  We present direct imaging of the emission pattern of individual
chromium-based single photon emitters in diamond and measure their quantum
efficiency. By imaging the excited state transition dipole intensity
distribution in the back focal plane of high numerical aperture objective, we
determined that the emission dipole is oriented nearly orthogonal to the
diamond-air interface. Employing ion implantation techniques, the emitters were
engineered with various proximities from the diamond-air interface. By
comparing the decay rates from the single chromium emitters at different depths
in the diamond crystal, an average quantum efficiency of 28% was measured.
