[Show abstract][Hide abstract] ABSTRACT: Using a sensitive optical wavelength modulation technique the surface-plasmon excited on a gold grating surface immersed in sulfuric 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.
Journal of Physics D Applied Physics 09/2010; 43(38):385301. · 2.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The emission of light from whispering-gallery modes excited in microscopic spheres is examined. An evanescent wave is produced by total internal reflection of an optical beam at a planar glass-air interface. This evanescent wave is used to excite whispering-gallery modes in single microscopic spheres placed behind the glass-air interface. The intensity of light emitted into the air half-space from such spheres is measured as a function of scattering angle for both p- and s-polarized input beams. These data are compared with a simple theory for the emission from a point source above a planar glass substrate.
Journal of the Optical Society of America A 10/2003; 20(9):1785-91. · 1.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of the Optical Society of America A 09/2003; 20(8):1589-94. · 1.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report measurements of photoluminescence from corrugated thin films of a light-emitting polymer. We find that emission into guided modes that would otherwise be trapped in the polymer may Bragg scatter off the corrugation to produce useful, far-field radiation. Analysis of the angle dependence of this far-field emission together with theoretical modeling enables us to establish the nature of the optical modes guided by the structure. We show that the dispersion of the modes supported by corrugated polymer films depends on the depth of modulation of the corrugation and find that if the periodic corrugation is strong enough photonic band gap effects may be induced. We also address the question of whether Bragg-scattering of the guided modes, including surface plasmon polariton modes, may increase the efficiency of the emission. We measure and compare the efficiency with which radiation is produced by planar and corrugated
structures, finding the corrugated structures to be up to a factor of 2.6 more efficient. We
indicate how our results may be used in the search for ways to improve the efficiency of devices
based on light emitting thin films.
The European Physical Journal Applied Physics 04/2002; 18(02):89 - 97. · 0.71 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present an experimental study of the emission properties and photonic band structure of a surface-emitting distributed feedback laser based on the conjugated polymer poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene). Measurements of the photonic band dispersion are compared with the spatial and spectral properties of the laser emission to understand how the substrate microstructure controls stimulated emission. The laser structure exhibits a 1D photonic bandgap around 610nm, with lasing occurring at one of the two associated band edges. The band edge selection mechanism is found to be different in the level of output coupling of the modes associated with the two band edges. The divergence of the laser beam is shown to be related to the dispersion of the photonic modes near to the band edges.
[Show abstract][Hide abstract] ABSTRACT: We report the use of wavelength-scale microstructure to control the intensity, spectrum and polarisation of light-emission from thin polymer films. It is shown that periodic corrugation of the emissive layer can substantially increase the efficiency of light-emission. Detailed photoluminescence (PL) studies of the angle dependence of the emission together with theoretical modelling show that the observed emission enhancement is associated with Bragg-scattering of waveguided light out of the polymer layer. The application of this approach to increase the efficiency of a light-emitting diode (LED) is demonstrated.
[Show abstract][Hide abstract] ABSTRACT: Experimental and theoretical light scattering data, for a microscopic sphere placed behind a glass/air interface and illuminated with p-polarized radiation, are compared. The intensity of light scattered from the sphere is measured as a function of scattering angle and these results are compared with established theory. This system is of interest in the field of optical biosensing.
Journal of Modern Optics 01/2001; 48(4):565-572. · 1.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
[Show abstract][Hide abstract] ABSTRACT: The optical dielectric function of indium is measured by optical excitation of surface plasmon polaritons on an indium-coated silica grating for a range of wavelengths in the visible region of the spectrum. By exciting the surface plasmon polariton at the buried indium-grating interface, the indium surface that supports the surface plasmon polariton is kept free from oxidation. Comparison of angle-dependent reflectivities with a grating modelling theory gives both the real and imaginary parts of the dielectric function of indium. These results are compared with free-electron models to obtain an estimate of the plasma frequency and relaxation time.
Journal of Modern Optics 06/2000; 47(7):1227-1235. · 1.16 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Summary form only given. The control of waveguided modes in light-emitting materials is an important goal in quantum optics. It is of particular practical interest in planar optical devices such as light emitting diodes (LED's), in which most of the generated light is confined in waveguided modes, leading to a loss of usefully extractable radiation. In this paper we report the use of wavelength-scale microstructure to control light emission from thin films. In particular we show that lateral microstructure can be incorporated into an LED structure giving a doubling of the efficiency of the device.
[Show abstract][Hide abstract] ABSTRACT: 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 p-polarized 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*10-6. Furthermore, by adding a chemically active overlayer to the system a concentration of 0.01 ppm NO2 in N2 was detected.
Measurement Science and Technology 12/1998; 6(8):1193. · 1.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Journal of Physics D Applied Physics 12/1998; 27(1):169. · 2.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this work we present a new, highly sensitive optical technique for studying electrochemistry. Optical excitation of a surface-plasmon resonance (SPR) is used to probe the working electrode/electrolyte interface in an electrochemical cell. The use of acousto-optics then provides a differential technique for monitoring the SPR position. This allows optical changes at the electrode/electrolyte interface to be very sensitively measured as cyclic voltammetry is performed.
Sensors and Actuators B Chemical 01/1996; 35(1):197-201. · 3.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A good basis has been established for the development of a prototype gas sensor using the phenomenon of surface plasmon resonance. By exciting a surface plasmon on a metallic diffraction grating that is twisted azimuthally so its grooves are not perpendicular to the plane of incidence, and with suitable choice of input and output polarization, a resonance maximum is detected (as opposed to the usual resonance minimum). the operation of the sensor is based on the measurement of this resonance maximum on a background of weak signal and incorporates a sensing head made remote from both the source and detector by means of fibre optics. Its use is demonstrated by sensing remotely the condensation of ≈0.9 nm of isopropyl alcohol onto a silver-coated grating surface.
Sensors and Actuators B-chemical - SENSOR ACTUATOR B-CHEM. 01/1994; 17(3):203-209.
[Show abstract][Hide abstract] ABSTRACT: The phenomenon of surface plasmon resonance is commonly observed by recording variations in the reflectivity of radiation incident upon a metallic film whilst scanning the angle of incidence. A new experimental configuration has been devised in which light passes through such a system twice. Normally, for a resonance minimum, as recorded in conventional arrangements, a double-passage experiment would result in a broadening of the resonance. In the present situation by suitable choice of input and output polarizations a resonance maximum is recorded. Then a double-pass experiment has the effect of sharpening the resonance maximum which may thereby provide increased sensitivity in the field of the optical sensing.
Journal of Modern Optics 01/1993; 40:1657-1662. · 1.16 Impact Factor