Intense Laser Sheds Light on Radiation Reaction

A ccelerated electrons emit electromagnetic radiation, an effect we can appreciate every day in the color of the sky or when antennas produce radio waves to send music to our cars. Perhaps a less familiar idea is that the emitted radiation exerts a backaction on the electron itself, which has a dampening effect like that of friction (Fig. 1). Physicists first studied this “radiation reaction” theoretically in the early 1900s. The effect, however, is only sizable when the electron’s energy loss is large compared with the work done by the accelerating force, which corresponds to the electron being accelerated in its rest frame within a few yoctoseconds (10−24 s) [1]. While this condition can be met in remote astrophysical environments, such as the plasma surrounding a pulsar, it is much harder to come by in the lab. Two papers [2, 3] report preliminary measurements of the energy loss of electrons from radiation reaction that results from “shaking” the electrons with an extremely intense electromagnetic field. Both experiments made use of one of the world’s most powerful lasers, but the two papers present differing conclusions about which model best describes the data.