Laser-driven soft-X-ray undulator source

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 large-scale radiofrequency electron accelerators means that only a few of these sources exist worldwide. Laser-driven plasma-wave 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 similar to 10 fs (inferred from plasma-accelerator physics). Our source draws on a 30-cm-long undulator(11) and a 1.5-cm-long accelerator delivering stable electron beams(10) with energies of similar to 210 MeV. The spectrum of the generated undulator radiation typically consists of a main peak centred at a wavelength of similar to 18 nm (fundamental), a second peak near similar to 9 nm (second harmonic) and a high-energy cutoff at similar to 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.