Abstract. Double-slit diffraction is a corner stone of quantum mechanics. It
illustrates key features of quantum mechanics: interference and the particle-wave
duality of matter. In 1965, Richard Feynman presented a thought experiment
to show these features. Here we demonstrate the full realization of his famous
thought experiment. By placing a movable mask in front of a double-slit to
control the transmission through the individual slits, probability distributions for
single- and double-slit arrangements were observed. Also, by recording single
electron detection events diffracting through a double-slit, a diffraction pattern
was built up from individual events.