Because the pulses have extremely high intensity, they ionize the air in their pathways, leaving a curved plasma stream in their wakes. Each bullet becomes an intense concentration of electromagnetic energy that travels along a curved trajectory and leaves a bent plasma channel behind. Overall, the self-bending beam does have its limits—the bullets do not deviate from a straight line by more than the beam's diameter. "If the beam is one centimeter [in diameter]," Polynkin says, "it won't curve more than one centimeter."
Although it may not seem like a dramatic curvature, the deviation is enough to enable scientists to measure, in detail, the distribution of the radiation produced by the bullets along their paths. When pulsed beams travel in a straight line, the radiation originating from different locations along the beam path overlap, and these overlapping patterns are difficult to observe.
"We don't really understand the [structure] of laser beams, which is very important," says study co-author Jerome Moloney, director of the U.A.'s Center for Mathematical Sciences. "The significance here is that you don't expect to see light change trajectory."
Once researchers know more about how ultra-intense laser pulses travel, they hope to put them to good use. One thought has been to shoot a pulsed laser into a cloud to draw out lightning in a storm and use the plasma channel formed in the laser's wake to guide the lightning away from homes and power lines. Another possibility: employ high-intensity lasers as remote illumination sources in spectroscopic studies of pollutants in Earth's upper atmosphere.