A fiber optic system for water analysis with high transparency in the deep-UV region (lambda >/= 190 nm) is presented. The system consists of special UV-improved silica fibers and a liquid-core waveguide (LCW) as an optical cell. The apertures of both light guides, the silica fiber and the LCW, are matched. The optical losses of the device are investigated experimentally and compared with theory, especially with a standard free-space geometry. The performance of the system with respect to UV absorption spectroscopy is demonstrated for nitrate and chlorine pollution in pure water. For a 203-mm-long LCW the detection limits have been determined to be as low as 22 mug/L for nitrate and 26 mug/L for chlorine.
A liquid-core waveguide (LCW) with pure water as core material has been fabricated by coating the inner core of a glass tube with Teflon AF® 2400. Its guiding properties are proven and the guiding losses are determined to be 0.016 dB/cm. A first theoretical model is proposed and its validity is shown by comparing theoretical and experimental results. As an example for application the LCW system is used for optical pH-value control. The proposed LCW system exhibits the same accuracy for pH-value determination as commercial electrochemical pH meters.
There are different types of optical capillary cells in use for the modern on-line UV-VIS analysis of liquids using fibre spectrometers. These cells have the advantages of low sample volume, long optical pathlengths and compatibility to fibre optics. In this paper, we will show that the liquid core waveguide (LCW) is a particularly useful device because the light intensity is confined in the liquid core. This is shown in two ways. Firstly, the measured total optical losses of the LCW capillary device indicate typical guiding losses less than 3 dB m-1 without a significant dependence on either fibre diameter or on the diameter of the capillary. Secondly, measurements of the radial intensity distribution exhibit a clear maximum in the core in the case of the LCW device.
The efficiency of a liquid core waveguiding cell is investigated for different core diameters (0.3-4 mm) in combination with different coupling fibre diameters (200-600 µm). A thin cell with a 360 µm diameter with a sample volume in the µl range and low coupling losses will be discussed as well.
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