Dust-Induced Modulation of the Atomic Emission in a Dusty Argon Discharge

The spectral emission of argon atoms in a dusty rf discharge plasma has been determined. For that purpose, the spatially and temporally resolved emission of the argon atoms during the rf cycle was measured using a gated intensified charge-coupled device camera. While dust particles of $2–3\mu \mathrm{m}$ diameter trapped in the sheath lead to an increased plasma emission during the sheath expansion phase, larger particles of $10–12\mu \mathrm{m}$ diameter result in a decreased emission. This behavior is explained by the combined action of electron density reduction due to the charging dynamics in the sheath and the increase of electron temperature to compensate plasma losses at the dust.

Figure 1

Scheme of the setup. See text for details.

Figure 2

Space and time-resolved emission (color coded) of the two Ar lines near 750 nm as recorded by the ICCD camera. Here, the $z$ coordinate denotes the height above the electrode. The time span covers 200 ns, thus roughly 3 rf periods. This reference emission was recorded without trapped dust.

Figure 3

(a) Difference of the space and time-resolved emission. Here, the difference of the argon emission (near 750 nm) with trapped dust particles of $3.46\mu \mathrm{m}$ diameter and the reference emission of Fig. 2 is shown. The region where the dust is also trapped is indicated. (b) Same as (a), but using dust of $10.2\mu \mathrm{m}$ diameter.

Figure 4

(a) Measured rf voltage at the lower electrode and calculated charge fluctuations around the equilibrium charge on a particle of $2.5\mu \mathrm{m}$ diameter due to sheath expansion and collapse. The inset shows the charging process from zero charge. (b),(c) Space and time-resolved excitation profile from deconvolution of the emission signal for (b) $2.5\mu \mathrm{m}$ and (c) $12\mu \mathrm{m}$ particles.