1. Council for Scientific and Industrial Research (CSIR) National Laser Centre, PO Box 395, Pretoria 0001, South Africa.
2. School of Physics, University of Witwatersrand, Johannesburg 2000, South Africa.
3. School of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa.
4. National Institute for Theoretical Physics, University of KwaZulu-Natal, Private Bag X54001, Durban 4000, South Africa.
5. Institute of Photonics and Quantum Science (IPaQS), Scottish Universities Physics Alliance (SUPA), Heriot-Watt University, Edinburgh EH14 4AS, UK.