Synchrotron infrared photoacoustic spectroscopy

The use of synchrotron radiation ~SR! as a farand mid-infrared source in the measurement of photoacoustic Fourier transform infrared spectra of solids is demonstrated for the first time in this work. Initial experiments were performed at beamline U10A at the National Synchrotron Light Source, Brookhaven National Laboratory. For synchrotron photoacoustic spectroscopy to be feasible, it must yield results superior to those obtained with a conventional thermal ~Globar! source; accordingly, SR and Globar photoacoustic spectra recorded under similar conditions were compared in detail. The intensities of SR far-infrared photoacoustic spectra were found to be consistently greater than the corresponding Globar spectra. At shorter wavelengths, SR always underfills the effective aperture ~or, alternately, sample size!; SR is a superior source in a spectral region that is a function of this aperture. The high wave number limit of this region exhibits a power-law dependence on aperture size. This investigation also showed that the entire mid-infrared photoacoustic spectrum is more intense using SR and apertures smaller than approximately 0.5 mm. © 2001 American Institute of Physics. @DOI: 10.1063/1.1416107#