*Quang Duc Pham1,2, Yoshio Hayasaki3
(1. National Center for Technological Progress, 25 – Le Thanh Tong – Phan Chu Trinh – Hoan Kiem – Hanoi – Vietnam, 2. Vietnam Institute of Science Technology and Innovation, 38 Ngo Quyen, Hoan Kiem, Hanoi Vietnam, 3. Center for Optical Research and Education (CORE), Utsunomiya University 7-1-2 Yoto, Utsunomiya 321-8585, Japan)