CONTRIBUTION TO THE PROBLEM OF OBSERVING THERMAL NONUNIFORMITIES IN A2-LAYER PLATE CONSISTING OF OPAQUE SOLID MATERIALS

The theoretical problem of determining the sizes delta of defects unde r opaque surface coatings according to the phase shift of the signals from a photodetector with two ring-shaped p-n junctions that detects r adiation from a concentric surface heat wave excited in the sample by harmonically-varying low-power probe radiation is studied. The problem is solved for the signal amplitude in the first approximation in the small parameter delta and for the phase in the second approximation. A n expression is derived for the resolution of the method for detecting defects. (C) 1997 American Institute of Physics.