Ursula Keller, Professor of Physics at ETH Zurich, will deliver her farewell lecture on Monday, 15 December 2025. Her talk, entitled “Ultrafast science: a 32-year journey in Physics at ETH Zurich,” marks the close of more than three decades at the forefront of ultrafast laser science – a field she helped build from the ground up.?
When Ursula Keller became ETH Zurich’s first tenured woman professor of physics in 1993, she set out to push laser technology to its limits, making light pulses ever shorter and more stable, and using them to reveal the hidden dynamics of the quantum world. Her groundbreaking invention of semiconductor saturable absorber mirrors (SESAMs) transformed solid-state lasers. Ultrashort “femtosecond” pulses – lasting just a millionth of a billionth of a second – soon became standard tools in laboratories and industry. Her group built a remarkable track record of successful ETH spin-offs. The latest, K2 Photonics, completed its spin-out phase just as Keller retired.
Expanding the limits of light
To reach even shorter pulses – lasting close to a single cycle of light – her team tackled one of the toughest challenges in ultrafast science: controlling the electric field within each pulse. Their breakthrough made possible what is known as the “frequency comb” revolution in precision measurement and paved the way for the first attosecond pulses, capturing electron motion in real time.
Keller’s group later developed the attoclock, a method for measuring the time it takes an electron to tunnel through a potential barrier, and the attoline, the first high-harmonic generation facility in Switzerland. These tools allow researchers to observe electron motion on attosecond timescales – billionths of a billionth of a second. The attoline will stay within the FastLab, a shared research platform within the Physics Department of ETH Zurich.
The group’s final work before her retirement, accepted by the journal Science at the end of October, reveals how electrons and atoms can dance out of sync. It showed that carriers and energy flow differently in novel two-dimensional, transition-metal-containing materials. In these systems, the effective-mass and instantaneous electron-phonon-coupling approximations break down, with important implications for future optoelectronic device designs.
Keller’s group helped establish ETH Zurich as a global centre for ultrafast science. Her 2022 textbook Ultrafast Lasers – an 800-page synthesis of three decades of progress – has already become a defining reference for students and researchers worldwide.
From Switzerland to Stanford and back
With a degree from ETH Zurich, a Fulbright fellowship and a PhD from Stanford, Keller began her independent research career at AT&T Bell Labs before returning to Switzerland to lead the newly founded Ultrafast Laser Physics group at ETH Zurich. “ETH gives you academic venture capital,” she once noted – the freedom and resources to test bold ideas quickly. That mindset helped her supervise 101 doctoral theses and six habilitations, many of whose authors now hold leading roles in academia and high-tech companies across the world.
Her research output includes over 500 peer-reviewed papers, 21 patents and two ERC Advanced Grants. Keller is one of the most-cited female scientists in Switzerland and has received numerous awards, including the Marcel Benoist Prize (2022), the IEEE Edison Medal, the OPTICA Ives Medal and the European Inventor Award for her lifetime achievements. Keller is a Fellow of both the Royal Society in London and the U.S. National Academy of Sciences.
Science, governance and inclusion
Beyond scientific achievements, Keller also helped shape how Swiss science governs itself. She led the NCCR MUST (National Centre of Competence in Research for Molecular Ultrafast Science and Technology) for 12 years from 2010 to 2022, served on the SNSF Research Council and co-founded the ETH Women Professors Forum, advocating transparency, excellence and equal opportunity in academia.
Her leadership philosophy, once shaped by the rigorous demands of Bell Labs, developed into what she calls a multiplier style: setting ambitious goals while creating an environment that empowers others to excel. That approach has produced not only world-class science but also a culture of collaboration and trust.
Legacy of light
Colleagues describe Keller as visionary, precise and fearless in asking difficult questions – qualities that helped her push both technology and institutions forward. Her blend of technical mastery, strategic insight and integrity has left a lasting impact on ETH Zurich and the wider photonics community.
Farewell Lecture
“Ultrafast science: a 32-year journey in Physics at ETH Zurich”
Monday, 15 December 2025, 5.15 p.m., Audi Max (HG F 30)
Lecture in English, followed by an apéritif. Open to the public.