Refractometry of microscopic objects with digital holography

Digital holography has some desirable properties for refractometry of microscopic objects since it gives phase and amplitude information of an object in all depths of focus from one set of exposures. We show that the amplitude part of the image can be used to observe how the Becke lines move between different depths of focus and hence determine whether an object has a higher or a lower index of refraction than its surrounding medium, i.e., the sign of the relief. It is also shown that one single-phase image provides an independent technique to determine the sign of relief between an object and the surrounding medium. (C) 2004 Optical Society of America.