Extended depth-of-focus by digital holographic microscopy.

A recurrent problem in microscopy is the finite depth-of-focus linked to the NA of microscope objectives. Digital holographic microscopy (DHM) has the unique feature of being able to numerically change the focus from a single hologram without the need of moving the sample. Extended depth of focus of amplitude images has been demonstrated, but it has marginal interest for the metrological application of DHM that needs the topography. In this Letter, we demonstrate that DHM is able to provide not only extended depth-of-focus amplitude images but extended focused complex data from which the topography is computed. For this purpose, reflection and transmission measurements on micro-optics (microlens and retroreflector) performed by using standard reconstruction or the extended focused complex data are compared. These experiments demonstrate that DHM measures, from a single hologram acquisition, the accurate sample topography on a numerically increased depth-of-focus.