Off‐axis Digital Holographic Microscopy

This chapter explains an off-axis configuration of digital holographic microscopy (DHM) for transmission imaging with transparent samples. The basic architecture of DHM is based on the Mach–Zehnder interferometer: a beam expander produces a plane wave in which the coherent beam comes from a coherent laser source. Object and reference wavefronts are then combined by a beam collector at the exit of the interferometer to create a hologram. A digital hologram is recorded by either a charge-coupled device (CCD) camera or a complementary metal oxide semiconductor camera and transferred to a personal computer for numerical reconstruction. In off-axis DHM, image focusing happens when the reconstruction distance is equal to the distance between the CCD plane and the image plane during the hologram recording. In classical off-axis holography, hologram reconstruction occurs by illuminating the hologram intensity with the reference beam.