Synchrotrons and free-electron lasers are the most powerful sources of X-ray radiation. They constitute invaluable tools for a broad range of research 1 ; however, their dependence on largescale radiofrequency electron accelerators means that only a few of these sources exist worldwide. Laser-driven plasmawave accelerators 2-10 provide markedly increased accelerating fields and hence offer the potential to shrink the size and cost of these X-ray sources to the university-laboratory scale. Here, we demonstrate the generation of soft-X-ray undulator radiation with laser-plasma-accelerated electron beams. The well-collimated beams deliver soft-X-ray pulses with an expected pulse duration of ∼10 fs (inferred from plasma-accelerator physics). Our source draws on a 30-cmlong undulator 11 and a 1.5-cm-long accelerator delivering stable electron beams 10 with energies of ∼210 MeV. The spectrum of the generated undulator radiation typically consists of a main peak centred at a wavelength of ∼18 nm (fundamental), a second peak near ∼9 nm (second harmonic) and a highenergy cutoff at ∼7 nm. Magnetic quadrupole lenses 11 ensure efficient electron-beam transport and demonstrate an enabling technology for reproducible generation of tunable undulator radiation. The source is scalable to shorter wavelengths by increasing the electron energy. Our results open the prospect of tunable, brilliant, ultrashort-pulsed X-ray sources for small-scale laboratories.Resolving the structure and dynamics of matter on the atomic scale requires a probe with ångstrøm resolution in space and femtosecond to attosecond resolution in time. Third-generation synchrotron sources produce X-ray pulses with durations of typically a few tens of picoseconds and can achieve 100 fs by using complex beam-manipulation techniques 12,13 . They have already proven their capability of imaging static structures with atomic (spatial) resolution 1 and upcoming X-ray free-electron lasers hold promise for also extending the temporal resolution into the atomic/sub-atomic range [14][15][16][17][18] . Both of these sources consist of an electron accelerator and an undulator, which is a periodic magnetic structure that forces the electrons to oscillate and emit radiation 19 . Whereas current facilities require a kilometre-scale accelerator, new laser-plasma accelerators offer the potential for a marked reduction in size and cost as well as pulse durations of a few femtoseconds.Femtosecond-laser-driven plasma accelerators have produced quasi-monoenergetic electron beams 2-7 with energies up to 1 GeV (refs 8, 9, 20, 21) from centimetre-scale interaction lengths. The concept is based on an ultra-intense laser pulse, which ionizes atoms of a gas target and excites a plasma wave. This trails the pulse at 1 Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching, Germany, 2 Department für Physik, Ludwig-Maximilians-Universität, Am Coulombwall 1, 85748 Garching, Germany, 3 Forschungszentrum Dresden-Rossendorf, Bautzner Landstraße 128, 01328 Dresden, Germany, 4 ...

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A recent breakthrough in laser-plasma accelerators, based upon ultrashort high-intensity lasers, demonstrated the generation of quasi-monoenergetic GeV-electrons. With future Petawatt lasers ultra-high beam currents of ∼ 100 kA in ∼ 10 fs can be expected, allowing for drastic reduction in the undulator length of free-electron-lasers (FELs). We present a discussion of the key aspects of a table-top FEL design, including energy loss and chirps induced by space-charge and wakefields. These effects become important for an optimized table-top FEL operation. A first proof-of-principle VUV case is considered as well as a table-top X-ray-FEL which may open a brilliant light source also for new ways in clinical diagnostics.

We present a general expression for the maximum ion energy observed in experiments with thin foils irradiated by high-intensity laser pulses. The analytical model is based on a radially confined surface charge set up by laser accelerated electrons on the target rear side. The only input parameters are the properties of the laser pulse and the target thickness. The predicted maximum ion energy and the optimal laser pulse duration are supported by dedicated experiments for a broad range of different ions.

Osterhoff, J.; Popp, A.; Major, Zs.; Marx, B.; Rowlands-Ree, T.P.; Fuchs, Matthias; Geissler, M.; Horlein, R.; Hidding, B.; Becker, S.; Peralta, E.A.; Schramm, U.; Gruner, F.; Habs, D.; Krausz, F.; Hooker, Simon M.; and Karsh, Stefan, "Generation of Stable, LowDivergence Electron Beams by Laser-Wakefield Acceleration in a Steady-State-Flow Gas Cell" (2008). Matthias Fuchs Publications. 4.