Radiologists and biologists have been dreaming - ever since the discovery of lasers - of a compact laboratory source emitting X-rays in one direction in a laser-like beam. Such a source would permit X-ray images to be recorded with far higher resolution at vastly reduced dose levels, allowing early-stage cancer diagnosis at dramatically reduced risk. Microscopes furnished with this source would make nanometer-sized biomolecules perceivable in their natural surrounding (in vivo). It may take many years before this dream comes true, but the experiment reported by an Austrian-German collaboration led by Ferenc Krausz indicates a promising way of realizing the dream some day. Researchers at Vienna University of Technology, the University of Wrzburg, the University of Munich and Max Planck Institute of Quantum Optics demonstrated the first source of laser-like X-rays at a wavelength of 1 nanometer with a compact laboratory apparatus [Nature 433, 596 (2005)] in an experiment in Vienna, funded by the Austrian Science Fund.

The colour of light is determined by the length of one cycle of the electromagnetic wave (referred to by physicists as the wavelength) that makes up light. Red light has a wavelength of around 700 nanometers, whereas our eye perceives radiation as violet light if its wavelength is only 400 nanometers. Light of even shorter wavelength is invisible (ultraviolet light), and with the wave cycle shortened to less than 1 nanometer, the X-ray regime is entered.

The Austrian-German team focused a sequence of intense ultrashort flashes of red light at a gas of helium atoms to convert 700-nm laser light into a 1-nm wave of X-ray light emitted by the excited atoms (Figure). The intense laser field makes the negatively charged electron cloud perform giant oscillations around the positively charged atomic core, thereby turning the atoms into antennas. Because of the giant amplitude of their oscillations, these radiate waves not only at the wavelength
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Contact: Prof. Ferenc Krausz
ferenc.krausz@mpq.mpg.de
49-89-3290-5612
Max-Planck-Gesellschaft
15-Feb-2005

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