A non-destructive optical characterisation technique is used for the investigation of Mercury Cadmium Telluride (HgCdTe) photovoltaic devices. The technique uses a scanning laser microscope to obtain Laser Beam Induced Current (LBIC) data from which it may be possible to extract information such as junction depth, array uniformity, and other material and device parameters. LBIC has been previously used only as a qualitative technique, but in this work the procedure is being developed into a quantitative tool. At present the only junction depth profiling techniques are destructive, while array uniformity can only be examined after bonding to readout circuits. In this paper we present both theoretical and experimental results which show that LBIC can be employed as a quantitative tool for device characterisation. The primary measure of performance of IR detectors is the zero bias dynamic resistance junction area product, R(0)A. LBIC measurements indicate that the peak LBIC signal varies by a factor of similar or equal to 2 for long wavelength infrared photodiodes for which the R(0)A varies between 70 Ohm cm(2) (acceptable for operation and the lower bound of typical values) and 8 Ohm cm(2) (unacceptable and typical for poor quality diodes). (C) 2000 Elsevier Science Ltd. All rights reserved.