Fig. 6.

Fluorescence PSF measured using a fluorescent bead in water. (a) and (c) 2D fluorescence image (raster scanned) of a bead at 300 µm and 1050 µm from the needle, respectively. (b) and (d) Corresponding fluorescence cross-sectional profiles (blue lines) and Gaussian curve fitting (red dashed lines) along x-axis (top panel) and y-axis (bottom panel) for a bead at 300 µm and 1050 µm from the needle, respectively. (e) FWHM diameters of the fluorescence PSF in x- and y-axes as a function of depth through water, obtained from Gaussian fitting. (f) Normalized amplitude of the fluorescence PSF as a function of depth in water. (g) Log (dB) normalized amplitude of the fluorescence PSF as a function of depth in water, with line of best fit (red line) showing rate of decay of fluorescence efficiency.