Design of Mirau white light phase-shifting interferometry

In order to inspect microsurface three-dimensional topography, Mirau white light phase-shifting interferometry is developed. The interferometry is composed of Mirau imaging part and illumination part. Kohler illumination is adopted to illuminate the sample uniformly. The phase shifter is the piezoelectric transducer (PZT). Mirau imaging part consists of Mirau interference objective and tube lens, and the collimated light is between them. Practical Mirau interference head structure is developed to reduce fabrication requirements. A long working-distance infinity tube-length microscope objective is designed which consists of a larger positive power lens and a smaller negative power lens. The intensity of the interference pattern is balanced using beam splitters with different transmission/reflection ratio. The central obscuration of reference plate is considered and the diameter of reference plate is 1mm. The parameters of Mirau interferometry are as follows: numerical aperture NA=0.3, the magnification beta =-10, working distance 5mm, field-of-view 0.64x0.48 mm, optical resolution 0.875mum, depth of field +/-2.96mum and central obscuration 0.129.