Complete fringe order determination in scanning white-light interferometry using a Fourier-based technique

Abstract

White-light interferometry uses a white-light source with a short coherent length that provides a narrowly localized interferogram that is used to measure three-dimensional surface profiles with possible large step heights without 2π-ambiguity. Combining coherence and phase information improves the vertical resolution. But, inconsistencies between phase and coherence occur at highly curved surfaces such as spherical and tilted surfaces, and these inconsistencies often cause what are termed ghost steps in the measurement result. In this paper, we describe a modified version of white-light interferometry for eliminating these ghost steps and improving the accuracy of white-light interferometry. Our proposed technique is verified by measuring several test samples.

A Novel Surface Recovery Algorithm for Dual Wavelength White LED in Vertical Scanning Interferometry (VSI)

“…Based on the interference signal simulation method introduced in Section 2.1 , the simulated experiment is to measure an inclined plane. In the experiment, three different measurement heights (P 1 , P 2 and P 3 ) are randomly selected at equal intervals, and the interference signal envelope peak positions of white LED and halogen light source are calculated, respectively, based on the traditional fast Fourier transform (FFT) envelope algorithm [ 19 ]. The simulation results are shown in Figure 5 .…”

“…Therefore, a variety of traditional reconstruction algorithms are used to solve the interference signals of two kinds of light sources at different heights on an inclined plane for further verification. In this paper, Centroid [ 20 ], FFT [ 19 ], and Stoilov white light phase shifting interferometry (WLPSI) [ 21 ] are used to calculate 40 groups of simulated white LED and halogen light source interference signals by measuring the same inclined plane at different heights with equal intervals based on simulation. The deviation between the calculation result of the center position of the zero-order fringe of the interference signal and the actual center position of the zero-order fringe at each height is obtained.…”

Quadrature wavelength scanning interferometry

“…The surface height can be estimated from the fringe data as the location at which the envelope of the interference signal reaches the maximum intensity value. Further resolution improvement is possible by estimating the surface height from the phase of the interference signal and solving for the fringe order through the envelope peak [11][12][13]. The advantage of CSI technique over PSI is removal of 2π phase ambiguity.…”

Improving demodulation accuracy of low-coherence interferometer against spatial-frequency nonlinearity

“…Many efforts and attempts have been devoted to correctly identify fringe-order and retrieve the absolute phase. Combining envelope information with the corresponding phase information is an effective way [8,9]. In 2002, de Groot et al proposed an improved SFDA algorithm which utilized the phase gap to obtain fringe-order [10].…”