3D particle measurements by single beam two-views magnified digital in-line holography

Holography technique can be used for 3D measurement of particle positions. However, in general in-line holography, accurate determination of the object’s position in the optical axis direction is difficult. In order to overcome this defect, we proposed a two-views recording technique combined with a digital in-line holography. The two-views recording is executed by only one camera with the assistance of one mirror, capturing the real image of a particle and the mirror image of the same particle simultaneously. This method keeps simplicity of optical alignment and is free from a difficult calibration of multiple cameras. It was confirmed that the proposed technique can reduce the uncertainty in the depth direction to about 1 pixel. For application of this method to micro-PIV, magnified recording is desired. In this paper, magnified holograms were also taken through a lens. It was confirmed that the uncertainty in the optical-axis direction can be reduced to a few pixels by the proposed technique for the magnified holograms.