Thermal Wave Imaging for Deposited Metal by Photopyroelectric Effect

For improved accuracy of nondestructive testing by photopyroelectric spectroscopy, a technique involving permanent contact between the pin electrode and the sensor layer was used. The technique was found to offer an improvement in resolution and a possibility to detect thermally dissimilar layers both at the surface and in the interior of a specimen. The specimens were made of nickel sheet 1 mm thick and subjected to nickel plating in Watt's bath to produce a coating 20 or 40 mu m thick. The polyvinylidene fluoride electrode was vapor deposition coated with an aluminum-nickel alloy on the side facing the specimen and provided with an aluminum pin on the reverse side. A 10 mW He-Ne laser was used in the experiments.