Cavity ring-down spectroscopy (CRDS) is an absorption spectroscopic technique. In CRDS the concentration of an analyte is determined by measuring the reduction in finesse of an optical cavity made from two highly reflective (R>99.9%) mirrors once a sample is introduced. Optical loss is traditionally determined from the exponential intensity decay of a short laser pulse that was injected into the cavity. This decay is the longest for an empty, high finesse cavity and is reduced when the sample absorbs or scatters light. In this project, the optical cavity is made from fiber optic waveguides and the light source is a continuous wave (cw) diode laser. It is used to detect analytes such as acetylene, ammonia and other amines through their overtone absorption in the telecom region at 1500 nm. The experiment is done by increasing the ratio of desired loss (extinction caused by the sample), to undesirable loss (from the waveguide or solvents) through amplification of the ringdown signal using an erbium doped fiber amplifier (EDFA). The EDFA is inserted into a fiber-optic loop and its gain is increased above the lasing threshold. The gain of the, now lasing, fiber loop is "clamped" to a high and constant value, thereby removing unwanted gain fluctuations, and all losses in the loop are compensated for. If one now inserts a laser light pulse at the lasing wavelength of the loop it would circulate through the loop indefinitely, whereas a light pulse at a wavelength that is being absorbed by an analyte would experience a decrease with time at a rate that depends only on the magnitude of the sample absorption. By enclosing the sample gap with a gas cell both acetylene and ammonia have been detected down to ~25 ppm and ~5.9 Torr respectively. Subsequently, a 1% solution of aminotoluene was detected in an interrogation volume of 5.65 pL by having inserted a fiber with a hole drilled in it as the sample gap. At present, the drilled fiber has been replaced with photonic crystal fiber such that small volumes of gases may be detected with a longer effective path length. / Thesis (Master, Chemistry) -- Queen's University, 2011-09-23 18:27:47.65

published_or_final_version / abstract / Chemistry / Master / Master of Philosophy

Thesis (M. Phil.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

Thesis (Ph.D.)--York University, 2008. Graduate Programme in Chemistry. / Typescript. Includes bibliographical references (leaves 143-152). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR38991

Thesis (M.S.)--University of Nevada, Reno, 2007. / "December, 2007." Includes bibliographical references (leaves 117-121). Online version available on the World Wide Web.

We combine the evanescent field (EF) sensing mechanism with the fiber loop ringdown (FLRD) sensing scheme to create FLRD-EF sensors. The EF sensor heads are fabricated by etching the cladding of a single-mode fiber (SMF), while monitoring the etching process by the FLRD technique in real-time, on-line with high control precision. The effect of the sensor head dimensions on the sensors' detection sensitivity and response time are investigated. The EF scattering (EFS) sensing mechanism is combined with the FLRD detection scheme to create a new type of fiber optic index sensor. The detection limit for an optical index change is 3.2×10-5. This is the highest sensitivity for a fiber optic index sensor so far, without using any chemical-coating or optical components at the sensor head. A new type of index-based biosensor using high sensitivity FLRDEFS technique to sense deoxyribonucleic acid (DNA) and bacteria (Escherichia coli) is created.

No description available.

No description available.

published_or_final_version / abstract / Chemistry / Doctoral / Doctor of Philosophy

Trace gases can have a significant impact on the Earth's climate, and the analysis of changes in these gases and an understanding of how much of these changes are a result of human activity is important for understanding global climate change. Methane (CH4) is the second only to CO2 in radiative forcing over the last 200 years, and its concentration in the atmosphere has more than doubled since 1750. Sources and sinks of CH4 have characteristic isotopic effects, which shift the relative concentration of the methane isotopologues. Spectroscopic techniques for of analysis the isotopic composition of methane have been evolving since the early 1990's, and promise real-time, in-situ measurements that would provide unprecedented information on the methane atmospheric cycle. Here we present our development and results of a new optical spectroscopic isotope ratio instrument using cavity ringdown spectroscopy in the near IR region using the ν2+2ν3 overtone band. This region has limited interference from other molecules, and an advantageous juxtaposition of a 13CH4 triplet, and a single 12CH4 peak, allowing near-simultaneous measurement of both isotopologues. We present the results of two datasets showing high linearity over a wide range of isotope ratios, which achieved a precision of ±4 /. We present analysis of the data and consider the effects of temperature and molecular interference.