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Physical Sciences and Engineering

Atomic, Molecular and Optical Physics

AMO
The atomic, molecular and optical (AMO) physics group explores the frontiers of X-ray science and lays the foundation of X-ray applications in other scientific domains.

X-ray phenomena at the high intensity frontier

Transient resonances modify ultrafast single-shot imaging of nanoclusters [P. J. Ho et. al., Nat. Commun. 11, 167 (2020)].

Understanding ultraintense X-ray interactions with matter is a new frontier with the advent of X-ray free electron lasers (XFELs), which provide femtosecond X-ray pulses of peak brightness a billion-fold greater than those available from synchrotrons.   We explore this frontier with a concerted experimental and theoretical approach, investigating new nonlinear X-ray phenomena and imaging modalities.  We use forefront tools, namely worldwide X-ray free electron lasers and high performance computers.

Ultrafast X-ray induced phenomena

X-ray pump/X-ray probe study of inner-shell electron and energy transfer in molecules [A. Picon, et. al., Nat. Commun. 7, 11652 (2016)].

Understanding X-ray initiated processes in complex environments is a grand challenge problem with broad implications for radiation chemistry, physics and biology. High-brightness tunable ultrafast X-ray pulses, as will be available with next generation X-ray free electron lasers, will be able to track both inner- and outer-shell electronic motion on their natural timescales with chemical site specificity.  We tackle this challenge with a combination of static and time-resolved pump-probe X-ray methods with a focus on prompt probes (photoelectron spectroscopy and transient absorption) to isolate motion prior to inner-shell decay.

X-ray probes of condensed phase photoinduced processes

X-rays capture the birth of free radicals in liquid water and reveal a unique signature for the transient hydroxyl radical [Z.-H. Loh et al., Science 367, 179 (2020), L. Kjellsson et al. Phys. Rev. Lett. 124, 236001 (2020).]

We focus on understanding the fundamentals of laser-induced phenomena in solution, from the first steps following photoabsorption, with changes in the electronic configuration occurring on the femtosecond time scale, to subsequent processes involved in the evolution of the excited states on the picosecond to microsecond timescales. X-ray spectroscopic probes are used both at synchrotrons and XFELs to track these electronic and structural changes. We are especially interested in understanding the influence of the solvent on the reactivity and on influencing the outcome of photoreactions using shaped laser pulses and X-ray feedback.

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