Nathalie Nagl wins Otto Hahn Medal of the Max Planck Society
As part of her doctoral thesis, Nathalie Nagl developed a new generation of ultra-short pulse lasers in the infrared range, which can be used, for example, to precisely analyze blood samples.
Starting with her Ph.D. thesis, Nathalie Nagl has continuously pushed the frontiers of high-repetition-rate femtosecond laser sources. In her research project, she was trying to generate high-intensity laser pulses with pulse durations of only a few optical cycles at exotic wavelengths in the mid-infrared spectral range. With her experimental findings, Nathalie Nagl has pioneered a new generation of highly compact, low-noise and powerful laser systems that can be used to analyze minuscule variations in the infrared response of body fluids. The goal is to detect – in a non-invasive way – early signs of diseases such as cancer. The Max Planck Society honours this success with the Otto Hahn Medal for outstanding achievements by young scientists.
“Maybe this laser will be a part of every clinic one day"
Ultra-short pulse lasers play a key role in Professor Ferenc Krausz' department. The researchers use it to generate ultrashort laser pulses in the femto- and attosecond range (a femto- or attosecond is a millionth or billionth of a billionth of a second, i.e. 10-15 respectively 10-18), with which they can observe and measure the ultrafast movements of electrons. They are also able to specifically excite molecules in biological samples which causes them to vibrate. This, in turn, reveals an enormous amount of information about their composition. Using a new measuring method, blood samples, for example, can be analysed for the early detection of diseases – an important medical application the scientists from the MPQ, the LMU and the Center for Molecular Fingerprinting (CMF) are currently working on.
Nathalie Nagl has now further developed the femtosecond laser technology as part of her doctoral thesis and launched a new generation that is far more compact, more powerful, creates less noise and, above all, is cheaper to manufacture than previous devices. "We're talking about just a few hundred dollars compared to thirty thousand euros that you had to invest in the pump light source for a laser of this kind before," says Nathalie Nagl. "In addition, the laser is extremely stable and low-noise by nature. That's very important for use in sensitive applications, for example, to avoid weak molecular signals from being drowned by laser noise."
Laser diodes from telecommunications
In the femtosecond laser, the laser medium – in this case a crystal – is excited with a pump laser. The excited crystal then again emits light, which is amplified many times over in an optical resonator consisting of several highly reflective mirrors, and then emitted in a bundle. However, a normal pump laser is typically not only very large and expensive, but due to its complexity usually also generates additional noise components that are directly transferred to the femtosecond laser. The manufacturing of a more compact, significantly cheaper and extremely stable femtosecond laser is particularly interesting for non-academic and industrial applications. Therefore, one idea Nathalie Nagl pursued in her work was whether the previous pump laser (a fiber laser) could be replaced by very compact, low-cost and low-noise laser diodes from telecommunications to excite the crystal in the same way.
"The idea has been around for some time, but has only been successfully implemented for very few types of lasers. However, for our type of ultrashort pulse lasers no one has done this in practice before as these lasers are far less researched than current standard systems. Replacing the pump source does not simply mean that I take out the fiber laser and put the laser diode in the same place instead. The fiber laser produces a perfect beam, just the way you want it to be for a pump laser. The light from the laser diode, on the other hand, is much more difficult to handle because it has an extremely low beam quality and is not so easy to focus into the crystal. So, it wasn’t clear at the start whether the beam quality and the much lower radiation intensity would be sufficient to build a powerful laser out of it – let alone a femtosecond laser, which is not supposed to emit a continuous beam, but extremely short laser pulses in the mid-infrared range", explains Nathalie Nagl about the research-related challenges of her project.
One million watts achieved
She has devoted a total of three years of intensive research to this topic, building three new types of ultrashort pulse lasers one after the other. The first laser was a kind of demonstrator to show that the principle works. But: "In the end, it is important that it is also suitable for the applications". That is why, in the second step, she focused on increasing the peak power of the laser many times over and precisely investigating the noise behaviour of the femtosecond laser. "In doing so, we were able to show for the first time what a promisingly low noise level the laser has. We have not yet achieved such stable laser radiation with any laser in our group." In the third and final step, she pushed the new technology to its limits and showed that the laser can emit ultrashort light pulses with an optical peak power of up to one million watts. The power even increased by a factor of 400 compared to the previous record.
Furthermore, the young scientist was able to show that the laser radiation can be used to generate very broadband mid-infrared radiation with high efficiency. The laser pulses are focused directly into a non-linear crystal without further amplification. This now makes the laser extremely interesting for research applications such as the early detection of cancer, which is being driven forward by the team around Ferenc Krausz.
"It took me a lot of time and nerves to set up and optimizse everything so that it fits in the end”, says Nathalie Nagl today with a smile. “You are also dependent on a number of external factors and experiments often don’t go as planned. But I can actually consider myself lucky that it basically went more or less smoothly from year one to three. In hindsight, of course, I'm very happy about that"."
With top marks in just three years
Thanks to smooth processes, personal ambition and excellent preparatory work, Nathalie Nagl managed to complete her PhD in the record time of only three years and with top marks. She had already been employed in the group as a Master's student before and was able to gain a lot of trust through her good work. "They then also trusted me to carry out the project on my own from start to finish".
What helped her most, she says, was a very structured way of working, also when writing the doctoral thesis. "I always carefully noted down which steps I performed in the experiment and which data I collected so that I could find them again at any time. If you work in a structured way from the beginning, it pays off in the end." The wide range of training courses offered by the Planck Academy has also supported her a lot on her way, she says.
“I’ll definitely take my group out to dinner with the prize money”
In the medium term, Nathalie Nagl intends to leave academia in favour of a position in the private sector. She enjoys taking responsibility, planning and coordinating, — skills that she can already test and develop further in her current postdoc position as a project manager.
"The academic world and my personal values and goals are not so easy to reconcile. As a native of Lower Bavaria, I like it a lot in Bavaria and I also want to stay here. For me, pursuing a career in academia means changing my place of residence frequently and having to apply for new jobs again and again. For family and private life, this flexibility and uncertainty can be a big challenge. However, moving to industry doesn't mean that I can't continue to research, develop, coordinate and work creatively – just as I have been doing up until now.”
But first, “I’ll definitely take my group out to dinner with the prize money”, Nathalie Nagl says rejoicing about her price.
About the Otto Hahn Medal
The Otto Hahn Medal has been awarded since 1978. Every year, the Max Planck Society awards it to up to 30 young scientists who have made outstanding scientific achievements in the course of their doctorate. In recognition of these achievements, the medal is endowed with 7,500 euros. The medal is named after the nuclear chemist and Nobel Prize winner Otto Hahn, who was President of the Max Planck Society from 1948 to 1960. The award is presented every year at the Society's Annual General Meeting, which will take place again this year in June in Berlin.