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Thomson Scattering of Laser Light from a Relativistic Electron Beam

Thomson scattering of laser light was applied to a relativistic cooling electron beam. High-power laser pulses were necessary because of the very low scattering cross section. A spectrometer of high resolution and large background suppression factor in combination with time-gated photon counting served for signal detection. Analysis of Doppler shift and broadening of the backscattered light provided the determination of the electron beam energy with a precision of 2 × 10-3, and an upper limit of the longitudinal energy spread of 10-3 eV. A ratio of longitudinal to transverse electron temperature of 10-2 was found, indicating a flattened velocity distribution as is expected from the acceleration of the electrons.