Creating the Broadest Spectral, Coherent-light Source with High-harmonic Generation

Jun. 25, 2012

This art represents an electron being ripped from an atom by a strong laser field, which stretches its quantum wave function over hundreds of atomic sizes. Just as electrons accelerated in an X-ray tube emit bremsstrahlung radiation, electrons accelerated by a laser can emit rainbows of coherent X-rays in a laser-like beam. X-ray light is "invisible to the human eye but is important for being able to 'see' the fine details and fastest motions of the nanoworld." Credit: Tenio Popmintchev, JILA and University of Colorado at Boulder

This art represents an electron being ripped from an atom by a strong laser field, which stretches ... more

For the first time, researchers have produced a coherent, laser-like, directed beam of light that simultaneously streams ultraviolet light, X-rays and all wavelengths in between (see video). One of the few light sources to successfully produce a coherent beam that includes X-rays, this new technology is the first to do so using a setup that fits on a laboratory table. An international team of researchers, led by engineers from the National Science Foundation's Engineering Research Center (ERC) for EUV Science and Technology, reports its findings in the June 8, 2012, issue of Science.

By focusing intense pulses of infrared light--each just a few optical cycles in duration--into a high-pressure gas cell, the researchers converted part of the original laser energy into a coherent super-continuum of light that extends well into the X-ray region of the spectrum.
The X-ray burst that emerges has much shorter wavelengths than the original laser pulse, which will make it possible to follow the tiniest, fastest physical processes in nature, including the coupled dance of electrons and ions in molecules as they undergo chemical reactions, or the flow of charges and spins in materials.

"This is the broadest spectral, coherent-light source ever generated," says engineering and physics professor Henry Kapteyn of JILA at the University of Colorado at Boulder, who led the study with fellow JILA professor Margaret Murnane and research scientist Tenio Popmintchev, in collaboration with researchers from the Vienna University of Technology, Cornell University and the University of Salamanca.

"It definitely opens up the possibility to probe the shortest space and time scales relevant to any process in our natural world other than nuclear or fundamental particle interactions," Kapteyn adds. The breakthrough builds upon earlier discoveries from Murnane, Kapteyn and their colleagues to generate laser-like beams of light across a broad spectrum of wavelengths.

The researchers use a technique called high-harmonic generation (HHG).

Imaging & Microscopy Issue 4 , 2012 as free epaper or pdf download

HHG was first discovered in the late 1980s, when researchers focused a powerful, ultra-short laser beam into a spray of gas. The researchers were surprised to find that the output beam contained a small amount of many different wavelengths in the ultraviolet region of the spectrum, as well as the original laser wavelength. The new ultraviolet wavelengths were created as the gas atoms were ionized by the laser.

Original publication:
Tenio Popmintchev , Ming-Chang Chen, Dimitar Popmintchev, Paul Arpin, Susannah Brown, Skirmantas Ališauskas, Giedrius Andriukaitis, Tadas Balčiunas, Oliver D. Mücke, Audrius Pugzlys, Andrius Baltuška, Bonggu Shim, Samuel E. Schrauth, Alexander Gaeta,Carlos Hernández-García, Luis Plaja, Andreas Becker, Agnieszka Jaron-Becker, Margaret M. Murnane, Henry C. Kapteyn: Bright Coherent Ultrahigh Harmonics in the keV X-ray Regime from Mid-Infrared Femtosecond Lasers, Science 8 June 2012: Vol. 336 no. 6086 pp. 1287-1291 , DOI: 10.1126/science.1218497

More information:
http://www.nsf.gov

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Creating the Broadest Spectral, Coherent-light Source with High-harmonic Generation

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