A wavelength meter based on a rotating parallelepiped interferometer

Describes a compact wavelength meter for CW laser radiation, which uses a rotating parallelepiped interferometer (RPI). Interference fringes for both the reference laser and the unknown laser beams are produced by the rotation of a parallelepiped in the interferometer, and counted by suitable electronic circuitry. A fraction-of-fringe counter is used to increase the sensitivity of the instrument. The system is connected to a desk-top computer that controls the acquisition both in single shot and repeated measurements. After the acquisition, the wavelength is calculated by means of a successive approximation routine. Calibration with a set of lines of a CW argon ion laser gives an overall accuracy, on single-shot measurements, of one part in 10⁶, and a precision of a few parts in 10⁷.