A diode laser absorption study on a 100 MHz argon ICP

Diode laser absorption on the 4s3 P2 - 4p3D3 - argon transition is used to measure heavy particle temperatures in a 100 MHz argon inductively coupled plasma. Radial profiles of this temperature are obtained from the Gaussian part of the absorption profile with an accuracy of about 500 K, for four different input powers and at two different heights. The integrated profile is used to calculate the 4s level density and to trace the ionizing and recombining plasma parts. The measurements also show that the method of attributing the Lorentzian width only to Stark broadening for calculating electron densities is not correct for this argon transition in atmospheric plasmas. A second broadening process with Lorentzian shape, Van der Waals broadening, has to be taken into account. Under the measured conditions at the hottest positions in the plasma about 50% of the Lorentz component is due to Van der Waals broadening and this increases to almost 100% at the edges of the plasma.