1. The Guo Photonics LaboratoryState Key Laboratory of Applied OpticsChangchun Institute of OpticsFine Mechanics and PhysicsChinese Academy of Sciences Changchun 130033 P. R. China
2. University of Chinese Academy of Sciences Beijing 100049 P. R. China
3. State Key Laboratory of Luminescence and ApplicationsChangchun Institute of OpticsFine Mechanics and PhysicsChinese Academy of Sciences Changchun 130033 P. R. China
4. The Institute of OpticsUniversity of Rochester Rochester NY 14627 USA