Colloquium with **Dr. Kathryn Hamilton, Postdoc at Drake University**

**R-Matrix calculations for ultrafast spectroscopy of noble-gas atoms**

R-matrix methods have achieved much success in the areas of time-dependent and time-independent computational atomic physics [1]. Originally developed to describe nuclear resonances, R-matrix theory has been extensively applied to the treatment of atomic and molecular physics problems since the late 1960s. One of the more recently developed R-matrix approaches, and the focus of this colloquium, is the R-matrix with time-dependence (RMT) method [2].

RMT solves the time-dependent Schrödinger equation for general, multielectron targets interacting with laser light. The code has been significantly updated since its first release in 2011, with extensions to describe the dynamics in arbitrarily polarized light fields [3], time-dependent processes in molecules [4], and to account for relativistic effects [5]. However, RMT truly distinguishes itself from competing approaches in its ability to describe the behavior of complex systems, such as irradiated noble-gas atoms beyond helium, where single-active electron approaches quickly run into their limits.

In this colloquium, I will first describe recent progress on extracting photoionization delays in argon using a variant of the RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) technique. Results from RMT calculations are compared against experimental data acquired at the Max-Planck Institute for Nuclear Physics, Heidelberg, with the goal of extracting continuum-continuum delays in a multi-sideband RABBITT scheme [6]. A variant of the method (uRABBITT) will also be discussed in connection with an experiment performed at the University of Freiburg for a neon target. Next, results highlighting the opportunity to both observe and control multielectron effects in argon using an XUV-initiated high-harmonic generation (XIHHG) scheme will be presented. Finally, I will comment on planned future extensions of the RMT code, including an interface with the B-Spline atomic R-Matrix (BSR) code [7] developed by the late Oleg Zatsarinny, and the operation of both codes via the Atomic, Molecular, and Optical Sciences (AMOS) Gateway [8].

**Dial-In Information**

Zoom https://bit.ly/3LVp4o3

Meeting ID: 999 1285 9775

Passcode: 174454

Tuesday, March 22, 2022 at 3:30pm to 4:30pm

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