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Proceedings Paper

Silver halide fiber-based evanescent-wave liquid droplet sensing with thermoelectrically cooled room temperature mid-infrared quantum cascade lasers
Author(s): Jian Z. Chen; Zhijun Liu; Claire F. Gmachl; Deborah L. Sivco
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Paper Abstract

Quantum cascade lasers coupled directly to unclad silver halide fibers were used to assemble mid-infrared fiber-optics evanescent-wave sensors suitable to measure the chemical composition of simple liquid droplets. Quantum cascade lasers can be designed to emit across a wide range of mid-infrared wavelengths by tailoring the quantum-well structure, and the wavelength can be fine tuned by a thermoelectric cooler. Here, laser wavelengths were chosen which offer the largest absorption contrast between two constituents of a droplet. The laser was coupled to an unclad silver halide fiber, which penetrates through the droplet resting on a hydrophobic surface. For the same liquid composition and droplet size, the transmitted intensity is weaker for a droplet on a 1H,1H,2H,2H-perfluoro-octyltrichlorosilane coated glass slide than for one on a hexadecanethiol (HDT) coated Au-covered glass slide because of the high reflectivity of the HDT/Au surface at mid-infrared wavelengths. The absorption coefficients of water, glycerol, α-tocophenol acetate, and squalane were measured by varying the immersion length of the fiber; i.e. the droplet size. A pseudo-Beer-Lambert law fits well with the experimental data. We tested both aqueous liquid mixtures (acetone/water and ethanol/water) and oil-base solutions (n-dodecane/squalane and α-tocophenol acetate/squalane); α-tocophenol acetate and squalane are common ingredients of cosmetics, either as active ingredients or for chemical stabilization. Using a 300μm diameter silver halide fiber with a 25mm immersion length, the detection limits are 1 vol.% for α-tocophenol in squalane and 2 vol.% for acetone in water for laser wavenumbers of 1208 cm-1 and 1363 cm-1, respectively. This work was previously been reported in J. Z. Chen et al. Optics Express 13, 5953 (2005).

Paper Details

Date Published: 17 November 2005
PDF: 8 pages
Proc. SPIE 6010, Infrared to Terahertz Technologies for Health and the Environment, 601009 (17 November 2005); doi: 10.1117/12.630225
Show Author Affiliations
Jian Z. Chen, Princeton Univ. (United States)
Zhijun Liu, Princeton Univ. (United States)
Claire F. Gmachl, Princeton Univ. (United States)
Deborah L. Sivco, Bell Labs./Lucent Technologies (United States)

Published in SPIE Proceedings Vol. 6010:
Infrared to Terahertz Technologies for Health and the Environment
Alexey A. Belyanin; Rebekah A. Drezek; Claire F. Gmachl, Editor(s)

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