2-PHOTON GEOMETRIC OPTICS

We report two-photon correlation experiments using spontaneous paramet ric down-conversion under a severe manipulation of the input pump fiel d. Considering the case of passing the laser beam through a focusing l ens before the down-conversion crystal, theoretical calculations and a series of imaging experiments demonstrate two-photon geometric optics effects. In particular, the imaging in coincidence counts of an apert ure placed in one of the down-conversion beams is found to be the anal og of a simple spherical mirror system, which displays a ''vacuum disp ersion'' effect in that the object and image distances are wavelength weighted.