FizeauInterferometer

The FizeauInterferometer, often written as Fizeau interferometer, is an optical metrology instrument used to assess the surface quality and wavefront of optical components by comparing a test surface with a reference wavefront. It relies on interference between light reflected from the surface under test and light reflected from a reference surface, producing a pattern of fringes whose geometry encodes surface deviations.

Principle and configuration: A beam splitter or partially reflective plate divides incident light. One beam reflects from the test surface; the other reflects from a reference surface, typically a plane surface close to the test piece or a dedicated mirror formed within the interferometer. The two reflected beams recombine to form an interference pattern observed in reflection. Straight, circular, or curved fringes indicate different types of distortion; counting fringes provides quantitative height or slope information relative to the reference.

History and use: Named after Hippolyte Fizeau, whose era contributed to the development of interferometric techniques in the 19th century, the Fizeau interferometer became a common tool for testing flats and lenses in optics manufacturing. It is valued for simplicity, robustness, and rapid qualitative and quantitative assessment, though sensitivity to vibration and alignment is a consideration.

Variants and modern practice: There are internal and external arrangements, and modern implementations may use laser sources or broadband illumination with digital fringe analysis to extract surface profiles. The method supports measurement of flatness, radius of curvature, and step heights, and remains a staple in precision optics laboratories and production environments.