Lichtgedanken 04

S C HW E R P U N K T 22 Michael Müller is 27 years old, a doc- toral candidate at the Institute of Ap- plied Physics and currently the world- record-holder for the most powerful ultra-short-pulse fibre laser. The young physicist has been working on the de- velopment of short laser pulses for three years within Prof. Dr Jens Limpert’s working group »Fibre and Waveguide Lasers«. Müller does not see this as a reason to withdraw from the group: »There are plenty of research groups working on the development of high-performance lasers, but we are currently following the most successful concept for output scaling«, he explains. Records are part of the day job in science That is why he believes it is likely to be himself that breaks the world record: »Perhaps in one or two years, when my colleagues and I have developed the next laser system.«What does the record mean to him? The physicist, who was born in Heiligenstadt and completed his bachelor's and master’s programme at the University of Jena, is laid back in this respect too: »In a fast-developing field like laser research, scientists are constantly eclipsing previous results. World records are quite common«, he smiles. In the experiment, the early-ca- reer researcher and his colleagues suc- ceeded in overlaying individual laser beams by exploiting the wave proper- ties of the light. Thus, he was able to generate light pulses with a duration of just 220 femtoseconds (10 -15 seconds) with an average output of 1.9 kW and with the best-possible quality of the laser beam—a previously unheard-of combination. He lengthened a classic fibre laser ex- periment to generate this level of light output in such short pulses and used several glass fibres to do so; 16 in total. This is because a single optical fibre is too small for so much energy; the non-linear effects either cause it to break or the pulse becomes too long. Thanks to the combination of 16 laser beams, however, it was possible to cre- ate »ultra-short pulses in a brilliant laser beam«. »The technical process of avoiding non-linear and thermal disruption is far more difficult than the physics that lies behind it«, reports Müller, »the devil really lies in the detail.« The next limit: »Increasing the output further would mean that the laser beam could no longer be propagated in the air; ex- periments would have to take place in a vacuum.« It may sound theoretical and far-re- moved from reality, but it is actually closer than you might think. Ultra-short laser pulses play a key role in the gene­ ration of coherent X-rays; in the micro- scopy of minute structures; and in the inspection of computer chips. The relev- ance of his findings surely played a part in the Jena doctoral candidate winning a Best Student Paper Award at the inter- national optics and photonics exhibition »SPIE.Photonics West« in San Francisco last February. At the sub-conference »Fibre Lasers XV: Technology and Sys- tems« he won second place with his re- search. Showcases by the laser designers: who has the best? Travelling to big conferences is not just part of the day job for the physicist; it is also one of the highlights of his work. That is why he packs his case once or twice a year and travels to a trade show—beginning with San Francisco in the USA, via Vienna and Munich, and as far as Nagoya in Japan. The entire thing is like a showcase event: »Everyone shows what they have. The big question is: who has the best laser?« He still gets nervous making presenta- tions in front of up to 100 scientists, but, like so much else, it is a case of getting used to it. Having the opportunity to present your own work is, at any rate, a requirement for winning a prize and for recognition within the world of sci- Last year saw early-career physicist Michael Müller build the world’s most powerful ultra-short-pulse fibre laser—and he proved this in February with the presentation of his research findings at the »Fibre Lasers XV: Technology and Systems« conference in the USA, where he came second in the Best Student Paper Awards. Who will be able to break his record? »At the moment, probably only me«, believes the doctoral candidate at the Institute of Applied Physics. World record with short-pulse laser BY JULIANE DÖLITZSCH F E AT U R E