Free‐Electron Lasers Take Small Steps Toward Distant Goal

Until recently, no free‐electron laser was able to convert more than 5% of the energy from an electron beam into microwave radiation. Last fall, however, a team from Lawrence Livermore National Laboratory and the University of California at Berkeley published a (previously classified) report that they had operated a free‐electron laser with an unprecedented 40% efficiency at a wavelength of 8.6 mm. The peak power exceeded 1 gigawatt. Meanwhile, researchers at Los Alamos National Laboratory who operate a free‐electron laser of different design at a shorter wavelength (10 microns) have reported a modest increase in efficiency from 1.3% to 2% with peak power output of 20 MW, as well as development of several promising enhancements of their laser operation. In yet another experiment, a Stanford‐TRW team has operated an FEL in the visible region of the spectrum (525 nm) with a peak power as high as 170 kW.