Journal or Book Title
Time-gated ballistic-photon imaging is a form of shadowgraphy in which an ultrashort, optical-Kerreffect (order 2 ps) time gate is used to enhance the relative intensity of ballistic versus multiply scattered photons. In the current work, this technique is adapted for what is believed to be the first time for use in the moderately dense environment (optical density ∼1:5 to 2) of a high-speed 5 to 15mm diameter rocket spray to improve image contrast and observe liquid-breakup phenomena. Unlike coherence gating, which is another form of ballistic imaging, the time-gating approach allows sufficient signal levels from ballistic and near-ballistic photons to enable time-resolved single-shot imaging. Direct comparisons with non-time-gated shadowgraphy indicate that the two techniques are sensitive to different features of the flowfield, with regions composed of a dense field of droplets being highly attenuated in conventional shadowgrams but appearing transparent to ballistic photons. This enables significant image contrast enhancement (∼6:6∶1) of liquid-core structures and facilitates improved understanding of the primary and secondary breakup processes in sprays of moderate optical density.
This paper was published in Applied Optics and is made available in an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: https://www.osapublishing.org/ao/abstract.cfm?uri=ao-48-4-B137. Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.
Optical Society of America
Schmidt, Jacob B.; Schaefer, Zane Donald; Meyer, Terrence R.; Roy, Sukesh; Danczyk, Stephen A.; and Gord, James R., "Ultrafast time-gated ballistic-photon imaging and shadowgraphy in optically dense rocket sprays" (2009). Mechanical Engineering Publications. 176.