A new method for harmlessly characterizing coats of paint can help prevent a vehicle’s body from rusting, and may have health and safety applications as well. Applied Research and Photonics Inc. has developed a way to harmlessly penetrate paint layers using terahertz reflectometry. With this technique, a beam of terahertz-frequency radiation is fired onto the paint to measure its thickness and the size of embedded particles. Coats of paint must be applied properly on a vehicle to prevent rusting; however, ensuring uniform thickness of all layers can be difficult. Accurately gauging auto paint thickness could help guard against rust. “None of the current methods are very successful in determining the thickness of individual layers and coatings in a nondestructive fashion,” said company founder Anis Rahman, who developed the new technique alongside his son, Aunik. In the research, Rahman found that a terahertz beam can penetrate the paint layers — each one tens of microns thick — and bounce back at different intensities depending on the thickness of each layer encountered, all without damaging the paint. Rahman noted that terahertz radiation is nonionizing and therefore harmless. Measuring the reflected beams’ intensity demonstrates the thickness of each coat of paint very precisely, down to tens of nanometers. The method also can be used to estimate the size of any particles added to the paint as small as 25 nm, the researchers said. The new technique could also be used for testing paints, and studying how certain paints react with different surfaces — such as wood, plastic or metal — potentially preserving those surfaces. In particular, terahertz reflectometry could prevent the topcoat from penetrating into the paint layers below, according to Rahman. Other potential applications include detecting lead paint in buildings, or analyzing paint on artifacts and antiques. Health and environmental applications could benefit from the terahertz reflectometry technique, too, Rahman said. It could be used to study the structure and layers of skin, possibly detecting early stages of skin cancer. The researchers will present their work at the 2014 Conference on Lasers and Electro-Optics (CLEO) next month in San Jose, Calif. For more information, visit www.arphotonics.net.