Fig. 4.

Axial resolution versus excitation power. Axial resolution was determined by imaging emission from a single, lipid coated nanoparticle at 0.5 μm steps for 40 μm along the $z$-axis. Images used were 255 by 255 pixels, and were taken with a 19.6 μs dwell time. The field of view used was 100 μm by 100 μm. Excitation power was calculated assuming a 1 μm radius spot size. The axial FWHM of the system was measured as $\sim 2.5\mu \text{m}$.