ANGULAR RESONANCE-ABSORPTION SPECTRA OF LANGMUIR-BLODGETT-FILMS STUDIED BY THE PHOTOACOUSTIC TECHNIQUE

The photoacoustic (PA) angular spectrum method was developed on the ba sis of attenuated total reflection (ATR) and PA spectroscopies. This m ethod was used to obtain the resonance absorptioin spectrum of Langmui r-Blodgett (LB) films on silicon substrates. The rigorous electromagne tic theory in a layered medium is also presented to explain the experi mental results and to characterize the films. By fitting theoretical r esults to the experimental spectrum, the refractive indices and the th ickness of the films can be evaluated. Moreover, as the intensity of t he laser beam increased, additional peaks were observed in the angular PA spectrum, predicted to be related to the optical non-linearity of LB films. Compared with conventional ATR spectroscopy, PA ATR spectros copy has the advantages of a simpler optical system and higher sensiti vity, as well as a wider application range.