He is recognized for “pioneering the development of atomic and molecular spectroscopies with third- and fourth-generation light sources including such new effects as higher multipole asymmetries, double -shell photoionization, and femtosecond electronic response of atoms to ultra-intense x-rays.”
Southworth is the leader of the Atomic, Molecular, and Optical Physics Group in the Argonne X-ray Science Division at the Advanced Photon Source (APS). His work has had a major impact on the field of atomic and molecular physics.
In synchrotron-based work, he did innovative experiments on the anisotropy of polarized x-ray emission from molecules, where distinctly different angular distributions were obtained for x-ray emission involving molecular orbitals of different symmetry. He also performed seminal experiments on double K-shell photoionization of atoms and non-dipole asymmetries in photoelectron angular distributions.
In recent work, x rays are being used to explore atoms and molecules that are excited, aligned or ionized by optical lasers. Two particularly challenging experiments included the development of an x-ray microprobe at the APS, and the observation of ultra-fast laser induced x-ray transparency at the Advanced Light Source at Lawrence Berkeley Laboratory.
Southworth was also a key player in the first experiments at the Linac Coherent Light Source, which studied femtosecond electronic response of atoms to ultra-intense x-rays. In this experiment, fully stripped neon was obtained in the course of a single femtosecond x-ray pulse, creating a condition of x-ray transparency induced by the intense pulse of x-rays.
Southworth emphasizes the importance of teamwork and is grateful to have worked with excellent collaborators on every project.
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