Moncy Sajeev Idicula
supervisor: Tomasz Kozacki
Digital holographic microscopy (DHM) is a profilometric tool used to reconstruct the object's topography under observation. Here topography is reconstructed by obtaining the complex field from the captured phase map. However, this method's main limitation is that when the object under the observation has a high gradient or higher surface discontinuities than λ/4 (reflective), there will be an error in the retrieved phase map recorded equal to multiple of 2π.
Multi-angle digital holographic profilometry (MIDHP) is a combination of coherence holography and multi-angle profilometry. This method enables to enlarge the measurement range and high axial resolution. it requires a certain number of holograms needed that are processed using longitudinal scanning function (LSF). The topography of the object is recovered by finding the maxima of the LSF.
Firstly, to reduce the time for capturing the hologram, we introduce a single-shot capture strategy. Based on MIDHP, using an appropriate illumination strategy, the object was reconstructed using a single hologram. Secondly, for an object with low or high surface gradient problems faced are 1.) finding accurate focus position for getting good reconstruction of topography and 2.) calculation of LSF is very time-consuming. In this work, we worked on an autofocusing method and a new strategy for quicker calculation of LSF without compromising accuracy. These proposed methods were verified numerically and experimentally.