Dynamic Imaging Of Matter At The Attosecond and Angstrom Scales

We will investigate a concept for ultra-fast dynamical imaging with attosecond and angstrom resolution (DIAA) of the atoms and electrons in matter. This will provide simultaneously time resolution less than a femtosecond (10.15s) (i.e. in the attosecond domain where las = 10-18s) and space resolution less than an angstrom (10-t 0m).The atomic scale structure of matter has long been studied by diffraction techniques using X-rays or electrons to provide spatial resolution at the subangstrom level. Whilst these powerful probes readily give the static structure they cannot yield information about the dynamics of structural change at the most fundamental level i.e. on the actual timescales at which they happen. The natural timescale for chemical and structural changes in matter at the atomic spatial scale is femtosecond and sub-femtosecond. Scientists are currently unable to image atomic scale fundamental physical and chemical changes on this timescale. This limits our understanding of the dynamics of structural changes that underpin the behaviour of matter at the quantum scale. Our new DIAA techniques will provide scientists for the first time with the tools required to tackle these fundamental issues.This idea originates from our group at Imperial and our collaborators at the National Research Council in Ottawa, Canada. It is based on electrons coherently driven by very strong pulsed laser fields. The electrons are first removed from a molecule by the strong field near the peak of the laser wave and then are driven back by the laser field when it switches direction -10 15 second later. The electrons then recollide with the parent molecule in a collision event lasting less than a femtosecond. The electrons return with energy >100eV and the recollision event results in either the emission of X-ray radiation or the scattering of the electrons. The emitted X-rays carry information about the electronic state of the matter and can be used to perform quantum state tomography of the molecules (in a way similar to CAT scans in medicine). The electron scattering arise from the various atoms in the molecule. Due to the wavelike nature of the electron this leads to interference in the distribution of the scattered electrons that carries structural information about the position of the atoms in the molecule analogous to conventional electron diffraction. In both cases the time structure of the event results in attosecond time resolution for the measurement. It has also the potential for single molecule imaging.Our research will examine in detail the DIAA using both experimental and theoretical techniques. Although we believe these ideas can be applied ultimately to large systems, they will first be tested upon small and medium sized molecules where proof of principle experiments are easiest to carry out. Techniques for fixing the molecules in the laboratory frame that are essential to the success of these measurements will be implemented.The project is an interdisciplinary collaboration between physicists and chemists at Imperial College, University College London, The University of Reading, The Open University and the Steacie Institute of the NRC in Ottawa.