Chen J.Z.Liu Z.Gmachl C.F.Sivco D.L.JIAN-ZHANG CHEN2019-09-262019-09-2620050277786Xhttps://scholars.lib.ntu.edu.tw/handle/123456789/425221Infrared to Terahertz Technologies for Health and the Environment,24 October 2005 through 25 October 2005,Boston, MAQuantum 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).Droplet,Evanescent waveFiberMicrofluidicsMid-infraredQuantum cascade laserSensorSilver halideconference paper10.1117/12.6302252-s2.0-33644775742https://www2.scopus.com/inward/record.uri?eid=2-s2.0-33644775742&doi=10.1117%2f12.630225&partnerID=40&md5=c2c9f5abe1edcdcc186ea09834fe98a5