Quantitative phase contrast interference microscopy by exploiting the coherence properties of LED using Fresnel biprism
Digital Holographic (DH) microscopy has evolved into a powerful non-destructive technique for quantifying morphological parameters along with real time analysis of living cells to study their dynamic membrane changes and cell fluctuations at nanometer and sub-nanometer scales. The conventional requirement for DH microscopy configurations is sources with a high degree of temporal coherence like gas lasers, laser diodes and solid state lasers which may mutually interfere resulting in speckles and disturbances due to parasitic reflections which degrade the reconstructed image quality. Quasi-monochromatic sources like Light Emitting Diodes (LEDs) as an alternative light source for holographic techniques can take care of this drawback. Two beam geometries are generally employed in DH microscopy, which are prone to external mechanical vibrations. In order to study the dynamics of samples like red blood cells (RBCs), a temporal stability that is much better than the membrane fluctuations of the RBCs is required. Two-beam geometries fail to provide this. Common path geometry can be used to reduce the unwanted fluctuations to a very large extent. In the present work digital holographic microscope employing a relatively broadband source is used to study the static as well as dynamic properties of RBCs using Fresnel's Biprism which is one of the simplest common path interferometers.
Keywords: Digital holographic microscopy, Quasi-monochromatic sources, Common path interferometers, self referencing geometry