1. Department of Engineering and Physics, Southern Arkansas University, 100 E. University, Magnolia, Arkansas 71753, United States
2. Department of Physics and Astronomy, University of Arkansas at Little Rock, 2801 South University Avenue, Little Rock, Arkansas 72204, United States
3. Department of Microelectronics and Photonics, University of Arkansas, 731 W. Dickson Street, Fayetteville, Arkansas 72701, United States