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Observation of Large Photoacoustic Signal Phase Changes During a Diffusion Process
Applied Spectroscopy
  • Stanley J. Bajic, Iowa State University
  • Roger W. Jones, Iowa State University
  • John F. McClelland, Iowa State University
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The phase of the photoacoustic signal is known to be a sensitive and accurate means to investigate, both qualitatively and quantitatively, static multilayer heterogeneous systems. According to theory, the maximum phase delay for a very weakly absorbing homogeneous sample should be within 45° of a very strongly absorbing sample, while for heterogeneous samples the phase delay can be greater than 45°. Here we report the observation of photoacoustic phase delays greater than 350° by extending the use of step-scan phase modulation photoacoustic spectroscopy to study a non-repetitive dynamic system in situ, in real time. These large phase delays correspond to sampling several thermal diffusion lengths into the sample. The model system used in this study consisted of a hydrocarbon grease diffusing through a porous Teflon film. The progress of the diffusion was tracked by monitoring both the photoacoustic signal magnitude and the phase of the hydrocarbon grease after isolation from the Teflon film signal contributions at two different phase modulation frequencies.

This paper was published in Applied Spectroscopy 59 (2005): 1420 and is made available as an electronic reprint with the permission of OSA. The paper can be found at the following URL on the OSA website: doi: 10.1366/000370205774783142.

Systematic or multiple reproduction or distribution to multiple locations via electronic or other means is prohibited and is subject to penalties under law.
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Society for Applied Spectroscopy
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Stanley J. Bajic, Roger W. Jones and John F. McClelland. "Observation of Large Photoacoustic Signal Phase Changes During a Diffusion Process" Applied Spectroscopy Vol. 59 Iss. 11 (2005) p. 1420 - 1426
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