1. THz-Photonics Group, Institut für Hochfrequenztechnik , Technische Universität Braunschweig , Schleinitzstraße 22 , 38106 Braunschweig , Germany
2. Department of Physics , Sidho-Kanho-Birsha University , Purulia , West Bengal , 723104 , India
3. Raja Narendra Lal Khan Women’s College , Midnapore , West Bengal , 721102 , India