This schematic depicts SCAPE's imaging geometry. The light sheet is swept at the sample by slowly moving a polygonal mirror mounted on a galvanometer motor. This alters the angle at which the light is incident at the edge of the objective's back aperture, causing the beam to sweep across the sample. The light emitted by fluorophores within this illuminated plane travels back through the same objective lens, and is de-scanned by the same polygonal mirror (from an adjacent facet). This light forms an oblique image of the illuminated plane that stays stationary and aligned with the illumination plane, even though the light sheet is moving through the sample (just as a confocal pinhole stays aligned with the scanning illuminated focal point in laser scanning confocal microscopy). So with one (<5 degree) movement of the polygon, the entire volume is sampled. (Credit: Elizabeth Hillman, Columbia Engineering)
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