Attosecond physics comes of age: from tracing to steering electrons at sub-atomic scales

Efforts to access ever shorter time scales are motivated by the endeavour to explore the microcosm in ever smaller dimensions. At the turn of the millennium, one and a half decades after the first real-time observation of molecular dynamics with femtosecond laser pulses (1 fs = 10-15 s), we witnessed the emergence of sub-femtosecond (that is: attosecond) pulses (1 as = 10-18 s). They have been produced in the extreme ultraviolet regime by nonlinear frequency conversion of femtosecond laser pulses. A precise control of the hyperfast electric field oscillations of the driving femtosecond pulses not only allowed the controlled generation of single attosecond pulses and their full characterization but also, for the first time, steering and tracing the atomic-scale motion of electrons.