Optical emission and microwave field intensity measurements in surface wave-excited planar plasma

A large-planar (22 cm diam.) high-density (similar to 2 x 10(12) cm(-3)) plasma is produced in argon gas at 140 Pa by 2.45 GHz-1 kW discharges, using a microwave launcher of small slot antennas. The two-dimensional distributions of optical emission intensities as well as microwave field intensities are measured near the plasma surface irradiated with microwaves. Both the optical emission and the microwave field clearly show stationary patterns of azimuthal mode m = 3 and radial mode n = 3 at higher pressures (140 Pa), while a mode change to m = 6 and n = 2 is observed at lower pressures (44 Pa). These patterns are attributed to the excitation and absorption of standing surface waves near the cutoff layer.