High-Efficiency Extraction of Microwave Radiation from a Tapered-Wiggler Free-Electron Laser

TLDR

By tapering the wiggler magnetic field to 45 % of its initial value at the end, the free‑electron laser’s output was increased to 1.0 GW. The tapered‑wiggler FEL achieved a 34 % extraction efficiency, a 34 dB/m gain, saturated after 1.3 m of interaction, and produced a 180 MW output from a 50‑kW input.

Abstract

We have substantially increased the output power and extraction efficiency of a free-electron laser operating at 34.6 GHz by tapering the wiggler magnetic field. In the exponential-gain regime, the laser exhibited a measured gain of 34 dB/m. With a 50-kW input signal, the amplifier saturated in 1.3 m with a 180-MW output signal. By using a taper that brought the magnetic field at the end of the wiggler down to 45% of its initial (peak) value, we increased the output signal to 1.0 GW. This corresponds to an extraction efficiency of 34%.