Improving explosives detection using fiber-optic sensing technology

The combination of thin-film-fluorescence (TFF) quenching with fiber-optic sensing technology is superior to other available means for explosives identification in many respects. However, collecting sufficient TFF power is a challenge because a low level of excitation light must be used to avoid the degradation of film material. The task becomes even more difficult given the tiny size of fibers involved. In this paper, we propose a significantly improved two-fiber sensor architecture for fast and efficient explosives detection based on TFF quenching. This architecture features small size, uses an easy thin-film coating technique and has a simple but rigid architecture. The most important advantage of the design is that it simultaneously enables highly efficient collection of evanescent-wave-form fluorescent (EF) signals and suppression of stray excitation light. These effects are experimentally confirmed. We also report a stable EF signal at a lower level of UV LED excitation. When exposed to DNT, the low-concentration TNT-related explosive vapor, the proposed sensor shows a fast quenching response that points to a promising future for the design. The high efficiency is further explained by revealing the unique physical mechanism behind the proposed design.