An Interview with Anne L’Huillier

Abstract

Romain Quidant: Thank you so much, Prof. L’Huillier, for your time. I’m very glad you accepted my invitation to participate in this ACS Photonics interview series. I would like to get started with a question you were probably asked many times: What initially sparked your interest in Science? What motivated the young Anne L’Huillier to study Physics and Mathematics? Was that an early fascination from your childhood or maybe an inspiring teacher in middle or high school? Anne L’Huillier: I do not entirely recall any specific trigger. As I remember, I have always been interested in physics and mathematics. Having scientists in my family has certainly been a source of inspiration. My grandfather was a radio engineer who used his skills during World War II to support the Resistance, and my father was an engineer in informatics. It seems to me I have always been drawn to science. Then I also had good teachers. I remember very good teachers in mathematics at the end of high school in Paris and then very good teachers in physics during my studies. Romain Quidant: Following up on this, who were your biggest mentors or role models in your early career, and how did they influence your research directions? Anne L’Huillier: Claude Cohen-Tannoudji stands out as a particularly influential figure for me. He was a fantastic teacher, and I greatly admired his approach. His teaching was rigorous and grounded in mathematics, yet he always emphasized the physical meaning behind the equations. I especially enjoyed his quantum mechanics course, particularly light–matter interaction. This sparked my interest in the field and ultimately led me to pursue a Ph.D., studying atoms in strong laser fields. So, yes, Cohen-Tannoudji was a true role model. Additionally, beyond my specific research area, learning about Marie Curie’s achievements was also significant. While her work was not related to my own, it was incredibly inspiring to know that a woman could achieve such remarkable success in science. Later in my career, I benefited from several mentors. Toward the end of my Ph.D., I reached out to a Swedish theoretician, Göran Wendin, for help in interpreting our experiments. I then spent six months in Gothenburg as a postdoc. Later Sune Svanberg provided invaluable support during the early stages of my career in Lund. Romain Quidant: While awareness of gender bias has grown considerably, it was far less prominent in the 1980s and 1990s. Can you share any experiences from that period that highlighted the challenges women faced in physics? Anne L’Huillier: That is a difficult question. It certainly was not always easy being a woman in a predominantly male environment. I would say yes, I likely experienced some challenges due to my gender. However, being a woman also brought a degree of visibility, and I was fortunate to receive support from those who were actively working to promote women in physics. Romain Quidant: I wonder whether you could describe a precise moment or a challenge in your early career that shaped your approach to research. Anne L’Huillier: Discovering high-order harmonic generation in 1987 was a pivotal moment. We were looking at fluorescence in a gas exposed to a strong laser field, and we observed these unexpected, very high-order harmonics. I somehow felt that this was something important. Understanding this phenomenon meant bridging atomic physics and nonlinear optics. I found myself immersed in trying to understand phase matching in this regime. It was so fascinating that, perhaps unconsciously, I decided this would become my research focus, and, remarkably, I’ve been working on it ever since–for 40 years! It was a truly decisive moment. Romain Quidant: You mentioned you felt it was an important discovery. Was that a rational assessment, or was there also an element of intuition or gut feeling involved? Anne L’Huillier: It was mostly a gut feeling, an intuition. Two or three years later, my supervisor suggested I might explore other avenues. But I was determined to continue, even though I could not fully articulate why at the time. The connection to attosecond pulses hadn’t yet emerged; that came later. It was a purely intuitive drive. It may sound strange, but intuition is a crucial part of my scientific process. I suspect I am in the minority among scientists in this regard, but it is how I approach my work. Romain Quidant: Fascinating! Anne L’Huillier: I should also emphasize the importance of the learning process. Research, at its core, is about learning–delving into new physics. With high-order harmonics, for example, I felt I hadn’t yet fully grasped the details and underlying physics. There was a sense of unfinished exploration, a feeling that I hadn’t reached the depths of the phenomenon. Perhaps this drive to understand is part of what I mean by intuition. It is more than just a gut feeling; it is a pull toward deeper comprehension. Romain Quidant: From this pivotal moment, the observation of high harmonic generation, what are the most significant breakthroughs you witnessed in the field during your career? Anne L’Huillier: A key step was the realization in the early 1990s that phase-locked harmonics could lead to attosecond pulses. This really energized the field. Then, in 1993, came a major theoretical breakthrough: the understanding of how atoms respond to strong laser fields, developed by Corkum, Kulander, Lewenstein, and their collaborators. This was crucial. However, it took nearly another decade to actually measure attosecond pulses, a feat achieved around 2001 by Ferenc Krausz and Pierre Agostini’s groups. The measurement itself was a significant challenge, as the method was not clear. Most of us, including my team, were trying to perform autocorrelation measurements, while Krausz and Agostini used a cross-correlation technique, which proved to be the key. If I could name another breakthrough, it would be the measurement, about ten years later, of photoionization time delays. With attosecond pulses came the promise of measuring electron motion. Understanding how to do that and, specifically, how to measure the tiny delays in photoionization was a major advance. Romain Quidant: How did the field develop initially? Was it a slow build, with a small core of researchers at first, or did it quickly gain momentum