|Title:||Silver halide fiber-based evanescent-wave liquid droplet sensing with thermoelectrically cooled, room temperature, mid-infrared quantum cascade lasers||Authors:||Chen J.Z.
|Keywords:||Droplet,;Evanescent wave;Fiber;Microfluidics;Mid-infrared;Quantum cascade laser;Sensor;Silver halide||Issue Date:||2005||Journal Volume:||6010||Source:||Proceedings of SPIE - The International Society for Optical Engineering||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, £\-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 £\-tocophenol acetate/squalane); £\-tocophenol acetate and squalane are common ingredients of cosmetics, either as active ingredients or for chemical stabilization. Using a 300£gm diameter silver halide fiber with a 25mm immersion length, the detection limits are 1 vol.% for £\-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).
Infrared to Terahertz Technologies for Health and the Environment,24 October 2005 through 25 October 2005,Boston, MA
|Appears in Collections:||應用力學研究所|
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