Free‐Electron Lasers Achieve High Microwave Power

The output wavelength of a free‐electron laser varies as the inverse square of the energy of the electrons whose undulation through the FEL generates the laser light. Accelerators and storage rings of the kind one uses for highenergy physics have provided FEL researchers with electron beams of sufficient energy to yield laser output in the near infrared and even in the visible (see PHYSICS TODAY, December 1983, page 17). But such rf linacs and storage rings are typically limited to rather low electron currents, thus seriously limiting the peak output power of the freeelectron lasers that depend on them.