Fiber optic sensor for chlorinated hydrocarbons in water based on infrared fibers and tunable diode lasers

A novel fiber optic evanescent wave spectroscopy (FEWS) system is based on a tunable diode laser (TDL) source, on a polymer-coated AgClBr infrared transmitting fiber, and on a mercury cadmium telluride detector. This system was used for sensing low levels of chlorinated hydrocarbons n water. The detection limit was 100 myg/l (100 ppb), which is an improvement by a factor of 50 in comparison to a similar system that is based on a Fourier transform infrared spectrometer, and the measurement time was reduced by a factor of 3. The TDL-FEWS system shows significant potential for in situ monitoring of ground water.