The electron energy is measured at the MLS by the method of Compton back-scattering of laser photons. A CO2-laser will be super imposed anti-parallel to the electron beam. The backscattered photons being in the range from 70 keV to 650 keV, for 200 MeV and 600 MeV operation of the MLS respectively, will be detected with a HPGe detector. The relative uncertainty in the determination of the electron energy is 1·10-4.
At BESSY II a similar set-up is used. There the energy of the backscattered photons are at about 1500 keV for 900 MeV operation of the ring and at approx 5.3 MeV for the operation with 1700 MeV electron energy. Alternatively at BESSY II the electron energy can be measured by the method of resonant spin depolarization when BESSY II is operated at 1700 MeV electron energy.
Spectrum of Compton backscattered photons for various electron energies at the MLS