Salén, P.; Hamberg, M.; van der Meulen, P.; Larsson, M.; Angelova-Hamberg, G.; Ziemann, V.; Schlarb, H.; Löhl, F.; Saldin, E.; Schneidmiller, E.; Yurkov, M.; Bödewadt, J.; Winter, A.; Khan, S.; Meseck, A.: Results from the Optical Replica Synthesizer at FLASH. In: Proceedings of FEL 2009, Liverpool, UK., 2009, p. 739-745
Abstract:
We present results from the new electron bunch diagnostic tool, Optical Replica Synthesizer (ORS), installed at FLASH. The ORS produces an optical replica of the electron bunch profile, which is analyzed with a GRENOUILLE, a device based on the Frequency Resolved Optical Gating (FROG) technique. This optical replica is generated by inducing a microbunching in the electron bunch and letting it pass through an undulator, called a radiator. The radiator emits coherently at the wavelength of microbunching, 775 nm. In order to create the microbunching a laser pulse is spatially and temporally overlapped with the electron bunch in another undulator, placed before the radiator. This introduces an electron energy modulation which is transformed into a density modulation in a chicane before the microbunched electron bunch is sent into the radiator. We observed an optical replica pulse of approximately 5 μJ corresponding to an electron bunch-spike of about 150 fs FWHM when the accelerator was set at optimal FEL conditions. We also showed that the ORS can run parasitically while maintaining SASE by steering the electron beam around the outcoupling mirror for the ORS pulses.