Revisiting up-conversion imaging in the single photon counting age

Up-conversion is a well-established nonlinear optical technique that can be used for active imaging in the infrared with silicon cameras. In this paper we demonstrate that the approach complements the single photon technique known as time correlated single photon counting (TCSPC). Up-conversion is used with a pulsed laser to provide an optical gate with TCSPC measuring the range data within the gate to capture a 3D image. The up-conversion efficiency is compared for bulk KTP and periodically poled KTP and conversion efficiency up to 50% is demonstrated in short-range optical bench tests. A portable imaging system is developed and used to capture range resolved imagery of 3D objects positioned at a stand-off distance of 80 m.