David Pepper '71, Ph.D.

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An article co-authored by David Pepper '71, “‘Seeing’ Into Opaque Materials With Light and Sound,” will be published in the November/December 2023 issue of American Scientist magazine.

The magazine is a publication of Sigma Xi, the Scientific Research Honor Society, and is available at selected newsstands. It publishes layman articles in a variety of scientific fields of research and is directed at the general, nontechnical audience.

The article provides an overview and history of “laser ultrasonics,” which involves the use of lasers to view the interiors of otherwise opaque objects. The technology can enable the inspection of, for example, weld joints, composite materials (used in advanced aircraft bodies), the thickness of red-hot metallic tubes at 1000°C, aging bridges, nuclear rods and the human body, all without touching or damaging the object, and at long distances from the part.

The scheme involves a pair of lasers: one laser zaps the part, like tapping it with a small hammer, and a second laser measures the minute surface vibrations. The system functions like a novel sonar system but uses lasers for the generation and detection of the ultrasound. “As long as you can see the part, you have the possibility to inspect it,” says Pepper.

Pepper earned his undergraduate degree, summa cum laude, in physics, under Professors Darrell Drickey and Charles Buchanan, and his master's degree (1974) and doctorate (1980) at Caltech in applied physics. He was senior research scientist at HRL Laboratories (formerly Hughes Research Laboratories) in Malibu, California, for 31 years and is currently owner of Malibu Scientific. He is an inventor on 68 U.S. patents.