Comparison between Photoacoustic and Other Spectroscopies

Abstract

Well established techniques as transmission-, reflectance- and diffuse reflectance spectroscopy (TS, RS and DRS, resp.) are compared with photoacoustic spectroscopy (PAS).

For weakly absorbing samples showing no light scattering, PAS gives precise absolute values of absorption coefficients, providing the unique possibility of depth profiling, which is inaccessible to all the other techniques. With strongly absorbing and light scattering samples, however, one may not dispense with the other methods. Especially with powders PAS will not give spectra in the sense of the Rosencwaig-Gersho theory, but rather DRS spectra, which may be more adequately understood by following the theory of Kubelka and Munk. Thus many famous “PAS”-spectra as the ones of rare earth oxides turn out to be in fact DRS-spectra monitored by acoustical means.