Simulation study of indirect positron generation by an ultra-short laser Yonghong Yan, Yuchi Wu, Kegong Dong, Bo Zhang, Zongqing Zhao, Zeen Yao and Yuqiu Gu Eur. Phys. J. D, 68 1 (2014) 4 Published online: 22 January 2014 DOI: 10.1140/epjd/e2013-40473-x