Efficient 20TW Ti:sapphire laser with two stage amplifiers Zhaohua Wang, Zhiyi Wei, Weijun Ling, Peng Wang, Hao Teng, Jinrong Tian, Jun Zhang and Jie Zhang J. Phys. IV France, 133 (2006) 691-695 Published online: 16 June 2006 DOI: 10.1051/jp4:2006133139