3-D particle imaging uses wavefront sensing

To eliminate the optical inefficiency and sensitivity to wavefront-slope error and vibration of 3-D particle-imaging techniques such as stereoscopic methods, defocusing digital particle-image velocimetry (PIV), and holographic techniques, researchers from Leeds University (Leeds, England) and Heriot-Watt University (Edinburgh, Scotland) have developed a new particle-imaging method that eliminates many of these problems and provides 3-D resolution from a single viewpoint with simple, inexpensive optics.

In the phase-diversity (PD) wavefront-sensing technique, the raw data is the image-intensity distribution measured in two planes within the imaging system. Particle depths are determined from the wavefront curvatures (or PD data) and lateral positions from the particle-image centroids. Two imaging systems were used to simultaneously capture the multiplane image data: one used quadratically distorted gratings to record images from three planes in the measurement volume on a CCD (yielding an 8 µm out-of-plane resolution over a 28 mm field of view), the other used anamorphic imaging to encode the intensity from two discrete planes of the image volume along orthogonal axes in a single volume (achieving a depth resolution of 30 µm over a range of 10 mm). Contact Catherine Towers at [email protected].