Stray-light correction in photoacoustic measurements of solid samples

Abstract

An experimental correction procedure is presented which allows one to measure separately and to eliminate signal contributions produced at the walls of photoacoustic cells by the directly incident light or by the light (diffusively) reflected from the solid sample. This stray-light correction procedure is tested for an opaque and a transparent photoacoustic cell. It helps to reduce the systematic error of photoacoustic measurements considerably when the solid to be analyzed and the reference material have different reflection properties and when in quantitative thermal depth profiling a larger interval for the modulation frequency of heating is needed.

On the thermal characterization of solids by photoacoustic calorimetry: thermal diffusivity and linear thermal expansion coefficient

“…1 in a heat transmission configuration, in which the intensity modulated (50% duty cycle), laser beam impinges and is absorbed on the sample's surface opposite to that facing the PA air chamber. This is a configuration that offers some advantages when compared with a frontal one (sample is illuminated at the surface facing the PA air chamber), among others the unwanted signal contribution produced by light absorption at the cell's walls [8,9] is eliminated. The generated PA signal is detected with a microphone (in our case an electret microphone) connected to the air chamber by a small diameter duct and it is measured with a Lock-In amplifier synchronized at the modulation frequency.…”

“…In this paper, we describe a new straightforward methodology that uses approximation formulas for different thermal regimes. It involves a normalization procedure using a thermally thin reference sample, as well as consideration of the sample's thermoelastic bending [8] in both the thermally thin and thick regime in addition to the thermodiffusion contribution used in the most works [5,6]. The usefulness of the methodology is demonstrated with measurements of thermal diffusivity in test samples of different materials.…”