Robust unbalanced Gires-Tournois mirror for group delay dispersion measurement evaluation by white light interferometer

•A robust unbalanced Gires-Tournois interferometer mirror for evaluating group delay dispersion measurement by white light interferometer.•A novel processing algorithm, the extrema searching method is proposed that search the positions of multi-order extrema from reconstructed interferogram intensity to exact the group delay dispersion characteristics of the sample.•Our method shows superiority in accuracy compared with windowed Fourier transform, wavelet transform and time-domain scanning method.