Fiber loop ring down spectroscopy for trace chemical detection

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2013
Cengiz, Betül
Fiber loop ring down (FLRD) spectroscopy is a sensitive spectroscopic technique that is based on absorption and it is convenient for trace chemical detection. Different FLRD systems are being improved in order to increase their sensitivity. In FLRD spectroscopy, detection of a sample is done by measuring of a leaking light at each trip within an optical cavity. Intensity of leaking light has an exponential decay where it is reduced by absorption of sample and scattering of light. In this project, two FLRD set-ups at 1535 nm and 808 nm were designed. In both set-ups, optical fiber and optical fiber couplers are used to form a cavity. At 1535 nm, a FLRD set-up is constructed by utilizing a pulsed laser and used for characterization of thin films, various pure liquids and fluorescein solutions. Two different sensor regions are designed with free space collimators and ferrules for the measurement of thin films and liquids, respectively. The future endeavor of the set-up is improvement for reliability and reproducibility of the system. For visible and NIR regions, a fiber coupled laser with four colors as 642 nm, 785 nm, 808 nm and 852 nm laser is used to design of a FLRD set-up. 808 nm laser is selected to build a prototype of the FLRD system. The construction of a closed loop FLRD set-up is completed and the system is characterized. Ultimate aim in our project is to be able to do trace detection at visible and NIR regions where the chemical sensitivity is higher.

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Citation Formats
B. Cengiz, “Fiber loop ring down spectroscopy for trace chemical detection,” M.S. - Master of Science, Middle East Technical University, 2013.