Partially Coherent Illumination-Based Digital Holographic Microscopy and Its Applications

The traditional digital holographic microscopy (DHM) usually adopts highly coherent lasers as an illumination source. Although the hologram has high contrast, the coherent noise induced by the coherent lasers reduces the signal-to-noise ratio of the reconstructed image. Partially coherent illumination-based DHM (PCI-DHM) can effectively reduce the coherent noise and maintain high phase-measurement accuracy. PCI-DHM can be divided into on-axis and off-axis PCI-DHMs depending on the interference angle between the object and reference waves. This study reviews the architectures of several typical PCI-DHMs and compares their advantages and disadvantages for different schemes. Specifically, on-axis phase-shifting PCI-DHM uses an on-axis optical configuration, where both the object and reference waves have the same optical path length, and amplitude/phase maps of the sample can be reconstructed using the phase-shifting technique. Moreover, a three-dimensional tomographic image of the internal microstructure in the sample can be obtained based on the short-coherence characteristic of light source. Off-axis PCI-DHM usually uses grating to introduce an angle between the object and reference waves, constructing an achromatic interferometer. The real-time measurement of amplitude/phase maps of the sample can be achieved only from an off-axis hologram. Finally, the practical applications of PCI-DHM in quantitative phase imaging of biological cells, biological tissue, microstructures, and nanostructures are introduced.