We report results from optical characterization of the stream of droplets emitted from the tip of a Taylor cone. We demonstrate the ability to image and track individual droplets emitted from a Taylor cone using fluorescence microscopy with pulsed laser illumination and statistical particle tracking velocimetry (SPTV). Additionally, we demonstrate the use of holographic imaging to examine the three dimensional electrospray droplet structure. Single-exposed images were used to measure droplet diameters between 1.5 to 2.5 μm for flow rates ranging from 15 to 25 nL/s. Velocity distributions with mean velocities over 40 m/s were obtained from analysis of double-exposure images using SPTV. In addition to droplet size and velocity distributions, we present data on the instability of the tip stream and on the formation and subsequent evolution of the spray cone for emission frequencies over 3.5 MHz.

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