White-light fringe restoration and high-precision central fringe tracking using frequency filters and Fourier-transform pair

Images obtained with a white-light interferometer (WLI) using a charge-coupled device (CCD) camera may be degraded for various reasons, greatly affecting the WLI central fringe tracking accuracy. The work reported in this paper uses frequency filters and forward/inverse Fourier transform to investigate the WLI fringe distribution in the frequency domain. Different rectangular filter combinations are studied to remove background noises and, at the same time, enhance the fringe visibility. Detailed experiments confirm the theoretical analysis and show that this technique could extract high-quality WLI fringe patterns from the background even with complex noise distribution. Temperature measurement results demonstrate that this approach could quickly track the central fringe shifts with high-precision.