Axial apodization in 4Pi-confocal microscopy by annular binary filters

We present a novel technique for considerably decreasing the sidelobe height of the axial point-spread function of one-photon 4Pi-confocal microscopes. By means of a numerical example, in which the ratio between the excitation and the fluorescence wavelengths was set to epsilon = lambda(exc)/lambda(det) = 0.8, we show that simply inserting a pair of properly designed two-ring binary masks in the illumination set allows the height of the axial sidelobes to be reduced from 20%, to 5% of the height of the central peak, This allows one to receive the full benefit of the strong narrowness of the central lobe provided by the 4Pi-confocal technique. (C) 2002 Optical Society of America.