Utilization of fiber loop ring down technique for sensing applications

Thesis Type: Postgraduate

Institution Of The Thesis: Middle East Technical University, Faculty of Arts and Sciences, Department of Physics, Turkey

Approval Date: 2017

Thesis Language: English


Principal Supervisor (For Co-Supervisor Theses): Mehmet Fatih Danışman

Co-Supervisor: Alpan Bek


Fiber loop ring down (FLRD) spectroscopy is based on multiple interaction of laser light with sample/analyte. It is evolved from cavity ring down spectrometer with addition of optical fiber. Measurement accuracy rises with multiple interactions and this enhances the minimum detection limit compared to other spectrometers using single pass interaction such as FTIR, UV-VIS spectrometer. The other advantages of this technique are its insensitivity to laser fluctuation and detector performance. In this study, three FLRD set-ups were constructed with two laser sources at 800 and 1534 nm. Sensor regions were designed with two interaction methods as transmission and scattering and optimization for measurement parameters and probe structure were performed. The spectrometers’ parameters were examined with chemicals such as ethanol, acetone, toluene, acetylene gas, nitrogen gas. The response of the spectrometers to sample/analyte were investigated and limitations were discussed. Finally, the performance of the spectrometers was compared with the literature.