Cover Story: Zhang W J, Zeng X L, Yang A, et al. Research on evanescent field ammonia detection with gold-nanosphere coated microfibers[J]. Opto-Electron Eng, 2021, 48(9): 200451

Ammonia (NH₃) is a toxic gas that can be harmful to humans, animals and plants in excess. Timely and accurate information on NH₃ emissions and distribution is of great importance for environmental protection and health and safety.Tunable diode laser absorption spectroscopy (TDLAS) is a highly sensitive laser absorption spectroscopy gas measurement technology, which determines the information of the target gas by detecting the absorption intensity of the spectrum has become the mainstream technology in the field of gas detection.However, traditional free-space light-path gas absorption cells are expensive, bulky and require high precision collimators and mirrors to work together, which greatly increase the cost of gas detection. This article proposed to combine TDLAS technology with evanescent field optical fiber sensing, using a microfiber as a sensitive element for gas sensing, to build a microfiber gas absorption cell to detect gas concentration through the absorption effect of the light escaping from the evanescent field.The team has designed and prepared a microfiber-based optic gas absorber cell built in an all-fiber NH₃ concentration detection system to achieve quantitative detection of different NH₃ concentrations in a 2 cm absorption path.To further improve the detection performance of NH₃ concentration, gold-nanospheres (GNS) were used to coat the microfiber to enhance the abrupt field effect of the fiber.According to the experimental results, the sensitivity of the microfiber coated GNSs NH₃ concentration detection system has been greatly improved and the lower detection limit of NH3 concentration can reach 260 ppm.