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Sub-attosecond pulses on the horizon

A technique to create the shortest X-ray pulses ever made has been proposed in Physical Review Letters, the publication of the American Physical Society.

The capability would generate a deeper understanding of how medicines interact within the body and of catalytic processes in new materials for energy storage.

Developed by researchers at the Science and Technology Facilities Council (STFC) at its Daresbury Laboratory, in close association with the University of Strathclyde, the proposed technique is expected to generate X-ray laser pulses shorter than an attosecond and would open the possibility of directly studying the dynamics of atomic nuclei.  Presently, the shortest pulse of laser light ever generated is 67 attoseconds.

Lead author David Dunning, an accelerator scientist at STFC’s Accelerator Science and Technology Centre (ASTeC), said: 'Such pulses will be important for observing and influencing processes within molecules, atoms and nuclei which occur at progressively smaller sizes and faster time scales.

'Such short timescales are difficult to conceive. To put them into context, stretching out one attosecond to one second is the equivalent to stretching out one second to 30 billion years - or more than twice the age of the universe.'

Although further development is needed to put this theory into practice, this is a significant step in the long-standing drive to film with atomic resolution, which can then be combined to produce movies.

Dunning said the concept has been extensively computer-modelled at STFC and it would only require a modest addition to an existing X-ray Free-Electron Laser (FEL). However, a more likely scenario might be that the idea be first proven in practice on a dedicated FEL test facility.

By using magnets to manipulate electrons from a particle accelerator, FELs generate intense light of exceptional quality. FELs operate across a much broader range of wavelengths than conventional lasers, and this ability to reach very short wavelengths, such as X-rays, is part of the key to generating ultra-short pulses.

Currently, FEL pulses flash on and off quickly enough to `freeze-frame’ the motion of electrons within atoms or molecules. By using the new technique to move to the scale of less than an attosecond, it may be possible to probe deeper and observe the much faster dynamics of electrons interacting with the nucleus, or even the dynamics of the nucleus itself.

Dunning added: 'Our proposed techniques can be applied to any present or future particle accelerator FELs.'

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