Photoacoustic Spectroscopy of Powders

Photoacoustic spectroscopy of powders, using microphone detection in the gas phase, has the avantage over conventional spectroscopic techniques to require no preparation and to leave the sample unaltered. When it is used with a Fourier Transform Interferometer, it promises to become a generally applicable powerful analytical technique. However, this technique appears still in its early stages of development, since there exists, to our knowledge, no theoritical description really applicable to the case of powders. The problem is certainly complexe, even more complexe than the one found in the competing technique of diffuse reflectance spectroscopy, since it is necessary to take in account the thermal, acoustical and optical (absorption and scattering) properties of the heterogenous medium constituting the powdered sample. We have derived a theoritical formulation applicable in this case and we are also conducting an experimental investigation with a low resolution infrared grating spectrometer.