• O. Grimm, H. Delsim-Hashemi, L. Fröhlich
  DESY, Hamburg
• E. Chiadroni
  Universita di Roma II Tor Vergata, Roma

Various activities at the TTF linear accelerator at DESY, Hamburg, that drives the VUV-FEL are geared towards measuring the longitudinal charge distribution of electron bunches with coherent far-infrared radiation. Examples are beam lines transporting synchrotron or transition radiation to interferometers mounted inside or outside the tunnel, and studies of single-shot grating spectrometers. All such approaches require a good understanding of the radiation generation and transport mechanism and of the detector characteristics to extract useful information on the charge distribution. Simulations and measurements of the expected transverse intensity distribution and polarization of synchrotron radiation emitted at the first bunch compressor of TTF have been performed. The transverse intensity scanning provided for the first time at DESY a visual image of the footprint of terahertz radiation. Detector response measurements have been performed at the FELIX facility, Netherlands, for wavelengths between 100-160 microns, and first studies with blackbody radiation and band pass filters in the terahertz regime have been done at PTB, Berlin. The paper will summarize these results.

• L. Fröhlich, O. Grimm
  DESY, Hamburg

The longitudinal charge distribution of short electron bunches can be characterized by a measurement of their coherent far-infrared radiation spectrum. This paper will present the results obtained at the DESY VUV-FEL linear accelerator by observation of synchrotron radiation with a Martin-Puplett interferometer. The reconstructed bunch shapes are strongly asymmetric with a full width at half maximum of about 1 ps.