Excited atoms offer a new way to measure plasma electric fields

It’s challenging to measure the electric fields of plasmas because they can vary spatially and temporally. The conventional method also involves insertion of a metal probe that risks disturbing innate properties of plasma.

Anderson et al. introduced a sensitive, non-invasive method for measuring the magnitude and spatial distribution of electric fields within and around plasma. The atom-based sensor is able to detect very small plasma electric fields with high resolution.

“This approach could provide a new way to map electric fields in plasmas that are too small, delicate, or difficult to access with conventional metal probes,” said author David Anderson. “Our approach should be suitable to quantify plasmas both in compact devices and in large-scale facilities.”

The technique relies on atoms in highly excited states called Rydberg atoms. The researchers put atoms of rubidium and cesium in the same compact vapor cell, then optically excited one species to create plasma and the other into a Rydberg state to act as a sensor. The optical response of the Rydberg atoms corresponded to the plasma’s electric field.

“The work shows how Rydberg quantum sensors can provide new measurement tools for plasma science and technology,” Anderson said.

The authors found that plasmas with higher initial photo-electron energy create larger electric fields. They also used the new technique to see how the field of plasma changes when it is magnetically confined and heated with a radiofrequency field. Magnetically confining the plasma increased the electric field.

Next, the authors plan to investigate the minimum and maximum electric fields this technique can detect, as well as how well it distinguishes macroscopic, coarse-grained fields from microscopic, fine-grained fields.

Source: “Non-invasive measurements of plasma electric fields using Rydberg electromagnetically induced transparency,” by David A. Anderson, Alisher Duspayev, Georg Raithel, Matthew Simons, and Christopher L. Holloway, AVS Quantum Science (2026). The article can be accessed at https://doi.org/10.1116/5.0340257 .