• V. R. Arsov, M.K. Bock, M. Felber, P. Gessler, K.E. Hacker, F. Löhl, F. Ludwig, K.-H. Matthiesen, H. Schlarb, A. Winter
  DESY, Hamburg
• S. Schulz, L.-G. Wißmann, J. Zemella
  Uni HH, Hamburg

The need for timing and bunch-length monitors for free-electron lasers and other accelerators makes the electro-optic spectral decoding (EOSD) a promising diagnostic technique. Being non-destructive, it allows a single shot-measurement within the accelerator environment. In some cases, e.g. low charge or necessity to resolve time-structures below 20 fs, the bunch length is measured indirectly, using the spectrum of the coherent transition radiation (CTR). We present results of EOSD measurements on the CTR beam line at FLASH, using a chirped Ti:Sapphire oscillator pulse focused simultaneously with the THz radiation on a GaP crystal in vacuum. The CTR spectrum is in the range 200 GHz-100 THz and and the pulse energy in the focus is over 10 mJ. The measured narrow CTR temporal profiles in the order of 400 fs FWHM demonstrate, that the ultra short THz-pulses, emitted by the compressed electron bunches are transported through the 19 m long beam line without significant temporal broadening.