Department of Physics University of Science and Technology of China Hefei 230026;
Institute of Polymer Science Zhongshan University Guangzhou 510275;
Institute of Polymer Science Zhongshan University Guangzhou 510275;
Department of Physics Zhongshan University Guangzhou 510275;
Department of Physics Zhongshan University Guangzhou 510275;
Institute of Quantum Electronics South China Normal University Guangzhou 510631;
Institute of Quantum Electronics South China Normal University Guangzhou 510631;