1. College of Engineering and Physical Sciences, Khalifa University, P.O. Box 127788 Abu Dhabi 51133, United Arab Emirates
2. Microsystem and Terahertz Research Center, Chengdu 610200, P. R. China
3. Department of Physics, Loughborough University, Loughborough LE11 3TU, U.K.
4. Department of Physics, College of Science, Princess Nourah Bint Abdulrahman University, P.O.
Box 84428, Riyadh 11671, Saudi Arabia