TITLERelationship between photonic band structure and emission characteristics of a polymer distributed feedback laser AUTHORS Turnbull, G. A.; Andrew, P.; Jory, M. J.; et al. JOURNAL Physical Review B DEPOSITED IN ORE September 2008This version available at http://hdl.handle.net/10036/37713 COPYRIGHT AND REUSEOpen Research Exeter makes this work available in accordance with publisher policies. A NOTE ON VERSIONSThe version presented here may differ from the published version. If citing, you are advised to consult the published version for pagination, volume/issue and date of publication Relationship between photonic band structure and emission characteristics of a polymer distributed feedback laser We present an experimental study of the emission characteristics and photonic band structure of a distributed feedback polymer laser, based on the material poly͓2-methoxy-5-͑2Ј-ethylhexyloxy͒-1,4-phenylene vinylene͔. We use measurements of the photonic band dispersion to explain how the substrate microstructure modifies both spontaneous and stimulated emission. The lasing structure exhibits a one-dimensional photonic band gap around 610 nm, with lasing occurring at one of the two associated band edges. The band edge ͑frequency͒ selection mechanism is found to be a difference in the level of output coupling of the modes associated with the two band edges. This is a feature of the second-order distributed feedback mechanism we have employed and is clearly evident in the measured photonic band structure.

We present a simple method of generating a periodic wavelength scale structure in the optically active layer of a light emitting diode. This is achieved by solution deposition of a light emitting polymer on top of a corrugated substrate. The periodic structure allows waveguide modes normally trapped both in the substrate and in the thin polymer film to be Bragg scattered out of the structure, thus leading to a doubling of efficiency. This scattering process gives rise to a polarization of the emission spectrum as well as angular dispersion effects.

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 nonlinear I/V characteristics of a molecular rectifier structure of the form Au/20 layers of C16H33Q-3CNQ/Au have been explored from 8 to 300 K. At 8 K the voltage-controlled nonlinear conduction is explored in the absence of thermal effects. At the highest voltages (±15 V) at 8 K the rectification ratio was about 4 with current densities as high as 1000 A m−2 and log I varying as |V|0.5, indicating voltage-controlled hopping. The likely explanation for the complete I/V characteristics rests with the insulating aliphatic tails, which provide substantial electrical barriers within the structure.

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Scattering of light from single spheres placed behind a glass-air interface with light incident through the glass is examined. This scattering is investigated for both p- and s-polarized light incident at angles below the glass-air critical angle. The intensity of light scattered into the air half-space from each sphere is measured as a function of scattering angle, and this response is compared in situ with the background scatter produced by the planar substrate. A detailed comparison between data and established theory are thereby obtained. This system is of interest in the field of optical biosensing.

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