Diamond inside a laser: Fraunhofer quantum sensor reaches 100 percent contrast

Researchers at the Fraunhofer Institute for Applied Solid State Physics IAF in Freiburg have presented a magnetic-field sensor that combines high sensitivity with a large measurement range. It is based on nitrogen-vacancy (NV) centres in diamond, which work at room temperature. The study appeared in Nature Communications; the institute reported on it on 22 October. In the video, first author Florian Schall talks about the method and the results.

In so-called laser threshold magnetometry, the diamond sits directly inside the cavity of a semiconductor laser. A change in the magnetic field can switch the laser off entirely – so the system achieves 100 percent optical contrast for the first time, instead of the usual few percent. The laser readout signal reaches up to 50 milliwatts. If photon shot noise dominates, the calculated sensitivity is below 400 femtotesla per root hertz for each of the three field components; according to IAF, the ratio of sensitivity to measurement range improves by a factor of up to 590.

"Our approach could resolve a trade-off that has long limited the development and application of magnetic-field sensors," says Schall. Possible applications include signals from the heart, muscles and brain, magnetic navigation and resource exploration. The work is part of the NeuroQ lighthouse project funded by the German research ministry, which is developing sensors to control exoskeletons.