Full-field quantitative phase imaging provides useful endogenous contrast in a variety of biological specimens
where contrast from other natural sources is small and the use of exogenous materials is undesirable. While
the concepts of interferometric microscopy are simple and have long been known, diffculties in implementation
have prevented this imaging modality from being exploited to its fullest capability. In recent years, as a result
of improvements in lasers and light-delivery systems, cameras, and computational ability, new technologies have
been developed to bring this capability within reach of a large number of users.
Phase imaging presents some unique issues. For example ambiguities between amplitude and phase and
ambiguities within a cycle of phase (eg. the cosine is an even function) require two measurements per pixel.
Ambiguities in the number of cycles require phase unwrapping. More fundamentally, ambiguity between refractive
index and thickness requires multiple views.
Furthermore, coherent images tend to contain artifacts caused by multiple reflections from optical components,
which require special attention to image processing. They also are more likely than incoherent images to include
significant energy at high spatial frequencies, which can interact in complex ways with realistic optical transfer
functions and discrete sampling.
Different full-field quantitative phase imaging hardware and software are discussed, with attention to the
practical limitations imposed by these considerations.