Fig. 2From: Complementarity in single photon interference – the role of the mode function and vacuum fieldsExperimental setup: For parametric down conversion a 2 mm long BBO crystal was used. The crystal was cut for collinear type I phase matching around 405 nm. The path delay between the two arms of the Mach-Zehnder-interferometer for observing the fringes and determining the visibility was realized by a motorized high resolution translation stage (Δl). The beam selection from different positions of the light cone structure as schemed in inset b was realized by a beam tilt and shift arrangement which also allowed for the perfect overlay of the selected two modes at the second beam splitter BS2. The detectors are single mode fiber coupled avalanche photo diodes SPCM-AQRH-13 from Perkin Elmer with lenses in front for determining the TEM00 modes of the idler- and the two signal-fieldsBack to article page