1. Department of Physics, Padjadjaran University 1 , Jl. Raya Bandung-Sumedang km. 21 Jatinangor, Sumedang 45363, Indonesia
2. Department of Engineering and Applied Sciences, Faculty of Science and Technology, Sophia University 2 , 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan