Sequential femtosecond X-ray imaging

Recording a 'molecular movie' with atomic spatial resolution on the femtosecond timescale set by atomic motion can be considered the ultimate goal of dynamic real-space imaging. Free-electron X-ray lasers, with their (sub)nanometre wavelength, femtosecond pulse duration and high brilliance, fuel the hope that this may ultimately become possible. Single-shot still pictures with sub-100 nm resolution achieved during femtosecond exposures have recently been demonstrated1-3. A femtosecond time-lapse movie requires a sequence of independent images taken with a controllable time delay. As a key step towards achieving a molecular movie, we demonstrate a holographic imaging approach capable of recording two fully independent images with a variable time delay over the entire femtosecond regime. The concept overcomes the fundamental readout time limitations of two-dimensional area detectors, as two subsequent X-ray holograms of a sample can be superimposed within one detector exposure and yet be unambiguously disentangled to reconstruct two independent images. © 2011 Macmillan Publishers Limited. All rights reserved.