Depth resolution by means of helical wavefronts for particle tracking applications

Tracking of Particles and biological cells is a common method for nano and micro fluidics as well as cytometry. Microscopy is an essential tool for biomedical research and applications, but it usually suffers from the lag of depth information. Distance information within the depth of field in a microscope is not easily accessible. We present a technique for three-dimensional measurements of flow fields. A double-helix point spread function can be generated by a spatial light modulator (SLM) through phase-only modulation. These engineered point-spread functions can create a double image of the object. The axis between those double images rotates around its centre when the object is driven through the depth of field of the microscope objective. The technique enables a robust axial localization of particles and cells. With the double-helix microscopy technique we intent to accomplish 3D measurements in micro-channel flows.