In medical care, magnetic fields of heart and brain activity are measured to detect diseases at an early stage. To measure even the smallest magnetic fields, researchers at Fraunhofer IAF are working on a new approach: diamond-based laser threshold magnetometry. The idea is to use diamond with a high density of nitrogen-vacancy centers in a laser system. Now the researchers have succeeded in reaching a milestone: They were able to demonstrate the world’s first measurement of magnetic-field-dependent stimulated emission and even set a new contrast record. Thus, they have demonstrated the principle of laser threshold magnetometry for the first time. The results were published in the journal Science Advances.