I read in one of your interviews that you consider yourself a “natural experimenter”, while others refer to you as a theoretician. Who are you?
I have indeed created models in my career, but I don't consider them to be really defining theoretical works. I have not formulated a fundamental formula such as the Schrödinger equation. I am not good at that, I am good at experimentation. So I consider myself an experimenter.
What experiences made you become a physicist?
I was an average student. I was not bad, but I was not a good student either, I think I was somewhere in the middle. But when my teachers translated real-world phenomena into a kind of abstract world - for example, describing motion in three-dimensional coordinate systems - I was enchanted. Everything to do with length was described by the physics teacher as L, and everything to do with time was T, and so I could tell an equation was wrong if there were different units on the two sides. I, being just an average student, thought, wow, this is really great. I really liked this physics. From then on I wanted to be a physicist. I got my BSc degree from Acadia University in Nova Scotia, Canada, and my MSc and PhD degrees in theoretical physics from Lehigh University in Pennsylvania, USA.
The participants of the LPHYS Conference visited ELI ALPS, where they heard presentations on the latest scientific advances and could learn about research opportunities first-hand during the laboratory visits. Paul Corkum is pictured in the scientific discussion after one of the presentations.
As you mentioned, you did a PhD in theoretical physics and then started working in a plasma physics laboratory. How did you prove your practical skills?
I'm from a remote part of Canada, so when my wife and I moved to the United States, I felt like we were in the centre of the universe, or at least somewhere very close to it. We bought a car, but after a while it started leaking oil and other technical problems. My wife was not very happy as we needed the car every day. I said with the arrogance of youth that okay, I'll fix the Ford Falcon. I got a book on the model. I took the car apart, but I knew I would have to put it back together again, so I had better be careful. I took all the parts into the living room, they were lined up against the wall. I replaced the bad cylinder, the broken piston and put it back together. The car started, worked perfectly. My wife was impressed. When I was interviewed at the National Research Council of Canada and asked what made me think I was qualified to do the experimental work, I said I could take my car apart and put it back together so it worked. I got a postdoctoral position in the experimental plasma physics laboratory.
How you went from plasma physics to attosecond light pulses?
In the plasma physics research group, we naturally worked with plasmas, intense light and similar phenomena. That's where I started thinking about the interaction of laser light and matter. I focused mainly on long-wavelength carbon dioxide lasers. I was looking at how to deal with the matter that interacts with this long-wavelength light. It was already well known at the time how to generate femtosecond pulses and I saw no reason why we couldn't generate attosecond pulses. I was quite excited in those days when I started to understand how this could be done. I was very, very excited because I felt that this could be a defining scientific result. My electron model – Plasma perspective on strong field multiphoton ionization - published in the Physical Review Letter in 1993, laid the foundation for the generation of laser attosecond pulses. It has since turned out that this result is much more important than I thought at the time. It works for transparent solids and even metals. I feel like I've done some exciting things in my career that I'm certainly proud of.
The model of high harmonic generation underlying the production of attosecond pulses was proposed by Paul Corkum in a paper published in 1993. It represents one of the key achievements in the scientific history of ELI ALPS and is commemorated on one of the milestones in the laser timeline on the pavement leading to the institute. During the 33rd Laser Physics Conference (LPHYS), Professor Paul Corkum visited ELI and recalled the outstanding achievements of the institute with Managing Director Gábor Szabó and Science Director Katalin Varjú. They are pictured standing by the milestone commemorating Corkum’s 1993 paper.
In recognition of your achievements, you were awarded the Physical Wolf Prize in 2022, together with Ferenc Krausz and Anne L'Huillier. This year you received the most important award of the American Physical Society. Which one is closer to you?
I am particularly proud of the recognition from the American Physical Society because it says that your work has been highlighted by your physics colleagues who really know what you have achieved. The Wolf Prize is indeed one of the most important prizes in the world, but the committee that awards it is probably not all professionals. Of all the awards I have received, the American Physical Society award is objectively the most important.
One of the highlights of the LPHYS conference in Szeged was the visit to ELI ALPS. Have you visited us before?
This is my second visit to Hungary but my first to Szeged. Of course I knew about ELI ALPS. I also knew Gérard Mourou, who pushed for the construction of the ELI institutes. Every single piece of equipment, every single laboratory at ELI ALPS is at the cutting edge of technology. I was very impressed. More than I expected. I've seen many ultrafast lasers, I've used a few myself, but I was impressed by the scale of ELI.
Are you in contact with Hungarian researchers?
In 1993 I was invited to spend a month in Vienna. There I met the young postdoctoral fellow Ferenc Krausz. I was very impressed by that meeting. That was the beginning of our relationship. From then on, every five to ten years we write a joint publication and then continue our own work. Then we meet again, which resulted in another publication. I follow his work, I consider him one of the friends that science has introduced me to. Peter Dombi worked with Ferenc Krausz and then came to Ottawa. I know him relatively well, because when someone works in your lab, you learn a lot about them. Of course, I also know several researchers at ELI ALPS, I met them at conferences.
What is your advice for students and early-career physicists?
It's a difficult question because you don't really want to give advice, because if a young scientist wants to do something really important, they shouldn't follow any advice. They should just go with their instincts.
On this subject, the Nobel Prize-winning American physicist Charles Townes told the following story. As a young researcher, he felt that his colleagues thought he was ruining his career by working on this crazy laser idea. So many people are working on something that won't work anyway. Townes created the device called the MASER in 1954. Six years later, the idea was improved by amplifying a beam of optical light instead of microwave energy. Bell Laboratories patented the new invention as a laser. Did it ruin Townes' career? Not a chance! This brilliant physicist followed his instincts. I advise young people to do the same. If you think you know a good way, try it. Don't spend a lot of time doing what someone else has done. Find a problem you can solve that no one else has solved. Then be bloody-minded. Forget about others who won't necessarily agree with you.
What did I do? I trusted myself and then came up with the idea of how to create attosecond pulses. In some ways it was a revolutionary approach. I felt that I was right and the world was wrong. I was confident in myself and in solving a problem that no one had ever solved before and that I considered important.
What has science given you?
Looking back, I cannot be dissatisfied, because I have had a wonderful journey. I have experienced how fantastic a career in research is. I have colleagues all over the world who are also my friends. Colleagues and friends in Canada, the United States, Russia, China, Europe, all kinds of places. I think it's a privileged connection to the world. I like going to conferences, meeting new people because they become my friends. They share my interest in technology and science. They share with me the same way you share with your neighbour an interest in flowers. I think science offers a wonderful life.
Biography:
Paul Corkum (1943) is a Canadian physicist and internationally renowned figure in attosecond physics and laser science. In the 1980s, he developed a model for the ionisation of atoms (i.e. the production of plasma) and, based on this model, proposed a new approach to the production of X-ray lasers, called optical field ionisation (OFI). Today, OFI lasers are one of the most important developments in X-ray laser research. His electron model laid the foundations for the generation of attosecond pulses in lasers. Using this method, Corkum and his colleagues in Vienna, including Ferenc Krausz, were the first to demonstrate laser pulses of less than 1 femtosecond duration in 2001.
He received the Wolf Prize for Physics in 2022 and the American Physical Society (APS) Medal for Exceptional Achievement in Research in 2025.
Cover image: Paul Corkum visited the laser and attosecond laboratories at ELI ALPS to see our state-of-the-art equipment. After the laboratory tours, he commended the high quality of the research infrastructure, the equipment, the technical parameters of the sources and the expertise of our colleagues. In this photo, he is asking about the technical challenges that emerged during the development of the lasers in the HR laser laboratory.
Photos: Gábor Balázs