Uni HH, Hamburg, Germany
DESY, Hamburg, Germany
MAX-lab, Lund, Sweden
PSI, Villigen PSI, Switzerland
DELTA, Dortmund, Germany
University of Hamburg, Hamburg, Germany
The sFLASH project at DESY is an experiment to study direct seeding using a source based on the high-harmonic generation (HHG) process. In contrast to SASE, a seeded FEL exhibits greatly improved longitudinal coherence and higher shot-to-shot stability (both spectral and energetic). In addition, the output of the seeded FEL is intrinsically synchronized to the HHG drive laser, thus enabling pump-probe experiments with a resolution of the order of 10 fs. The installation and successful commissioning of the sFLASH components in 2010/2011 has been followed by a planned upgrade in autumn 2011. As a result of these improvements, in spring 2012 direct HHG seeding at 38 nm has been successfully demonstrated. In this contribution, we describe the experimental layout and announce the first seeding at 38 nm.
DESY, Hamburg, Germany
Uppsala University, Uppsala, Sweden
Uni HH, Hamburg, Germany
DELTA, Dortmund, Germany
FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
New infrastructure was built at FLASH to enable 30-100 fs long, milliJoule pulses of 270 nm light to seed the electron beam with HGHG and EEHG techniques, targeting wavelengths in the range from 10 nm to 40 nm. HGHG, or High Gain Harmonic Generation, and EEHG, or Echo-Enabled Harmonic Generation, utilize an external laser together with chicanes and undulators in order to generate a bunched beam which will radiate in a subsequent undulator. In the case of HGHG, the beam is bunched at the seed laser wavelength, radiating harmonics thereof in the radiator. In the case of EEHG, the beam is bunched at a harmonic of the seed wavelength, radiating that same harmonic in the radiator. The properties of the setup, commissioning difficulties and the inital attempts at HGHG seeding at 38.5 nm will be described.
DESY, Hamburg, Germany
Uppsala University, Uppsala, Sweden
DELTA, Dortmund, Germany
FYSIKUM, AlbaNova, Stockholm University, Stockholm, Sweden
The Optical Replica Synthesizer at FLASH was first commissioned in 2008 with an 800 nm seed. This wavelength proved to be problematic due to the fact that the COTR resulting from a microbunching instability at that wavelength was often as strong or stronger than the radiation from the seeded and bunched beam. It has since been observed that the microbunches which are responsible for the unwanted COTR can be smeared out in the dogleg if they are shorter than 600 nm. This opens the possibility to try the same experiment with a shorter wavelength and avoid the problems with the unwanted background signal from the microbunching instability. This is the motivation behind a new experimental design involving a new 270 nm seed laser and a new pulse length detection device to replace the old 800 nm seed and pulse length detection device. Details about the experiment design and commissioning plans will be described.
DELTA, Dortmund, Germany
Since 2011, a new Coherent Harmonic Generation (CHG) source* is under commissioning at the 1.5 GeV storage ring DELTA. Following first experiments using the fundamental wavelength of a Ti:sapphire laser for seeding a non-symmetrical optical klystron, 400 nm pulses from a second-harmonic conversion unit (SHG) are used since early 2012. With the radiator tuned to the second harmonic thereof, 200 nm CHG pulses are routinely observed. In order to detect higher harmonics and to proceed to a seed wavelength of 266 nm, an evacuated diagnostics beamline is under construction. Additionally, an existing VUV beamline is being upgraded to allow for the detection of the CHG pulses and their utilization in pump-probe experiments. Furthermore, a dedicated THz beamline provides valuable information about the laser-induced energy modulation of the electrons. In this paper, the status of the project and technical details will be presented.
* Huck et.al., FEL 2011