Optical coherence tomography has also been applied to several non-medical applications where accurate surface or thickness measurements are required in a non-invasive non-contact manner. For example, OCT allows performing non-contact thickness measurements of multilayer coating stacks with a clear differentiation of all layers and their thicknesses. This is especially critical when real-time monitoring is required. Also when aligning a system of lenses to a common optical axis. The system includes mainly an interferometer which is operated with SLED light.