Hyperspectral interferometry for single-shot absolute measurement of two-dimensional optical path distributions

We propose a method that we call hyperspectral interferometry (HSI) to resolve the 2π phase unwrapping problem in the analysis of interferograms recorded with a narrow-band light source. By using a broadband light source and a hyperspectral imaging system, a set of interferograms at different wave numbers are recorded simultaneously on a high resolution image sensor. These are then assembled to form a three-dimensional intensity distribution. By Fourier transformation along the wave number axis, an absolute optical path difference is obtained for each pixel independently of the other pixels in the field of view. As a result, interferograms with spatially distinct regions are analysed as easily as continuous ones. The approach is illustrated with a HSI system to measure 3D profiles of optically smooth or rough surfaces. Compared to existing profilometers able to measure absolute path differences, the single-shot nature of the approach provides greater immunity from environmental disturbance