Depth Resolution of Dynamic Phase Contrast Microscopy

Microfluidics is one of the most up-to-date fields of physical research because microfluidic devices are able to carry out many tasks in medicine and biology with much lower reactant consumption. Of special interest is the measurement of the full three-dimensional velocity field for different flow geometries for which optical sectioning via depth of field is one of the easiest ways to implement. However, Particle-Image-Velocimetry (PIV) algorithms are strongly dependent on sufficient Signal-to-Noise-Ratio (SNR) and intensity stability. A method to improve the SNR, which is even more important in microPIV, and to minimize the error rate of PIV algorithms is Dynamic Phase Contrast (DynPC) microscopy. It suppresses the statical background and thus highlights the dynamics in microfluidic systems. In this talk we will present a detailed investigation of the microscopes particle response function. We present our results for typical numerical apertures used in microPIV ranging from 0.45 to 1.4 and compare them to the according results with conventional microscopy. These results allow conclusions about the usability of DynPC microscopy for optical sectioning in microfluidic velocimetry.