Laser-driven soft-X-ray undulator source

Synchrotrons and free-electron lasers (FELs) are the most powerful sources of Xray radiation. They constitute invaluable tools for a broad range of research in physics, biology, materials science, chemistry, and medicine. However, their dependence on large-scale radio-frequency electron accelerators restricted diversification of these X-ray sources to only several sites worldwide. Laser-driven plasma-wave accelerators provide dramatically 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 wellcollimated beams deliver soft-X-ray pulses with an expected pulse duration of ~10 fs, inferred from the physics of plasma-wave accelerators. Our source draws on a dedicated 30-cm-long undulator and a 1.5-cm-long accelerator delivering stable electron beams5 with energies of ~210 MeV. The spectrum of the generated undulator radiation typically consists of a main peak centered at a wavelength of ~18 nm (fundamental), a second peak near ~9nm (second harmonic) and a highenergy cutoff at ~7 nm. Magnetic quadrupole lenses ensure efficient electron beam transport and demonstrate an enabling technology for reproducible generation of tunable soft-X-ray undulator radiation. The source is scalable to shorter wavelengths by increasing the electron energy. Our results open the prospect of brilliant, ultrashort-pulsed X-ray sources becoming available in smallscale laboratories