The ultrafast motion of electrons in the microcosm, governing everything relevant to our life, is dictated by very strong forces acting within atomic and molecular structures. For any influence on the inner life of these structures, scientists need a force of comparable strength that can be switched within the extremely brief time electrons take to change their position within or between atoms. Only the electric force of ultrashort-pulsed laser light meets these requirements.

On the following pages we review how the hyperfast field vibration is controlled in very brief visible or infrared laser pulses, providing the controlled force that now enables researchers to steer and trace the atomic-scale motion of electrons. One of the most striking implications of this capability has been the generation and measurement of isolated attosecond pulses. Along with the laser pulses used for their generation, they have now for the first time allowed real-time observation of hitherto unresolved electron dynamics, such as inner-atomic quantum transitions, the tunnelling out of atoms and charge transport in solids.