The IMGC calibration setup for microdisplacement actuators

For the calibration of piezo-capacitive displacement actuators, we use an interferometric setup with subnanometric resolution. In order to minimize the periodic nonlinearity effect of the laser interferometer, the optical path difference is changed in steps of /spl lambda/, obtained from a computer-based loop control of the out-of-phase difference between the reference and the measuring signal of the interferometer. Experimental results show an expanded uncertainty of about 0.7 nm +0.1/spl times/10/sup -3/ L. The calibrated actuator is then used as a transfer standard at the nanometer level, both for testing the nonlinearity of the laser interferometer and for calibrating the linear variable differential transformer (LVDT) probe of the Istituto di Metrologia "G. Colonnetti" (IMGC), Torino, Italy, roundness instrument (used for measuring silicon spheres for the Avogadro constant).