Two-dimensional argon metastable density measurements in a radio frequency plasma reactor by planar laser-induced fluorescence imaging

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Abstract
Two‐dimensional, relative measurements of the argon 1s5 metastable density distribution were obtained in a low‐pressure, 13.56 MHz, parallel‐plate, Gaseous Electronics Conference reference cell discharge using planar laser‐induced fluorescence imaging. For the conditions examined (pure argon, 75–300 V, 13.3–133.3 Pa), the measured density fields show significant radial and axial variations that depend more strongly on pressure than applied voltage. Generally speaking, the metastable density increases radially from the center to the edge of the discharge by ∼10%–30%. As the pressure is increased, the peak metastable density increases by ∼4 times and the axial distribution changes from a center‐peaked parabolic‐like profile to an asymmetric profile peaked near the powered electrode. Comparisons of centerline metastable and excited‐state emission profiles indicate that, while the metastable distribution is largely determined by the spatially dependent electron‐impact excitation function, variations in quenching can significantly affect the resulting metastable density profile at some conditions.