1. College of Information Science and Engineering, Dalian Polytechnic University, Dalian 116034, P. R. China
2. Key Laboratory of Chemical Lasers, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, P. R. China
3. School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024, P. R. China