We have designed and tested a Orbitron MASER that utilizes a quasi-optical coupled cavity. This device could be turned off by tilting (q-spoiling) one of the mirrors of the cavity. We have also operated a tuneable quasi-optical orbitron.
Mark Rader, Mark Rader,
"A quasi-optical orbitron laser", Proc. SPIE 1514, 15th International Conference on Infrared and Millimeter Waves, 15146W (1 December 1990); doi: 10.1117/12.2301658; https://doi.org/10.1117/12.2301658