Wang X., N. Saleh, M. Krishnan, H. Wang, S. Backus, M. Murnane, H. Kapteyn, D. Umstadter, Q. Wang, and B. Shen, Journal Of The Optical Society Of America B 20, 132 (2003).
Wang X., W. Yu, S. Backus, M. Murnane, H. Kapteyn, and D. Umstadter, in Unknown (IEEE, Chiba, Japan, 2001).
and 
