Observations of frequency, phase and saturation characteristics of a Raman, free-electron laser amplifier

Summary form only given, as follows. Observations of frequency phase and saturation characteristics of a free electron laser (FEL) amplifier operating in the Raman regime are reported. The FEL is driven by a mildly relativistic electron beam (750 kV, 300 A, 25 ns) subjected to a combined axial magnetic field (2-12 kG) and a helical wiggler field (300-1600 G; 3.18 cm periodicity). The input into the FEL amplifier is provided by a high-power magnetron (/spl sim/5- kW) tuned to a frequency of 33.39 GHz. It is found that in the Group I regime of FEL operation the output frequency is upshifted by /spl sim/100 MHz, but smaller upshifts are observed in the group II or the reversed field configurations. Phase shift measurements and further saturation studies in all three regimes have also been performed.