Interferential formulization and interpretation of the photoacoustic effect in multi-layered cells

Mathematical formulization of the thermal response in a two-layer photoacoustic cell, where the interference of thermal waves in a sample is compounded by the inter-layer interference effect, has been carried out by employing the thermal-wave interference theory. The physical meanings of the obtained formulae are then discussed in terms of the thermal-wave interference to explain the origin of the thermal phase lag for various cases. In addition, it is found that the inter-layer thermal-wave interference results in an extra phase lag.