1. CAS Key Laboratory of Geospace Environment and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, People’s Republic of China
2. Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA
3. Center for Ultrafast Optical Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA
4. Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA