Digital holographic microscopy (DHM) is a quantitative phase imaging technique, where both the amplitude and phase of light interacting with a sample are measured. The phase contains information on the height and refractive index variations on a sample. In the off-axis configuration, the hologram is created between light from a sample and a reference wavefront hitting a sensor at an angle, allowing the separation of the direct reflections and the interference pattern in the frequency domain. This permits the observation of fast dynamics for a full 2D area, as the phase of the reflected/transmitted light can be retrieved numerically from a single hologram. Thus, the update rate in the surface topography and refractive index profile of a sample is limited only by the frame rate of the camera used to record the holograms.
See also a thesis on Holographic Recording in Azobenzene Films : A Digital Holographic Microscopy Approach