Rayleigh scattering is used in order to deduce the gas temperature from neutral density measurements inside a microwave discharge in argon. Rayleigh scattering is a powerful non-intrusive method which provides direct heavy particle density measurements with a very high spatial resolution. The gas pressure ranges from 1 to 40 torr and the microwave power ranges from 35 to 900 W. We show that temperature gradient is very sharp at the edge of the plasma column: T g drops to nearly room temperature within 3 cm. In contrast, T g is nearly constant in the bulk of the plasma region. The gas temperature is determined over a large range of power and pressure conditions. We show that the gas temperature in the centre of the tube, ranging from 300 to 2500 K, is a linear function of the averaged power density per unit of length. Analytical calculations are in good agreement with experimental results.

Diode laser absorption spectroscopy is used for determination of the translation temperature of hydrogen in surface-wave-created microwave discharges in a 16 mm inner diameter quartz tube, both in pulsed and continuous modes. It is shown that the gas temperature, deduced from the Doppler profile of H α , 656.3 nm line, is almost constant along the plasma column. It increases from 1000 to 2500 K as the pressure increases from 1 to 10 Torr for microwave powers ranging from 150 to 700 W. In a steady-state discharge, the influence of pressure and power is explained by considering thermal diffusion and power balance via an analytical calculation. Over a wide range of power and pressure, the gas temperature is proportional to the injected power density. In time-resolved temperature measurements with pulsed discharges, the characteristic time for the gas heating and the establishment of the steady-state is found to be of the order of 80 µs.