THE METHOD OF OPTICAL MULTISPECTRAL IR FLAW DETECTION

An infrared flaw-detection method is described in which the IR radiati on transmitter also serves as a double-area ''sandwich'' type photorec eiver, operating simultaneously in two spectral bands, namely, 2-5 mu m and 8-14 mu m. After the surface of the opaque object being investig ated is heated by a short pulse of laser radiation, the photosignals I -1 and I-2 and their rate of change (dI(1)/d(t)au) and (dI(2)/d tau) a re recorded synchronously and independently in two spectral bands from the same part of the object at a temperature in the 400-600 K range. The thermal parameters and the depth at which the defects lie are foun d from the ratio of the quantities (dI(1)/d tau)/I-1 and (dI(2)/d tau) /I-2 for the different spectral bands. The method eliminates the effec t of the emissive power of the object on the results of the measuremen ts, and also increases the instrumental accuracy by eliminating the ap paratus functions of both spectral bands.