MEASUREMENT OF THE THERMAL-DIFFUSIVITY OF THE SURFACE-LAYERS OF OPAQUE SOLID OBJECTS

A method is discussed for the layer-by-layer determination of the ther mal diffusivity a and thickness d of the subsurface layers of opaque s olid objects from measurements of the phase difference of signals of t wo centered ring-shaped p - n photodiode junctions by successively var ying the coefficient of angular magnification of the optical system of the device in which a radiation source with Gaussian cross-sectional beam power density creates a thermal object on the surface of the obje ct in the form of harmonically varying concentric heat waves. Estimate s are found for the frequency range and minimum angular magnification corresponding to the limits of validity of the relations used to calcu late a and d. (C) 1997 American Institute of Physics.