Instantaneous one-dimensional ammonia measurements with femtosecond two-photon laser-induced fluorescence (fs-TPLIF)

Ammonia (NH₃) has been identified as a potential hydrogen-carrier fuel with no carbon emissions. Non-intrusive in-situ NH₃ diagnostic technique is of great interest. In this work, femtosecond two-photon laser-induced fluorescence (fs-TPLIF) was demonstrated in NH₃/N₂ mixtures to achieve NH₃ measurements. A femtosecond laser at 305 nm was used for two-photon excitation of NH₃ to its excited state (X–C′), and the subsequent fluorescence at ~565 nm from transition C′-A was detected. In addition, a detection limit of 730 ppm was achieved in NH₃/N₂ mixtures. Furthermore, one-dimensional single-shot images of NH₃ were obtained in both laminar and turbulent flow fields. This work is the first attempt of fs-TPLIF for polyatomic molecular gases measurements, and the obtained results indicate that fs-TPLIF could be a promising tool for NH₃ measurements.