Widely tunable compact terahertz gas lasers

Filling the terahertz gap Compared with other wavelengths, coherent sources of electromagnetic radiation in the terahertz regime are relatively scarce. Despite a number of applications in security imaging, spectroscopy, and chemical analysis, it has been experimentally challenging to produce such light. Chevalier et al. demonstrate an approach involving the excitation of a molecular gas with a quantum cascade laser. They show that they can tune into a broad range of desired wavelengths by carefully selecting the required molecular transition. A compact platform—the size of a shoe box—and widely tunable source of coherent terahertz radiation should find immediate application across a number of fields. Science , this issue p. 856