1. Department of Physics, University of Bamenda, Bambili, Cameroon
2. Center for Atomic Molecular Physics and Quantum Optics (CEPAMOQ), University of Douala, Douala, Cameroon
3. Department of Physics, University of Yaoundé I, Yaoundé, Cameroun
4. Department of Physics, University of Maroua, Maroua, Cameroon