Alfred Mueller on atomic physics

We talk to Professor Dr Alfred Mueller from the Institut für Atom- und Molekülphysik at Justus Liebig University Giessen about his work on the interactions of atoms, molecules, ions and electrons, as well as his interests outside of physics.

Q: Which research projects are you and your group currently working on?

My collaborators and I are working on a variety of atomic and molecular physics problems which include the properties and structure of atomic size particles and their behaviour in collisions. We want to obtain fundamental knowledge about the sub-nanoscopic structure of matter that surrounds us and we want to contribute to the scientific and technical development in other fields of science such as controlled nuclear fusion, astrophysics and plasma applications in general. We investigate, in particular, the interactions of electrons and energetic photons with ionized atoms and molecules. Our objects of interest range from few-electron atomic ions such as N5+ or even U91+ to electrically charged endohedral fullerenes such as Xe@C60+, i.e., large carbon-cage molecules, in this case the miniature soccer-ball C60, encapsulating and thus isolating a single xenon atom. In our research we have repeatedly discovered new physical processes, unexpected atomic properties and collisional phenomena whose general importance had previously not been recognized. Our work often relates to the boundaries between atomic and nuclear physics.

Q: What motivated you to pursue this field of research?

The starting point of this research was the preparation of special beams of particles for nuclear research: polarized nuclei as a probe for spin effects in nuclear collisions and multi-charged ions for efficient acceleration of projectiles to high energies. While being motivated by grand fundamental questions of nuclear science these preparatory developments required detailed knowledge of atomic physics and provided increasing insight into the equally grand issues related to the intricate properties of atoms and ions and their interactions among one another and with electrons and photons. Understanding the properties of atomic particles and their physics is the basis for understanding the many-body nature and complexity of the world that surrounds us.

Many of the experiments that I conducted were possible in a laboratory-size environment where one experimenter can control and optimize the whole experiment. I found this more attractive and more rewarding than working at large-scale facilities where the success of an experiment depends on many external factors. However, advances in science usually require advances in technology. Making use of new developments at ion accelerator laboratories and synchrotron radiation light sources has been key in my career to obtain many exciting new results.

Q: Where do you think the field is heading?

New experimental techniques and facilities as well as newly emerging applications are offering great opportunities and perspectives for the field of atomic interactions. The introduction of heavy-ion storage rings and the cooling of ion beams with electrons have facilitated big steps in my field of interest. Now, combinations of several storage rings with advanced ion-preparation possibilities can be expected to open new avenues for fundamental and applied research in atomic physics. The rapid development of high-intensity high-quality photon beams in the UV to x-ray regime has had tremendous impact on the field of photon-matter and, in particular, photon-atom interactions and this development still has a steep gradient.

Q: What current problem facing humanity would you like science to provide a solution to?

The energy problem and the obvious threat of global warming are among the most urgent issues of mankind. I would be glad if controlled nuclear fusion could provide a timely, partial solution to these problems. Fusion science is a field where many fundamental physics issues are being addressed and it is a motor of technical developments. Atomic and molecular physics and particularly atomic collisions and spectroscopy provide important ingredients for reliable plasma modeling and for the understanding of the inner workings in a fusion reactor.

Q: What interests you outside of science?

My wife and I keep horses. We like horse-back riding and we enjoy carriage rides to the fields and forests around our home town. We often take along guests, friends and family, on our carriage and share the pleasure of slow-pace traveling with two horse powers. Usually a picnic at a forest edge rounds off the trip.

Over the years we have explored even the remotest corners of the American West in numerous tent-camping and hiking trips with our family and friends. The fascination started when I saw a movie about the Panamerican Highway as a boy in the late 1950s.

Q: What has been the most exciting development in physics during the course of your career?

The understanding of how the universe is developing has made huge progress during my life as a physicist. The discovery of the cosmic microwave background by Penzias and Wilson while I was a student and the subsequent further investigations with the observation of accelerated expansion have been most exciting scientific developments.  The fact that the understanding of atomic physics is essential for interpreting astrophysical observations makes me proud of my field of research.


On behalf of JPhysB I would like to thank Professor Dr Mueller for answering our questions and for recently publishing “Single-photon single ionization of W+ ions: experiment and theory” in our journal.

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Image 1: copyright Alfred Mueller; used with permission.

Categories: Journal of Physics B: Atomic, Molecular and Optical Physics

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