PHASE PUPIL FILTERS FOR IMPROVEMENT OF THE AXIAL RESOLUTION IN CONFOCAL SCANNING MICROSCOPY

Two phase pupil filters whose axial impulse response is asymmetric wit h respect to the focal point ale proposed. It is shown that when eithe r of the filters is placed both in the illuminating and collecting par t of the system the impulse respon se becomes symmetric and the axial resolution increases The filters are designed on the basis of the Four ier-transform properties of the Hermitian functions. They consist of a small number of zones (less than or equal to 3) whose amplitude trans mittance is constant and its module is equal to unity. The width of al l zones is adequately chosen. Several quantitative characteristics of the proposed filters which evidence the improvement of the axial resol ution are presented.