Laser light is like a perfectly aligned row of soldiers on parade: all waves oscillate in the same plane. Such light is called polarized. In a new study, physicists have for the first time produced polarized gamma rays by colliding electrons with a powerful laser pulse.
Spectroscopy is not needed here — the polarization was measured from the distribution of neutrons from a deuterium target. When a polarized gamma ray knocks a neutron out of a deuterium nucleus, the neutron does not fly off in any random direction but in a specific one. This asymmetry revealed the degree of polarization — about 50%, just as theory predicted.
The result matters beyond its immediate significance. It shows that in strong fields, quantum interference effects alter the scattering picture — old simplified models did not account for this. Now compact sources of polarized gamma radiation can be built right on a tabletop, rather than at giant accelerators.
Polarized gamma rays could help peer inside the atomic nucleus and even "illuminate" hidden defects in materials.