Study of the Ar II spectral line shape in the cathode sheath region of glow discharge

We present the results of an experimental study of Ar II line shapes emitted side-on from the cathode sheath (CS) region of an abnormal glow discharge operating in pure argon with different cathode materials. The shape of Ar II lines is recorded side-on to the discharge axis and parallel to the plane cathode surface by using the optical emission spectroscopy technique. Our experimental line shape analysis shows that the atomic line shapes can be used for determination of the electric field strength distribution and the thickness of the CS region, whereas the broadened wings of the Ar II lines provide an insight into line shape formation as a result of electric field strength distribution, which is essential for discharge particle dynamics, and interaction with the discharge gas and sputtered cathode material. The results are summarized in two analytic formulas: one for the half width of wings as a function of the cathode distance from the recording position and the other for correlation between Ar II line width and electric field strength.