Confocal theta microscopy and 4Pi-confocal theta microscopy

Confocal theta microscopy is a novel method by which the axial resolution in confocal fluorescence microscopy can be substantially improved. The basic idea is to observe the sample with two or more objective lenses and to detect the emission light at an angle theta to the illumination axis. The observation volume is considerably decreased when the detection axis is rotated by 90 degree(s) relative to the illumination axis. This leads to an almost spherical observation volume, which is three times smaller than in a comparable confocal fluorescence microscope. Confocal theta microscopy can be combined with 4Pi-confocal microscopy and is the first viable method proposed for fully exploiting the resolution increase achievable with 4Pi-techniques. The axial side lobes of the 4Pi-point spread function are suppressed, and the observation volume is reduced by a factor of 4. The resolution properties of confocal theta fluorescence microscopies are investigated for single- and two-photon absorption. Evaluations of confocal theta point spread functions are presented and the resolution improvement achieved by theta observation is discussed.