1. Key Laboratory of Advanced Films of Hebei Province College of Physics Hebei Normal University Shijiazhuang 050024 P. R. China
2. State Key Laboratory of Functional Materials for Informatics Shanghai Institute of Microsystem and Information Technology Chinese Academy of Sciences Shanghai 200050 P. R. China
3. University of Chinese Academy of Sciences Beijing 100049 P. R. China
4. State Key Laboratory of High Field Laser Physics Shanghai Institute of Optics and Fine Mechanics Chinese Academy of Sciences Shanghai 201800 P. R. China