Structured illumination microscopy: a new way to improve the axial spatial resolution of microscale particle velocimetry

Many visualizations of microchannel flows illuminate a significant portion, if not all, of the channel. This volume illumination degrades the axial spatial resolution of microscale particle velocimetry measurements because signal from out-of-focus tracer particles “contaminates” the image. We present here a novel way to improve the axial spatial resolution of such velocimetry measurements, structured illumination microscopy (SIM) particle-tracking velocimetry (PTV). In these initial proof of concept experiments, double-exposure SIM PTV was used to measure velocities in plane Poiseuille flow. The velocity results obtained from the SIM images have significantly less error and standard deviation than standard microscale PTV data obtained with volume illumination. Our estimates also suggest that the axial spatial resolution of the SIM results is a twofold improvement over those obtained with “standard” microscale PTV.