Speaker
Description
Measurements of the photoionization of rare gases have been an essential method for photon diagnostics at FLASH since the start of operation in 2005. Particularly at FLASH2, photoelectron TOF spectroscopy has been used for non-destructive monitoring of the FEL wavelength. With the online-photo-ionization spectrometer OPIS – a 4-channel eTOF spectrometer device – information about beam properties can be provided to the FLASH users as well as machine operators. In particular for the special two-color mode of FLASH2, we could demonstrate its ability for efficient monitoring of both wavelengths.
Recently, an APPLE-III type undulator has been added to the radiator beamline in FLASH2 to enable variable polarization of the FELs 3rd harmonic. With an afterburner scheme FLASH2 can now generate increased output power in a high photon energy range up to 860 eV with selectable polarization between the two linear and two circular modes. Here again photoelectron spectroscopy has been applied for polarization diagnostics with a 16-channel eTOF spectrometer instrument by measuring the angular distribution of photoemission. Results from the experimental studies of the afterburner undulator commissioning will be presented.
