Bridges, AngusYacoot, AndrewKissinger, ThomasHumphreys, David A.Tatam, Ralph P.2021-09-222021-09-222021-08-31Bridges A, Yacoot A, Kissinger T, et al., (2021) Correction of periodic displacement non-linearities by two-wavelength interferometry. Measurement Science and Technology, Volume 32, Issue 12, December 2021, Article number 1252020957-0233https://doi.org/10.1088/1361-6501/ac1dfahttps://dspace.lib.cranfield.ac.uk/handle/1826/17093Non-linearities in interferometric displacement measurements commonly affect both homodyne and heterodyne optical interferometers. Unwanted back reflections (ghost reflections) or polarisation leakage introduce non-linearity terms at harmonics of the illuminating wavelength that cannot be fully corrected for with standard non-linearity correction techniques. A two-wavelength interferometric approach, operating at 632.8 and 785 nm, is presented here that is capable of correcting such non-linearities. Non-linearities are separated from the difference between two displacement measurements made at differing wavelengths with a Fourier approach. Compared to a standard Heydemann ellipse fitting correction, the proposed approach reduces estimated residual non-linearities from 84 to 11 pm in the case of a linear displacement profile. In particular this approach is applicable to the correction of higher order non-linearities that are caused by multiple reflections, and that are therefore very sensitive to alignment conditions.enAttribution 4.0 Internationalhttp://creativecommons.org/licenses/by/4.0/dimensional metrologynon-linearityinterferometryArticle