Did your parents encourage you to pursue a career in physics, or was it your own decision?
My father is an electrical engineer, and my mother is a process engineer. Even as a very young child, I wanted to be an electrical engineer. In my first year at secondary school, my father told me that, at my age, he had built a radio. I thought to myself: I haven’t built one yet, so it’s too late for me to embark on that career path now. In the end, I decided to focus on physics.
Our physics teacher, Csaba Tóth, who was just starting his career at the time, was very enthusiastic; he regularly ran a physics club where we conducted experiments and worked on challenging problems. He captivated many of us in the class, but I was the only one to go on to become a physicist. Szeged was among the universities I considered, but eventually I applied to Eötvös Loránd University (ELTE), where I graduated in 1997.
What did the university give you?
The strong emphasis on theory taught me that if you want to understand phenomena, you need to be familiar with the theoretical background. In my second year, I spent a month and a half in Vienna, where I was able to observe matter at the atomic scale using an atomic force microscope. My Austrian colleagues tried to persuade me to stay, but I felt that the world of optics and lasers interested me more, and this was something I could explore in depth in Budapest as well.
As a fifth-year student, I was looking for a research group with a strong focus on optics and laser physics. I spent a semester in Jena on a Tempus scholarship. I was fascinated by the fact that they had a high-power laser. A few weeks later, my professor offered me the opportunity to continue my research there as a PhD student. I hesitated for a long time, but in the end, I chose Jena. At home I would have been able to construct a laser, whilst there I could already be conducting experiments with a high-power laser.
How did you end up in Vienna?
After completing my PhD, I got in touch with Ferenc Krausz, who was working at the Vienna University of Technology, and he invited me to join his group. Shortly afterwards, he took up the post of Director of the Max Planck Institute for Quantum Optics in Garching, Germany, and I soon followed him. We worked together from 2004 to 2016.
In Vienna, we tried to accelerate and observe electrons using relatively low-energy lasers. We did not make much progress; eventually it became clear that energy in the millijoule range was nowhere near enough for these experiments. In Garching, we went on to build short-pulse, high-energy lasers.
You moved to Umeå in 2016. Why did you choose Sweden rather than ELI ALPS, which opened a year later?
I had already been involved with ELI previously. For example, I took part in drafting the so-called ELI White Book – a comprehensive strategic and scientific framework document often referred to as the cornerstone of the ELI project. In 2013, I applied for a post in Szeged, but that did not work out at the time. Meanwhile, my desire to lead my own research group grew stronger, and the Swedish university made my dream come true by offering me a professorship.
Why is the development of large laser systems progressing so slowly?
With a system like this, it is not enough that the laser itself is working. For the experiments to succeed, many other components must all be functioning flawlessly at the same time. Many problems only come to light during use. When they do, we must go back, identify the problem, modify the system, and then test it again.
With smaller systems, we often found solutions that, whilst not perfect, still produced usable results. With large systems, however, even a minor fault in a single component can cause further problems.
For example, there was a project in Vienna where we thought we could increase the repetition rate from one kilohertz to ten kilohertz in a matter of days. In the end, it took about a year and a half to achieve the target, which was later reduced to three kilohertz. And that was a relatively small system. Today we are talking about equipment with a repetition rate of one hundred thousand hertz, but with increasing output and complexity, the number and complexity of problems are also growing rapidly.
Can you please name one of these?
One such example is thermal load. The issue is very different in a 10-watt system compared to one rated at several hundred watts. In the latter, even a minor deviation can cause a thermal load sufficient to deform an optical element or even a mirror mount. In a high-precision system, this can have serious consequences.
How is your research in Umeå connected to ELI ALPS?
I have a consultancy contract with ELI, primarily in the field of laser systems. We also work on OPCPA systems and, on certain issues, petawatt-class lasers. In addition, we collaborate in the field of electron acceleration. One possibility is to implement the specialized technology we have developed in Szeged too, and it is also conceivable that researchers might come to us to try out certain methods.
We also have joint plans for research into relativistic harmonics, including plasma-based processes. We previously conducted a joint experiment, the data from which were further analyzed in Szeged. We are now planning another experiment. At ELI, we will be able to collect a large amount of data, enabling us to determine more precisely even those parameters that we cannot measure directly.
What is the international reputation of ELI?
The facilities here are unique even by international standards. Even amongst the smaller laser systems in operation here, there are some that would be unimaginable in a traditional university laboratory, not to mention the larger ones. No university-based research group would be able to maintain such infrastructure on its own.
The better the results and source parameters we manage to achieve, the more external research groups will come here. This is one of ELI’s most important tasks: to provide unique infrastructure that researchers from all over the world can and will want to use.
What are your expectations for the coming years?
The development of large laser systems is a slower process than you might imagine at the start of your career, but many technological problems that previously posed obstacles are now being resolved. Today, it is possible to conduct experiments that would have been unimaginable a few decades ago.
It’s not about having a powerful laser; it’s about what we can use it for. If we can ensure the right funding, stable operation and international collaboration, considerable research opportunities will open up.