1. Photonics Research Centre, Department of Physics, University of Malaya 1 , 50603 Kuala Lumpur, Malaysia
2. Low Dimensional Material Research Center, Department of Physics, University of Malaya 2 , 50603 Kuala Lumpur, Malaysia
3. Institute of Photonics and Optical Science (IPOS), School of Physics, The University of Sydney 3 , Camperdown, NSW 2006, Australia
4. Laser Physics Centre, Research School of Physics, The Australian National University 4 , Canberra, ACT 2601, Australia