• Special Issue
  • Free Electron Lasers
  • 6 Article (s)
Generating quasi-single-cycle THz pulse from frequency-chirped electron bunch train and a tapered undulator
Zhuoran Ma, Zhe Wang, Feichao Fu, Rui Wang, and Dao Xiang
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.4 Issue, 1 010000e1 (2016)
How the optical timing system, the longitudinal diagnostics and the associated feedback systems provide femtosecond stable operation at the FERMI free electron laser
Mario Ferianis, Enrico Allaria, Eugenio Ferrari, Giulio Gaio, Giuseppe Penco, Fabio Rossi, and Marco Veronese
FERMI, the seeded free electron laser (FEL) in operation in Italy, is providing the User Community with unique fully coherent radiation, in the wavelength range 100–4 nm. FERMI is the first FEL fully synchronized by means of optical fibers. The optical timing system ensures an ultra-stable phase reference to its distributed clients. Several femtosecond longitudinal diagnostics verify the achieved performance; the bunch length monitor (BLM) and the bunch arrival monitor (BAM) will be presented in this paper. Feedback systems play a crucial role to guarantee the needed long-term electron beam stability. A real-time infrastructure allows shot-to-shot communication between front-end computers and the servers. Orbit feedbacks are useful in machine tuning, whereas longitudinal feedbacks control electron energy, compression and arrival time. A flexible software framework allows a rapid implementation of heterogeneous multi-input–multi-output (MIMO) longitudinal loops simply by selecting the appropriate sensors and actuators.
High Power Laser Science and Engineering
  • Publication Date: Apr. 04, 2016
  • Vol.4 Issue, 2 02000e13 (2016)
Stabilization of a high-order harmonic generation seeded extreme ultraviolet free electron laser by time-synchronization control with electro-optic sampling
H. Tomizawa, T. Sato, K. Ogawa, K. Togawa, T. Tanaka, T. Hara, M. Yabashi, H. Tanaka, T. Ishikawa, T. Togashi, S. Matsubara, Y. Okayasu, T. Watanabe, E.J. Takahashi, K. Midorikawa, M. Aoyama, K. Yamakawa, S. Owada, A. Iwasaki, and K. Yamanouchi
A fully coherent free electron laser (FEL) seeded with a higher-order harmonic (HH) pulse from high-order harmonic generation (HHG) is successfully operated for a sufficiently prolonged time in pilot user experiments by using a timing drift feedback. For HHG-seeded FELs, the seeding laser pulses have to be synchronized with electron bunches. Despite seeded FELs being non-chaotic light sources in principle, external laser-seeded FELs are often unstable in practice because of a timing jitter and a drift between the seeding laser pulses and the accelerated electron bunches. Accordingly, we constructed a relative arrival-timing monitor based on non-invasive electro-optic sampling (EOS). The EOS monitor made uninterrupted shot-to-shot monitoring possible even during the seeded FEL operation. The EOS system was then used for arrival-timing feedback with an adjustability of 100 fs for continual operation of the HHG-seeded FEL. Using the EOS-based beam drift controlling system, the HHG-seeded FEL was operated over half a day with an effective hit rate of 20%–30%. The output pulse energy was at the 61.2 nm wavelength. Towards seeded FELs in the water window region, we investigated our upgrade plan to seed high-power FELs with HH photon energy of 30–100 eV and lase at shorter wavelengths of up to 2 nm through high-gain harmonic generation (HGHG) at the energy-upgraded SPring-8 Compact SASE Source (SCSS) accelerator. We studied a benefit as well as the feasibility of the next HHG-seeded FEL machine with single-stage HGHG with tunability of a lasing wavelength.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.3 Issue, 2 02000e14 (2015)
The European X-ray Free-Electron Laser: toward an ultra-bright, high repetition-rate x-ray source
M. Altarelli
The status of the European X-ray Free-Electron Laser (European XFEL), under construction near Hamburg, Germany, is described. The start of operations of the LCLS at SLAC and of SACLA in Japan has already produced impressive scientific results. The European XFEL facility is powered by a 17.5 GeV superconducting linear accelerator that, compared to these two operating facilities, will generate two orders of magnitude more pulses per second, up to 27 000. It can therefore support modes of operation switching the beam up to 30 times per second among three different experiments, providing each of them with thousands of pulses per second. The scientific possibilities opened up by these capabilities are briefly described, together with the current instrumental developments (in optics, detectors, lasers, etc.) that are necessary to implement this program.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.3 Issue, 3 03000e18 (2015)
The free-electron laser FLASH
Siegfried Schreiber, and Bart Faatz
FLASH at DESY, Hamburg, Germany is the first free-electron laser (FEL) operating in the extreme ultraviolet (EUV) and soft x-ray wavelength range. FLASH is a user facility providing femtosecond short pulses with an unprecedented peak and average brilliance, opening new scientific opportunities in many disciplines. The first call for user experiments has been launched in 2005. The FLASH linear accelerator is based on TESLA superconducting technology, providing several thousands of photon pulses per second to user experiments. Probing femtosecond-scale dynamics in atomic and molecular reactions using, for instance, a combination of x-ray and optical pulses in a pump and probe arrangement, as well as single-shot diffraction imaging of biological objects and molecules, are typical experiments performed at the facility. We give an overview of the FLASH facility, and describe the basic principles of the accelerator. Recently, FLASH has been extended by a second undulator beamline (FLASH2) operated in parallel to the first beamline, extending the capacity of the facility by a factor of two.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.3 Issue, 3 03000e20 (2015)
A study on low emittance injector and undulator for PAL-XFEL
J. Hong, J.-H. Han, S.J. Park, Y.G. Jung, D.E. Kim, H.-S. Kang, and J. Pflueger
For the success of PAL-XFEL, two critical systems, namely a low emittance injector and a variable gap out-vacuum undulator, are under development. In order to realize the target emittance of the PAL-XFEL injector we carried out an optimization study of various parameters, such as the laser beam transverse profile, the laser pulse length, the laser phase, and the gun energy. The transverse emittance measured at the Injector Test Facility (ITF) is . An undulator prototype based on the EU-XFEL design and modified for PAL-XFEL was built and tested. A local- pole tuning procedure was developed and tested. A significant reduction (90%) of the local- fluctuation was observed. The requirement of undulator field reproducibility better than and the undulator gap setting accuracy below were achieved for the prototype. The optical phase jitter after the pole height tuning at the tuning gap was calculated to be rms, which satisfies the requirement of .
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.3 Issue, 3 03000e21 (2015)