Ultra short pulses in XUV region

So far, it has been difficult to observe nonlinear responses to an optical field in the extreme ultraviolet (XUV) and soft X-ray regions. A research group from the University of Tokyo recently succeeded in generating intense isolated XUV pulses (photon energy 27.9 eV) that were shorter than 1 femtosecond through high-harmonic (9^th) generation by using a sub-10-femtosecond blue laser (photon energy 3.1 eV) producing a large dipole moment. For more information, see the paper, "Nonlinear optics in the extreme ultraviolet", T. Sekikawa et al., Nature, 432, 605-608 (2004).