High-accuracy three-dimensional position measurement of tens of micrometers size transparent microspheres using digital in-line holographic microscopy

Digital in-line holographic microscopy has a strong potential in measuring various three-dimensional (3D) microscale flow phenomena. However, the axial elongation problem in reconstructing particles severely degrades the measurement accuracy along the light propagation direction. In this Letter, we utilize the lenslike characteristic of tens of micrometers size transparent spherical particles to extract their 3D position. A sharp intensity peak is observed in the reconstructed wave field, resulting from the light-focusing effect of the particle. As a result, the depth-of-focus constraint caused by the particle size is eliminated and the measurement accuracy is drastically improved up to submicrometer resolution.