Multiplexed holography for single-shot three-dimensional shape and displacement measurements

Abstract

Holographic interferometric methods for measuring 3D displacement fields require at least three individual sensitivity vectors. Methods based on multiple directions of illumination have limited application when studying transient phenomena, including, but not limited to, measurements of biological tissues that have temporally-varying responses, such as the eardrum or Tympanic Membrane (TM). Therefore, to measure 3D displacements in such applications, all the measurements have to be done concomitantly. In this paper, we propose a new multiple illumination direction approach to measure 3D displacements from a single-shot hologram that contains displacement information from three sensitivity vectors. In our approach, the hologram of an object of interest is recorded with three simultaneous incoherently-superimposed pairs of reference and object beams, such that the modulation image corresponding to each illumination direction is reconstructed at a particular position on the image. Incoherent superposition of the beams is implemented by using three different laser diodes. Because of the differences in the position of each reference beam and wavelength of each pair of beams, the reconstruction distance and magnification of each sensitivity vector are different. We, therefore, developed and implemented a registration algorithm to accurately translate individual views into a single global coordinate system. Representative results will include measurements of shape and sound-induced 3D displacements of the TM.