@article {bergues2018tabletop,
	title = {Tabletop nonlinear optics in the 100-eV spectral region},
	journal = {Optica},
	volume = {5},
	number = {3},
	year = {2018},
	pages = {237{\textendash}242},
	abstract = {Nonlinear light\&amp;\#x2013;matter interactions in the extreme ultraviolet (XUV) are a prerequisite to perform XUV-pump/XUV-probe spectroscopy of core electrons. Such interactions are now routinely investigated at free-electron laser (FEL) facilities. Yet, electron dynamics are often too fast to be captured with the femtosecond resolution of state-of-the-art FELs. Attosecond pulses from laser-driven XUV-sources offer the necessary temporal resolution. However, intense attosecond pulses supporting nonlinear processes have only been available for photon energy below 50\&amp;\#x00A0;eV, precluding XUV-pump/XUV-probe investigation of typical inner-shell processes. Here, we surpass this limitation by demonstrating two-photon absorption from inner electronic shells of xenon at photon energies around 93\&amp;\#x00A0;eV and 115\&amp;\#x00A0;eV. This advance opens the door for attosecond real-time observation of nonlinear electron dynamics deep inside atoms.},
	keywords = {AS-6, AS6, nonlinear XUV},
	issn = {2334-2536},
	doi = {10.1364/OPTICA.5.000237},
	url = {https://www.osapublishing.org/abstract.cfm?uri=optica-5-3-237},
	author = {Bergues, B. and Rivas, D. E. and Weidman, M. and Muschet, A. A. and Helml, W. and Guggenmos, A. and Pervak, V. and Kleineberg, U. and Marcus, G. and Kienberger, R. and Charalambidis, D. and Tzallas, P. and Schr{\"o}der, H. and Krausz, F. and Veisz, L.}
}
