Model for efficient upconversion detection at mid-infrared

Due to advantages of room-temperature and low dark-noise, upconversion is an alternative to state-of-the-art mid-infrared (MIR) detecting technique. The upconversion technique has been applied in a diverse fields such as imaging, analsing spectroscopy and Lidar. A comprehensive theory for upconversion employing collinear quasi phase matching (QPM) is presented. In this work, we present a upconversion model with considering the collinear beams separately focused into periodically poled lithium niobate (PPLN) bulk. Based on the known comprehensive theory of QPM, we build the efficiency function about incident angle by investigating the minimum phase-mismatch of the signal in PPLN. Then we rewrite the upconversion efficiency function according to the pump light field distribution. Finally, by calculating the integral of the efficiency function over the incident angle, the upconversion theoretical model is developed for upconversion process with both beams focused. To check the upconversion theoretical model, we simulate the upconversion efficiency curve about temperature and measure the upconversion efficiency curve of our system with the same temperature range. In our system, the pulse signal at 1550 nm with the peak power 40mW is upconverted to 863 nm with the continuous wave pump laser at continuous-wave 1950 nm with 800mW in a 10 mm long and 1 mm thick PPLN bulk. The experimental results show that the upconversion modeling is agreement with experimental data and it can be used in upconversion imaging.