Boedewadt, J.

Paper	Title	Page
TUPPH003	Tolerance Studies on the High Harmonic Laser Seeding at Flash	235
	V. Miltchev, A. Azima, J. Boedewadt, H. Delsim-Hashemi, M. Drescher, S. Khan, Th. Maltezopoulos, M. Mittenzwey, J. Rossbach, R. Tarkeshian, M. Wieland Uni HH, Hamburg S. Düsterer, J. Feldhaus, T. Laarmann, H. Schlarb DESY, Hamburg R. Ischebeck PSI, Villigen
	Currently, the Free-electron-LASer at Hamburg (FLASH) operates in the Self-Amplified Spontaneous Emission (SASE) mode, delivering to users photon beams with wavelengths between 6.5 nm and 40 nm. In order to improve the temporal coherence of the generated radiation, it is planned to externally seed FLASH with higher harmonics of an optical laser. The project aims at seeding in the 30-13 nm range with stability suitable for user operation. In this contribution the performance of the seeded FEL is studied in simulations. Emphasis is placed on the tolerances of the most critical parameters such as transverse offset and angle between the electron beam and the external seed, timing jitter, energy of the seed pulse and the influence of the electron optics.
TUPPH051	Conceptual Ideas for the Temporal Overlap of the Electron Beam and the Seed Laser for sFLASH	363
	R. Tarkeshian, J. Boedewadt, M. Drescher, J. Rossbach Uni HH, Hamburg R. Ischebeck PSI, Villigen H. Schlarb, S. Schreiber DESY, Hamburg
	sFLASH is a seeding FEL experiment at FLASH/DESY, to introduce a 30nm HHG-based XUV-beam laser to the electron bunches of FLASH at the entrance of a 10m variable-gap undulator. The temporal overlap between the electron beam and HHG is important for the FEL process. The installation of a 3rd harmonic cavity at FLASH will provide a long high current electron beam (at kA level) over ~600fs (FWHM) bunch duration. The duration of the HHG laser pulse will be about 30fs (FWHM).The desired overlap can be achieved in steps. One approach will be to synchronize the drive laser (Ti:Sapphire, 800nm) of HHG and the incoherent spontaneous synchrotron radiation of the undulator at a sub-picosecond precision. In a following step the overlap can be improved by scanning within the sub-picosecond uncertainty. The possibility of using a streak camera to detect both the 800nm laser and the spontaneous undulator radiation pulses without perturbing FLASH user operation is investigated. To match the power levels, the laser beam has to be attenuated by several orders in magnitude. The layout of the experiment and preliminary simulation results of generation and transport of both light pulses are presented.
TUPPH072	sFLASH: An Experiment for Seeding VUV Radiation at FLASH	405
	S. Khan, A. Azima, J. Boedewadt, H. Delsim-Hashemi, M. Drescher, V. Miltchev, M. Mittenzwey, J. Rossbach, R. Tarkeshian, M. Wieland Uni HH, Hamburg S. Düsterer, J. Feldhaus, T. Laarmann, Th. Maltezopoulos, H. Schlarb DESY, Hamburg A. Meseck BESSY GmbH, Berlin
	The paper describes an FEL seeding experiment at VUV wavelengths,to be installed at the existing SASE FEL user facility FLASH. Beyond a proof-of-principle demonstration in the VUV, the emphasis will be on high stability in terms of intensity and timing thus providing a future alternative operation mode of FLASH for users. The seed laser generates high harmonics (HHG) by focusing a near-infrared laser into a noble gas jet. The efficient transport of the short wavelength (30nm) radiation and the spatial and temporal overlap with the electron beam are among the challenging tasks. The interaction of the seed laser and the electron beam takes place in a new undulator section to be installed in front of the existing FLASH undulator. Four hybrid variable-gap undulators are foreseen with a total length of 10 meters. In the space between undulator sections there are diagnostics devices for both the electron beam and the seed laser. After the undulators there is a weak magnetic chicane as a separator of the electron beam and the seeded FEL radiation. Finally a VUV beamline transports the radiation to an experimental hutch where the temporal characterization of the amplified pulses takes place.
THBAU04	Results from the Optical Replica Experiments at FLASH	497
	S. Khan, J. Boedewadt Uni HH, Hamburg G. Angelova, V. G. Ziemann Uppsala University, Uppsala M. Larsson Stockholm University, Department of Physics, Stockholm F. Loehl, E. Saldin, H. Schlarb, E. Schneidmiller, A. Winter, M. V. Yurkov DESY, Hamburg A. Meseck BESSY GmbH, Berlin P. M. Salen, P. van der Meulen FYSIKUM, AlbaNova, Stockholm University, Stockholm
	We present experimental results from the optical replica synthesizer,a novel device to diagnose sub-ps electron bunches by creating a coherent optical pulse in the infrared that has the envelope of the electron bunch and analyzing the latter by frequency resolved optical gating methods. Such a device was recently installed in FLASH at DESY. During an experiment period the spatial and temporal overlap of a several ps long electron bunch and a 200 fs laser pulse were achieved within an undulator. Coherent transition radiation due to the induced micro-bunching was observed on a silver-coated silicon screen and varying the timing between electrons and laser pulse produced two-dimensional images of the slices as a function of the longitudinal position within the electron bunch. In a second experiment the strongly compressed electron bunch is modulated by the laser pulse and replica pulses that are emitted from a second undulator are observed and diagnosed by frequency resolved optical gating methods.
	Slides