Bunch length measurements using a Martin Puplett interferometer at the TESLA Test Facility linac

The longitudinal charge distribution of the electron bunches in the TESLA Test Facility linac has been determined using coherent transition radiation produced at a thin metal foil. The autocorrelation of the radiation pulse is measured with a Martin Puplett interferometer and then Fourier transformed to yield the coherent radiation spectrum and the bunch form factor. Several techniques, including a Kramers-Kronig analysis, have been applied to determine the longitudinal bunch charge distribution. Measurements with a thermionic electron gun and a RF photoinjector are presented. The influence of frequency-dependent acceptance corrections is discussed.