Over the past few years interest has increased in optical communications systems. These require new materials - in particular ternary and quaternary III-V alloys - to produce the necessary devices. Pulsed laser atom probe (PLAP) has been shown to be capable of providing accurate analyses of bulk III-V alloys and, with its extremely high resolution, is ideal for studying the microchemistry of interfaces in quantum wells and the fine scale decomposition processes that occur in III-V alloys. The key to successful analysis of epitaxial layers lies in specimen preparation. Methods for preparing samples lying in the plane of the layer and perpendicular to it are discussed. Some of the first results of these analyses are also presented