1. Department of Physics, Laser and Fibre Optics Centre, University of Cape Coast, Cape Coast, Ghana
2. Department of Applied Physics, University for Development Studies, Navrongo, Ghana
3. Department of Mathematics, University of Cape Coast, Cape Coast, Ghana
4. Department of Physics, The Pennsylvania State University, Altoona, Pennsylvania 16601, USA
5. Materials Research Institute, The Pennsylvania State University, University Park, Pennsylvania 16802, USA