Fig. 1.

csi of a fluorescent specimen with counterpropagating light sheets. (A) Two microscope objective lenses are used to illuminate the specimen and at least one microscope objective lens collects the fluorescence light. (B) The two coherent counterpropagating light sheets interfere in the specimen and generate the structured illumination pattern in the focal plane of the detection lens. (C) The interference of two complementarily tilted counterpropagating light sheets generates a structured illumination pattern of the same spatial frequency that is rotated around the optical axis of the detection system.