Sub-100nm Axial Resolution in 3D Widefield Optical Microscopy Using Two Opposing Objective Lenses

Abstract It has been understood since the days of Ernst Abbe that an optical microscope can reach higher resolution the wider the set of angles from which it can observe the specimen — this angular range, of course, is what is indicated by the Numerical Aperture (NA) of the objective lens. Over more than a century of objective lens development, this light collecting angle has been increased closer and closer to the full 180° angle available above a microscope slide. There is, however, a second, equally large and easily accessible set of observation angles available on the other side of the specimen slide, and a standard microscope makes no use whatsoever of light emitted in these directions. One might then ask whether there is not a substantial resolution advantage to be had by devising a microscope that does make use of this "back side" light. The answer, in fact, is yes.