• G. Geloni, P. Ilinski, E. Saldin, E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

Electron bunch imagers based on incoherent OTR constitute the main device presently available for the characterization of ultrashort electron bunches in the transverse direction. One difficulty to obtain high-resolution images is related with the very peculiar particle-spread function of OTR radiation, which has a large width compared to the usual point-spread function of a point-like source. In this contribution we explore the possibility of using coherent OTR instead of incoherent OTR radiation, by integrating an ORS setup with a high-resolution coherent optical transition radiation imager. Electron bunches are modulated at optical wavelengths in the ORS setup. When these electron bunches pass through a metal foil target, coherent radiation pulses of tens MW power are generated. It is thereafter possible to exploit the large number of available coherent photons. In particular we manipulate the particle spread function of the system, so that the imaging problem can be reduced to the usual (coherent or incoherent) imaging theory for point-like radiators.

• G. Geloni, P. Ilinski, E. Saldin, E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

We describe a novel technique to characterize ultrashort electron bunches in X-ray Free-Electron Lasers. Namely, we propose to use coherent Optical Transition Radiation to measure three-dimensional (3D) electron density distributions. Our method relies on the combination of two known diagnostics setups, an Optical Replica Synthesizer (ORS) and an Optical Transition Radiation (OTR) imager. Electron bunches are modulated at optical wavelengths in the ORS setup. When these electron bunches pass through a metal foil target, coherent radiation pulses of tens MW power are generated. It is thereafter possible to exploit advantages of coherent imaging techniques, such as diffractive imaging, Fourier holography and their combinations. The proposed method opens up the possibility of real-time, wavelength-limited, single-shot 3D imaging of an ultrashort electron bunch.