In order to achieve reproducible layer thicknesses and compositions in samples which may be grown several weeks apart it is critical that the growth conditions are kept constant throughout this time. With this in mind the more in situ tools which are available to the grower, the better the control over critical parameters will be. In this paper we show that the interference effect which is seen when growing layers of differing refractive index on top of one another can be extended from the GaAs/AlAs materials system to include compounds containing Indium up to compositions near 55%. © 2005 Elsevier B.V. All rights reserved.