Stylus and constant force transducers form the basis of a broad range of instruments for metrological characterization of fine surface features.~1,2,3 Typically, stylus based instruments consist of a long range traverse mechanism for translation of the specimen relative to the probe, with the probe system mounted with its axis of measurement perpendicular to the traverse direction. In practice, it is the Abbe errors associated with the misalignment between the axis of the probe that interrogates the surface and the measurement axis of the transducer used to sense the displacement of the probe that dominate the achievable precision in profile height measurement. Currently, a force probe system is being developed to measure fine optical surfaces with an accuracy of 1 nm and a resolution of 0.1 nm for vertical surface profile deviations of up to 3 mm. The heart of this profiler consists of a constant force probe similar to that developed by Howard and Smith,~4,5 combined with a laser interferometer. Since the Abbe error is due to both the offset and the angle of tilt, control of either parameter can be used to minimize this error. The precision of alignment between the axis of the laser interferometer and the stylus probe is limited by manufacturing considerations. the strategy used to minimize this error is to ocntorl the angle of tilt. To this end a novel, three-axis flexure arrangement has been devised that allows for active control of two rotations over a range of 30 murad while allowing a displacement of approximately 1.5mum. The tilt control mechanism may also be exploited to obtain an estimate of the Abbe offset by monitoring the displacement as measured by the laser and the probe while rocking the probe head through a known angle.
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