Quantitative Zernike phase-contrast microscopy by use of structured birefringent pupil-filters and phase-shift evaluation

摘要

Zernike phase-contrast is a well known and a often used method for the visualization of phase-structures. Because it applies a fixed phase-shift between the zero'th order and the scattered field, quantitative phase-measurements are only possible for small phase-shifts but not for arbitrary ones. The basic idea of the presented generalization of the method is to use polarization-optical pupil-filters for a separation of the zero'th from the higher orders in combination with phase-shifting polarization interferometry: In the simplest version, a drilled half-wave retarder is used in connection with linearly polarized illumination. This pupil-filter rotates the polarization of the scattered field by π/2 while the de-term is unaffected because it traverses the hole. The transmitted field is analyzed by phase-shifting polarization-interferometry: Using a liquid-crystal phase shifter (LCPS), both components can be phase-shifted relative to each other; they interfere at a subsequent analyzer. By means of a signal-evaluation according to phase-shifting interferometry, the complex amplitude of the scattered field can be determined relative to the de-term enabling a computation of the complete field's phase. The method works for general complex objects. The applications we consider are in the field of microstructure inspection.