Dual-sheet interferometric particle imaging for opaque particle size and 2D location measurement

Abstract

Dual-beam interferometric particle imaging (DIPI) has been proposed to measure opaque spherical particle size in the single-point region of interest. This work extends DIPI to measure the size and two-dimensional position of opaque spherical particle in a plane with dual-sheet illumination. A general DIPI model based on geometric optics is established to formulate the interference signal formation of DIPI by modeling the phase difference of two reflected light at far-field. Proof-of-concept experiments, incorporating digital inline holography (DIH), are performed for validation. An interferogram processing algorithm which adopts the sum-of-squared-difference image registration method and Fourier spectrum analysis has been proposed to locate the centroid of each out-of-focus pattern and extract the spatial frequency of fringes, and subsequently particle position and size. The average relative deviation values of DIPI in size measuring and two-dimensional locating are 2.4% and 1.9%, respectively, compared to those values by DIH, which demonstrates the practicability of DIPI in both respects. The extension of DIPI from point-probe to planar measurement promotes its applications to real scenarios, e.g., metal droplet in solid rocket propulsion.