Electrons hang-ten on laser-made waves.

Electrons have surfed the wake of a laser torpedo in the latest demonstration of laser-driven particle acceleration.

Theorists proposed the idea of laser "wakefield" acceleration 20 years ago as a scheme for replacing hulking, conventional accelerators with nimble, laser-driven, tabletop devices (SN: 2/10/96, p. 95). Experimental proof had to await major advances in lasers, but a 15-person team of French and British scientists now reports the first laboratory realization of the technique in the Aug. 3 PHYSICAL REVIEW LETTERS. The wakefield technique is the most recent of three laser-based acceleration methods to make the leap from theory to experiment.

At the Ecole Polytechnique in Palaiseau, France, researchers led by Francois Amiranoff fired a powerful laser pulse, lasting only 400 trillionths of a millisecond, into a chamber of helium gas. The intense pulse shattered gas molecules into a cloud of charged particles known as a plasma and created a wake of oscillating electrons that wriggled behind the pulse at nearly the speed of light. Simultaneously, the researchers shot a 3-million-electronvolt (MeV) electron beam into the wake. Bunches of injected electrons rode the speeding wake waves for roughly 2 millimeters, reaching a maximum energy of 4.6 MeV.

The energy gain was puny, compared to that produced by conventional accelerators, which routinely boost particles to billions and trillions of electronvolts. Nonetheless, the wakefield technique holds the most promise as an eventual challenger to today's vast machines because of its relative stability, the researchers assert.

In pursuit of higher energy with laser methods, the team is planning November tests to increase the accelerating length to a centimeter, says E cole Polytechnique's Victor Malka. One approach calls for using a long laser pulse to bore a channel in the plasma to guide a second, shorter pulse.