Patent ID: 8362448

Claim:
An apparatus comprising: a diffraction-limited resolution volume configured to contain a sample including a plurality of dye molecules which can be switched between different states, wherein at least one state is fluorescing; an objective lens configured to collect the fluorescence; and an optical system configured to image the fluorescence collected by the objective lens on a spatially resolving detector; and one or more light sources for emitting a switching radiation to switch a first subset of the dye molecules in the sample and for emitting an excitation radiation to excite the first subset of the dye molecules; wherein, in at least a portion of the sample, the dye molecules have a distribution density which is greater than the inverse of the diffraction-limited resolution volume; wherein at least one of the light sources is arranged in such a way that it radiates through the sample; wherein the apparatus is configured to carry out at least one of a switching and fluorescence excitation of the dye molecules in the sample at least in one direction approximately perpendicular to the optical axis and in the focus of the objective lens, and wherein a flat light sheet is generated by a focusing arrangement which penetrates through the sample and is at least approximately perpendicular to the optical axis of the objective lens.