“…While for resolving the atomic motion in molecules in time, for example, by creating and taking snapshots of a vibronic wavepacket, laser pulses with duration of several femtoseconds (10 −15 s) are sufficient, accomplishing a similar feat for the electronic motion in atoms, molecules, or condensed matter requires sub-femtosecond, that is attosecond (as), time resolution (1 as = 10 −18 s). Advances during the last decade in the development of phasecontrolled few-cycle infrared (IR) laser pulses (cycle period IR ≃ 2.7 fs at = 800 nm) and ∼ 100 attosecond XUV pulses, temporally well correlated with each other through the underlying high-harmonic generation (HHG) process Hentschel et al, 2001;Paul et al, 2001) have opened up the possibility to observe and to control electronic dynamics in matter in real time and has developed into a new field dubbed attosecond physics (see e.g., Agostini and Dimauro, 2004;Reider, 2004;Scrinzi et al, 2006;Corkum and Krausz, 2007;Bucksbaum, 2007;Kling and Vrakking, 2008;Krausz and Ivanov, 2009;Chang, 2011;Gallmann et al, 2012;Plaja et al, 2013;Schultz and Vrakking, 2013;Kim et al, 2014;Lepine et al, 2014;Krausz and Stockman, 2014;Peng et al, 2015, for reviews of the subject). Previously, time-resolved electronic dynamics was accessible only for high-lying excited states.…”