“Swiss Nobel Prize” for Ursula Keller

Ever since the laser was invented, scientists have been keen to use the technology – to transform materials, for example. Unfortunately this was not possible with continuous-wave lasers, as they were too imprecise, and unsuitable for heat-sensitive materials. The eventual solution was to use a pulsed laser beam, although this required more complex technology. ETH Professor Ursula Keller solved the problem by using semiconductors, and in 1991 invented SESAM technology (Semiconductor Saturable Absorber Mirror).

With SESAM, she handed science, industry and medicine a new instrument that enabled previously unimaginably precise interventions. SESAM makes it possible to send light pulses from solid-state lasers at femtosecond intervals. One femtosecond is equivalent to one millionth of one billionth of a second (10^-15). Over this incredibly short time it is possible to measure the movement of atoms, for example, or investigate the mechanisms of chemical reactions.

As professor in the Department of Physics, Ursula Keller has continued to develop the SESAM concept. She also succeeded in producing ever shorter laser pulses, until only one or two light oscillations were contained in one laser pulse. However, these oscillations were not synchronised from one pulse to the next, which was a critical factor for the development of further applications. The solution to this problem led to a revolution in frequency measurement and the invention of the most accurate clocks in the world: the “optical clock” and the “attoclock”. The optical clock allows time measurement to be improved by a factor of roughly five in comparison with existing standards. The attoclock is so accurate that it can measure the fundamental processes of quantum mechanics, such as the speed of electron tunnelling.

“The epitome of Swiss excellence in research”

Scientists see the Marcel Benoist Prize, worth 250,000 Swiss francs, as a type of Swiss Nobel Prize. It is awarded together with the Fondation Latsis prize and is to be presented on 3 November 2022. This year the Latsis prize for young researchers up to the age of 40 goes to Professor Kerstin Noëlle Vokinger at the University of Zurich. Guy Parmelin, Member of the Federal Council and President of the Marcel Benoist Foundation, congratulates the award winners: “We are delighted to award our top Swiss science prizes this year to Ursula Keller and Kerstin Noëlle Vokinger. Both are outstanding scientists and the epitome of Swiss excellence in research.”

Naturally Ursula Keller is delighted as well: “It’s an incredible honour to receive the Marcel Benoist Prize, in recognition of almost 30 years of applied and basic research at ETH Zurich. It’s also the first science award I have received in Switzerland. I would like to thank my incredible research group, along with all the postdocs, doctoral students and external partners who made this work possible.

This award is very special to me. My appointment as the first female professor of physics at ETH Zurich, coming straight from the USA, was partly thanks to a policy of recruiting more female scientists to leadership roles. That’s why I am particularly glad to see this award confirm that such initiatives really do help promote integration and excellence.”

Joël Mesot, President of ETH Zurich, comments how much the professor deserves this accolade: “Ursula Keller is an outstanding scientist. As a pioneer in ultrafast laser research, she has made a huge impact in her specialist field. She epitomises the quality of research for which ETH is renowned, made possible through the generous support of the Swiss National Science Foundation and the institutions of the ETH Domain, with funding from the Federal Government.”

Extremely versatile technology

The principle of SESAM has made the industrial application of short-pulsed lasers possible. Today they are used in a variety of practical applications: for cutting virtually any material, for surface treatment, or in the production of computers and smartphones. They are also used in medical technology, where laser pulses are deployed, for example, as scalpels in eye operations. In addition, ultrafast laser technology can be used in the development of high-precision measuring instruments.