Calibration of particle position on digital holography using transparent resin block with dispersed particles

Abstract

This paper describes the use of a Calibration Block (CB) for evaluating the accuracy of digital holography in particle position measurement. CB made of acrylic has three layers and the gap between the layers is filled with transparent resin. The refractive index of the resin and the layers is almost the same (1.49). Fin Block (FB), which is not filled with resin, is introduced in order to evaluate effects of the resin. The fringe edges of several holographic patterns are observed by using three kinds of CB and FB. Each layer is coated with spherical particles (diameter: 16.36 ± 0.42 μ m). The influence of multiple scattering on the detected depth of the particles is evaluated by changing the number density of particles. Three kinds of CB and FB are prepared (averaged particle density in the holographic pattern; 83.2, 166.5 and 249.7). The fringe edges of the holographic patterns generated in CB and FB are observed, respectively. It is found that the fringe edges of CB are clearer than FB. Also, Multiple scattering acts as a source of background noise with high spatial frequency, which has almost the same frequency as that of the particle diffraction on the fringe patterns, and reduces the effective signal-to-noise ratio of the holographic pattern. CB can be used to evaluate the influence of multiple scattering on the detected particle depth.