The LaserStrobe Optical Probe is an advanced laser-augmented video-imaging system that observes and measures particle behavior in the harsh environment of a plasma-spray chamber. The need for a reliable diagnostic and feedback control system during thermal-spray processing spurred the development of this sophisticated system.

Figure 1. The LaserStrobe Optical Probe assembly is mounted to the main access door of the plasma-spray chamber to protect the components of the system during operation.

LaserStrobe is intended to enable manufacturers of aerospace engine components to reduce production costs, while meeting the strict standards of quality for parts that are commonly coated using the plasma-spray process.

The conditions inside the low-pressure chamber during plasma-spray processes include an extremely bright plasma flame, strong electromagnetic fields, high temperature, and contamination from powder overspray circulating throughout the chamber during operation. LaserStrobe was designed to endure this harsh environment and enable scientists and engineers to measure parameters such as particle velocity and particle distribution during the spraying process.

Figure 2. The Optical Probe camera provides clear video of "twin imagery" of the particle dynamics inside the plasma-spray chamber.

This water-cooled optical probe has a pulsed laser illumination system and a special-purpose camera head that provide images of extremely bright industrial processes  such as electric arc welding and plasma spray. The optical probe components are attached to a 14-in. (29-cm) diameter flange. The flange is then mounted on the main access door of the plasma-spray chamber.

The LaserStrobe Optical Probe system was installed and tested in the Low-Pressure Plasma Spray chamber at Marshall Space Flight Center in Huntsville, Alabama. Two fan-shaped laser beams are superimposed in the focal plane of the camera head, providing two spot images of each traveling particle in the video frame. With a few microseconds of delay between the first and second laser pulse, "twin images" are produced as the particles move across the camera field of view. During these tests, the optical probe system provided clear imagery of plasma-spray plume particles inside the chamber.

This work was done by Jon D. Bolstad, John C. Lagerquist, and Craig L. Shull of Control Vision, Inc., for Marshall Space Flight Center. For further information, access the Technical Support Package (TSP) free on-line at under the Electronic Systems category, or circle no. 103on the TSP Order Card in this issue to receive a copy by mail ($5 charge). Inquiries concerning rights for the commercial use of this invention should be addressed to

the Patent Counsel, Marshall Space Flight Center; (205) 544-0021.

Refer to MFS-26424.

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NASA Tech Briefs Magazine

This article first appeared in the April, 1998 issue of NASA Tech Briefs Magazine.

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