Phase References and Cell Effects in Photoacoustic Spectroscopy

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2001-10-01
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McClelland, John
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Ames National Laboratory

Ames National Laboratory is a government-owned, contractor-operated national laboratory of the U.S. Department of Energy (DOE), operated by and located on the campus of Iowa State University in Ames, Iowa.

For more than 70 years, the Ames National Laboratory has successfully partnered with Iowa State University, and is unique among the 17 DOE laboratories in that it is physically located on the campus of a major research university. Many of the scientists and administrators at the Laboratory also hold faculty positions at the University and the Laboratory has access to both undergraduate and graduate student talent.

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Abstract

In Fourier transform infrared (FT-IR) photoacoustic spectroscopy, advanced scanning and data-handling techniques have placed increasing emphasis on the phase of the photoacoustic signal. Unfortunately, there is no agreement on the best material to use as a phase reference. We have examined the frequency dependence of the signal from several candidate phase references and found that cell effects dominate the absolute phases and magnitudes observed. The absolute phase is exceptionally fast at low frequencies and exceptionally slow at high frequencies because of the cell effects. Accordingly, details such as sample position must be scrupulously controlled to achieve accurate, reproducible results. Because of the cell effects, no candidate material behaves like an ideal phase reference. If relative phases are used, however, glassy carbon comes closest to the ideal, differing from theory by no more than 8° at any frequency examined.

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This paper was published in Applied Spectroscopy 55 (2001): 1360 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:10.1366/0003702011953487.

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Mon Jan 01 00:00:00 UTC 2001
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