Coherent transition radiation diagnostic for electron bunch shape measurement at FELIX

An optical autocorrelation system using coherent transition radiation has been set up to determine the electron bunch shape at FELIX. A polarisation interferometer and a 10 × 10 mm2 pyroelectric detector are used to allow operation over a wide range of wavelength (from 30 μm to 10 mm) without strong variation in efficiency. An evacuated 15 m long overmoded waveguide is used to transport the transition radiation to the experimental area. The intensity of the transition radiation was measured and compared with our calculation. The phase-retrieval technique applied to the measured spectrum provides details of the electron bunch. The bunch shapes have been studied at different buncher phase settings. Measurements of coherent transition radiation and coherent undulator radiation are compared.