1. Introduction . The upconversion imaging technology is a promising alternative to the infrared imaging due to the low background noise level [ 1 – 4 ]. Normally, the upconveriosn imaging is based on quasi-phase match and the general formulation has been proposed in [ 5 , 6 ]. An important aspect of an upconversion system is the conversion efficiency. High conversion efficiency typically requires a sufficiently strong pump in a quadratic transparent crystal with a large optical nonli...