• M. Veronese, M.B. Danailov, M. Ferianis
  ELETTRA, Basovizza
• D. Filippetto
  INFN/LNF, Frascati (Roma)
• S.P. Jamison
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire

EOS and coherent radiation based diagnostics of sub-psec electron bunches are longitudinal diagnostics adopted for FERMI and other 4th generation light sources. The performance of both kind of diagnostics depends on the material properties in the THz spectral range. There is a need to characterise the transmission of windows materials and to understand the absolute efficiency of electro-optic detectors. This requirement for absolute EO efficiency is particularly important given observed variations between individual crystals with nominal identical specifications. In this paper we report measurements with THz pulses produced with photoconductive emitters. Our main goal was the characterization of EO crystals such as ZnTe and GaP for EOS and THz windows materials and humidity absorption. Good agreement is found for EO between experimental results and theoretical calculations concerning temporal resolution.

• R.B. Fiorito, M. Cornacchia, A.G. Shkvarunets, J.C.T. Thangaraj
  UMD, College Park, Maryland
• S. Di Mitri, M. Veronese
  ELETTRA, Basovizza
• H. Loos, J. Wu
  SLAC, Menlo Park, California

Recent observations of coherent optical transition radiation (COTR) at LCLS and other laboratories have been recognized as a signature of theμbunching instability, which affects the longitudinal phase space of the electron beam and ultimately the performance of the Free Electron Laser. In addition, the COTR emission limits the utility of OTR screens as beam profiling diagnostics. In an effort to understand and predict the extent of COTR emission and to help specify required instrumentation for new FELs, we have developed codes at UMD and SLAC-LCLS that use the output from the ELEGANT particle tracking code to predict the emission of COTR at specific wavelengths or within a band width. The COTR codes provides plots of the intensity patterns in the transverse plane, simulating a virtual OTR screen. Both incoherent and coherent intensities are produced thus providing an estimate of theμbunching gain at the observed wavelengths. Since the ELEGANT simulation of microbunching strongly depends on the number of particles, efforts have been carried out to speed up the COTR code analysis. The results of these codes applied to the LCLS and FERMI@elettra linac FELs are presented.