and attract a larger community? Anne L’Huillier: Attosecond science has seen a tremendous surge in activity recently, especially in the last 10 to 15 years. In the early days, it was a very niche area. The experiments required high-intensity lasers, which were then only available at large national laboratories, not at universities. There were only a handful of groups globally─maybe ten─working on strong-field atomic physics. The real turning point came with advancements in laser technology, particularly the development of titanium–sapphire laser systems, including the chirped pulse amplification, in the 1990s. This made the technology more accessible and led to a significant expansion of the field. It was the availability of this technology that prompted the construction of the laser facility in Lund, which drew me here and ultimately led me to make Sweden my home. The field truly blossomed after the measurement of attosecond pulses, marking the beginning of attosecond physics research. Romain Quidant: How has attoscience advanced our understanding of fundamental processes in physics and chemistry? Anne L’Huillier: What truly captivates me is the level of detail attosecond techniques provide. Take photoionization, for example. For decades, we have measured cross sections. But with attosecond pulses, we gain access to so much more. We can measure the complex amplitude, which includes both the magnitude and the phase. This phase information is crucial. It allows us to connect to the time domain and actually watch these processes happen in time. It is a somewhat abstract concept–measuring a complex amplitude–but it boils down to measuring the wave-like properties of the emitted electron. Romain Quidant: Looking ahead, what are some of the most promising directions you see for the field of attosecond physics? Anne L’Huillier: Attosecond science is currently evolving in several exciting directions. Two stand out for me. First, we need to move beyond simple atomic systems and apply these techniques to more complex systems like molecules and condensed matter. Understanding electron motion in these environments is crucial for tackling fundamental questions about nature, particularly light-induced processes. This is a major challenge: to extend attosecond science to systems like those involved in photosynthesis, for example, and probe the very initial steps involving electron transitions. Second, I’m fascinated by the quantum aspects. The idea of a coherent electron wave packet works in specific cases, but often we’re dealing with more complex systems requiring a quantum mechanical description using density matrices─incoherent superpositions of wave packets. The question then becomes can we measure these quantum properties? I believe we’re developing the tools to do just that, to perform, for example, a quantum state tomography of photoelectrons. This level of control over light allows us to observe nature in a truly fundamental way, which I find incredibly exciting. Romain Quidant: Shifting gears a bit, talking about important skills in science, how do you cultivate creativity and innovative thinking among your team members? Anne L’Huillier: What I’m trying to establish in my research group is to create a supportive and collaborative atmosphere. I actively work to minimize the competitive element often found in research environments and instead foster teamwork. Projects are typically tackled by small groups of three or four; individual work is rarely feasible due to the complexity of our experiments. We deal with intricate lasers, vacuum chambers, and detectors, requiring a critical mass of expertise. I encourage open communication within these groups and in our larger group meetings, where everyone is empowered to share their ideas. I particularly emphasize to new students that they should not hesitate to contribute with their thoughts and suggestions. Romain Quidant: We briefly touched on this earlier, but I’d like to delve deeper into your thoughts on the importance of diversity and inclusion in science and how we scientists promote these values in our own work. Anne L’Huillier: This is a crucial question. I firmly believe that research groups thrive on diversity–diverse backgrounds, educational experiences, interests, and of course, gender. My experience has shown me that this is the optimal environment for research. Promoting this diversity is a complex issue, and I do not pretend to have all the answers. Early in my career, I often worked in predominantly male environments. However, that is changing, and thankfully, there are more and more women in science. Currently, about 30% of my research group are women, which is very encouraging. I am not entirely sure why, perhaps being a woman myself plays a role, but whatever the reason, it is a positive trend. Romain Quidant: Along the same line, what advice would you give to young women scientists who are interested in pursuing careers in physics? Anne L’Huillier: I would wholeheartedly encourage young women to pursue their passion for physics. It is an incredibly rewarding career, filled with intellectual challenges and the potential for real impact. My advice would be to be courageous, embrace opportunities, and do not be afraid to make unconventional moves. Romain Quidant: While institutional efforts to address gender imbalances in science are crucial, are they enough on their own? Anne L’Huillier: I see two key challenges. The first arises early on, during schooling and within society as a whole. Stereotypes often prevent young girls from envisioning themselves as scientists, particularly in physics and engineering. This is a societal issue, compounded by the influence of schools. Supportive teachers who encourage girls as much as boys are essential. The second challenge occurs later, during career development and the pursuit of permanent positions. This is what’s often called the “leaky pipeline”, where women leave science for various reasons: dual-career challenges, family responsibilities, lack of suitable positions, or perhaps a form of self-censorship. Universities and research institutions need to address these issues by providing support and mentorship in various ways. Romain Quidant: In your experience with faculty hiring committees, have you observed any shifts in the evaluation criteria or recruitment processes