Scientists have sought a convenient source of radiation in the far-infrared portion of the spectrum for the study of semiconductor nanostructures and constituents in the atmosphere. In an effort to achieve that, researchers from Dartmouth College in Hanover, N.H., have built a compact, low-power free-electron laser that generates tunable coherent beams from 10 µm to 1 mm. They modified a scanning electron microscope to send a beam of electrons across a metal diffraction grating so that electromagnetic coupling forms oscillating arrays that emit IR light. By tuning the grating period, the user can tune the wavelength.