Scaling combs into the XUV

■ ■ What are the motivations for working on extreme-ultraviolet technology today? The extreme-ultraviolet (XUV) spectral range is a largely unexplored frontier for high-resolution laser spectroscopy. Until very recently, no one thought it possible to have access to continuous-wave-like radiation in this spectral region. Now, with the convergence of ultrafast laser science, strongfield physics and precision measurements, it has become possible to venture into this region. This opens the door for new scientific opportunities in precision measurement, high-resolution spectroscopy and strongfield science. There are many simple atomic systems, such as H-like and He-like ions, which possess long-lived excitations of fundamental interest that exist only in the XUV region. We now have the ability to go after them. Furthermore, the possibility of using phase-stable XUV radiation to probe long-lived nuclear transitions and highly charged ion species, possibly for nextgeneration nuclear clocks, is truly exciting.