Department of Precision Machinery and Precision Inst rumen tat ion;
University of Science and Technology of China;
Hefei 230027;
China;
School of Instrument Science and Technology;
Hefei University of Technology;
Hefei 230009;
China;
School of Electromechanical Engineering;
Guangdong University of Technology;
Guangzhou 510643;
China;
Science and Technology on Optical Radiation Laboratory;
Beijing 100039;
China;