Low-frequency excitations could soon be mapped with nanometer precision Researchers propose a method to detect and map low-frequency excitations in nonlinear materials at nanometer resolution, enabling far-infrared fingerprints. Indeed, a method capable of accessing information in the far-infrared to terahertz regime with nanometer resolution does not yet exist. The approach, reported in Nature Communications ("Wave-mixing cathodoluminescence microscopy of low-frequency excitations"), relies exclusively on visible light, eliminating the need for specialized low-frequency light sources and detectors. The WMCL method begins by directing an electron beam onto the sample, where it gives rise to low-frequency excitations, such as phonon vibrations. “In other words, nonlinear mixing allows invisible low-frequency excitations to imprint themselves onto visible photons,” explains Leila Prelat, first author of the article.