Peterborough, N.H. - The production of laser-like radiation at X-ray wavelengths has been achieved for the first time in a collaborative effort among the Max Planck Institute for Quantum Optics, the Vienna University of Technology and Germany's Universities of Wurzburg and Munich. Not only was the beam of photons coherent, but the researchers suspect that it may also have been the shortest pulse ever achieved: 0.1 femtosecond, or 100 attoseconds.
The experiment, led by Ferenc Krausz at the Max Planck institute, produced the radiation by striking helium atoms with 700-nanometer laser light, which then emitted coherent X-rays at 1-nm wavelength. The same technique has been used to create coherent radiation in the extreme-ultraviolet range (10-nm wavelength), but previous attempts to push the experiment to X-rays hit a wall. The laser light striking the helium atoms causes their electrons to oscillate, which in turn stimulates the emission of the shorter coherent radiation. To get to shorter wavelengths, more energy is required, but that in turn tends to tear the electrons from their helium nuclei, destroying the effect.
The new experiment got around that barrier by using shorter pulses, down to 5 fs, to let the electrons emit the X-rays before they are affected by the intensity of the beam.
Toward practical apps
The researchers hope to enhance the experiment to yield a practical source of laser X-rays. The new form of X-ray would be a boon to medical imaging, since it would enable higher-resolution-image capture with far less intense beams than current X-ray systems use. The laser radiation would also allow imaging of soft tissue and could be used in other applications, such as microscopes that could resolve individual biomolecules.