NONDESTRUCTIVE TESTING OF POLYMERS BY MEA NS OF PHOTOTHERMAL TESTING METHODS .3. INFLUENCE OF MICROSCOPIC AND MACROSCOPIC SURFACE-ROUGHNESSON THE PHOTOACOUSTIC SIGNAL

The photoacoustic spectroscopy is becoming a useful technique in the t extile analysis for the examination of dyestuff. The roughness of the surface has a significant influence on the photoacoustic signal. This paper reports the influence of the microscopic and macroscopic roughne ss of surfaces on the photoacoustic signal. The modulation frequency o f the incident light determines the thickness of the layer contributin g to the photoacoustic signal. It is documented that only the microsco pic roughness of a surface has a qualitative influence on the photoaco ustic signal, whereas the macroscopic structure has a quantitativ infl uence. The macroscopic structure can be considered as an ,,effective s urface'', having no influence on the frequency dependence of the photo acoustic signal.