Shuang Liu

A piano tuner in a noisy hall doesn't listen to all sounds indiscriminately: they isolate one string among dozens. A similar challenge is tackled by the new laser radar: among the many reflected beams, it identifies those carrying information about the target's vibration. A conventional radar sends a short pulse and waits for the echo.

When a laser beam hits a gas, it tears electrons from atoms and accelerates them to nearly the speed of light. As these electrons fly through the plasma, they emit X-rays, like a glowing trail from a fast particle. In the new work, physicists made a single laser pulse create not one but two such trails in succession.