Sir

Your News in Brief story “Spending spree gives German physics a high-energy boost” (Nature 421, 682; 2003) reported that free-electron lasers generate intense X-ray radiation for the study of molecules during chemical reactions. In fact, these lasers have operated from the microwave to the vacuum ultraviolet and can be used to study not only molecules but atoms, condensed matter, plasmas and even elementary particles via Compton back-scattering. Thanks to their performance advantages, which include tunability, pulse brevity, high repetition rate, capacity for pump–probe synchronization with other light sources, and high average and peak powers, the development of free-electron lasers is being advanced on many fronts.