The ultrafast laser is a scientific tool unlike any other. When focused, terawatt-level pulses produce large intrinsic electric and magnetic fields that accelerate ions. Also, the femtosecond pulse durations can provide snapshots of chemical reactions. Although technological uses of the ultrafast laser are already being discovered, they will take decades to explore--just as with many of the greatest inventions. Part of understanding just what femtosecond pulses can do comes from developing the right techniques for measuring their effects.
Researchers at Hamamatsu Photonics (Hamakita-City, Japan) have demonstrated a device that produces a femtosecond-resolution series of images—akin to a movie—showing areas of instantaneous birefringence induced by a focused ultrafast laser pulse in air. When the individual frames are summed, the result is a spatial representation of a light cone that reveals filaments of high birefringence in a distribution very unlike what might be expected near a focus. Such information is important not only to high-field physics in laser plasma interactions but also to inertial-confinement fusion and will undoubtedly be important in the future to ultrafast-laser-based industrial processing.