Backus S., R.A. Bartels, S. Thompson, R. Dollinger, M. Murnane, and H. Kapteyn, in Unknown (Opt. Soc. America, Baltimore, Md, Usa, 2001).
Backus S., R.A. Bartels, S.T. Thompson, R. Dollinger, H. Kapteyn, and M. Murnane, Optics Letters 26, 465 (2001).