A scanning microscope includes first and second focusing means arranged confocally, at least one focusing means being of annular form, (for example a lens and closely-spaced opaque screen having an annular aperture); coherent radiation detection means arranged to receive radiation from one focusing means;...http://www.google.fr/patents/US4198571?utm_source=gb-gplus-shareBrevet US4198571 - Scanning microscopes
