Many scientific disciplines ranging from physics, chemistry and biology to material sciences,
geophysics and medical diagnostics need a powerful X-ray source with pulse lengths in the
femtosecond range [1–4]. This would allow, for example, time-resolved observation of chemical
reactions with atomic resolution. Such radiation of extreme intensity, and tunable over a wide
range of wavelengths, can be accomplished using high-gain free-electron lasers (FEL) [5–10].
Here we present results of the first successful operation of an FEL at a wavelength of 32 nm,
with ultra-short pulses (25 fs FWHM), a peak power at the Gigawatt level, and a high degree
of transverse and longitudinal coherence. The experimental data are in full agreement with theory.
This is the shortest wavelength achieved with an FEL to date and an important milestone towards
a user facility designed for wavelengths down to 6 nm. With a peak brilliance exceeding the
state-of-the-art of synchrotron radiation sources [4] by seven orders of magnitude, this
device opens a new field of experiments, and it paves the way towards sources with even
shorter wavelengths, such as the Linac Coherent Light Source [3] at Stanford, USA, and
the European X-ray Free Electron Laser Facility [4] in Hamburg, Germany. |
