Enhanced diffraction radiation from two dimensional periodical structure Tao Zhao, Renbin Zhong, Sen Gong, Ping Zhang, Xiaoxing Chen, Min Hu and Shenggang Liu Eur. Phys. J. D, 68 10 (2014) 300 Published online: 16 October 2014 DOI: 10.1140/epjd/e2014-50341-x