Our group uses femtosecond (10-15s) and attosecond (1018 s) laser technology to initiate and observe some of the fastest processes in nature. By studying DNA, amino acids, and other organic molecules we can study how these key building blocks of life respond to light at the molecular level. Ultrafast structural changes or charge transfer in these systems initiate processes in vision, photosynthesis, DNA damage, and molecular motors.
One of the research areas involves pump-probe studies of a range of molecular species, where an initial femtosecond/attosecond pulse (pump) excites or ionises a molecule setting electrons and the nuclei in motion. At a controlled delay later, another short (probe) pulse is used to observe a property of the molecule at that instant in time. By repeating this experiment with different delays, a “movie” of the molecular motion can be retrieved. With this technique we have observed how DNA molecules dissipate ultraviolet radiation in DNA, how charge oscillates coherently following exposure to ionizing radiation, and de-excitation of the pigment molecules such as the green fluorescent protein.
An emerging research area for the group, is using these laser pulses to detect the handedness of chiral molecules by studying the angular emission of electrons emitted from irradiation of the molecule by a circularly polarised laser pulse. A molecule is chiral if its mirror image cannot be superimposed on the original. Amino acids and sugars (and hence proteins and DNA) in natural systems are chiral but possess only one of these forms. As a result chirality is a key property in the development of pharmaceutical drugs. We are currently developing an apparatus which can identify what form the chiral molecule takes, but also to use this chiral observable as a way of sensitively tracking ultrafast changes in these molecules. This work is current funded by the Royal Society’s Paul Instrument Fund.
KEY RECENT PUBLICATIONS:
F. Calegari, D. Ayuso, A. Trabattoni, L. Belshaw, S. De Camillis, S. Anumula, F. Frassetto, L. Poletto, A. Palacios, P. Decleva, J. B. Greenwood, F. Martín, M. Nisoli, Ultrafast Electron Dynamics in Phenylalanine Initiated by Attosecond Pulses, Science, 346, 336 (2014)
S. De Camillis, J. Miles, G. Alexander, O. Ghafur, I. D. Williams, D.Townsend, J. B. Greenwood , Ultrafast Non-Radiative Decay of Gas-Phase Nucleosides, PCCP, 17, 23643 (2015)
A. Comby, E. Bloch, C. M. M. Bond, D. Descamps, J. Miles, S. Petit, S. Rozen, J. B. Greenwood, V. Blanchet & Y. Mairesse, Real-time determination of enantiomeric and isomeric content using photoelectron elliptical dichroism, Nature Comm., 9, 5212 (2018)
For more information, go to www.ultrafastbelfast.com