State Key Laboratory of Materials Modification by Laser;
Ion and Electron Beams;
School of Physics and Optoeleetronic Technology;
Dalian University of Technology;
DaIian 116024;
P. R. China;
State Key Laboratory on Integrated Optoelectronies;
College of Electronic Science and Engineering;
Jilin University;
Changchun 130012;
P R. China;