Control of Electrons by Few-Cycle Intense Laser Pulses

Lead Research Organisation: Imperial College London
Department Name: Physics


Intense, phase-stabilised, femtosecond laser pulses comprising only a few optical cycles ( few-cycle pulses) offer a unique new tool for the manipulation of electrons in matter The strong oscillating electric field of the pulse moves valence electrons in quasi-classical trajectories, but the interaction on the sub optical-cycle timescale is too brief for nuclear motion to occur. Thus the motion of the electrons in small quantum systems (e.g. atoms, molecules, clusters, surfaces, nanosystems) can be controlled whilst the nuclei are fixed in position. This proposal outlines an in-depth programme of research in this rapidly emerging area.The breakthrough of intense carrier envelope phase-stabilised (CEP stabilised), few-cycle pulses provides precisely defined strong electric field optical waveforms. These fully controlled few-cycle pulses permit, for the first time, the control of strongly driven electron motion down to the quantum limit with sub-optical period (< 1 fs) temporal resolution and near atomic scale (~10^-10m) spatial resolution. It is now possible to implement a new type of coherent control of strong field electron processes that are inherently sensitive to the CEP. It is important to stress that it is the electric field waveform, rather than the pulse intensity envelope , that is harnessed to control the system. Control of electrons is provided by these fields at the natural spatial and temporal scales relevant to electronic states in matter (i.e. < 10^-10m and < 10^-15s) - this opens up exciting new possibilities in quantum control. The control we will exercise isolates electron motion from the ion (nuclear) motion, the latter being effectively frozen on the timescale of the pulse duration. Thus the control of quasi-classical electron states within otherwise unaltered material will be feasible.This proposal concerns the development of these new optical techniques and their application to the investigation and control of electron processes in matter. The timeliness of this proposal is underlined by the growing interest in this field internationally with major efforts starting up, for instance in Sweden (Lund), France (Saclay), USA (Boulder, Berkeley, Ohio) and most notably in Germany (MPG-MPQ, Garching). The motivation for all these projects is the prospect of achieving the highest degree of quantum control in matter that can lead to new breakthroughs in chemical, material and optical sciences. Our project objectives include demonstration of selective bond cleaving via controlled electron recollision, optimisation of brightness and minimisation of pulse duration in coherent XUV and incoherent hard X-ray light sources, creation of spin entangled electronic states via ionisation of two-electron systems and development of compact detectors for laser phase.


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Description New understanding of how multiple colour fields can be used to control strong laser fielod processes like HHG were obtained. In particular we demonstrated theoretically and experimentally the improvements to harmonic spectral range and efficiency of using a multi-colour field. Further we demonstrated how the quantum trajectory is controlled in a 2-colour field (omega/2omega).

Other important outcomes were in generation of few cycle pulses and in HHG spectroscopy for making sub-cycle measurements of molecular cation dynamics.
Exploitation Route Potential that techniques may be used in bioimaging or in energy research. Publication via usual journals and presentation at conferences, but no immediate non-academic impacts were found.
Sectors Chemicals


Pharmaceuticals and Medical Biotechnology

Description This research has led to widely cited results.