A flexible quantitative phase imaging microscope for label-free imaging of thick biological specimens using aperture masks

A flexible quantitative phase imaging microscope is reported that offers new capabilities in terms of phase measurement from both thin and thick biological specimens. The method utilises Zernike9s phase contrast approach for label-free imaging with a Twymann-Green-based phase-shifting module in the back focal plane. The interfering wavefronts are manipulated by laser-cut apertures to form the scattered and non-scattered fields. The design is flexible enabling a wide range of phase-shifting algorithms to be implemented. Phase maps of the cell membrane, nucleus, and nucleolus of transparent epidermis cells of allium cepa have been examined as proof of concept. The implementation of the phase-shifting module is