Interferometers are essential measurement tools for the production and quality control of optical components and systems. Their applications range from testing the flatness and sphericity of surfaces to measuring radii and testing the performance of optical systems.

Technical mass products with flat surfaces specified to better than 0.1 µm over a few cm are produced by the millions per month. The production processes are lapping and polishing — and, increasingly, micro-machining; 90% have diameters under 50 mm. ISO 9000 requires tight inspection, often 100%. The most common tool for this is the interferometer, as valuable to engineers as the stethoscope is to the medical practitioner.