Free electron lasers show their power

Recent investigations of high-efficiency free-electron lasers (FELs) operating in the mm wavelength range are surveyed. The potential military and scientific applications of FELs are indicated; the general physical principles involved are explained; experiments using field-emission-diode accelerators, undulators, and solonoidal guide fields to produce pulses of up to 50 nsec are described; and the use of linear induction accelerators without guide fields to produce longer pulses with higher energy and higher current is discussed. FEL amplification of 23-kW 8.6-mm radiation from a magnetron to 80 MW (with efficiency 5 percent) is reported for a device with a 3.5-MeV 600-A linear-induction-accelerator beam, and the applicability of this approach to the amplification of 10-micron radiation (using the 50-MeV 10-kA beam from the accelerator under construction at Livermore) is considered.