Ultrasensitive Mid-infrared Up-conversion Imaging At Few-photon Level

Recently, the infrared sources, the infrared spectral imaging and detection techniques are becoming the focus of scientific research. With the development of laser techniques, the mid-infrared sources can be readily attained by quantum cascade lasers, semiconductor lasers, and four-wave mixing in filaments. Mid-infrared lasers are widely used in revealing molecular rovibrational transitions, detecting spectral fingerprints of carbon-hydrogen bonds, monitoring atmospheric trace molecules, sensing various types of environmental gases, and even analyzing exhaled human breath for medical diagnostics. Though many efforts have been focused on developing semiconductor detectors such as HgCdTe, InSb, GaSb, and PbSe, most of the mid-infrared detectors have quite low sensitivities and large dark noise, which will largely limit the applications of the mid-infrared sources. Based on the new type of technology, the nonlinear frequency conversion, mid-infrared photons could be up-converted into visible or near-infrared ones, and then captured by a high performance silicon detector.In order to realize ultrasensitive, high efficient, low background mid-infrared up-conversion detection and imaging at few-photon level, we have carried out research and innovation from the following aspects:1. Based on the nonlinear frequency up-conversion, we realized high efficient, low background few-photon level mid-infrared up-conversion detection by a strong pump field and a MgO:PPLN crystal. The maximum conversion efficiency was32.9%. In this setup, the largest total background noise was about1.1×103cps, meaning that the noise probability per pulse was about6×10-5.2. We built the4f imaging system based on the ultrasensitive few-photon level mid-infrared up-conversion imaging system. The electronic enhanced charge-coupled device (EMCCD) was used to receive the mid-infrared images to improve the sensitivity of the system. The maximum conversion efficiency was12.5%. And we considered the influence of the blackbody radiation on the system of background noise...