Measurement of polarisation dependent all-optical nonlinearity in GaAs/AlGaAs quantum well waveguides far from the bandedge

The all-optical nonlinearity of a quantum well waveguide is studied by measuring the intensity dependent transmission through a Fabry-Perot cavity formed around the guide. Values for the nonlinear refractive index coefficient, η 2, at a wavelength of 1.06μm are obtained for light whose polarisation is either parallel or perpendicular to the quantum well layers. A simple measurement to estimate the two photon absorption coefficient, B2, using relatively low optical power levels is also described.

Polarisation dependent all-optical nonlinearity far from the bandedge in active GaAs/AlGaAs quantum well waveguides

This paper describes a measurement on a GaAs quantum well waveguide with a high built in field across the quantum wells at a wavelength far from the bandedge. The device structure used for the measurement has been fabricated at STC Technology Ltd and is that of a standard laser ridge structure. In fabrication double heterostructure layers are grown on a [001] n + GaAs substrate, with the active region containing two intrinsic GaAs quantum wells of 10nm thickness separated by 10nm. A 4μm wide ridge is etched to provide transverse optical guiding. The experimental work has involved the use of 1.06μm wavelength light from a Q-switched Nd:YAG laser. Any induced change in refractive index is determined by measuring the change in transmission of the quantum well waveguide Fabry-Perot cavity. The waveguide is placed on a Peltier temperature controller to allow thermal tuning.

The long road to freedom: the end of apartheid has signalled a new beginning for women in South Africa’s fisheries but real equality is still a far-off dream

Women in fishing communities are increasingly moving from traditional, community based occupations to seeking employment in the labour market. While this is an opportunity for women, their employment is also largely in the male dominated fishing industry, where job segregation into ‘less skilled and low paid’ jobs for women define employment opportunities. However, engagement as members in local non-government networks help women to challenge these stereotypes. In South Africa, for instance, the recent legislation promoting opportunity for women in male dominated sectors of employment is an opportunity for women to earn wages equal to those of men.

Far-infrared emission and absorption by hot carriers in superlattices

Some of the earliest theoretical speculation, stimulated by the growth of semiconductor superlattices, focused on novel devices based on vertical transport through engineered band structures; Esaki and Tsu promised Bloch oscillators in narrow mini-band systems and Kazarinov and Suris contemplated electrically stimulated intersubband transitions as sources of infrared radiation. Nearly twenty years later these material systems have been perfected, characterized and understood and experiments are emerging that test some of these original concepts for novel submillimetre wave electronics. Here we describe recent experiments on intersubband emission in quantum wells stimulated by resonant tunnelling currents. A critical issue at this time is devising a way to achieve population inversion. Other experiments explore 'saturation' effects in narrow miniband transport. Thermal saturation may be viewed as a precursor to Bloch oscillation if the same effects can be induced with an applied electric field.

Precise description of the different far fields encountered in the problem of diffraction of acoustic waves by a quarter-plane

This paper provides a review of important results concerning the Geometrical Theory of Diffraction and Geometrical Optics. It also reviews the properties of the existing solution for the problem of diffraction of a time harmonic plane wave by a half-plane. New mathematical expressions are derived for the wave fields involved in the problem of diffraction of a time harmonic plane wave by a quarter-plane, including the secondary radiated waves. This leads to a precise representation of the diffraction coefficient describing the diffraction occurring at the corner of the quarter-plane. Our results for the secondary radiated waves are an important step towards finding a formula giving the corner diffraction coefficient everywhere. © 2012 The authors.