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

Abstract

In this paper, we investigate how the field of application of phase shifting interferometry could be extended to the reconstruction of bidimensional phase maps of vibrating samples or of static samples located in a mechanically unstable environment. The possibility to perform instantaneous recording of the necessary phase shifted interferograms is discussed and a wavelength sampling approach is proposed. In that technique, the phase shift is introduced through a variation of the optical wavelength. The implications of that choice on the range of optical path differences that can be analysed are discussed. Since the necessary wavelengths can illuminate simultaneously the inspected sample, instantaneous acquisition procedures can be considered, providing that we dispose of a multi-spectral band image sensor for the parallel recording of the set of phase shifted interferograms. The choice of the phase computation algorithm is discussed and four of them are compared. An experimental set-up was built for the sequential recording of the necessary set of phase shifted interferograms and the proposed algorithms are evaluated experimentally. Results show that sub-nanometre accuracy can be obtained over a measurement range of a few microns. Therefore, the successful application of phase shifting methods to vibrating samples can be imagined through the development of an adapted image sensor.