a, 3P image of a small fluorescein-labeled blood vessel (blue arrowhead) imaged about 200 μm deep into the optic tectum. Image stack was taken with 0.3 μm axial steps at 3 µs pixel time (512x512 pixels/frame) and 4 times averaging. b, Intensity profile along the axial direction fitted with a Gaussian curve to characterize the upper bound of axial resolution. The full width at half maximum of the Gaussian fit is 2.9 μm. N=1.