Digital Holography Applied to Microscopy

Abstract

Digital Holographic Microscopy (DHM) is an imaging technique offering both sub-wavelength resolution and real time observation capabilities. The reconstruction of the wavefront from the hologram provides the amplitude and the absolute phase of the wave diffracted by the microscopic objects. Absolute phase contrast yields longitudinal accuracies as low as one nanometer in air or even less in dielectric media. The lateral accuracy and the corresponding resolution can be kept at a sub-micron level by the use of a high Numerical Aperture (N.A.) microscope Objective (M.O.). In the present state of the art, it can be kept commonly below 600nm. The principles of hologram formation, acquisition and wavefront reconstruction from digital holograms, acquired in a non-scanned modality, are described in details. The role of the M.O. in the capture of high spatial frequencies components of diffracted light and their restitution for high fidelity imaging is developed. A variety of applications of this new type of optical microscopy are described: material research, surface and interface sciences, microtechnologies, micro-optics and MOEMS. Applications to cell dynamics studies: nano-movements and cyto-architectures deformations, are demonstrated. Tomographic images of tissues can be also obtained by DHM.