Advances in femto-nano-optics: ultrafast nonlinearity of metal nanoparticles Tatjana Stoll, Paolo Maioli, Aurélien Crut, Natalia Del Fatti and Fabrice Vallée Eur. Phys. J. B, 87 11 (2014) 260 Published online: 05 November 2014 DOI: 10.1140/epjb/e2014-50515-4