Holographic background-oriented schlieren

Simultaneous measurement of dispersed and continuous phases in multiphase flows remains a fundamental challenge. This Letter proposes holographic background-oriented schlieren (HoloBOS), and it enables numerical refocusing of both the background pattern and dispersed-phase particles from a single acquisition, thereby allowing simultaneous characterization of both phases. The method is demonstrated in a gas flame experiment with an effective distance of 45 mm and is further applied to a multiphase propellant combustion plume to characterize dispersed agglomerates and flow structures. The results support the feasibility of HoloBOS for the simultaneous extraction of particle morphology, size, and three-dimensional position, as well as the line-of-sight integral of the refractive-index gradient in the continuous phase, indicating its potential as a practical tool for complex multiphase diagnostics.