Atmospheric pressure plasma jets (APPJ) present rich gas-phase chemistry, transient electric fields and electron densities, low gas temperatures, etc., which make them very promising in various novel applications such as ambient ionization mass spectrometry [1]. Due to their operation at atmospheric pressure, collisional quenching of generated reactive species becomes significant, and, in some cases (e.g., excited atomic hydrogen), the corresponding effective lifetimes may fall to subns timescales [2]. In most published studies, classic optical diagnostics (such as nanosecond –ns– TALIF and ICCD cameras) are employed to understand the kinetics of reactive atoms in APPJ. However, precise measurements of their densities using ns-TALIF may become challenging at atmospheric and higher pressures [2]. In this case, the use of picosecond (ps) or femtosecond (fs) TALIF as well as ultrafast detectors for atomic density and lifetime determination is a better solution [2,3]. This work focuses on the investigation of a μs-pulsed microtube helium APPJ by means of ps-TALIF (laser: Ekspla®; pulse width: ~10 ps) and a streak camera (C1091005, Hamamatsu®; few ps time resolution). The achieved spatial resolution can be as low as 400 μm, while we were able to measure laser-excited H-atom lifetimes down to a few hundred ps (Figure 1). The obtained H-atom density and lifetime values depend on the distance from the tube exit and the APPJ parameters (voltage, helium flow rate, …). These results are supported by electrical and OES diagnostics. This study provides useful information for APPJ kinetic models while it helps in the optimisation of APPJ for novel applications [1]. [1] S. Brandt et al., Anal. Chim. Acta 951, 16–31, 2017 [2] K. Gazeli et al., Plasma 4, 145–71, 2021 [3] S-J. Klose et al., Plasma Sources Sci. Technol. 29, 125018, 2020