2Coherent Optical Imaging
This chapter provides a basic understanding of the scientific principles associated with optical image formation based on Fourier optics [1–3] for numerous biomedical applications. Digital holographic microscopy (DHM) is a powerful method for three‐dimensional (3D) and quantitative sensing, imaging, and measuring of biological and microscopic samples. Methods explored in this chapter form the basis of DHM systems used in biomedical imaging.
2.1 Monochromatic Fields and Irradiance
A monochromatic scalar field with a single‐frequency propagating in free space can be described by (2.1):
where A is the amplitude, φ is the phase at a position (x, y, z), and f is the temporal frequency. A highly monochromatic light source, like lasers, can provide a specific form of Eq. (2.1), which is a plane wave that propagates in the z direction:
The wavenumber k is defined as 
where λ is the light wavelength. This plane wave can be interpreted as extending infinitely in x and y directions. If the monochromatic light is propagating in a linear medium such as air, the temporal frequency of the resulting light field will be unchanged. Therefore, the temporal term ...
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