Infrared fiber-optic evanescent wave spectroscopy and its applications for the detection of toxic materials in water, in situ and in real time

We have been developing a novel infrared fiberoptic system for on-line monitoring of toxic materials in water. The system is based on fiberoptic evanescent wave spectroscopy (FEWS) and it operates in the middle infrared (Mid-IR) spectral range 3μm - 30μm. This spectral range covers the "fingerprint" region where many molecules have characteristic absorption. The system is based on silver halide (AgClBr) fibers which are flexible, non-toxic, non-hygroscopic and highly transparent in the Mid-IR. A short segment of unclad AgClBr serves as a sensing element, which is coupled to a tunable IR source (e.g. FTIR or tunable IR laser) via two long IR fibers. This setup makes it possible to carry out absorption measurements on water, in a remote location (in situ) and in real time. By flattening the short sensor element one can increase the sensitivity. Using this system we have already monitored pollutants in water in concentrations of the order of 1ppm. The system allows a highly sensitive and selective detection of several pollutants, simultaneously. With additional improvement this fiberoptic sensor system will be more sensitive, selective, affordable, robust and easy to operate. Such a system could to detect the presence of toxic chemicals, such as pesticides, in drinking water at levels lower than 1ppm.