Now a team led by Anne L’Huillier and Johan Mauritsson of Lund University in Sweden has combined this laser technique with precisely timed trains of ultrashort light pulses to cleanly image electron motion. The pulses in the train were just three hundred attoseconds (10-18 seconds) long. The researchers synchronized the pulse train with the oscillations of a relatively weak infrared laser, so that their cloud of helium atoms received a strong, ionizing "kick" at a precise time during each laser cycle. Each attosecond pulse released a few electrons, some of which were thrown back against their atoms before being pushed sideways and detected.
Accumulating data from many ionization events, the team created clean images of the quantum state of electrons ionized at a single moment in the laser oscillation cycle. The images are the first of their kind that show such controlled electron-atom scattering. The team calls their system a stroboscope, after another device that uses periodic flashes of light to capture a still image of a hummingbird's wings, for example.
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