Lars Bojer Madsen: strong-field and attosecond physics

By Thomas Farrell on September 18, 2015

Professor Lars Bojer Madsen works in the theoretical Atomic, Molecular and Optical Physics group at Aarhus University in Denmark. His research focusses on strong-field and attosecond physics. We talk to him about where attosecond physics might go in the future, who inspired him to become a scientist and why some of the hottest topics in AMO physics are actually the coldest.

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

Our research is in theoretical strong-field and attosecond physics. The research is driven by experimental progress. The current development of new light sources makes it possible to investigate electron and nuclear motion in atoms and molecules at an unprecedented time scale – the scale of attoseconds (1 as = 10^-18s). With these developments, researchers can now study some of the most fundamental aspects of basic natural science, such as chemical bond formation and charge migration, in real time! However, the theory that adequately describes such dynamics, even in a much, much simpler setting, is lacking. In particular the correlation between charged particles has to be more accurately accounted for. The development of such a theory is what we are working on.

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

To fully exploit the promises held by the new ultrashort and ultrastrong light sources, experiments have to be accompanied by accurate theory for interpretation and understanding. This theory will help us to elucidate how electrons and nuclei move in atoms and molecules – the building blocks of nature. We have a chance to gain new insights that are fundamental and could pave the way for new scientific and technological breakthroughs.

At a more practical and day-to-day level, this research field allows one to work with both analytical and numerical approaches, a possiblity I find attractive.

Q: Where do you think the field is heading?

The production of attosecond pulses is based on the interaction between matter and intense laser pulses, so one can consider attosecond physics as a spin-off from strong-field physics. We have had attosecond pulses for a little more than a decade, so the field is maturing. A number of measurement techniques have been established and have been accompanied by theoretical modelling for relatively simple atomic systems that could often be reasonably accurately described by an effective theory involving only a single electron. The next new challenge is to extend the attosecond physics schemes to larger molecules and condensed matter systems, a process that has recently started.

Calculated angle-dependent ionization rate for C2H4

Calculated angle-dependent ionization rate for C₂H₄, from C Wang et al 2012 J. Phys. B: At. Mol. Opt. Phys. 45 131001

Q: What do you consider to be the hot topics in AMO physics at the moment?

I see AMO physics as driven mainly by experimental progress. As I mentioned previously, I am fascinated by the progress in light source technology in my own field of research. I would also like to point to the impressive progress in cooling and trapping techniques that have allowed us to reach exceedingly low temperatures, i.e. the field of cold atoms and molecules.

Q: Who inspired you to become a scientist?

My interest in science started in high school. I was fascinated by the fragments of quantum theory that we were taught. I remember Bohr’s theory with its completely new quantum ideas striking me as truly extraordinary – mind-blowing – so being a Dane and working with physics, I would point to Niels Bohr.

Q: What would you say to a student who wanted to shape their future with a career in science?

Be focused, and persistent. Feel whether you have the drive and dedication. The largest ‘kicks’ you will get if you have worked hard and succeed.

On behalf of JPhysB I would like to thank Professor Madsen for talking to us and for supporting the journal. You can read some of his recent publications in JPhysB here: