Tzallas, P., Charalambidis, D., Papadogiannis, N. A., Witte, K., & Tsakiris, G. D. (2003). Direct observation of attosecond light bunching. Nature, 426(6964), 267-271. Retrieved from http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v426/n6964/abs/nature02091_fs.html.