<title>IR fiber optic evanescent field sensors for gas monitoring</title>

In this work, the main emphasis is given to the development and optimization of new fiber optic sensors for on-line gas monitoring and gas analysis. Gaseous halogenated hydrocarbons such as dichlorodifluoromethane (R 12) and trifluoromethane (R 23) have been investigated with a sensor system based on polymer coated silver halide fibers. Calibration curves down to a concentration of 0.1% have been established. Polyisobutylene, ethylene/propylene copolymer and polydimethylsiloxane have been tested according to their diffusion properties accompanied by the determination of the diffusion coefficient of gases inside the polymer layer. Particular attention is given to the application of sapphire fibers for high temperature gas sensors enabling the assignment of fiber optic sensors for the measurement of hydrocarbons like methane and butane under rough conditions. Temperature dependent calibration curves (20 to 300 degrees C) in the low percentage concentration range and the pressure dependence of the methane absorption at 3017 cm<SUP>-1</SUP> could be obtained.