US Patent 11156448 Interference observation device and interference observation method

An interference observation apparatus includes a light source, a splitting beam splitter, a combining beam splitter, a mirror, a beam splitter, a mirror, a piezo element, a stage, a photodetector, an image acquisition unit, and a current control unit. An interference optical system from the splitting beam splitter to the combining beam splitter forms a Mach-Zehnder interferometer. The current control unit controls a wavelength of laser light output from the light source to adjust a phase difference between two split light components at the combining by the combining beam splitter.