Optical measurements of paired luminous rings in capacitive radio-frequency hydrogen discharges

Optical measurements of paired luminous rings separated by a narrow dark ga p have been conducted in capacitive radio-frequency (rf) hydrogen discharge s. The lines of molecular H-2 are strongly excited at the ring emission com pared with a weaker emission of the H-alpha line. The number of ring pairs increases with gas pressure, and the outermost ring pairs near the electrod es start to appear earlier than the inner ones. Each ring emission is turni ng on and off with the applied rf frequency, i.e., the left-side (right-sid e) ring of a paired ring is on when the left-side (right-side) electrode is biased positively. The axial light intensity profile, which is time resolv ed with the applied rf frequency, indicates that the emission profiles are similar to those of de glow discharges, and the luminous rings correspond t o the standing striations at the positive column. [S1063-651X(99)12911-8].