Attenuation Coefficients of Tubular Conduits for Liquid Phase Absorbance Measurement: Shot Noise Limited Optimum Path Length

We trace the history of liquid core waveguides (LCWs, also called liquid core optical fibers) and the role Teflon AF (TAF) has played in their development. We show that, in any shot noise limited situation, the optimum signal-to-noise ratio (S/N) occurs at a path length of 1/αa{ln­[1 + 2­(αa/αb)]},...

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Bibliographic Details
Published in:Analytical chemistry (Washington) 2019-08, Vol.91 (15), p.9481-9489
Main Authors: Dasgupta, Purnendu K, Qin, Chuchu, Shelor, Charles Phillip, Kadjo, Akinde Florence, Su, Jianzhong, Kraiczek, Karsten G, Marshall, Graham D
Format: Article
Language:English
Subjects:
Attenuation coefficients
Chemistry
Impurities
Light transmission
Liquid phases
Noise
Noise measurement
Optical fibers
Polyether ether ketones
Polytetrafluoroethylene
Shot noise
Signal to noise ratio
Silica
Silicon dioxide
Tetrafluoroethylene
Tubes
Wall thickness
Wave attenuation
Waveguides
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Summary:We trace the history of liquid core waveguides (LCWs, also called liquid core optical fibers) and the role Teflon AF (TAF) has played in their development. We show that, in any shot noise limited situation, the optimum signal-to-noise ratio (S/N) occurs at a path length of 1/αa{ln­[1 + 2­(αa/αb)]}, approximately 2/αb under most conditions, αa and αb being the light attenuation coefficient due to the analyte and the background, respectively. The analysis shows that LCW length should be selected depending on the applicable αb value. An overly long LCW may exhibit a lower signal-to-noise ratio. Water-filled TAF-clad fused-silica (FS) tubes show the lowest attenuation across the wavelength range. Nevertheless, except at λ ≥ 600 nm, the observed αb values far exceed those reported for pure water: it appears that both impurities in the water and waveguide losses are involved. In examining the attenuation in various water-filled tubes, we find that the transmission of air-surrounded FS tubes is second only to TAF-clad FS tubes and is better than that of TAF tubes or externally mirrored FS tubes. Surprisingly, except for a window centered at ∼250 nm, light transmission in a water-filled poly­(tetrafluoroethylene) (PTFE) tube is worse than in poly­(ether ether ketone) (PEEK) tubing. Light transmission in PTFE tubes improves with increasing wall thickness.
ISSN:0003-2700
1520-6882
DOI:10.1021/acs.analchem.9b00067