Michael J. Jory

Bragg scattering from periodically microstructured light emitting diodes

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.

A surface-plasmon-based optical sensor using acousto-optics

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.

Modification of polymer light emission by lateral microstructure

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.

Surface-plasmon-enhanced light scattering from microscopic spheres

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.

Acousto-optic surface-plasmon resonance measurements of thin films on gold

In this work a highly sensitive optical technique was used to study the adsorption of thin organic layers onto a gold film from water, in situ and in real-time. Optical excitation of a surface-plasmon resonance (SPR) was used to probe the gold/water interface. The use of an acousto-optic tunable filter then provides a differential technique for monitoring the SPR position in optical wavelength. This allows optical changes at the metal/liquid interface to be measured as the adsorption of thin organic layers occurs. Adsorption of a poly(ethylene glycol) monododecyl ether surfactant (C12E8) and a 30-mer DNA oligonucleotide with a mercaptohexyl group at the 5′-phosphate end (DNA-SH) onto gold from water were examined. Conventional, angle-dependent reflectivity measurements taken on the same system provided complementary SPR data, allowing the sensitivity of the two techniques to be compared.

Surface-plasmon opto-electrochemistry

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.

Light scattering by microscopic spheres behind a glass–air interface

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.

Measurement of light scattering from a dielectric sphere behind a glass/air interface

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.

Light emission from whispering-gallery modes in microscopic spheres

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.

Control of light output from planar optical devices using wavelength-scale microstructure

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 (LEDs), 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.