Scientists from the US Department of Energy's (DoE) Brookhaven National Laboratory in Upton, N.Y., and Argonne National Laboratory in Argonne, Ill., have demonstrated a high-gain harmonic-generation free-electron laser. They hope it will lead to the development of hard x-ray lasers. The proof-of-principle experiment, which was described in the Aug. 11 issue of Science, seeded the free-electron laser at Brookhaven with a 200-ps, 10.6-µm pulse from a 0.5-MW CO2 laser. The seed pulse interacted in the first undulator section with a 40-MeV electron beam, producing an energy modulation. A dispersion magnet converted the energy modulation into a coherent spatial density modulation, which produced coherent 5.3-µm light in a second undulator. The researchers plan to use a Ti:sapphire laser at the 266-nm third harmonic to seed the device and produce vacuum-UV light. Further experiments may use more gain stages to boost output into the x-ray region.