uni'wissen 01-2012_ENG

While this extensive ring system surrounding the main beam helps the beam to reconstruct itself, it also leads to poor image contrast in a micro scope. Higher Image Contrast, Higher Resolution However, Rohrbach has also succeeded in solving this problem: He has developed a method for exploiting the stability of the beam in pene trating the object in which the latter is not illumi nated all at once, but rather line by line – similar to the movement of a windshield wiper that travels over the entire surface of a windshield. At the same time, a camera also captures the object line by line as through a single-slit diffraction. This masks the light from the ring system. In comparison to traditional light sheet microscopy with conventional laser beams, this leads to a 50-percent increase in image contrast and an almost 100-percent improvement in the axial resolution – the smallest resolvable distance between consecutive image points – of the three-dimensional image. In addition to providing new insight into the physically complex processes of light scattering, the optical microscopes developed by Rohr bach’s group also enable researchers in biology and medicine to perform new analyses. For example, the beams can penetrate around one and a half times deeper into human skin samples than conventional laser beams. The new method also allows scientists to observe processes like the cell movements within various layers of skin following contact allergies or sunburns in four dimensions – with 3D images that change in time. “The new method is no magic bullet, but in light sheet microcopy it’s the best we are currently capable of in physical terms.” Rohrbach is planning on teaming up with colleagues from the Freiburg research cluster BIOSS, Centre for Biological Signalling Studies, to conduct further research with his microscopes, among other things on the dynamics of cancer Prof. Dr. Alexander Rohrbach has served as professor of bio- and nanophotonics at the Department of Micro- systems Engineering of the University of Freiburg since January 2006 and as a member of the Faculty of Physics and the research cluster BIOSS (Centre for Biological Signalling Studies) since November 2007. After graduating from the University of Erlangen- Nuremberg with a degree in physics in 1994, Rohr- bach earned his PhD in Heidelberg in 1998. While writing his dissertation he conducted research on optical microscopy and cell biology at the Kirchhoff Institute of Physics and the Max Planck Institute of Medical Research in Heidel- berg. After conducting various studies on optical forces and cytological applications, he completed his habilitation in physics at the University of Heidel- berg. His research inter- ests include optical traps with interferometric particle tracking, molecular motors, cytoskeletal mechanics, and new methods in laser microscopy. Photo: Zahn Further Reading Fahrbach, F. O./Rohrbach, A. (2012): Contrast- enhanced imaging based on the propagation stability of self-reconstructing Bessel beams. In: Nature Communications 3, pp. 632. Fahrbach, F. O./Simon, P./Rohrbach, A. (2010): Microscopy with self-reconstructing beams. In: Nature Photonics 4, pp. 780–785. Rohrbach, A. (2009): Artifacts resulting from imaging in scattering media: a theo retical prediction. In: Optics Letters 34/19, pp. 3041 – 3043. Florian Fahrbach, a member of Prof. Dr. Alexander Rohrbach’s team, shares multimedia content and shows how the microscopes illuminate remote corners. www.surprising-science.de/einzelforschun gsprojekte/mikroskopie cell clusters. With an eye to such future projects, he and his team will continue to work on improving the image quality of microscopes with self- reconstructing laser beams and computer holo grams: “The future of modern microscopy lies in the use of lasers and computers to optimize the interaction between light and cell – and that goes for each individual beam position.” “The future of modern microscopy lies in the use of lasers and computers to optimize the interaction between light and cell – and that goes for each individual beam position” 23

uni'wissen 01-2012_ENG

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