Reflective optical system for time-resolved electron bunch measurements at PITZ

The Photo-Injector Test facility at DESY, Zeuthen site (PITZ), produces pulsed electron beams with low transverse emittance and is equipped with diagnostic devices for measuring various electron bunch properties, including the longitudinal and transverse electron phase space distributions. The longitudinal bunch structure is recorded using a streak camera located outside the accelerator tunnel, connected to the diagnostics in the beam-line stations by an optical system of about 30 m length. The temporal resolution is severely degraded by this optical system, mainly due to dispersion in the achromatic lenses. This article presents initial studies toward a system based on reflective optics which will restore the temporal resolution to a level close to the streak camera resolution of 2 ps FWHM. The study includes simulations and measurements of different mirror systems, with an emphasis on systems of parabolic mirrors. A hybrid system of lenses and mirrors, which can serve as a proof of principle, is discussed in detail.