Interview With Nobel Laureate Anne L'Huillier, Discovering Her Vision Of The Attosecond Laser Pulse

The 2023 Nobel Prize in Physics was awarded to Anne L'Huillier and her two colleagues Pierre Agostini and Ferenc Krausz, and just recently the Berthold Leibinger Stiftung awarded thephysicist the Berthold Leibinger Future Prize. Leibinger Future Award. In an exclusive interview, Anne L'Huillier, who has just been awarded the Nobel Prize in Physics, tells us about the research on attosecond laser pulses.
Q: Prof. L'Huillier, if you were at a barbecue and someone asked you what you do for a living, what would you say?
L＇Huillier: Normally I would say that I work mainly in laser physics and atomic physics. Our team can illuminate with very, very short pulses of laser light, which makes it possible to photograph some processes that move very fast, such as those involving the movement of electrons. You can think of it as what the flash of a normal camera does.
Q: When you say "very, very short" do you mean ......?
L＇Huillier: Only a few attoseconds long laser pulses.
Q: Can you briefly describe an attosecond?
L＇Huillier: It's actually very difficult to describe. I think it might be easier to understand an analogy: 1 attosecond is to 1 second what 1 second is to the total age of the universe (14 billion years). But I'm not so sure that this description really helps you understand the attosecond.
Q: Well, it might help a little.
L＇Huillier: We will always have the habitual feeling that an attosecond can't be perceived in terms of time that people can understand. Fortunately, however, we can verify it with the help of mathematical and scientific theories of abstraction as well as experiments, and from this we know that 1 attosecond = 10-18 seconds. Moreover, a more interesting question than thinking about the length of an attosecond is why we want such a small time scale.
Q: So why do we need pulses of attosecond length?
L＇Huillier: Because certain processes in nature are so fast that we can only measure them with the help of attosecond light pulses, the most important of which is the motion of electrons. The faster the flash, i.e. the shorter the light pulse, the closer we can observe the process. Nowadays, my research group still focuses on photographing simple processes in and around atoms, because this is easier to achieve. However, if we can make further progress in this area, we will be able to observe the movement of electrons in more complex systems, such as in molecules. Electron motion causes chemical reactions. One day, we will be able to measure these initial motions.
Q: And then what?
L＇Huillier: Measurement is the first step toward control. So in the long run, our biggest goal is to be able to control chemical reactions at the electron level.
Q: Control it and use it for what?
L'Huillier: It's hard for me to predict where it will be used or what it will change in the future, but that's basic research.
Prof. Anne L'Huillier's research team in Lund, Sweden, uses femtosecond lasers to generate pulses of high-harmonic light. These pulses are then used to generate attosecond laser pulses to visualize atomic processes
Q: In an experiment in 1987, you discovered the high harmonics that are a prerequisite for generating attosecond pulses.
L＇Huillier: Yes, that was a delightful coincidence. That's the best thing when you discover something that takes you by surprise! It means that something is waiting for you to fix it. What we really wanted to do at that time was to bombard noble gases with a strong laser and study the fluorescence effect. It turned out that the strongest light observed in the process was not fluorescence, but a high harmonic of the laser frequency, a discovery that changed my scientific career. With the generation of high harmonics, it was possible to generate attosecond pulses. That's what I'm still doing now.
Q: Is it possible to form at least a mental picture of high harmonic generation?
L＇Huillier: Yes! I have a better comparison than the attosecond and the age of the universe. If you pass a bow through the strings of a violin, you will get not only pure tones (pure tone frequencies) but also other frequencies. In music, these frequencies are called overtones, and they give tone color; overtones are also called harmonics. A similar thing happens when you expose a gas to a femtosecond laser pulse under certain conditions, which creates new laser frequencies with shorter wavelengths. You could say that the higher harmonics are the overtones of laser physics.
Q: What can a high-harmonic light pulse do?
L＇Huillier: You can use them to generate attosecond pulses, but they are also useful in their own right. We're currently working with a manufacturer of lithography and metrology equipment for the semiconductor industry to use high harmonics to inspect semiconductor microstructures. This is a very tangible project for someone like me doing basic research. I'm surprised and pleased that our work is useful to society.
Prof. Anne L＇Huillier helped establish the physics of attosecond lasers. This work may soon light up the world of electronics.
Q: Has your research also contributed to the development of laser technology?
L＇Huillier: Certainly, our work in attosecond physics has continued to inspire laser manufacturers to develop new and better ultrashort-pulse lasers over the past few decades. Of course, we also benefit from better beam sources. The better the initial laser source, the better the higher harmonics will be able to produce attosecond pulses. For us, this leads to further technological advances, such as new diagnostics and measurement methods in the field of USP laser technology - in other words, we keep inspiring each other. But beyond these pleasant side effects, there is something else in my work that is very important to me.
Q: What else is very important to you?
L＇Huillier: I'm a researcher, but I'm also a teacher. That means I get to teach a bunch of bright young people and watch them grow and enrich their experience, which I think is my greatest contribution.
Anne L'Huillier's profile
Anne L'Huillier, born in Paris in 1958, is a French physicist and currently Professor of Atomic Physics at Lund University. She was one of the key figures in establishing the research field of attosecond physics and has received numerous awards. Earlier this year, she received the Berthold Leibinger Future Prize for her research achievements, and just a few days later she was awarded the 2023 Nobel Prize in Physics along with Pierre Agostini and Ferenc Krausz.