Pixelated Mask Polarization Based Spatial Carrier Interference Microscopy

Abstract

The following dissertation demonstrates the advantages of using a camera with a pixelated polarization mask allowing spatial carrier phase shifting in interference microscopy. An interference microscope in the Michelson and Linnik configurations integrates a camera equipped with a pixelated polarization mask. The camera utilizes polarization to simultaneously capture four phase shifted interferograms. Each set of four phase shifted fringe patterns permits the calculation of fringe contrast and phase at a point in the vertical scan of a test surface. The use of a short coherence source enables construction of a coarse surface profile by estimating the localization of the peak fringe contrast over the vertical scan. The coarse profile allows unwrapping of the less noisy, though circumstantially ambiguous, phase data. Established phase shifting interference microscopy methods utilize temporal phase shifting techniques. Temporal methods contrast spatial methods by acquiring each set of interferograms necessary for calculating fringe contrast and phase by scanning the test object. The scanning changes the optical path difference between the interferometer arms thus inducing the phase shifts. While both methods scan the test surface, spatial methods acquire all of the information needed to calculate fringe contrast and phase simultaneously while the temporal methods require data from multiple points in the scan. Furthermore, the focus and fringe contrast also change between phase shifts and introduce a small error in temporal methods. However, the largest source of error results from the time taken between capturing the phase shifted frames comprising each set where environmental disturbances such as vibration can change the fringe pattern. The subsequent work shows the practicality of performing interference microscopy with a pixelated polarization mask as well as the technique's relative vibration insensitivity.