1. College of Electrical and Photoelectronic Engineering, West Anhui University, Lu'an, Anhui 237012, People's Republic of China
2. Department of Physics and Materials Science, University of Memphis, Memphis, Tennessee 38152, USA
3. Research Center of Atoms Molecules and Optical Applications, West Anhui University, Lu'an, Anhui 237012, People's Republic of China
4. Department of Physics and Astronomy, University of Arkansas at Little Rock, Little Rock, Arkansas 72204, USA
5. Department of Physics, Anhui Agriculture University, Hefei, Anhui 230036, People's Republic of China
6. School of Physics and Materials Science, Anhui University, Hefei, Anhui 230039, People's Republic of China