into the resonant modes of the system and may be coupled out of the cell in an orthogonal polarization. The observed reflectivity is a series of sharp peaks on a low background response at certain well-defined incident angles. These sharp resonant features make the prism-coupling technique a possible route for commercial fabrication of voltage-modulated devices. However, previous prism-coupled cells with sharp resonant guided mode features are not practical from a device point of view because they incorporate silver layers not used in conventional cell design. In this paper we demonstrate for the first time operating a leaky guided mode FLC cell with conventional surface layers, in a sp-mixed polarization mode of operation, allows sharp features to be observed which are modulated in intensity by an applied d.c. voltage. The prism-coupled cells used here are designed to be compatible with current FLC device technology

The optical dielectric tensor configuration in aligned ferroelectric liquid crystal cells

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Characterisation of secondary silver ion-exchange into potassium ion-exchanged glass waveguides

Local enhancement of refractive index in potassium-ion-exchanged optical waveguides in glass is of interest for realization of low-loss bends and intersections and more complex structures such as gratings for reflection and phase-matching. Local enhancement may be realized through subsequent ion exchange with an ion having higher polarizability, such as silver. However, in order to design such structures, the diffusion of silver ions into potassium ion-exchanged waveguides must be characterized. In this paper, we present and compare diffusion profiles and coefficients of silver ions in soda-lime glass and in potassium-ion-exchanged waveguides in this glass

A preliminary investigation of the anomalous out-of plane tilt alignment in an orthogonal-twist ferroelectric liquid-crystal cell using the prism-coupling technique

Recent prism-coupling results are presented which clearly demonstrate that in ferroelectric liquid crystal cells, prepared with the alignment directions of the two surfaces orthogonal, with sputtered indium tin oxide conductive layers and spun polyimide alignment layers, there is no out-of-plane tilt of the liquid crystal optic axis. Unlike most techniques which give an integrated optical response throughout a cell, the prism-coupling technique allows a separate analysis of in-plane and out-of-plane tilt. Conventional optical polarized microscopy yields good lateral resolution but poor section resolution. For a uniform sample we can obtain information on the section (across the cell) resolution. We report that an optical dielectric tensor configuration is formed in which the major optic axis lies in the plane of the surface across the cell, but that as expected, in an orthogonal-twist cell, there is no axis of preferred alignment within this surface plane

Electrochemically controlled optical waveguide sensors

Optical techniques are at the forefront of modern analytical methods due to their inherent high specificity. From the point of view of sensor technology, the transfer of chemical information into a measurable signal is of utmost importance. In this respect, planar optical waveguides show great promise for realising novel chemical and biological sensors which use evanescent fields to probe specifically sensitised films on the waveguide surface. Such sensors may detect changes in the refractive index of films using, for example, surface plasmon resonance (SPR) [1], light emission from the binding of proteins labelled with fluorophores [2], or the change in absorption spectrum of a film caused by a chemical reaction [3]. The use of photolithography in integrated optics technology allows mass production of complex multisensors on small and robust substrates. Electrochemical methods allow electrical resetting of reactions, or improved sensitivity through phase-sensitive detection

Electrochemically-controlled waveguide-coupled surface plasmon sensing

A surface plasmon resonance sensing device has been constructed, in which excitation of a surface plasmon on a metal film is achieved by coupling from light propagating in an optical waveguide. The metal film cladding has been used as an electrode surface and it is proposed that these structures may be applied as novel optoelectrochemical sensors. Specific cationic adsorption has been monitored in potential regions where the metal free-electron contribution is small, and the sensitivity of this sensing technique has been deduced by comparison with ellipsometric measurements. The interfacial model used to analyse the ellipsometric results has been tested by calculating coverage by water in the water + ethylene glycol mixture employed in the surface plasmon device. The high sensitivity of this technique to adsorbed films is found to be greater than that predicted by the theoretical model described, and reasons for this discrepancy are discussed