The free electron cyclotron resonance laser, based on conversion of synchrotron radiation to a coherent oscillation, operates at an extremely hight harmonic with a frequency of about .39, with the transverse relativistic factor and wc the relativistic cyclotron angular frequency. By introduction of the field amplitude spontaneous modified coefficient and by local expansion of the interaction light field, the linear efficiency and the start-up current are derived. It is shown that this device possesses a striking narrow width of the efficiency profile and so can successfully oscillate on a single longitudinal mode to produce light output of good coherence.
"Small-signal Analysis of a Free Electron Cyclotron Resonance Laser", Proc. SPIE 1039, 13th Intl Conf on Infrared and Millimeter Waves, (18 November 1989); doi: 10.1117/12.978771; https://doi.org/10.1117/12.978771