4PI-CONFOCAL IMAGES WITH AXIAL SUPERRESOLUTION

We present two-photon excitation 4Pi-confocal images of clustered fluo rescence beads demonstrating three-dimensional far-field light microsc opy with unprecedented resolution. For an excitation wavelength of 760 nm, the lateral and axial resolution amounts to 200 and 145 nm, respe ctively. The four-fold improved axial resolution is achieved by engine ering the point-spread function through a suitable combination of aper ture enlargement, two-photon excitation, confocalization and three-poi nt deconvolution. In contrast to their confocal counterparts, 4Pi-conf ocal images do not exhibit the typical axial elongation, The axial res olution in the 4Pi-confocal images corresponds to about one-fifth of t he wavelength and surpasses the lateral resolution by 25%.