The Attosecond Revolution

The most intuitive way to understand the extreme nonlinear interaction that leads to attosecond pulses is through the semi-classical re-collision model. A strong infrared light pulse illuminating an atom or molecule creates a "free" electron wave packet by multiphoton ionization, usually approximated by tunneling. Tunneling occurs over a range of phases of the fundamental pulse near each crest of the laser electric field - a time window of roughly 300 attoseconds (as). In practice, in the infrared, multiphoton ionization intensities in the range of 10¹⁴ to 10¹⁵ W/cm² are needed, corresponding to peak electric field strengths of 3-10 V/Å...

This article by Paul Corkum and Zenghu Chang is the cover story in the October Optics & Photonics News, the trade journal of the Optical Society of America. The full text is available as a web page or as an Acrobat file.