Confocal microscopy with an increased detection aperture: type-B 4Pi confocal microscopyStefan W. Hell, Ernst H. K. Stelzer, Steffen Lindek et al.|Optics Letters|1994Cited by 166
Measurement of the 4Pi-confocal point spread function proves 75 nm axial resolutionStefan W. Hell, Ernst H. K. Stelzer, Christoph Cremer et al.|Applied Physics Letters|1994Cited by 151
Nonlinear absorption extends confocal fluorescence microscopy into the ultra-violet regime and confines the illumination volumeErnst H. K. Stelzer, N. J. SALMON, Stefan W. Hell et al.|Optics Communications|1994Cited by 113