Relevant for Research Area

A - Foundations

B - Core Technologies


In order to optically stimulate neurons at high spatio-temporal resolution, we proposed a non- invasive miniaturized tool for the simultaneous multi-focal stimulation of small animal brains by means of light pulses. An array of miniaturized laser sources combined with the refractive capabilities of conically shaped lenses (axicons) allows to shape Bessel beams which are believed to have enhanced penetration depth into scattering tissue. Exploiting this unique feature, we want to realize optogenetic stimulation without invasive penetration of the brain. We proved to produce Bessel beams using blue edge emitting laser diodes as light sources that provide elliptic beam profiles. With the objective of creating an array of 3x3 parallel beams, we established a manufacturing process for microoptical lens arrays. Using a rapid- prototyping process, we designed and fabricated four different aspherical lens arrays. Furthermore, we demonstrated the successful sectioning of a Bessel beam along the optical axis using a 3x3 array of liquid crystal based tunable ring apertures. In a further improvement step, a more compact and highly integrated optical system was manufactured by combining the tunable ring apertures and the lens arrays in a single device. First in vitro tests on acute brain slices have been performed. An accurate assembly method for a 3x3 laser diode array has been developed, the thermal properties of the laser diodes have been investigated and a first prototype has been built. A suitable 9-channel laser driver with advanced pulsing capabilities has been built as a portable, user programmable control device, including a driver module for the liquid crystal ring aperture. In summary, we have built a compact and highly integrated optical system for optogenetic neural stimulation, which includes 9 individually addressable blue laser channels providing depth-controlled Bessel beams generated by a tailor-made lensacon array.

Publications and Achievements


Savanthrapadian S., Meyer T., Elgueta C., Vida I., Bartos M., “Properties of dendritic synaptic inhibition in the dentate gyrus depends on the nature of pre- and postsynaptic neurons”, Journal of Neuroscience, vol.34, pp.8197-8209, 2014.

Elgueta C., Köhler J., Bartos M., “Persistent discharges in dentate gyrus perisoma-inhibiting interneurons require hyperpolarization-activated cyclic nucleotide-gated channel activation”, Journal of Neuroscience, vol.35, pp.4131-4139, 2015.

Ni J., Wunderle T., Lewis C. M., Desimone R., Diester I., Fries P., “Gamma- Rhythmic Gain Modulation”, Neuron, vol.92, pp.1–12, 2016.

Müller A., Wapler M.C., Schwarz U.T., Reisacher M., Holc K., Ambacher O. and Wallrabe U., Quasi-Bessel beams from asymmetric and astigmatic illumination sources”, Optics Express, vol. 24, no. 15, pp. 17433– 17452, 2016. DOI: 10.1364/OE24.017433

 Müller A., Wapler M.C., and Wallrabe U., Segmented Bessel beams”, Optics Express, vol. 25, no. 19, pp. 22640-22647, 2017. DOI: 10.1364/OE.25.022640

Müller A., Wapler M.C., and Wallrabe U., “A quick and accurate method to determine the Poisson’s ratio and the coefficient of thermal expansion of PDMS”, Soft Matter, vol. 15, no. 4, pp. 779-784, 2019. DOI: 10.1039/C8SM02105H


Conference contributions

Holc K., Jakob A., Weig T., Köhler K., Schwarz U.T., Müller A., Pauls M., Wapler M., Wallrabe U. and Ambacher O., “New tools for optogenetics: nitride laser diodes combined with axicons for non-invasive neuronal stimulation”, Proceedings of the International Workshop on Nitride Semiconductors (IWN), Wroclaw, Poland, 2014.

Müller A., Wapler M.C., and Wallrabe U., Depth controlled Bessel beam”, International Conference on Optical MEMS and Nanophotonics (OMN), Singapore, pp. 243–244, 2016. Doi:10.1109/OMN.2016.7565918

Wallrabe U., Müller A., Reisacher M., Ambacher O., Holc K., and Wapler M.C., “Controlling Bessel beams for optophysiology”, Dreiländertagung, Biomedizinische Technik, Basel, Swiss, 2016.

Müller A., Wapler M.C., Reisacher M., Holc K., Ambacher O. and Wallrabe U., Bessel beams for depth-controlled quasi-noninvasive optogenetic stimulation”,3rd International Workshop on Technologies for Optogenetics (OPTOGEN), Freiburg, Germany, 2016.

Müller A., Wapler M.C., Reisacher M., Ambacher O. and Wallrabe U., “Tiefenkontrollierbare Bessel-Strahlen für quasi-nichtinvasive optogenetische Stimulation”, 118. Jahrestagung der Deutschen Gesellschaft für angewandte Optik (DGAO), Dresden, Germany, 2017.

Wallrabe U., Brunne J, Müller A., Lemke F., Bruno B., Stürmer M. and Wapler M.C., “Nicht-sphärische adaptive Optik für die Lebenswissenschaften”, 118. Jahrestagung der Deutschen Gesellschaft für angewandte Optik (DGAO), Dresden, Germany, 2017.

Müller A., Wapler M.C., Vaity P., Reisacher M., Ambacher O., Okujeni S., Egert U., Bartos M., Diester I., and Wallrabe U. Non-diffracting light beams for optogenetics”, BLBT International Conference, Freiburg, Germany, 2017.

Müller A., Wapler M.C., and Wallrabe U., Steuerbare Ringblenden für segmentierte Besselstrahlen”, MikroSystemTechnik Kongress (MST Kongress), München, Germany, pp. 128-130, 2017.