Spot size measurement and focusing of momentum entangled photon pairs

We show the use of gold nanoparticles in a confocal microscope setup to determine the point-spread function of a high NA objective and to show the enhancement in resolution using momentum entangled states of light. In this experiment a microscope objective with an numerical aperture (NA) of 1.4 is used to focus either light from a laser diode (808nm, coupled to single mode fiber) or momentum entangled photon pairs from a type I spontaneous parametric down-conversion (SPDC) pumped by a fiber coupled 404nm laser diode.