X-ray laser pulses light up the nano-world

An international team of scientists using the soft X-ray free-electron laser FLASH at DESY has achieved a world first by taking a high-resolution diffraction image of a non-crystalline sample with one extremely short and intense laser shot. This first successful application of “flash diffractive imaging” opens a new era in structural research.

The experiment suggests that in the near future images from nanoparticles and even large individual macromolecules – viruses or cells – may be obtained using a single ultra-short high-intensity laser pulse. This would provide new possibilities for studying the structure and dynamics of nanometre-sized particles and molecules without the need for the crystallizing required in conventional X-ray structure analysis.

In the experiment at FLASH, the researchers directed a very intense free-electron laser pulse of 32 nm wavelength and 25 fs duration at a test sample, a thin membrane into which 3 μm-wide patterns had been cut (Chapman et al. 2006). The energy of the laser pulse heated the sample up to around 60,000 K, making it vaporize. However, the team was able to record an interpretable diffraction pattern before the sample was destroyed. The image obtained from the diffraction pattern showed no discernible sign of damage, and the test object could be reconstructed to the resolution limit of the detector. Damage occurred only after the ultra-short pulse traversed the sample.

In order to take images of large molecules with atomic resolution, such experiments will have to be carried out using radiation of even shorter wavelengths, i.e. hard X-rays such as the ones that will be produced from 2009 on by the Linac Coherent Light Source (LCLS) in Stanford, or by the European X-ray Free-Electron Laser (XFEL) in Hamburg, which should begin operation in 2013. Since the method demonstrated at FLASH does not require any image-forming optic, it can be extended to these hard X-ray regimes, for which no lens currently exists.