  The structural complexity and instability of many interference phase
microscopy methods are the major obstacles toward high-precision phase
measurement. In this vein, improving more efficient configurations as well as
proposing new methods are the subjects of growing interest. Here we introduce
Fresnel diffraction from a phase step to the realm of quantitative phase
imaging. By employing Fresnel diffraction of a divergent (or convergent) beam
of light from a plane-parallel phase plate, we provide a viable, simple and
compact platform for three-dimensional imaging of micron-sized specimens. The
recorded diffraction pattern of the outgoing light from an imaging system in
the vicinity of the plate edge can be served as a hologram, which would be
analyzed via Fourier transform method to measure the sample phase information.
The period of diffraction fringes is adjustable simply by rotating the plate
without the reduction of both field of view and fringe contrast. The high
stability of the presented method is affirmatively confirmed through comparison
the result with that of conventional Mach-Zehnder based digital holographic
method. Quantitative phase measurements on silica microspheres, onion skin and
red blood cells ensure the validity of the method and its ability for
monitoring nanometer-scale fluctuations of living cells, particularly in
real-time.
