In order to non-invasively measure the unsteady, 3D velocity field of a jet plume from a stationary aircraft engine, Nov. 18, 2021, a laser beam is redirected and spread into a wider plane as it crosses behind the engine at the Propulsion Research Facility operated by Arnold Engineering Development Complex on the campus of the University of Tennessee Space Institute in Tullahoma, Tenn. Cameras are then aimed at a 45-degree angle to the laser plane to observe the scattered laser light from soot particles in the exhaust and measure their velocity. (U.S. Air Force photo by Jill Pickett)