Keywords: interferometry, nanometrology, regression, fringe interpolation, linearity, displacement, nanotechnology, interference fringes, quadru-phase detectors, QPD, homodyne counting, laser interferometers
Linearisation of counting interferometers with 0.1 nm precision
The paper describes a simple method for linearising interference fringes interpolation of quadru-phase detectors (QPD) used in homodyne counting laser interferometers. The linearisation of displacement measurement is obtained without any additional equipment by means of fitting ellipse to signals from QPD and removing eccentricity by calculated correction. Residual non-linearity less than 0.1 nm can be achieved by this method. The results from the experimental data obtained in interferometrical comparator IK-1 are presented. However, these preliminary results show that a circle is not always correct as an ideal counting interferometer signal.