Focused shadowgraph systems employing schlieren quality optics have been used successfully in AEDC Ranges G and K to study the location of transition from laminar to turbulent flow in the boundary layers of test models. A spark light source proved advantageous in flow visualization studies of relatively low velocity models, while a pulsed ruby laser with its very short exposure time (20 nanoseconds) allowed excellent stop-motion shadowgraph photography at higher speeds. Use of the pulsed laser also allowed the preliminary evaluation of a combination front light/focused shadowgraph system - a unique instrumentation system in ballistic range application, to the best of the author's knowledge.
O. H. Bock, O. H. Bock,
"Focused Shadowgraph Visualization of Boundary-Layer Transition in Aeroballistic Range Studies*," Optical Engineering 13(2), 132143 (1 April 1974). https://doi.org/10.1117/12.7971688