High resolution and sensitivity up-conversion mid-infrared photon-counting LIDAR

A single-photon-counting mid-infrared LIDAR is presented. 2.4 µm mid-infrared photons were up-converted to 737 nm by intra-cavity mixing in a periodically poled rubidium-doped KTiOPO₄ crystal inside a Nd:YVO₄ laser. The up-converted photons were detected by a Si single-photon avalanche photodiode (SPAD). A temporal resolution of 42 ps and a dark count rate of 500 Hz were achieved, limited by the SPAD and ambient light leakage. It allowed for detection of two targets separated by only a few millimeters. This technique is easily extendable to longer wavelengths, limited primarily by the nonlinear crystal transparency.