Design of the bunch length measurement for the photo injector test facility at DESY Zeuthen

For measuring the electron bunch length of the photo injector test facility at DESY Zeuthen, a streak camera based system is designed to investigate the longitudinal phase space experimentally at different settings of the photoinjector and make detailed comparisons between theoretical predictions and experimental results. The Cherenkov radiation mechanism is used to convert the electron beam information into a photon beam in the visible range. In order to obtain a better time resolution from Cherenkov radiators, we will employ silica aerogels that have very low refractive index as well as a specially shaped fused silica plate as radiators. The design considerations of the radiators and the optical set-up are discussed with an emphasis on a good time resolution.