Subsurface Layer Detection by Fourier Transform Infrared Photoacoustic Spectroscopy

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Abstract
Fourier transform infrared photoacoustic spectroscopy was applied to the nondestructive detection of subsurface layer of bilayered films. Spectral separation of the subsurface layer was carried out by the application of the subtraction technique to the photoacoustic amplitude spectra of bilayered films whose top layer has various values in thickness. As a result, it was found that the spectrum corresponding to the subsurface layer could be separated, and that the photoacoustic depth profiling was possible as far as the depth, which is approximately half the value of the thermal diffusion length.