Efficient generation of mid-infrared photons at 3.16 μm by coincidence frequency downconversion

We experimentally demonstrate a pulsed mid-infrared photon source at 3.16 μm with a bandwidth of 3.7 nm by coincidence frequency downconversion with a conversion efficiency of 65%. The mid-infrared photons were generated by frequency downconversion in the saturation regime where the signal photons at 1.04 μm were synchronously pumped by intense laser pulses at 1.55 μm. In principle, the mid-infrared photon source could not only inherit the complete quantum characteristics of the input photon state, but could also be coherently manipulated in the spectral and temporal domains by engineering the classical pump field.