Two years ago physicists demonstrated that a laser beam traveling through the air can bend slightly if certain components are asymmetrical, forming what is called an Airy beam. Now researchers have shown that pulsed, high-intensity versions can leave curved trails of plasma. Shot out like a stack of pennies, each pulse, one centimeter wide and lasting 35 femtoseconds, passes through a glass plate that turns it into a triangular shape, in which an intense peak falls on one side of several weaker peaks. The brightest part heads in one direction, while the dimmer ones go the opposite way. (The momentum of the entire pulse remains straight, however.)

Being extremely intense, the bright spots ionize the air behind them and leave a curved plasma stream in their wake. The self-bending beam, described in the April 10 Science, does not curve by more than the beam's diameter, but that amount is enough to help physicists probe the structure of laser pulses.