Measurement of the temporal evolution of electron density in a nanosecond pulsed argon microplasma: using both Stark broadening and an OES line-ratio method

The temporal evolution of electron density in a nanosecond pulsed argon microplasma is measured using a combination of Stark broadening and the optical emission line-ratio method. In the initial discharge period (0–100 ns), the electron density can reach as high as ∼1018 cm−3. It decreases to ∼1017–1016 cm−3 in the early afterglow period (100 ns–1 µs after the ignition) and ∼1016–1013 cm−3 in the late afterglow period (1–20 µs). It is demonstrated that the optical emission spectroscopy (OES) line-ratio method can obtain the electron density in the range 1013–1016 cm−3, while in the range 1016–1018 cm−3, the Stark broadening technique with argon 2p–1s lines (in Paschen's notation) is a better choice. These results are in good agreement with those from the Stark broadening technique with hydrogen Balmer lines. Finally, a possible mechanism for such a density evolution is briefly discussed.