Three-dimensional weight-accumulation algorithm for generating multiple excitation spots in fast optical stimulation
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We report here an algorithm for calculating a hologram to be employed in a high-access speed microscope for observing sensory-driven synaptic activity across all inputs to single living neurons in an intact cerebral cortex. The system is based on holographic multi-beam generation using a two-dimensional phase-only spatial light modulator to excite multiple locations in three dimensions with a single hologram. The hologram was calculated with a three-dimensional weighted iterative Fourier transform method using the Ewald sphere restriction to increase the calculation speed. Our algorithm achieved good uniformity of three dimensionally generated excitation spots; the standard deviation of the spot intensities was reduced by a factor of two compared with a conventional algorithm.
KeywordsSpatial light modulators Liquid–crystal devices Multi-beam generation Brain activity monitoring Laser beam shaping
The authors are grateful to A. Hiruma (president) and T. Hara (director) of Hamamatsu Photonics for their encouragement throughout this work, as well as to Y. Ohtake, T. Ando, T. Inoue, T. Otsu-Hyodo and H. Sakai for their helpful support with the spatial light modulator and optical setup. This work was partially accomplished as a collaboration between the Laser Biomedical Research Center (Massachusetts Institute of Technology) and Hamamatsu Photonics K.K. A part of this study was supported by a JSPS Grant-in-Aid for Specially Promoted Research, Grant number JP16H06289.
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