3D Localisation and Orientation of Micron Sized particles Using Digital Holographic Measurements

Off-axis digital holographic measurements were used to image micron sized particles,both in simulations and by real experimental measurements. In simulations particles withellipsoid shape were used, but in experiments spherical ones were used because of lack ofnon-spherical particles. These measurements enables one to reconstruct 3D informationfrom a 2D hologram. In this thesis it is used to capture the scattered light from particlesto determine properties of said particles. The properties that are of interest are theposition, orientation and size of the particles. An algorithm based on the in-plane phasegradients has been developed to determine these properties. To find the depth along theoptical axis where the particle was located the algorithm searched for the position wherethe phase gradient became zero. From simulated results it was found that the gradientdid become zero at the depth were the particle was located, hence, the algorithm returnedthe correct position. From experimental results there were no way of knowing the exactposition of the particle but from visual inspection of the refocused image one couldconclude that the returned depth at least was close to the correct one. The orientationwas found by computing the two main directions of the gradient vector field around eachparticle which coincided with the semi-axis of the particle. Size estimations were madeby using a model based on a Gaussian beam. From simulations it was found that thismodel deviated from the obtained result and further development is needed.Validerat; 20150615 (global_studentproject_submitter