2008 Moseley medal and prize

Professor Helen Fielding

University College London

For her unique work on the coherent control of electronic and molecular dynamics using ultra-fast lasers. This research is significant for quantum-information studies as well as the possible laser control of chemical reactions.

The Moseley medal and prize for distinguished research in experimental physics has been awarded to Professor Helen Fielding, Professor of Chemical Physics at University College London,for her unique work on the coherent control of electronic and molecular dynamics using ultra-fast lasers. This research is significant for quantum-information studies as well as the possible laser control of chemical reactions.

Professor Fielding has carved out an international reputation in chemical physics in carrying out experiments that are highly original and difficult to perform. She probes molecules that are in a highly excited, so-called Rydberg state in which very distant electrons ‘orbit’ around the remaining positively charged atomic or molecular-ion core. She exploits the coherence of laser light to control the phase of the Rydberg electron wave-packets as they circulate a molecular core, by using sequences of phase-locked or phase-shaped laser pulses. This is a new field pioneered by Fielding, and is of great interest, offering a route to manipulate molecular dynamics at the quantum level.

A recent experiment has demonstrated the control of the dissociation/ionisation ratio in a highly excited nitric oxide molecule, where a returning electron wave-packet re-collides with the molecular core. In so doing, it can transfer electronic energy to vibrational energy, and the molecule can dissociate into neutral nitrogen and oxygen atoms. Alternatively, the electron can escape, leaving behind a positive nitric oxide ion. Control of the optical phase provides a means of manipulating the interferences between the different pathways, so that the branching between them can be experimentally controlled.

Fielding’s current research interests include extending these techniques into the attosecond regime, to monitor or manipulate the motion of individual electrons in less esoteric excited-state systems with a range of potential applications.