Optical Low‐Coherence Reflectometry (OLCR) is a white‐light interference technique which can be used as a sensor in a number of processing applications. Research at the Center for Process Analytical Chemistry focuses on analysis of both transparent and highly‐scattering materials. OLCR has been applied to monitor the thickness of polymer films and clear coatings on scattering matrices. Additional process applications include fermentation monitoring and non‐invasive thickness determination of highly scattering coatings on both conducting and non‐conducting substrates. © 2003 American Institute of Physics