新加坡南洋理工大学熊启华教授报告

报告题目： Laser Cooling of Semiconductors 报告人：熊启华报告时间： 2013.9.26（周四）下午13:00 报告地点：物理楼南208 摘要： Optical irradiation accompanied by spontaneous anti-Stokes emission can lead to cooling of matter, a phenomenon known as laser cooling or optical refrigeration proposed in 1929 by Peter Pringsheim. In solid state materials, the cooling is achieved by annihilation of lattice vibrations (i.e., phonons). Since the first experimental demonstration in rare-earth doped glasses, considerable progress has been made particularly in ytterbium-doped glasses or crystals with a recent record of ~110 K cooling from ambient, surpassing the thermoelectric Peltier cooler. On the other hand, it would be more tantalizing to realize laser cooling in direct band-gap semiconductors. Semiconductors exhibit more efficient pump light absorption, much lower achievable cooling temperature and direct integrability into electronic and photonic devices. However, no net-cooling in semiconductors has been achieved despite of many experimental and theoretical efforts in the past few decades. In this presentation, we demonstrate the first net laser cooling in semiconductors using cadmium sulfide (CdS) nanobelt facilitated by multiple longitudinal optical phonon assisted upconversion due to strong and enhanced Fröhlich interactions, with a ~40 K net cooling in achieved starting from 290 K pumped by 514 nm. Our findings suggest alternative II-VI semiconductors for laser cooling and may find promising applications in the field of cryogenics with the advantage of compactness, vibration- and cryogen-free, high reliability and direct integrability into nanoscale electronic and photonic devices. In the end of this work, preliminary results on all-solid-state semiconductor cooler and laser cooling of bulk crystal will be discussed. About the speaker： Qihua Xiong received his B.S. degree in physics from Wuhan University in 1997, and then finished three years graduate studies at Shanghai Institute of Applied Physics, Chinese Academy of Sciences. He went to the United States in 2000 and received a Ph.D. degree under the supervision of Prof. Peter C. Eklund from The Pennsylvania State University in 2006. After three years postdoctoral experience in Prof. Charles M. Lieber’s group at Harvard University, he joined Nanyang Technological University as an assistant professor in 2009. He is a Fellow of Singapore National Research Foundation awarded in 2009. Prof. Xiong’s research focuses electrical and optical properties of semiconductor nanomaterials. He recently ventured into the field of 2D layered materials and laser cooling of semiconductors. 联系人： yudp@pku.edu.cn 俞大鹏