Fiber optic evanescent field sensor for detection of explosives and CO2 dissolved in water

A fiber optic approach for the determination of the carbon dioxide concentration in the gas or fluid phase during sequestration, as well as for the sensing of the explosive TNT is described. The sensor consists of a quartz glass multimode fiber with core diameter of 200 mu m and is based on the evanescent field principle. Cladding and jacket of the fiber are removed in the sensing portion, therefore interaction between light within the fiber and the surrounding medium is possible. A single-mode distributed feedback (DFB) laser diode with an emission wavelength around lambda = 1.57 mu m and a frequency doubled passively Q-switched Cr4+:Nd3+:YAG microchip laser (lambda = 1064 nm)are used as light sources. The experimental setup and the sensitivity of the evanescent field sensor are characterized.