1. Laboratory of Weak Light Nonlinear Photonics; Ministry of Education; School of Physics and Teda Applied Physics Institute; Nankai University; Tianjin 300071 China
2. Beijing National Laboratory for Condensed Matter Physics; Institute of Physics; Chinese Academy of Sciences; P.O.Box 603 Beijing 100190 China
3. Center for Integrated Nanotechnologies; Los Alamos National Laboratory; Los Alamos NM 87545 USA