1. Key Laboratory of Optoelectronic Technology and System, Ministry of Education of China, College of Optoelectronic Engineering Chongqing University Chongqing 400044 P. R. China
2. Chongqing Key Laboratory of Multi‐Scale Manufacturing Technology Chongqing Institute of Green and Intelligent Technology Chinese Academy of Sciences Chongqing 400714 P. R. China
3. Institut für Physik Carl von Ossietzky Universität Oldenburg D‐26111 Germany