1. Research Center of Laser Crystal, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, P. R. China
2. Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
3. School of Semiconductor and Technology, South China Normal University, Foshan, Guangdong, 528225, P. R. China
4. Hangzhou Institute of Optics and Fine Mechanics, Hangzhou 311421, P. R. China