Artificial Intelligence in Digital Holographic Imaging

5Off‐axis Digital Holographic Microscopy

5.1 Off‐axis Digital Holographic Microscopy Designs

In this chapter, we will study an off‐axis configuration of digital holographic microscopy (DHM) [1–5] for transmission imaging with transparent samples (e.g. biological cells) as shown in Figure 5.1. 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. The beam is then divided into object and reference beams using a beam splitter with a small tilt angle between them (see Figure 5.1). The object beam illuminates the specimen and creates the object wavefront. A microscope objective (MO) magnifies the object wavefront. Object and reference wavefronts are then combined by a beam collector at the exit of the interferometer to create a hologram.

At the exit of the interferometer, interference between the object beam O and the reference beam R creates the hologram intensity

where R* and O* are complex conjugates of the reference beam and the object beam, respectively. A digital hologram is recorded by either a charge‐coupled device (CCD) camera or a complementary metal oxide semiconductor (CMOS) camera and transferred to a personal computer for numerical reconstruction. The digital hologram I_H(k, l) (CCD size: L × L) is an array of N × N that results from a 2D sampling ...