Last year, Ferenc Krausz, Theodor Hänsen, and their collaborators used femtosecond laser pulses to make isolated attosecond bursts of UV light. 1 To pull off the feat, the team wielded precise and reproducible control over the five or so electric field oscillations that fit inside the amplitude envelope of a femtosecond pulse. With the right phasing between field and envelope, one specific oscillation in each pulse spawned an attosecond burst on demand (see Physics Today, Physics Today 0031-9228 56 4 2003 27 https://doi.org/10.1063/1.1580040 April 2003, page 27 ).
Getting the phasing right depended on measuring the bursts’ UV spectrum, which was fed back into a sophisticated setup of amplifiers, interferometers, and other equipment. But now Krausz, who has joined Hänsch at the Max Planck Institute for Quantum Optics in Garching, Germany, can see the phasing directly. In a new experiment, he and a group led by Ulrich Heinzmann of...
