For more than a decade, pulses of laser light just a few hundred femtoseconds (10−15 s) long have been used to follow the movement of atoms and molecules during chemical reactions. But tracking electrons requires even shorter pulses. An electron orbits a hydrogen atom in just 24 attoseconds (10−18 s), for example. Methods for producing suitably short pulses have emerged in the past couple of years1,2, and 2002 saw their first real application.

To get a sufficiently short laser pulse, Krausz bombarded neon gas with pulses of visible light 7 femtoseconds long, which sparked collisions between the neon atoms' nuclei and their electrons. This activity generated bursts of X-ray radiation about 100 attoseconds long, which Krausz focused and combined to make a single 650-attosecond pulse.

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