We use intense femtosecond laser pulses to excite and probe ultrafast molecular dynamics. By combining ultrafast laser techniques with advanced fast beam imaging techniques we develop time resolved photo-fragment imaging that allows detection of molecular dissociation events on the relevant ultrafast time scales. Of specific interest are dissociation dynamics of superexcited states that exhibit extremely non-Born-Oppenheimer competition between autoionization and fragmentation decay pathways, multiple fragmentation mechanisms and evolution of molecular dynamics with increasing system complexity.
New: "Ultrafast EUV probe" project is aimed at developing a general technique for time resolved visualization of structural dynamics using the emerging technology of high order
harmonic generation (HHG) of ultrafast EUV pulses for single photon coulomb explosion imaging (CEI)
Here are some representative research topics:
Ultrafast EUV probe project (HHG based single photon CEI)
This research is aimed at developing and validating a novel approach for time resolved imaging of structural dynamics, using single photon Coulomb explosion imaging (CEI) with ultrafast extreme UV (EUV) pulses to probe laser initiated ultrafast structural rearrangement and fragmentation dynamics. The emerging field of ultrafast EUV pulses attracts increasing amount of scientific attention, predominantly concentrated on understanding aspects of the generation process itself, as well as on measuring record breaking attosecond pulses at increasingly high photon energies and photon flux. I propose to direct the unique properties of ultrafast EUV pulses towards time resolved studies of molecular reaction dynamics that are inaccessible with conventional ultrafast laser systems. Time resolved single photon CEI will make possible the visualization of complex dynamics in polyatomic systems; specifically, how laser driven electronic excitation couples into nuclear motion in a wide range of molecular systems. In contrast to earlier attempts, in which CEI was driven with intense near-IR pulses that can alter the observed dynamics, the proposed single photon CEI will remove the masking intense field effects and provide a simple and general probe. A comprehensive experimental effort is proposed - to conduct a direct comparison of intense field CEI to the proposed single EUV photon approach. Successful implementation of this research will endow us with a new way to visualize and understand the underlying quantum mechanisms involved in chemical reactions. With this new technology I hope to be able to provide unique insight into molecular fragmentation and rearrangement dynamics during chemical reactions and to resolve long standing basic scientific questions, such as the concerted or sequential nature of double proton transfer in DNA base-pair models. Finally, the "table top" techniques developed in my lab will mature and become applicable to the emerging ultrafast EUV user facilities.
Intense field interaction with molecular and cluster anions:
By combining fast beam 3D coincidence imaging methods with ultrafast intense laser pulses, we can explore the uncharted regime of intense laser field interactions with molecular anions. After a decade of studies directed at intense field interactions with neutral and cationic species, the resulting insights led to an intuitive understanding of highly non-linear processes such as high order harmonic generation (HHG) opening new research avenues on the attosecond time scale. However, intense field interaction with anionic species can be expected to be very different. For example due to the absence of an attractive Coulomb potential following the removal of the first electron, along with the high contrast between the first electron binding energy and the ionization potential energy required to remove additional electrons. Thus, anionic systems may exhibit new mechanisms of intense field interaction with matter. Our preliminary results indicate a highly efficient non-sequential mechanism for double detachment of molecular anions, which does not rely on rescattering dynamics that dominate intense field interaction with neutral species.