Phase pupil filters for improvement of the axial resolution in confocal scanning microscopy.

Two phase pupil filters whose axial impulse response is asymmetric with respect to the focal point are proposed. It is shown that when either of the filters is placed both in the illuminating and collecting part of the system the impulse respon se becomes symmetric and the axial resolution increases. The filters are designed on the basis of the Fourier-transform properties of the Hermition functions. They consist of small number of zones (=3) whose amplitude transmittance is constant and its module is equal to unity. The width of all zones is adequately chosen. Several quantitative characteristic of the proposed filters which evidence the improvement of the axial resolution are presented.