Holographic Measurement of Drop-on-Demand Drops in Flight

Abstract

The analysis of images of ink drops in flight can provide information about jet straightness, drop velocity and volume. However trade-offs between field of view, optical and digital resolution and other factors such as depth of field and optical distortion, limit the accuracy and amount of information available from a single image. In-line, digital holograms of drops in flight can capture information from fields of view at least as large as the area of the digital sensor. Using mathematical reconstruction techniques particularly suited to sparse, small objects of regular geometry the accuracy of measurement can potentially be submicrometer on drop position and diameter. This paper describes our experimental apparatus, hologram reconstruction techniques and the results of experiments on imaging drops. We also discuss techniques to improve the accuracy of the technique in the direction of the optical axis.