Department of Applied Physics Shanghai Jiao Tong University Shanghai 200030;
Laser Spectroscopy Laboratory Anhui Institute of Optics and Fine Mechanics Chinese Academy of Sciences Hefei 230031;
Department of Applied Physics Shanghai Jiao Tong University Shanghai 200030;
Department of Applied Physics Shanghai Jiao Tong University Shanghai 200030;
Department of Applied Physics Shanghai Jiao Tong University Shanghai 200030;