Two-dimensional surface profile imaging technique based on a double-grating frequency shifter

A two-dimensional surface profile imaging technique that uses a low-coherence heterodyne interferometer is proposed. A double-grating frequency shifter was used in a tandem interferometer to provide the achromatic frequency shift for low-coherence light. A chopper, together with a processing circuit, was implemented to modulate the interference fringes. The surface profile was measured from the interference fringes taken by a CCD camera using a five-step method. The uncertainty in the displacement measurement is 0.34 (mu)m for a displacement range of 43 (mu)m. The surface profile of a glass sample with low effective reflectivity was acquired.