Form measurement of thin cylinders using three-wavelength interferometry

A new interferometric measurement technique for form measurements of cylindrical objects with diameters up to 2.5 mm is presented. This technique provides a contactless and non-scanning form measurement of reflective cylinders with a resolution in the nanometre range. The specimen is placed in the centre of an inverse conic mirror and is illuminated by a diode laser. The reflected light is superposed under a slight angle with a reference beam and imaged on a CCD camera. From the recorded interferogram the surface topography of the specimen can be derived by a spatial phase shifting algorithm. The measurement range can be varied from the nanometre to the micrometre range by using three lasers with different wavelengths. Results of form measurements of different samples are presented and discussed.