"Physics is incredibly cool"

The 2018 Nobel Prize in Physics went to three laser physicists. Christoph Lienau, head of the Ultrafast Nano-Optics working group at the University of Oldenburg, is delighted with his honoured colleagues. In this interview, he takes a look at the future of his subject.

QUESTION: Professor Lienau, were you surprised when Arthur Ashkin, Gérard Mourou and Donna Strickland were awarded the Nobel Prize in Physics?

ANSWER: No, not really. The award-winning researchers have made ground-breaking discoveries that have not only revolutionised the field of laser physics, but have also enabled a large number of completely new technological applications. They have therefore long been considered potential candidates. At the same time, there are of course many research achievements in physics that are worthy of awards, so I was somewhat surprised that colleagues from my own specialist field were once again honoured.

QUESTION: What is the achievement of the three researchers?

ANSWER: Arthur Ashkin has developed non-contact optical tweezers for tiny particles, such as small plastic spheres or biological cells. He discovered that laser light can exert strong mechanical forces on these particles. If the light is focussed very strongly with a microscope lens, particles are drawn into the focal spot. If the light spot is moved, the particles can be pushed back and forth without contact. This discovery has opened up numerous new applications in biology and medicine. For example, it is now possible to isolate individual cells and analyse their properties.

Laser pulses with extremely high energy

QUESTION: And Strickland and Mourou?

ANSWER: Donna Strickland and Gérard Mourou have developed a new technique for generating extremely intense, ultra-short laser flashes. They have succeeded in massively increasing the brightness of the flashes. In her doctoral thesis, Donna Strickland showed for the first time that such ultrashort flashes of light can be amplified much better if they are "chirped" before being amplified. Only after this "chirped pulse amplification" are they compressed again in time. In this way, solid-state lasers can generate ultrashort laser pulses with extremely high pulse energies.

QUESTION: What can such ultrashort laser pulses be used for?

ANSWER: Ultrashort pulse lasers are now being used very successfully in eye operations, dentistry and for high-precision material processing. They can now also be used to accelerate protons, for example in cancer therapy.

QUESTION: You also use ultrashort laser pulses in your research. What are you investigating with them?

ANSWER: We want to see things that were previously hidden from us. Here in Oldenburg, we use ultrashort light pulses to build cameras with which we can film chemical reactions, for example. Or we observe how electrons move in new materials, such as organic solar cells.

QUESTION: How long do the laser flashes last?

ANSWER: We can now produce flashes of light that last only a few attoseconds. An attosecond is a billionth of a billionth of a second. These flashes are so short that even the electrons and atomic nuclei that make up molecules and solids simply stand still during them.

QUESTION: What are you planning to do next?

ANSWER: Together with my colleagues Niklas Nilius, Sascha Schäfer and Matthias Wollenhaupt, we are currently setting up a laboratory for attosecond physics in Wechloy, one of the latest topics in experimental physics. In particular, we want to gain a much better understanding of how electrons move in the smallest nanostructures. This could contribute significantly to the development of new optoelectronic components, for example photocatalysts, solar cells or nanophotonic circuits.

Circuits made of light

QUESTION: What is this all about?

ANSWER: Nanophotonic circuits are tiny circuits that work with light instead of electricity. Ideally, we would like to have ultrashort pulse lasers that are so small that they can be built into miniaturised components. This will certainly require a few more years of basic research into nanolasers. The development of such lasers could be a very important step on the way to fast optical computers. Martin Silies' junior research group in Oldenburg is conducting research into this.

QUESTION: Donna Strickland was the first woman to win the Nobel Prize in Physics in 55 years - how can women in physics be better supported?

ANSWER: First of all, I think that both women and men need to realise that physics is simply fun or - to put it another way - incredibly cool. If you listen to the interviews with Donna Strickland, you will realise exactly how much enthusiasm she has for her academic appointment. I myself caught fire at the beginning of my Diplom thesis when I was sent into a large, dark laser laboratory with all kinds of colourful laser beams for the first time by my future doctoral supervisor. The fascination for optics and physics has never left me since.

QUESTION: What are the benefits of events specifically for women, such as the German Women Physicists' Conference, which took place in Oldenburg in September?

ANSWER: They offer female physicists an excellent opportunity to network. At the conference organised by my colleague Jutta Kunz, 150 highly talented young female scientists came to Oldenburg to discuss and learn from each other. Our aim must be to utilise this creative potential and show as many young women as possible that physics is not just a way of earning a fairly secure living, but is incredibly exciting and inspiring.

Interview: Ute Kehse