Absolute Length (thickness) Measurements Using Wavelength Scanning Interferometry

Wavelength scanning interferometry offers a new dimension in precision metrology by measuring the cavity length (thickness), the cavity length variation over the cavity area (flatness), and the optical homogeneity within a transparent cavity; without any mechanical movement by implementing a tunable laser. This property is useful when the physical movement of a large optic is not feasible using traditional phase shifting methods and for characterizing solid optical cavities. The use of Fourier analysis on the intensity (interference) time history as a post processing step enables the measurement of cavity lengths without any 2π phase ambiguity [1,2].