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undulator radiation
Brilliant X-ray sources, such as third-generation synchrotrons or free-electron-lasers (FELs), are indispensible for a broad range of scientific research, such as femto-chemistry, structural biology, or developments of future medical applications. However, their diversification is limited by size and costs, implying the need for university-lab-sized brilliant light sources. We have published the first detailed design study towards a lab-scale, laser-driven, table-top FEL. The concept is based on a laser-driven accelerator delivering few-femtosecond-duration, ultrahigh-peak-current, low-emittance electron bunches. The electron beam exits into vacuum and needs to be shaped with special focusing optics, before it can produce brilliant radiation within an undulator. We have developed the first instruments dedicated to this end: miniature quadrupole lenses for relativistic electron beam transport and a compact undulator with millimetre-scale period. Thanks to these technological developments, we have been able to demonstrate the first laser-driven soft-X-ray undulator source, wich delivers few-fs, 18-nm pulses in collimated beam.
By gradually increasing the electron energy towards 1GeV → 1.5GeV → 2 GeV in our HF-4/5 beamline and optimizing beam transport and undulator structure we pursue scaling our soft-X-ray source towards hard-X-ray energies in the 5 keV range and beyond. On the long run, with PFS being used as the driver of the electron accelerator, we aim at improving the electron beam quality to enable us to demonstrate FEL operation, first at XUV energies, and later gradually at ever higher photon energies in the soft-X-ray and eventually hard-X-ray regime. Simultaneously with source development, the brilliant soft-X-ray → hard-X-ray sources becoming available will be used for proof-of-concept experiments towards protein structure analysis and medical imaging.

contact: F. Grünerlink to the personal page of Florian Grüner, S. Karschlink to the personal page of Stefan Karsch
references:
Design considerations for table-top laser-based VUV and X-ray free electron lasers, F. Grüner et al. Appl. Phys. B. 86, 431 (2007)
Miniature magnetic devices for laser-based table-top free-electron-lasers, T. Eichner et al. Phys. Rev. STAB 10, 082401 (2007)
Laser-driven soft-X-ray undulator source, Matthias Fuchs et. al. NatPhys 5, 826 (2009)
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Fig. 1. Miniature quadrupole lenses focus the relativistic electron beam to a diameter of ∼100 micrometre within a relative bandwidth of ∼1.5%. This spatial and energy confinement is unprecedented for a laser-accelerated electron beam and creates ideal prerequisites for undulator seeding.
Fig. 1. Miniature quadrupole lenses focus the relativistic electron beam to a diameter of ∼100 micrometre within a relative bandwidth of ∼1.5%. This spatial and energy confinement is unprecedented for a laser-accelerated electron beam and creates ideal prerequisites for undulator seeding.
Fig. 2. The world's first laser-driven soft X-ray undulator source delivers a brilliant few-fs light beam.
Fig. 2. The world's first laser-driven soft X-ray undulator source delivers a brilliant few-fs light beam.