Jefferson Laboratory's kW-level infrared free-electron laser utilizes a superconducting accelerator that recovers about $75\%$ of the electron-beam power. In achieving first lasing, the accelerator operated “straight ahead” to deliver 38-MeV, 1.1-mA cw current for lasing near $5\mu \mathrm{m}$. The waste beam was sent directly to a dump while producing stable operation at up to 311 W. Utilizing the recirculation loop to send the electron beam back to the linac for energy recovery, the machine has now recovered cw average currents up to 5 mA, and has lased cw with up to 1720 W output at $3.1\mu \mathrm{m}$.

• Received 3 September 1999

DOI:https://doi.org/10.1103/PhysRevLett.84.662