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The article studies properties of the appropriate optical setup by simulating the propagation of the light. Relevant test patterns and sensitivity parameters of the system will be analyzed. Our results illustrate the main opportunities of the concept with particular focus on the tilt mirror technology. They indicate a promising path to realize the complex light modulation at frame rates above 1 kHz and resolutions well beyond 10,000 complex pixels.
Our second interest is the applicability of 4f methods to high-power applications. We discuss the variants of 4f intensity shaping by phase modulation from a system-level point of view which requires the consideration of application relevant boundary conditions. The discussion includes i) the micro mirror based phase manipulation combined with amplitude masking in the Fourier plane, ii) the Generalized Phase Contrast, and iii) matched phase-only correlation filtering combined with GPC. The conceptual comparison relies on comparative figures of merit for energy efficiency, pattern homogeneity, pattern image quality, maximum output intensity and flexibility with respect to the displayable pattern. Numerical simulations illustrate our findings.
In our setup, we use a combination of two micromirror arrays, which allow not only to spatially structure the light in the field of view, but also to control the direction and angle of the incident light. In order to achieve this, a first MMA is imaged in the focal plane and used as a black and white (or even greyscale) mask. With a fully illuminated objective, this image would normally be formed from the complete light cone. By imaging the second MMA onto the backfocal plane of the objective only a portion of the light cone is used to form the image. This enables avoiding the unwanted illumination of out of focus objects. The MMAs in our setup consist of an array of 256x256 micromirrors, that can each be individually and continuously tilted up to 450nm, allowing the creation of greyscale images in real time in the illumination pattern. The mirrors themselves can be tilted for times as short as 10μs up to several seconds. This gives unprecedented control over the illumination times and intensities in the sample. Furthermore, our enhanced coating technology yields a high reflectivity over a broad optical spectrum (240- 1000nm).
Overall, the setup allows targetted illumination of subcellular regions enabling the precise, localized activation of optogenetic probes or the activation and deactivation of signaling cascades using photo-activated ion-channels.
Micro mirror arrays as high-resolution spatial light modulators for photoactivation and optogenetics
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