  We present the analysis of emission profile of downconverted photons from a
critically phase-matched nonlinear crystal. This is done via direct imaging of
down converted photons by a CMOS camera. The effects of nonlinear crystal
thickness in collinear and non-collinear geometries on the down converted
photon pair rate is directly observed and the experimental results show that
the photon pair rate increases linearly with the crystal thickness. However,
the rate of the photon pairs collected to a single mode fiber goes
quadratically with the crystal length because of the cylindrical asymmetries in
the optical path and the exit angle around the pump mode within the nonlinear
crystal. The use of cameras for real-time and direct imaging of down conversion
emission profile significantly simplifies the phase-matching alignments and the
collecting the entangled photons.
