H-ALPHA (BALMER) SPECTRAL PROFILES OBTAINED FROM H2 RF PLASMA DISCHARGES STUDIED BY INTRACAVITY LASER SPECTROSCOPY

H(alpha) (Balmer) spectral absorption profiles are obtained for 13.56 MHz rf discharges of hydrogen at pressures from 25 m Torr to 3.0 Torr. The H(alpha) transitions are monitored by intracavity laser spectroscopy using high spectral resolution. Spatially resolved concentrations of atomic hydrogen in the n=2 state (H*) are measured across the region between the power and ground electrode. The H* density distribution follows the glow space. The electron densities are (1-3) x 10(10) cm-3. The profiles indicate that the 2S1/2 and 2P1/2 states are populated first in the discharges. The system is not in thermodynamic equilibrium but comes closer to it at pressures greater than 500 m Torr.