Phase optimization for quantitative analysis using phase Fourier transform photoacoustic spectroscopy

Abstract

The phase of the photoacoustic signal is of prime importance for obtaining accurate optical absorption coefficients using the photoacoustic technique. Variations in the spectrometer or the photoacoustic cell parameters between the measurement of the sample spectrum and the carbon black reference spectrum are the main source of phase shifts. We reconsider a simple model that provides an accurate description of the photoacoustic effect—including photoacoustic saturation—for thermally thick, homogeneous samples. The model includes absorption from a thin layer at the sample surface. We propose a method for optimizing the photoacoustic phase for this model. The method is based on the internal calibration at the onset of the photoacoustic saturation, and on a simple analysis of the shape of the calculated surface absorption spectrum. Optimization is illustrated with a simulated spectrum and an experimental spectrum of ethylene-propylene-rubber.