Vertical axis non-linearities in wavelength scanning interferometry

The uncertainty of measurements made on an areal surface topography instrument is directly influenced by its metrological characteristics. In this work, the vertical axis deviation from linearity of a wavelength scanning interferometer is evaluated. The vertical axis non-linearities are caused by the spectral leakage resulting from the Fourier transform algorithm for phase slope estimation. These non-linearities are simulated and the results are compared with experimental measurements. In order to reduce the observed non-linearities, a modification of the algorithm is proposed. The application of a Hamming window and the exclusion of edge points in the extracted phase are shown to increase the accuracy over the whole instrument range