The Fizeau Interferometer is an optical device used to measure the interference of light waves. It consists of a beam splitter that divides a single light beam into two paths, which are then reflected back to create an interference pattern. This pattern can reveal information about the optical properties of materials or the precision of surfaces. Developed by Hippolyte Fizeau in the 19th century, the interferometer is essential in various scientific fields, including metrology and optics. It helps in assessing the quality of lenses and mirrors, as well as in experiments that test the fundamental principles of light and wave behavior.