1. Beijing Key Laboratory of Nanophotonics and Ultrafine Optoelectronic SystemsCenter for Micro‐NanotechnologySchool of PhysicsBeijing Institute of Technology Beijing 100081 P. R. China
2. Key Lab of Advanced Optoelectronic Quantum Design and MeasurementMinistry of EducationBeijing Institute of Technology Beijing 100081 P. R. China
3. Kunming Institute of Physics Kunming 650223 P. R. China
4. Beijing Key Laboratory for Precision Optoelectronic Measurement Instrument and TechnologySchool of Optics and PhotonicsBeijing Institute of Technology Beijing 100081 P. R. China
5. Research Center for Materials ScienceBeijing Institute of Technology Beijing 100081 P. R. China