Spiral phase mask shadow-imaging for 3D-measurement of flow fields.

Particle tracking velocimetry (PTV) is a valuable tool for microfluidic analysis. Especially mixing processes and the environmental interaction of fluids on a microscopic scale are of particular importance for pharmaceutical and biomedical applications. However, currently applied techniques suffer from the lag of instantaneous depth information. Here we present a scan-free, shadow-imaging PTV-technique for 3D trajectory and velocity measurement of flow fields in micro-channels with 2 µm spatial resolution. By using an incoherent light source, one camera and a spatial light modulator (LCoS-SLM) that generates double-images of the seeding particle shadows, it is a simply applicable and highly scalable technique.