PHASE OPTIMIZATION FOR QUANTITATIVE-ANALYSIS USING PHASE FOURIER-TRANSFORM PHOTOACOUSTIC-SPECTROSCOPY

The phase of the photoacoustic signal is of prime importance for obtai ning accurate optical absorption coefficients using the photoacoustic technique, Variations in the spectrometer or the photoacoustic cell pa rameters between the measurement of the sample spectrum and the carbon black reference spectrum are the main source of phase shifts, We reco nsider a simple model that provides an accurate description of the pho toacoustic effect-including photoacoustic saturation thermally thick, homogeneous samples. The model includes absorption from a thin layer a t the sample surface. We propose a method for optimizing the photoacou stic phase for this model. The method is based on the internal calibra tion at the onset of the photoacoustic saturation, and on a simple ana lysis of the shape of the calculated surface absorption spectrum. Opti mization is illustrated with a simulated spectrum and an experimental spectrum of ethylene-propylene-rubber. (C) 1997 Society of Photo-Optic al Instrumentation Engineers.