Confocal microscopy with an increased detection aperture: type-B 4Pi confocal microscopy Hell, Stefan W. ; Stelzer, Ernst H. K. ; Lindek, Steffen ; Cremer, Christoph Abstract Publication: Optics Letters Pub Date: February 1994 DOI: 10.1364/OL.19.000222 Bibcode: 1994OptL...19..222H