Narrow-band photon beam via laser Compton scattering in an energy recovery linac

Narrow-bandwidth photon beams in the x-ray and.-ray energy ranges are expected to be applied in various fields. An energy recovery linac (ERL)-based laser Compton scattering (LCS) source employing a laser enhancement cavity can produce a high-flux and narrow-bandwidth photon beam. We conducted the first experiment of an ERL-based LCS source in combination with a laser enhancement cavity. We obtained LCS photons with an energy of 6.95 +/- 0.01 keV by colliding an electron beam of 20 MeV with a laser of 1064 nm wavelength. The photon flux at the interaction point was evaluated to be (2.6 +/- 0.1) x 10(7) photons/s with an average beam current of 58 mu A and an average laser power of 10 kW. The energy bandwidth was evaluated to be 0.4% (rms) with an opening angle of 0.14 mrad. The technologies demonstrated in this experiment are applicable for future ERL-based LCS sources.