Evidence for Thermal Wave Interference in Thin Particulate Carbon Samples

It is well known that thermal wave interference will affect the photoacoustic signal arising from very thin samples; (1,2) in this report we present experimental evidence for thermal wave interference effects in thin layers of elemental carbon particles which have been deposited on three commonly used filter substrates. Not only are these results important to our present objectives concerning the calibration of an ambient soot monitor, they may be of significance to those engaged in a photoacoustic study of samples which are less than a thermal wavelength in thickness.