Particle Tracking Using Digital In-Line Holography Coupled With Magnification Lenses
P. Bresson (1), L. Rossi (1), V. Biscay (2), F. Lamadie (2)
(1) CEA, DES, IRESNE, DTN, STCP 13108 St Paul lez Durance Cedex, Cadarache, France
(2) CEA, DES, ISEC, DMRC, Univ Montpellier, 30207 Bagnols-sur-Ceze, Marcoule, France
Digital in-line holography (DIH) is a robust volumetric particle tracking technique suitable for the characterization of dilute flows. In a free space propagation setup the accuracy of the particle positioning is directly limited to the sampling conditions which depend on the size of the sensor and its position with respect to the particle field along the optical axis. Therefore, it may be interesting to place a magnification optical system between the particle field and the sensor to improve this accuracy. This work investigates the influence of a beam magnifier on an in-line digital holography setup to measure the size and three-dimensional positions of particles within a flow. First, a physical optical numerical model suitable for the simulation and reconstruction of magnified holograms is proposed. Then, based on a twin numerical and experimental study, the influence of a beam magnifier on the signal collection is evaluated and compared with the usual case of free propagation, especially regarding three relevant parameters: the focusing accuracy, the particles center positioning in space and the diameter measurement. Experimental results on an academic flow of calibrated micrometer beads moving through a particle size analyzer flow cell confirm that it is possible to improve accuracy by more than a factor 3 using a simple afocal system composed of two spherical lenses.