Intense laser beams travelling in a plasma twist around each other to form a braid of light. Although Maxwells equations state that light beams in a vacuum do not interact, in a nonlinear medium such as a plasma there is a self-interaction, principally generated by relativistic mass corrections. Starting from the Schrodinger equation, with added nonlinearity, the physicists calculated that the beam centroids of two gaussian laser pulses would move like point particles with a mass proportional to the power of each pulse. The force between the pulses is always attractive and depends on the beam spot sizes; as the beam separation increases, the spiralling period increases exponentially. The braiding effect happens because the beam tails rotate faster than the heads. This is partly due to the smaller beam spot size in the tail, but the researchers also noticed a significant contribution from Raman scattering, as the tails get caught in the wake of plasma waves. Experimental studies are now underway in California and Portugal, with the prospect of future application in optical steering. The braiding effect might also occur when streams of photons emanate from supernovas and gamma-ray bursters.
Posted on: Mon, 18 Aug 2014 06:30:02 +0000
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