Potential of a wavelength sampling approach for profilometry by phase shifting interferometry

In this paper, we investigate how the field of application of phase shiftin g interferometry could be extended to the reconstruction of bidimensional p hase maps of vibrating samples or of static samples located in a mechanical ly unstable environment. The possibility to perform instantaneous recording of the necessary phase shifted interferograms is discussed and a wavelengt h sampling approach is proposed. In that technique, the phase shift is intr oduced through a variation of the optical wavelength. The implications of t hat choice on the range of optical path differences that can be analysed ar e discussed. Since the necessary wavelengths can illuminate simultaneously the inspected sample, instantaneous acquisition procedures can be considere d, providing that we dispose of a multi-spectral band image sensor for the parallel recording of the set of phase shifted interferograms. The choice o f the phase computation algorithm is discussed and four of them are compare d. An experimental set-up was built for the sequential recording of the nec essary set of phase shifted interferograms and the proposed algorithms are evaluated experimentally. Results show that sub-nanometre accuracy can be o btained over a measurement range of a few microns. Therefore, the successfu l application of phase shifting methods to vibrating samples can be imagine d through the development of an adapted image sensor.