Ultrasensitive detection system for fiber-optic-based ultraviolet spectroscopy

A fiber optic based deep W-absorption sensor system is characterized, using fibers for light delivery and a Liquid core waveguide (LCW) for analyzing liquids. UV-improved (WI) fibers with 500 mu m core diameter are capable of transmitting light intensities below 230 nm with spectral radiant powers above 500 nW/nm at 214 nm. Their short-term behavior and lifetime in respect to UV-stability have been investigated, using a broadband deuterium lamp. To raise the sensitivity of the total system, the absorption path length has been increased significantly using the lightguiding properties of the LCW consisting of a cylindrical glass tube with a Teflon AF(R) 2400 inner coating of about 50 mu m thickness. Due to lower refractive index of Teflon in comparison to water, the LCW concept offers significant advantages, especially for long optical pathlengths (larger than 100 mm). However, the basic attenuation of the liquid in dependence on the wavelength has to be taken into account. Results on the use of such a system monitoring concentrations of acetylsalicylic acid, acetone and toluene in water are reported and discussed.