Digital holographic multi-focus quantitative phase contrast microscopy

Digital holography allows non-destructive, marker-free and quantitative high resolution full field measurement of morphology and refractive index changes of transparent objects such as living cells. The lateral resolution of digital holography is normally restricted by the pixel pitch of the applied imaging sensor. For this reason the setup for digital holography is integrated into a commercial microscope which improves the lateral resolution up to the diffraction limit. The interferometric determination of the phase gives an axial resolution that amounts to less than ten nanometers (quantified by the analysis of noise). The application of microscope lenses with high numerical apertures causes a decreased depth of field. Therefore, a focus tracking during the measurement is necessary. Here, digital holographic microscopy enables the advantage of multiple object plane reconstruction from a single hologram. Thus, focus adjustment can be carried out numerically after the measurement and mechanical auto focus tracking during the measurement is avoided. Measurement results of technical objects for system characterization are shown as well as investigations on biological specimen.