1. Nanophotonics Lab, Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
2. Laser Lab, Department of Electrical and Computer Engineering, University of Virginia, Charlottesville, Virginia 22904, United States
3. Institute of Physics and Center for Nanotechnology, University of Münster, Wilhelm-Klemm-Str. 10, 48149 Münster, Germany