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??s after the ignition) and ?1016?1013?cm?3 in the late afterglow period (1?20??s). 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.