A research team at Argonne National Laboratory in Argonne, Ill., has reported saturation at the 530- and 385-nm wavelengths in its free-electron laser, which is based on self-amplified spontaneous emission. In a saturated free-electron laser, the radiation power ceases to grow exponentially with distance as the electron beam passes through the wiggler magnets. The achievement suggests that the technique may be suitable for the production of high-brightness, tunable sources of coherent x-ray radiation. Such x-ray lasers would enable scientists to study ultrafast chemical and biological reactions, to generate higher-resolution holographic images of molecules and to investigate matter in hot plasma states. Argonne is collaborating with the University of California in Los Angeles, Brookhaven National Laboratory, Los Alamos National Laboratory and Lawrence Livermore National Laboratory to demonstrate the feasibility of a fourth-generation x-ray source to be built at the Stanford Linear Accelerator Center.