1 Center for Terahertz Waves and College of Precision Instrument and Optoelectronics Engineering, Key Laboratory of Optoelectronic Information Technology (Ministry of Education of China), Tianjin University, Tianjin 300072, China
2 Institute of Solid State Physics, College of Physics and Electronic Science, Shanxi Province Key Laboratory of Microstructure Electromagnetic Functional Materials, Shanxi Datong University, Datong 037009, China
3 Nonlinear Physics Centre, Australian National University, Canberra, ACT 2601, Australia
4 School of Electrical and Computer Engineering, Oklahoma State University, Stillwater, Oklahoma 74078, USA
5 e-mail: cmouyang@tju.edu.cn
6 e-mail: xiaoqiang.su@sxdtdx.edu.cn
7 e-mail: weili.zhang@okstate.edu