RESOLVING FLUORESCENCE BEADS AT 100-200 NM AXIAL DISTANCE WITH A 2-PHOTON 4PI-MICROSCOPE OPERATING IN THE NEAR-INFRARED

We show the possibility of resolving point objects having an axial dis tance of 100-200 nm with a precision of +/- 15 nm with a two-photon ex citation 4Pi-microscope. The resolution is demonstrated by axial imagi ng of clustered fluorescence beads. A comparison of the axial resoluti on of the two-photon excitation 4Pi-microscope with a regular two-phot on excitation microscope shows a four-fold improvement in axial resolu tion.