for junior scientists? Specifically, have these changes had a positive impact on the representation of women, and is this trend continuing or accelerating? Anne L’Huillier: Throughout my career, I’ve observed a marked increase in awareness of the gender imbalance in science, which I believe is a positive development and should continue. The changes are evident: the number of women in science is growing. However, we must proceed cautiously and avoid the pitfalls of positive discrimination, such as quotas. Instead, I value the increased awareness of the problem, and the efforts to increase the representation of women as speakers at conferences and on committees are valuable steps forward. Romain Quidant: Researchers contribute to scientific progress but also shape future generations through teaching. How do you personally value the role of teaching in your work? Anne L’Huillier: For me, being a researcher is inherently linked to being a teacher. Interestingly, as a young girl, I aspired to be a teacher, not a researcher. I was not confident I could succeed in research, but teaching was my primary goal. When I came to Lund from a research institute without a teaching component, I discovered the joy of teaching, something I still greatly enjoy. It provides a valuable balance to my research. With teaching, the impact is immediate and visible. Research, particularly basic research, often has a delayed impact or, perhaps, no discernible impact at all. Teaching offers the opposite experience. In general, I believe researchers could benefit from teaching more. Romain Quidant: Explaining concepts to others forces us to clarify our own thinking, leading to a deeper understanding and potentially new insights. Anne L’Huillier: Yes, and there’s a third crucial aspect of a professorship: supervising Ph.D. students. This role bridges research and teaching, focusing on guiding a young researcher toward independence. It involves helping them develop their own ideas, write scientific articles, and navigate the entire Ph.D. process. I find this process incredibly rewarding. It is a form of education, regardless of whether the student pursues a career in academia, industry, or elsewhere. Supporting a young researcher through their Ph.D. journey is a vital part of our work. Romain Quidant: Another key aspect of our work, for which we may be less prepared, is communicating with the public. How important do you feel it is for scientists to communicate their work to society? Did your Nobel prize come with an increased sense of responsibility to engage in public communication? Anne L’Huillier: I believe communicating science to the public is crucial, and it is becoming increasingly so, especially given the prevalence of misinformation. It is more vital than ever for scientists to engage with the general public. Since receiving the Nobel Prize, I’ve dedicated significant time to this, and I find it quite enjoyable, particularly speaking with students in schools, but also with diverse audiences. I feel a strong sense of responsibility as a Nobel Laureate to do this. I’ve been given this incredible honor and recognition, and as long as I enjoy it and am able, I should prioritize public communication. This is what I’ve been doing this past year, and I intend to continue, though I’m unsure for how long. It is almost like taking on a new job when you become a Nobel Laureate, a job focused on communicating science to the public. Romain Quidant: Beyond the intrinsic value of sharing knowledge, is there a pragmatic necessity for scientists to communicate their work, given that it is often funded by taxpayer money? Do we have a responsibility to justify how those funds are used and demonstrate the societal benefits of our research? Anne L’Huillier: That is an interesting question. I believe we have a responsibility to communicate our work, though perhaps not in a purely justificatory way. I’m particularly concerned about the current trend of questioning established scientific truths. Previously, scientific progress was built upon the work of our predecessors. Now, however, fundamental scientific concepts are being challenged. I believe the most effective way to address this is through clear and consistent communication of science, especially to young people. Romain Quidant: As we near the end of this interview, I have a more personal question for you: Looking back on your career, what are you most proud of accomplishing? Anne L’Huillier: I can mention two things. First, I’m proud of my belief in the potential of high-order harmonics and my efforts to advance the field, even when it was not a popular area of research. Second, I’m proud of successfully rebuilding my career in a new country. Coming to Sweden was not about being handed a professorship; I had to start from scratch, applying for positions and working my way up. Starting over was challenging at first, but I’m very happy and proud that I did it. Romain Quidant: As scientists, we dedicate a lot of time to our work. However, life extends beyond the lab. I’m curious to learn about your personal passions and interests outside of science. Could you share some of those with us? Anne L’Huillier: First, and this is perhaps a message especially to women, the most important thing in my life is not science, it is my family. Taking care of my children together with my husband, and keeping tight relations with the young adults they have become, and maintaining strong relationships with my relatives in France and Sweden have been and are my priorities. Science is important, of course, and to be a good scientist, you need a passion for your work. Research careers have their ups and downs, so passion is essential. Science is a significant part of my life, absolutely. But I want to emphasize that it is possible to combine family life and a scientific career. As for other interests, I like music very much–my youngest son is a professional jazz musician, and I’ve always enjoyed sports. I’ve been active throughout my life, enjoying skiing, swimming, and playing tennis. These are important to me, but not as important as what I mentioned first. Romain Quidant: Thank you, thank you so much, Anne, for your time and for all these fascinating insights into your career, your work, and science in general. This article has not yet been cited by other publications.