Keynote
André D. Bandrauk
Département de Chimie, Faculté de Sciences, Université de Sherbrooke, Sherbrooke (Québec), Canada
Circularly Polarized Molecular High Order Harmonics – Generation and Applications in Attosecond Science
Abstract: MHOHG, Molecular high order harmonic generation is a highly nonlinear nonperturbative response of molecules to ultrashort (fs=10-15 s) intense (I>1014 W/cm2) laser pulses leading to multiphoton ionisation and laser induced electron recollisions in linear polarisation. MHOHG is suppressed with intense single circularly polarized pulses but has been shown in 1995 to be generated with co- or counter-rotating pairs of bichromatic (ω1/ω2=n1/n2) circularly polarised pulses [1-2] leading to the generation of circularly polarised attosecond (10-18 s) pulses [3], the time scale of electron motion in atoms and molecules. Parallel computer simulations of electron TDSE,s, Time Dependent Schrödinger Equations coupled with photon Maxwell,s equations show that molecules are the ideal systems for circular polarised harmonic and attosecond pulse generation due to lower rotational symmetries than atoms. The TDSE simulations confirm the electron-parent ion recollision mechanism in the presence of bichromatic circular pulses and maximum circular polarised MHOHG efficiency is obtained when the net time dependent electric field of the combined pulses is compatible with molecular symmetry. The resulting circularly polarised attosecond pulses are shown to generate in molecules coherent attosecond quantum electron currents from which one can create intense attosecond magnetic field pulses for studying ultrafast magneto-optics [4] and dynamical symmetry in molecules [5].
[1] T Zuo, A D Bandrauk, J Nonlinear Opt Phys Mater 04, 533 (1995)
[2] S Long, W Becker, J K McIver, Phys Rev A 52, 2262 (1995)
[3] K J Yuan, A D Bandrauk, Phys Rev Lett 110, 023003 (2013)
[4] A D Bandrauk, J Guo, K J Yuan, J Opt 19, 124016 (2017)
[5] K J Yuan, A D Bandrauk, Phys Rev A 97, 023408 (2018)
Bio: B.Sc. (Hon. Chem.) from l’Université de Montréal, M.Sc. in theoretical chemistry from M.I.T. and Ph.D. in Chemical Physics from McMaster University (Hamilton, Canada), NATO Fellow at Oxford University’s Mathematical Institute (1968-70), assistant at the Technische Hochschule Munchen (1970) before being appointed as an assistant professor of theoretical chemistry at l’Université de Sherbrooke. He has been an invited researcher and lecturer at prestigious institutions: International Collaborator, Los Alamos Natl. Lab., USA (1984); Senior Visiting Scientist, NRC-Ottawa (1985); Foreign Lecturer, Institute of Chem. Phys., Moscow, USSR (1985); C.A. McDowell Lecturer, University of British Columbia, Vancouver (1990); Foreign Professor, Institute for Molecular Science, Okazaki, Japan (1992); Japan Society for Promotion of Science Lecturer, (Tohoku Univ.-1997); Visiting Professor, Université de Paris Sud (Orsay), (1998); Invited speaker, Harvard University (2008, 2005, 2002, 1995, 1993), M.I.T. (2000, 2018). In 1982, awarded a Killam Research Fellowship by the Canada Council, was elected as a Fellow to the Royal Society of Canada in 1992. In 1989 received the Herzberg prize from the Canadian Spectroscopy Society, awarded the prestigious John Polanyi (Nobel Prize 1986) Awardby the Chemical Society of Canada in 2001, became director of the Center for parallel computing and IBM Center of Excellence at l’Université de Sherbrooke and is member of the new National Center of Excellence in Photonics. He is appointed a Canada Research Chairin Computational Chemistry & Molecular Photonics from 2002 to 2016 and a new Fellow of the American Association for the Advancement of Science, AAAS (2003). He became Chair of the Department of Chemistry in 2005 and in 2007 received a Prize from the Humboldt Foundation (Berlin, Germany). He was awarded the NSERC – J. C. Polanyi Prize for Attosecond Science (with P. B. Corkum, NRC) in 2008. He has also been elected Fellow of the American Physical Society (FAPS). In 2009 he is elected Fellow of SIAM (Society for Industrial and Applied Mathematics, USA). The 8th International Symposium on Ultrafast Intense Laser Science (ISUILS8) was held in his honour in 2009. In 2010 he receives the Prix du Québec. The Governor General of Canada appoints him in 2012 as an Officer of the Order of Canada for pioneering work in Attosecond Chemistry. The MUST (Molecular Ultrafast Science Technology) program of ETH-Zurich has invited him to deliver the FAST (Femto-AttoSecond Science-Technology) Fellow lectures in 2014. The Wuhan Institute of Physics and Mathematics of the Chinese Academy of Sciences nominates A.D. Bandrauk to the Wang T.C. Lecture Professorship in 2017.
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Invited
Simon Neville
Research Computing Specialist at the National Research Council Canada, Ottawa, Canada
Using electronic coherences to probe excited state molecular dynamics: a user guide
Abstract: Understanding the fate of molecules following photo-excitation is of central importance in many areas, including studies of vision, photosynthesis, and light harvesting systems. Ultrafast electronic relaxation driven by strong non-adiabatic interactions of the nuclear and electronic degrees of freedom are key to understanding these processes, and constitutes an area of intense and continued study.
Experimentally, such ultrafast internal conversion processes can be probed using femtosecond pump-probe spectroscopies. The choice of probe here is key to being able to disentangle the vibronic dynamics initiated by the pump pulse. Traditionally, spectroscopic probes sensitive to electronic state populationshave enjoyed great success. Recently, however, there has been great interest in using probes which are instead sensitive to the electronic coherencesthat may form as a result of non-adiabatic coupling of the initially excited state to its complement. The aim of this talk is to explore whether electronic coherences are a general descriptor of excited state dynamics, and to highlight the situations in which they are likely to be of use.
Using simple symmetry arguments, we show that large amplitude electronic coherences are, in fact, not guaranteed to form during the course of excited state dynamics. In particular, this will occur when the electronic states involved possess different point group symmetries at the Franck-Condon point. Furthermore, we explore the role of conical intersection topography and the nuclear coordinate dependence of transition dipole moments, with both being found to play important roles in governing the magnitude of the coherence that can form.
The upshot of these results is that spectroscopies sensitive to electronic coherences are not general probes of excited state molecular dynamics, and will only be of use for a subset of systems, which may be identified using a simple set of rules.
Bio: Simon Neville is a Research Computing Specialist at the National Research Council Canada, Ottawa, with an interest in the theory and simulation of non-adiabatic excited-state dynamics and ultrafast pump-probe spectroscopies. Prior to this appointment, he was a postdoctoral research fellow at the University of Ottawa working in the groups of Michael Schuurman and Albert Stolow, and obtained his PhD in the group of Graham Worth at the University of Birmingham.
