X-ray free-electron-laser pulses can be compressed to attosecond-scale durations
As a result, FEL pulses can be used to do attosecond physics.
Researchers from the Department of Physics at Oxford University, with colleagues at the Rutherford Appleton Laboratory (near Oxford) and the University of Strathclyde, have demonstrated via computer simulation that it is possible to generate attosecond-scale x-ray pulses using existing ultrabright free-electron lasers (FELs).1
Simulations of stimulated Raman backward scattering (RBS) show that today's few-femtosecond-duration x-ray pulses could be compressed down to a fraction of a femtosecond.
"X-ray pulses from free-electron lasers are being used in a whole host of ways, from biomedical technology and work on superconductors to research into proteins and states of matter in dense planets," says James Sadler, lead author. "We have shown, through our simulations, that it is possible to shorten the pulse length of x-rays by a factor of a hundred or a thousand -- flashes of light shorter than the time it takes for a chemical reaction to take place. This could have exciting implications across a range of scientific disciplines."
The simulations, using code written by Warren Mori at UCLA and Professor Luís Silva of the Instituto Superior Técnico in Lisbon, were carried out on the UK's SCARF and ARCHER supercomputers.
Physical processes amenable to exploration by ultrashort-pulse x-rays include some of the shortest events in physics, such as electrons moving in atoms. The key now, say the researchers, is to demonstrate the technique under laboratory conditions.
Attosecond-scale pulses can also be created via high-harmonic generation; however, the resulting pulses have energies of 10 μJ or less. The RBS technique could produce pulses with millijoule-scale energies.
1. James D. Sadler et al., Scientific Reports (2105); doi: 10.1038/srep16755