Gamma-Ray Production in a Storage Ring Free-Electron Laser

A nearly monochromatic beam of 100% linearly polarized $\ensuremath{\gamma}$ rays has been produced via Compton backscattering inside a free electron laser optical cavity. The beam of 12.2 MeV $\ensuremath{\gamma}$ rays was obtained by backscattering 379.4 nm free-electron laser photons from 500 MeV electrons circulating in a storage ring. A detailed description of the $\ensuremath{\gamma}$-ray beam and the outlook for future improvements are presented.