Applications of optical coherence in interferometric metrology

Limited light source coherence can be both a complication and a benefit to interferometric optical metrology. Although high-coherence lasers are great for displacement measuring interferometry, holography and Fizeau interferometry, many instruments rely on low coherence as part of the measurement principle. Examples include systems that separate parallel surfaces of transparent parts, coherence scanning interferometers for surface topography, and coupled-cavity fiber position sensors. In cases where high coherence is essential, there can nonetheless be a benefit to synthesizing reduced coherence to suppressing spurious fringes, coherent noise, and unwanted speckle.