Laser, spectroscopic, and Langmuir probe diagnostics of an inductively‐coupled rf discharge H− ion source

A number of laser, spectroscopic, and probe diagnostic techniques has been used to study inductively coupled radio frequency discharges used as H− ion sources. Time‐resolved detection of Balmer‐alpha emission has been used to study the excited state hydrogen atoms. Vacuum ultraviolet laser absorption spectroscopy and 2+1 multiphoton laser‐induced fluorescence have been used to measure the ground state atomic hydrogen populations. Langmuir probe measurements which are synchronized with the exciting rf radiation have also been made. The Balmer‐alpha emission exhibits a modulation in its intensity at a frequency of twice the exciting rf radiation. On the other hand, the laser absorption measurements show that the density of ground state hydrogen atoms does not vary significantly with the phase of the exciting rf. At the same time, the probe measurements indicate that the plasma density and the temperature of the thermalized electrons are also invariant with respect to the rf phase. These results are qualitat...