CONTROLLABLE LIGHTPATTERN FOR USE IN MICROOPTICAL NEURAL STIMULATION
Prof. Dr. Ulrike Wallrabe (Contact PI)
In the COLUMNS project we develop an implantable depth-controlled stimulation tool for in vivo optogenetic stimulation of local neuronal populations. Our approach is based on an array of Bessel beams that feature an extended focal zone and self-healing properties. The systems comprises an array of blue laser diodes, micro-lenses and micro-axicons and allows control over multiple independent channels without stiff fiber connections. The additional integration of a liquid crystal-based ring aperture allows us to control the penetration depth of the Bessel beam – giving us a quasi-noninvasive stimulation tool with full spatial and temporal control. We expect to be able to stimulate the cortex at different depths without the need of tissue penetration. Nowadays, most optogenetic stimulation tools deliver the light by fibers or needles that incorporate waveguides close to the area of interest. Such approaches involve tissue penetration and thus the risk of undesired neuronal damage.
We proved that we can generate Bessel beams using edge-emitting laser diodes that have an asymmetric intensity distribution and verified the concept of depth-controlled Bessel beams by a variable ring aperture [1, 2]. We further were able to align and assemble the laser diode array with flat flexible PCB connections. We optically measured acute brain slices to assess Bessel beam scattering in slices of different thickness and with axicons of different angles.
 Müller A, Wapler MC, Schwarz UT, Reisacher M, Holc K, Ambacher O, Wallrabe U (2016) Quasi-Bessel beams from asymmetric and astigmatic illumination sources. Optics Express, volume: 24, pp. 17433–17452.
 Müller A, Wapler MC, Wallrabe U (2016) Depth controlled Bessel beam. 2016 International Conference on Optical MEMS and Nanophotonics (OMN).