1. Division of Physics
and Applied
Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371,
Singapore
2. Department of
Physics, Hangzhou Normal University, Hangzhou
310036, P. R.
China
3. Division
of Materials Science, School of Materials Science and Engineering and Facility for Analysis, Characterization,
Testing, Simulation (FACTS), Nanyang Technological University, Singapore 639798, Singapore
4. Centre for Disruptive Photonic
Technologies (CDPT), Nanyang Technological University, Singapore 637371, Singapore