Wired: Because it passes through clothes, terahertz radiation can reveal hidden weapons and explosives. Unfortunately, water vapor absorbs in the THz band, making it difficult to measure reflected THz signals remotely. Now, Xicheng Zhang of Rensselaer Polytechnic Institute and his colleagues have developed a way of circumventing that limitation. In a paper published on 11 July in Nature Photonics, they describe an ingenious method for what amounts to converting the THz signal into a more penetrating UV signal.