Absorption spectroscopy by diode laser tuning and fibre optic sensor of evanescent waves for gas detection application

This paper discusses the development of a new technique for atmospheric pollution detection using an infrared laser coupled to a fibre optic sensor. We have developed a laboratory apparatus for detection of certain important pollutants. The authors have demonstrated the feasibility of the apparatus with commercially combusted materials. The construction of a portable and cheap industrial prototype is envisaged. The experimental work has revealed several difficulties to be overcome before this objective is reached, in particular the control and stability of the laser emissions used. The system was coupled to fibre optic sensors but their feasibility is insufficient. A metallic thin film deposited oil the fibre sensor permits reinforcement of the penetration of the evanescent waves in the exterior medium using the effect of surface plasma resonance. Also realised was the modal selection with the aid of a fibre with an integrated Bragg system. It remains to be seen if the cost and the complexity of the system will be compatible with a commercial prototype.