Andrew Brown

Dr

  • Room 01.005 - Old Physics

    United Kingdom

20122020

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Recent advances in laser technology have facilitated the experimental analysis of atomic structure and electron dynamics in undprecedented detail. The process of harmonic generation in particular has been central to these advances both as a basis for ultrashort and high-energy laser pulses and as a tool for elucidating ultrafast dynamics. Typically, now, we are interested in dynamics which occur on the attosecond scale (1 as = 10-18 s), which is the fundamental time scale of electronic motion in the atom.

Theoretical methods capable of describing attosecond scale electronic motion typically adopt a classical approach where an electron is driven by a laser field in the net potential of the residual ion. However, methods pioneered at QUB allow us to address the interaction of all the electrons in an atomic system. It is these multielectron interactions which mediate ultrafast dynamics and thus it is imperative to address them accurately.

Time-dependent R-matrix (TDRM) theory, and the associated TDRM and RMT (R-matrix incorporating time dependence) codes, are among the only methods in the world capable of describing multielectron and multichannel effects in ultrafast laser atom interactions. For my PhD thesis I used the TDRM method to address harmonic generation-- the production of high frequency laser light via stimulated subcycle electron motion-- and uncovered a series of multielectron aspects to the process. For instance, interference bewteen electrons competing in the harmonic generation process can lead to an increase in the harmonic yield at particular frequencies.

I have since extended these studies of ultrafast processes to experimentally relevant (mid-IR) wavelengths. Now my research focuses on extracting experimental observables from the detailed ab-initio calculations performed with RMT. To this end I have investigated several cutting-edge experimental schemes using the RMT approach, including attosecond transient absorption spectroscopy, strong-field rescattering and, most recently, XUV initiated high harmonic generation.

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