A novel approach to perform time-resolved laser-induced fluorescence (LIF) measurements in plasma discharges is presented. The LIF technique relies on a photon counting method associated with a sinusoidal potential modulation on a floating electrode located in the plasma to ensure time coherence. By tuning the modulation frequency, resonance can be reached with the discharge current in order to guarantee repeatable measurement conditions. Time-averaged characteristics of the discharge (such as Te, ne, Vp, and Vion) remain unaffected by the modulation. As an example, the association of the photon counting method with the modulation system is employed to determine the time evolution of several ion velocity groups inside an E × B discharge. Interesting features of the velocity oscillations are examined and pave the way for more focused studies.

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