Block diagram of the sample-hold method for time-resolved laser-induced fluorescence spectroscopy. A comparator chip triggers the creation of a measurement gate of width $τ$ and delay time $Δt$ from the point at which the discharge current crosses a defined threshold. The fluorescence signal from the PMT is sampled, held until the following update one discharge current cycle later, and fed into a lock-in amplifier that extracts the LIF line shape at the chosen phase in the current cycle. Reproduced with permission from Young et al., Plasma Sources Sci. Technol. 27, 094004 (2018). Copyright 2018 IOP Publishing.