I have covered the 2023 Physics Nobel earlier on this blog. Several platforms since then have pointed out the omission of Paul Corkum from the list of awardees. Corkum pioneered the 'recollision' model which subsequently served as the foundation for attoscience.
In fact Corkum, L'Huillier and Krausz were awarded the 2022 Wolf Prize - considered to be the second most prestigious prize in science (awarded to Koshiba for his work on neutrinos, for example, as I have mentioned in an earlier post) - for their pioneering work in attoscience.
I became aware of the commentary regarding Corkum's omission especially when I came across it in Michal Lipson's editorial in this November's Optics and Photonics News.
In this post I will discuss the formal (apparent) reason for the Nobel committee ignoring Corkum's work, his contribution, as well as an interesting story about him putting together a Mustang engine, that played a role in his career, and has become legendary.
Why no Nobel for Corkum?
The formal citation for the prize says the prize recognizes advances in experimental methods for generating attosecond light. Corkum's contribution was theoretical.
Before we move on, it might be worthwhile to point out the experimental contributions of the winners. Anne L'Huillier produced harmonics of light by shining infrared beams into a noble gas (1987); Agostini and Krausz (both in 2001) produced pulses that were hundreds of attoseconds long.
Paul Corkum: A brief Scientific History
Corkum originally trained as a theoretical plasma physicist. Plasma is a state of matter whose constituents carry electrical charge (the two types of charge, positive and negative, can exist separately in the same sample, which can therefore have overall electrical neutrality). The Sun is made of a plasma.
A plasma can be created on earth by starting with a gas of neutral atoms and then somehow removing the electrons from the atoms, leaving them positively charged. In previous posts, for example, I have discussed plasma discharge tubes, where the atomic electrons are ripped off by collisions with free electrons from an electric current produced in the atomic gas.
Notwithstanding his theoretical background, Corkum managed to get hired as a laser experimentalist at the National Research Council in Ottawa, Canada, by informing the employers that he could take apart and reassemble a car engine, and have it work right away after that (around 1973). Once he got the job, he began performing experiments on laser light interacting with matter.
Sometimes the light was energetic (or intense) enough to remove electrons from the matter ('multiphoton ionization' in the jargon) - see the connection with plasma physics? - and also cause the generation of high harmonics (see the connection with attophysics?) which had been observed earlier by L'Huillier and others.
Corkum's contribution
In 1993, Corkum wrote a seminal paper "Plasma Perspective on Strong Field Multiphoton Ionization", which clarified the basis of attosecond physics and set a whole field in motion (the paper has 8710 citations as of today - for a poor comparison, my highest cited paper has 200).
The basic idea of Corkum's paper was simple: in most cases, when photons try to rip an electron away from an atom, the electron does not get away from the remaining positive ion at once. It comes back a few times, essentially because the electric field of the light oscillates in time and exerts an oscillating force on the electron.
The electron typically returns with high velocity (accelerated by the light) and this 'smashing back into the ion' provides the energy for high harmonic generation and creates flashes of light - attosecond pulses!
You can see Corkum explain the physics with the analogy of seaweed and a rock here. The model presented in his paper put the field on a strong theoretical as well as intuitive basis and a lot of scientists were able to make many exciting advances based on this work. I should emphasize this is not the only contribution that Corkum has made to the field - there are many (his h-index is 119). But this is probably the most Nobel-worthy.
Conclusions
While it is too bad that Corkum's contribution was not recognized with a Nobel, eventually science is about the joy of discovery (which his talks definitely reflect), and finding things that are useful (in this case there are applications to, e.g. solid state electronics, chemistry and medicine).
In this story, however, there are a couple of twists worth thinking about: I wonder if this discovery would have happened if i) Corkum had not originally been a theorist and ii) if he had not been trained in plasma physics (the importance of which is conveyed by the title of his paper).
I think the moral is that there is much to be found by bringing disciplines together.
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