Christian Schulze,1 Filippus S. Roux,2 Angela Dudley,2 Ronald Rop,3 Michael Duparré,1 and Andrew Forbes2,4,* 1Institute of Applied Optics, Friedrich Schiller University, Fröbelstieg 1, 07743 Jena, Germany 2Council for Scientific and Industrial Research, P.O. Box 395, Pretoria 0001, South Africa 3Department of Physics, Egerton University, P.O. Box 536, Egerton 20115, Kenya 4School of Physics, Un...